U.S. patent application number 13/739013 was filed with the patent office on 2013-05-16 for methods and compositions for metal nanoparticle treated surfaces.
This patent application is currently assigned to KIMBERLY-CLARK WORLDWIDE, INC.. The applicant listed for this patent is KIMBERLY-CLARK WORLDWIDE, INC.. Invention is credited to Bruce L. Gibbins, Bhalchandra M. Karandikar.
Application Number | 20130122321 13/739013 |
Document ID | / |
Family ID | 54011454 |
Filed Date | 2013-05-16 |
United States Patent
Application |
20130122321 |
Kind Code |
A1 |
Karandikar; Bhalchandra M. ;
et al. |
May 16, 2013 |
Methods and Compositions for Metal Nanoparticle Treated
Surfaces
Abstract
The present invention comprises methods and compositions
comprising metal nanoparticles. The invention comprises metal
nanoparticles and surfaces treated with a metal nanoparticle
coating. The present invention further comprises compositions for
preparing nanoparticles comprising at least one stabilizing agent,
one or more metal compounds, at least one reducing agent and a
solvent. In one aspect, the stabilizing agent comprises a
surfactant or a polymer. The polymer may comprise polymers such as
polyacrylamides, polyurethanes, and polyamides. In one aspect, the
metal compound comprises a salt comprising a metal cation and an
anion. The anion may comprise saccharinate derivatives, long chain
fatty acids, and alkyl dicarboxylates.
Inventors: |
Karandikar; Bhalchandra M.;
(Tigard, OR) ; Gibbins; Bruce L.; (Lake Oswego,
OR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KIMBERLY-CLARK WORLDWIDE, INC.; |
Neenah |
WI |
US |
|
|
Assignee: |
KIMBERLY-CLARK WORLDWIDE,
INC.
Neenah
WI
|
Family ID: |
54011454 |
Appl. No.: |
13/739013 |
Filed: |
January 11, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11704167 |
Feb 8, 2007 |
8361553 |
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13739013 |
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11194951 |
Aug 1, 2005 |
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11704167 |
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PCT/US2005/027261 |
Aug 1, 2005 |
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11194951 |
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60771306 |
Feb 8, 2006 |
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60771504 |
Feb 8, 2006 |
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60592687 |
Jul 30, 2004 |
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60592687 |
Jul 30, 2004 |
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Current U.S.
Class: |
428/553 ;
427/125; 428/34.1; 428/412; 428/425.8; 428/433; 428/447; 428/457;
428/458; 428/460; 428/461; 428/463; 428/465; 977/773 |
Current CPC
Class: |
Y10T 428/31707 20150401;
Y10T 428/31681 20150401; B22F 1/0022 20130101; Y10T 428/31692
20150401; C09D 5/14 20130101; C09D 5/1681 20130101; B05D 5/12
20130101; Y10T 428/12111 20150115; B05D 5/00 20130101; B82Y 30/00
20130101; C08J 7/06 20130101; Y10S 977/773 20130101; Y10T 428/13
20150115; Y10T 428/31663 20150401; A01N 59/16 20130101; Y10T
428/31699 20150401; B22F 9/24 20130101; B32B 15/01 20130101; C08J
2300/26 20130101; A01N 59/20 20130101; Y10T 428/31678 20150401;
A01N 59/20 20130101; H01B 1/02 20130101; B22F 7/08 20130101; Y10T
428/31605 20150401; A01N 59/16 20130101; Y10T 428/31507 20150401;
Y10T 428/31688 20150401; C09D 7/67 20180101; A01N 25/02 20130101;
Y10T 428/12063 20150115; A01N 25/02 20130101 |
Class at
Publication: |
428/553 ;
427/125; 428/457; 428/447; 428/425.8; 428/465; 428/458; 428/460;
428/461; 428/463; 428/412; 428/433; 428/34.1; 977/773 |
International
Class: |
B05D 5/12 20060101
B05D005/12; B32B 15/01 20060101 B32B015/01 |
Claims
1-33. (canceled)
34. An article produced by a method of rendering an elastomeric
surface electrically conductive, wherein the method comprises: a)
mixing an aqueous solution of a stabilizing agent, wherein the
stabilizing agent is a polymer, a surfactant, or both; sodium
saccharinate; and a soluble silver salt, and further wherein there
is a molar excess of sodium saccharinate to soluble silver salt,
wherein the ratio of the sodium saccharinate to soluble silver salt
is between 1 and 5, and adding a reducing agent to the aqueous
solution to form silver nano particles; b) contacting the
elastomeric surface with the aqueous solution for a time sufficient
for an effective amount of the nanoparticles to adhere to the
surface; and c) rinsing the surface, thereby rendering the surface
electrically conductive.
35. The article of claim 34, wherein the method further comprises
heating the aqueous solution.
36. The article of claim 34, wherein the contacting step is
repeated multiple times to increase the amount of silver adhering
to the surface.
37. The article of claim 34, wherein the elastomeric surface is
silicone, polyurethane, synthetic or natural rubber, a synthetic or
natural polymer, flexible polymers of polyimides, polyamides,
polyacetals, polysulfones, PBTs, PBO's, ethylene and propylene
based polymers, acetate polymers, polyacrylates, polycarbonate,
PET's, PEN's or blends thereof or co-polymeric derivatives.
38. The article of claim 34, wherein the reducing agent is a
tertiary amine, a secondary amine, or a primary amine; a
homopolymer having a primary amine, a secondary amine, or a
tertiary amine moiety; or a copolymer having a primary amine, a
secondary amine, or a tertiary amine moiety.
39. The article of claim 34, wherein the polymer is a
naturally-derived or synthetic homopolymer, a naturally derived or
synthetic copolymer, acrylamide and its derivatives, methacrylamide
and its derivatives, a polyamide, a polyurethane, a polymer having
no particular backbone but with urethane segments or tertiary amine
groups in the side chains, other polymers predominantly polar in
nature or co-polymers having a portion derived from polar
co-monomers, methacrylamide, substituted acrylamides, substituted
methacrylamides, acrylic acid, methacrylic acid, hydroxyethyl
methacrylate, acrylonitrile, 2-acrylamido-2-methylpropane sulfonic
acid and its salts (sodium, potassium, ammonium), 2-vinyl
pyrrolidone, 2-vinyl oxazoline, vinyl acetate, or maleic
anhydride.
40. The article of claim 34, wherein the surfactant is an anionic,
nonionic, or amphoteric surfactant.
41. The article of claim 34, wherein the soluble silver salt is
converted to a less soluble silver saccharinate due to the molar
excess of sodium saccharinate.
42. The article of claim 34, wherein the ratio of the sodium
saccharinate to soluble silver salt is between 1.05 and 2.
43. The article of claim 34, wherein the ratio of the sodium
saccharinate to soluble silver salt is between 1.1 and 1.5.
44. The article of claim 34, wherein the article comprises flexible
mirrors, stretchable elastic conductive polymers, and articles used
to reduce electromagnetic interference, to shield devices and
circuits against electrostatic discharging, and to impart radar
invisibility to aircraft or other vehicles.
45. An article produced by a method of rendering an article or
surface contacting a fluid resistant to biofilm formation, wherein
the method comprises: a) mixing an aqueous solution of a
stabilizing agent, wherein the stabilizing agent is a polymer, a
surfactant, or both; sodium saccharinate; and a soluble silver
salt, and further wherein there is a molar excess of sodium
saccharinate to soluble silver salt, wherein the ratio of the
sodium saccharinate to soluble silver salt is between 1 and 5, and
adding a reducing agent to the aqueous solution to form silver
nanoparticles; b) contacting the article or surface with the
aqueous solution for a time sufficient for an effective amount of
the nanoparticles to adhere to the article or surface; and c)
rinsing the surface, thereby rendering the article or surface
resistant to biofilm formation.
46. The article of claim 45, wherein the method further comprises
heating the aqueous solution.
47. The article of claim 45, wherein the contacting step is
repeated multiple times to increase the amount of silver adhering
to the article or surface.
48. The article of claim 45, wherein the article or surface is made
of steel, stainless steel, glass, titanium, copper, gold, synthetic
and natural polymers, polypropylene, polycarbonate, polyurethane,
polyvinyl chloride, polystyrene, polysulfone, silicones, HTV, RTV,
blends or co-polymer derivatives.
49. The article of claim 45, wherein the reducing agent is a
tertiary amine, a secondary amine, or a primary amine; a
homopolymer having a primary amine, a secondary amine, or a
tertiary amine moiety; or a copolymer having a primary amine, a
secondary amine, or a tertiary amine moiety.
50. The article of claim 45, wherein the polymer is wherein the
polymer is a naturally-derived or synthetic homopolymer, a
naturally derived or synthetic copolymer, acrylamide and its
derivatives, methacrylamide and its derivatives, a polyamide, a
polyurethane, a polymer having no particular backbone but with
urethane segments or tertiary amine groups in the side chains,
other polymers predominantly polar in nature or co-polymers having
a portion derived from polar co-monomers, methacrylamide,
substituted acrylamides, substituted methacrylamides, acrylic acid,
methacrylic acid, hydroxyethyl methacrylate, acrylonitrile,
2-acrylamido-2-methylpropane sulfonic acid and its salts (sodium,
potassium, ammonium), 2-vinyl pyrrolidone, 2-vinyl oxazoline, vinyl
acetate, or maleic anhydride.
51. The article of claim 45, wherein the surfactant is an anionic,
nonionic, or amphoteric surfactant.
52. The article of claim 45, wherein the soluble silver salt is
converted to a less soluble silver saccharinate due to the molar
excess of sodium saccharinate.
53. The article of claim 45, wherein the ratio of the sodium
saccharinate to the soluble silver salt is between 1.05 and 2.
54. The article of claim 45, wherein the wherein the ratio of the
sodium saccharinate to the soluble silver salt is between 1.1 and
1.5.
55. The article of claim 45, wherein the article comprises food
storage and preparation devices, marine or water vehicles, hulls,
propellers, anchors, ballast tanks, motors, pilings, liquid
filtering equipment, tubing ropes, chains, fish tanks, liquid
containers, water bowls, cooling towers, water tanks, canteens,
fuel tanks, or storage bins.
Description
RELATED APPLICATIONS
[0001] This application claims the priority of U.S. Provisional
Patent Applications No. 60/771,306, filed Feb. 8, 2006 and
60/771,504, filed Feb. 8, 2006, and is a continuation-in-part of
U.S. patent application Ser. No. 11/194,951 and PCT/US2005/27261,
filed Aug. 1, 2005, each of which claim the priority of U.S.
Provisional Patent Application No. 60/592,687, filed Aug. 1, 2004,
each of which is herein incorporated in its entirety.
FIELD OF THE INVENTION
[0002] The invention relates to compositions comprising metal
nanoparticles, their preparation, the application of the
compositions to surfaces and methods of preparation.
BACKGROUND OF THE INVENTION
[0003] Silver, which is commonly used in jewelry, is also known for
its antimicrobial properties and has found widespread use in
biological and medical applications. A large number of commercial
medical products with antimicrobial silver are used in wound care
and other medical applications. Silver has high electrical
conductivity (63.01.times.10.sup.6 S/m at 20.degree. C.) and
thermal conductivity (429 W/mK) which has led to its application in
electrical, electronics and thermal transfer fields. In addition,
silver has very high reflectivity and low emissivity and has found
uses in adaptive optics and in making items such as optical mirrors
and reflectors.
[0004] Silver has been used to make conductive elastomers. Such
elastomers may be found as sheets or gaskets and are filled with up
to 60% of a fine powder silver and such constructs have high
conductivities. These elastomers typically can maintain their
conductivities even after being stretched by 300%. An example of
use of such products is a sheet form of a silver powder-filled
elastomer applied to the surface of a large object, such as an
airplane. The silver powder-filled sheet absorbs radio frequencies
thus making the surface invisible to radar. Such silver-powder
elastomeric covered objects are potentially useful in military
applications. Covering surfaces with these materials adds
considerable weight to the object because sixty percent of the
weight of the covering is silver or other conductive metal.
[0005] One approach to making lighter conductive elastomers is to
apply a metallic layer only on the surface. The layer or coating is
applied by traditional methods such as electro-less plating or
vapor deposition. In general, coated fibers are not robust as the
metal does not adhere well to the underlying elastomer substrate
and often fail under even small strains. Coatings or layers of
metals, such as silver, have been used on many types of fibers or
other surfaces to render the surface antimicrobial or to resist
growth of organisms, or to provide for a highly reflective surface.
These coatings or layers often release metal, due to chemical or
mechanical forces, and thus provide an unhealthy amount of metal to
the environment or the surface fails to meet its intended use.
[0006] What is needed are methods and compositions for treating
surfaces with metals, such as silver and others, so that the metal
is retained on the surface and the surface is capable of meeting
its intended usage for an extended time.
SUMMARY OF THE INVENTION
[0007] The present invention comprises metal nanoparticles,
compositions comprising nanoparticles, such as stabilized silver
nanoparticles, that are formed in a fluid environment and comprises
methods of making and using these compositions. The nanoparticles
and compostions of metal nanoparticles of the present invention
generally comprise metal-containing nanoparticles in the size range
of 0.1 to 100 nm with approximately 50 nm being the largest
proportion of a size distribution of the nanoparticles.
[0008] The compositions of the present invention can be made with
aqueous or non-aqueous solvents. The compositions of the present
invention possess good shelf life and can be utilized in rendering
surfaces with a coating of metal nanoparticles. Non-aqueous
compositions may be based on solvents that have a range of boiling
points from room temperature to above 300.degree. C. for some
thermal transfer fluids. Non-aqueous metal nanoparticle
compositions may be made by extracting the nanoparticles from
aqueous compositions into a non-aqueous phase. As used herein,
non-aqueous means organic media that are generally immiscible with
water over large composition ranges as are generally understood by
those skilled in the art. The amount of metal, such as silver,
zinc, copper, gold, palladium, rhodium, or iridium, content in
nanoparticle compositions can be adjusted by choosing the desired
amount of metal in the preparation of the initial composition.
[0009] Differing amounts of metal loading (by amount of
nanoparticles attached) on the surfaces can be achieved, for
example, by successive multiple treatments or continued immersion
of the treated object or surface in a uniform nanoparticle
composition until the desired metal loading amount is reached. In
general, the compositions are not viscous which allows for ease in
coating many preformed articles uniformly and thus rendering them
metal treated. Often the techniques such as thermal evaporation or
plasma deposition processes are unsuitable to achieve uniform
deposition of metal, such as silver, inside objects with small
ratio bores and long lengths because of the inherent concentration
gradients. The compositions of the present invention easily coat or
treat such surfaces, in addition to uniform and non-uniform
surfaces, in part due to the low viscosity and low surface tension
of a nanoparticles composition.
[0010] Materials which may be metal treated using the methods and
compositions herein include, but are not limited to, catheters
(venous, urinary, Foley or pain management or variations thereof),
stents, abdominal plugs, feeding tubes, cotton gauzes, fibrous
wound dressings (sheet and rope made of alginates, CMC or mixtures
thereof, crosslinked or non-crosslinked cellulose), foam materials,
collagen or protein matrices, hemostatic materials, adhesive films,
contact lenses, lens cases, bandages, sutures, hernia meshes, mesh
based wound coverings, ostomy and other wound products, hydrogels,
creams, lotions, gels (water based or oil based), emulsions,
liposomes, microspheres, ointments, adhesives, porous inorganic
supports such as titania and those described in U.S. Pat. No.
4,906,466, chitosan or chitin powders, metal based orthopedic
implants, metal screws and plates, synthetic fabrics, nylon fibers,
fabrics or its blends, and fabric fibers and woven and nonwoven
materials, such as silk, rayon, wool, polyester, acrylic, acetate,
Other surfaces, including dental and veterinary products and
non-medical devices, made of silicone, polyurethanes, polyamides,
acrylates, ceramics, thermoplastic and elastomeric materials may be
treated with the nanoparticles compositions of present invention.
The nanoparticles compositions of the present invention deposit
nanoparticles on surfaces, and thus the surfaces that can be
treated or coated by the present invention are not limited to those
listed herein.
[0011] Nanoparticle compositions for different polymeric or metal
surfaces that can be prepared from liquid compositions are also
contemplated by the present invention. Such coating compositions
can be hardened by solvent loss or cured by thermal or radiation
exposure. Another aspect of the present invention comprise
compositions comprising the nanoparticle compositions taught herein
in combination with other active agents and antimicrobial agents
such as glasses and zeolites similar to those disclosed in U.S.
Pat. No. 5,049,139 and U.S. Pat. No. 6,248,342 which are
incorporated by reference in their entirety.
[0012] Different methods are taught to treat the surfaces with
nanoparticle compositions of the present invention. A method
comprises making nanoparticle compositions comprising
nanoparticles, contacting the nanoparticle composition and the
surface or surfaces for a sufficient period of time and rinsing the
surface of the excess of the nanoparticle composition and drying
the surface with nanoparticles adhered thereto. Several
modifications of the disclosed method are possible without
departing from the scope of the invention. Surfaces may also be
treated with non-aqueous metal nanoparticle compositions.
[0013] Silver or other metal nanoparticles may be formed in situ on
a surface. For instance, a method comprises providing a suspension
comprising finely dispersed particles of a silver or metal compound
in which a surface is immersed or contacts the suspension, followed
by addition of a reducing agent for a specified period of time or
until the silver or metal compound is reduced to nanoparticles,
that are predominantly mono-disperse, and the nanoparticles attach
or adhere to the surface.
[0014] The nanoparticle compositions of the present invention can
be used in other compositions where an antimicrobial environment or
antifouling environment is desired or where a reduction in
microbial growth, or a reduction in odor would be useful. For
example, the silver nanoparticles compositions may be added to
paints, cosmetics, on wound dressings to control of odor from wound
exudates, in dental compositions, in products used in bowel or
vascular surgery, oral hygiene products, bathroom products, textile
products, coatings, natural or synthetic polymers adhesives, paint
products, polymer films, paper, leather, rubber and plastic
articles. Unfinished and finished articles such as yarn or bolts of
cloth may also be rendered antimicrobial.
[0015] Other applications for silver nanoparticle compositions of
the present invention contemplated are in the catalysis of
oxidation of olefins, in catalytic reduction of hydrogen peroxide,
as polishing slurries, dissipation of static charge from surfaces,
increasing thermal conductivity of liquids, increasing electrical
conductivity, in the preparation of radio frequency or similar
radiation shields, and in analytical chemistry for surface enhanced
Raman spectroscopy.
[0016] The nanoparticle compositions of the present invention are
made by relatively straightforward methods, are water or solvent
based, possess long shelf life (nearly a year) and can be made in
large volumes and thus, the production process is scalable. The
components of the compositions are relatively non-hazardous and can
be washed off from treated surfaces to leave behind the
nanoparticles. The nanoparticle compositions may be optically
clear, non-viscous and may be stored for long periods of time at
room temperature, require no special storage conditions, are
resistant to discoloration when exposed to light, are thermally
stable, fairly stable to acids and bases, and are able to withstand
thermal cycling and conventional centrifugation.
[0017] The compositions of the present invention may comprise
silver or other metal nanoparticles. The silver or metal compounds
from which the nanoparticles of the present invention may comprise
any type of anion, including inorganic or organic anions. Such
anions may be organic, and include, but are not limited to, those
taught in PCT Applications Serial Nos. PCT/US05/27260 and
PCT/US05/27261 such as imidic organic anions, saccharine and
saccharinates.
[0018] The nanoparticles of the present invention are made by
combining a solvent, which may be water or a mixture of water and
known miscible organic solvents, generally less than 35% v/v
alcohol, a stabilizer which may be a polymer and/or a surfactant, a
silver compound and a reducing agent. A surfactant capable of
preventing agglomeration of the particles, such as a anionic,
non-ionic or amphoteric surfactant. Known water miscible organic
solvents include lower straight chain (C.sub.1-C.sub.6) or branched
alcohols, acetone, tetrahydrofuran, formamide, dimethyl formamide,
acetamide and other similar solvents. The reducing agent, which is
thought to trigger the nanoparticle formation in solution, includes
monomeric or polymeric organic chemical compounds comprising one or
more electron donating groups with substituted or non-substituted
nitrogen atoms, including but not limited to, triethanolamine and
N,N,N',N' tetramethyl ethylene diamine (TEMED).
[0019] The aqueous silver nanoparticle compositions may be
stabilized with a polymer. The polymer may be a homopolymer or
copolymer and may be synthetic or natural and is usually
water-soluble. Non-limiting examples of polymers are those
comprising amide or substituted amides, primary, secondary or
tertiary nitrogen, and urethane moiety in the main chain or side
chains.
[0020] Treated surfaces take on a coloration that increases in
intensity as more nanoparticles deposit. An aspect of the present
invention comprises a method for creating a more whitened surface
appearance for treated surfaces by applying to nanoparticle treated
surface a hydrogen peroxide solution, washing off the solution, and
drying the surface.
[0021] Antimicrobial silver compositions have utility not only in
imparting an antimicrobial property to medical devices but can also
reduce the odor causing bacteria, in items, including, but not
limited to, hosiery products such as panty hose, socks,
undergarments, swim wear products, outfits for hunters and
trekkers, ski wear products, athletic wear products for a variety
of sports, for disinfection purposes, it can be used in household
or consumer products such as bathroom or kitchen products, filters
for humidifiers, shower curtains, cutting boards, sink sponges,
bath sponges, and pumice stones. Compositions of the present
invention can be also be used to treat a foam or porous matrix that
can be added to unpotable water to disinfect it. In the
construction industry, for the control of mold and mildew in homes
the wooden structures during construction may be sprayed with the
antimicrobial silver compositions of the present invention.
Production of electrically conductive or reflective elastomeric
materials is made by causing nanoparticles of the present invention
to adhere to such elastomeric materials.
[0022] The present invention also contemplates use of radioactive
metals (for example .sup.110mAg.sup.+) compositions and their
methods of preparation and their uses, for example, in articles
that may be used as tracers. The nanoparticle compositions of the
present invention can also be the starting material for producing
dry nanoparticle powders suitable for many uses in material science
and metallurgical applications.
BRIEF DESCRIPTION OF FIGURES
[0023] FIG. 1 shows a representative spectrogram obtained by
UV-Visible spectroscopic analysis of an aqueous silver nanoparticle
composition in accordance with the present invention.
[0024] FIG. 2 shows a representative spectrogram obtained by
UV-Visible spectroscopic analysis of a non-aqueous silver
nanoparticle composition in accordance with the present invention,
wherein the solvent comprises chloroform.
[0025] FIG. 3 shows a representative transmission electron
micrograph of an aqueous silver nanoparticle composition in
accordance with the present invention.
[0026] FIG. 4 shows the particle size distribution of an aqueous
silver nanoparticle composition in accordance with the present
invention.
[0027] FIG. 5 shows a representative transmission electron
micrograph of a non-aqueous silver nanoparticle composition in
accordance with the present invention, wherein the solvent
comprises chloroform.
[0028] FIG. 6 shows the particle size distribution of a non-aqueous
silver nanoparticles composition in accordance with the present
invention, wherein the solvent comprises chloroform.
[0029] FIG. 7 shows representative spectrograms obtained by
UV-Visible spectroscopic analysis of an aqueous silver nanoparticle
composition in accordance with the present invention, wherein, as
indicated in the figure, the aqueous silver nanoparticle
composition was either prepared fresh (4 h) or analyzed at after
storage at about 25.degree. C. for about 11 months.
[0030] FIG. 8 shows representative spectrograms obtained by
UV-Visible spectroscopic analysis of various aqueous silver
nanoparticle compositions in accordance with the present invention
which were prepared from various sodium salts.
[0031] FIG. 9 shows representative spectrograms obtained by
UV-Visible spectroscopic analysis of various aqueous silver
nanoparticle compositions in accordance with the present invention
which were prepared from various sodium salts, wherein the various
aqueous silver nanoparticle compositions comprise the anion
indicated.
[0032] FIG. 10 shows representative spectrograms obtained by
UV-Visible spectroscopic analysis of various aqueous silver
nanoparticle compositions in accordance with the present invention
which were prepared from various sodium salts, wherein the various
aqueous silver nanoparticle compositions comprise Tween 20 (CAS No.
9005-64-5; C.sub.58H.sub.114O.sub.26; known alternatively as
polyoxyethylene (20) sorbitan monolaurate) at the indicated
concentrations (g/L).
[0033] FIG. 11 shows representative spectrograms obtained by
UV-Visible spectroscopic analysis of various aqueous silver
nanoparticle compositions in accordance with the present invention,
wherein the various aqueous silver nanoparticle compositions were
prepared from solutions comprising silver nitrate at a fixed
concentration of 0.1 M and sodium saccharinate at concentrations as
indicated.
[0034] FIG. 12 shows representative spectrograms obtained by
UV-Visible spectroscopic analysis of various aqueous silver
nanoparticle compositions in accordance with the present invention,
wherein the aqueous silver nanoparticle compositions were prepared
from solutions comprising silver nitrate at concentrations as
indicated.
[0035] FIG. 13 shows representative spectrograms obtained by
UV-Visible spectroscopic analysis of aqueous silver nanoparticle
compositions in accordance with the present invention, wherein the
aqueous silver nanoparticle compositions were prepared from
solutions comprising TEMED (CAS No. 110-18-9;
C.sub.6H.sub.16N.sub.2; known alternatively as
N,N,N',N'-Tetramethylethylenediamine) added in the volumes
indicated.
[0036] FIG. 14 shows representative spectrograms obtained by
UV-Visible spectroscopic analysis of aqueous silver nanoparticle
compositions in accordance with the present invention, wherein the
aqueous silver nanoparticle compositions were prepared by reverse
addition from solutions comprising addition of silver nitrate in
the volumes indicated.
[0037] FIG. 15 shows representative spectrograms obtained by
UV-Visible spectroscopic analysis of a non-aqueous silver
nanoparticle composition in accordance with the present invention,
wherein, the solvent comprised chloroform and as indicated in the
figure, the non-aqueous antimicrobial silver nanoparticle
composition was either prepared fresh (4 h) or analyzed at after
storage at about 25.degree. C. for about 3 months.
[0038] FIG. 16 shows a representative experiment measuring the
release of non-radioactive ("normal") and radioactive silver from a
nylon surface comprising an antimicrobial silver nanoparticles
composition in accordance with the present invention.
[0039] FIG. 17 shows representative results obtained for testing
relative biofilm formation on nylon tubing samples comprising an
antimicrobial silver nanoparticles composition in accordance with
the present invention.
[0040] FIG. 18 shows representative spectrograms obtained by
UV-Visible spectroscopic analysis of an aqueous antimicrobial
silver nanoparticle composition in accordance with the present
invention, wherein various aqueous antimicrobial silver
nanoparticles compositions were prepared from solutions comprising
various surfactants as indicated.
DETAILED DESCRIPTION OF THE INVENTION
[0041] The present invention comprises metal nanoparticles and
compositions comprising metal nanoparticles and methods for making
and using such compositions. The compositions comprising
nanoparticles may comprise aqueous solutions or non-aqueous
solutions. The nanoparticles of the compositions are generally
uniform in size, generally spherical, and can be preformed or made
in situ. Methods for using the compositions include, but are not
limited to providing antimicrobial characteristics to surfaces,
compositions and materials; providing odor control to compositions
and materials, preparation of silver- or metal-coated surfaces,
metal coating of flexible or elastomeric surfaces, anti-fouling
coatings of metal nanoparticles for surfaces, preparation of
ultra-smooth surfaces that are metal nanoparticle coated, surfaces
or articles that are reflective and/or conductive due to the
presence of the metal nanoparticles, and for use in manufacturing
and other applications. An aspect of the invention is to provide
medical devices that are antimicrobial for an extended period of
time and to provide methods for coating or treating medical devices
and materials to render them antimicrobial, and to provide a range
of amounts of silver to surfaces. Use of the metal silver, as an
example for metal nanoparticles of the present invention, is not
intended to be limiting to the metal nanoparticles taught and
claimed herein, and other metals can be used including, but not
limited to, silver, copper, zinc, gold, platinum, rhodium, iridium
and palladium, to form nanoparticles with an average size
.ltoreq.50 nm in diameter that are generally spherical.
[0042] The nanoparticle compositions of the present invention are
made from chemicals that are relatively non-hazardous. The metal
nanoparticle compositions of the present invention may be water
based and prepared by a wet process. Unlike the thermal evaporation
and other vacuum based processes that produce dry silver
nano-powders, the wet process produces silver nanoparticles that
stay in solution, unlike dry powders that may be a dust hazard
risk. As taught herein, the nanoparticles may be made with a metal,
and for ease of reference, these metal nanoparticles are often
referred to as silver nanoparticles. This reference is in no way is
a limitation of the nanoparticles taught herein and all metals
which function to make nanoparticles in the methods taught herein
are contemplated by the present invention.
[0043] A nanoparticle composition of the present invention
comprises metal, including but not limited to silver, copper, zinc,
gold, platinum, rhodium, iridium and palladium nanoparticles with
an average size .ltoreq.50 nm in diameter that are generally
spherical and having relatively narrow particle size distribution.
Although most particles are spherical other types of shapes can
also form and be present in the compositions of the present
invention.
[0044] Upon nanoparticle formation, the metal nanoparticles may
impart a characteristic color to the treated surface or article.
For example, silver nanoparticles impart a characteristic yellow to
yellow amber color, depending on the concentration of nanoparticles
present. When examined by UV-VIS spectroscopy a silver nanoparticle
compositions yielded a characteristic spectrum (FIG. 1) having a
wavelength maximum around 420-425 nm. According to the physics of
nanoparticles, the color is due to the plasmon resonance band
associated with spherical silver nanoparticles having size of 5 to
10 nm. Even after increasing the starting concentration of silver,
the peak value of 420-425 nm remains unchanged. This suggests that
the average particle size obtained in the compositions is
relatively independent of the starting concentration of the silver
nanoparticles. With an increase in nanoparticle size the absorption
peaks tend to red shift to a higher wavelength. The type of
stabilizing agent used may also affect the wavelength maximum and
the average particle size and the distribution. In the case of a
composition stabilized by polyacrylamide, the wavelength maximum at
445 nm suggests that average nanoparticles size is somewhat larger
than the composition stabilized by Polysorbate 20. The nanoparticle
compositions of the present invention generally show only a single
peak under UV-VIS spectroscopy.
[0045] Using the formula below, on a unit mass basis, one can
calculate the available surface area of an example of silver
nanoparticles of the present invention
Surface Area=6/[density.times.particle dia]
[0046] The available surface area per unit gram for a 15 nm
diameter particles is 3.81e5 per cm.sup.2/gm. The surface area for
other nanoparticles of the present invention can easily be
determined.
[0047] Non-aqueous compositions are contemplated by the present
invention. By non-aqueous it is meant that the solvent component of
the nanoparticle composition is non-aqueous, as in organic
solvents, those that are not miscible with water such as
chlorinated alkanes, esters of carboxylic acids (ethyl acetate,
butyl acetate), esters of ethylene glycol, propylene glycol,
toluene, xylene, lower alkenes, and this list is not exhaustive.
Generally, non-aqueous solvents are non-polar in nature, though
small amounts of water may be present. Even when solvents are
immiscible with water they will have some finite solubility in
water and similarly water will have a finite solubility in the
organic solvent. Generally, dissolved water in an organic solvent
will be less than 5% v/v. The non-aqueous solvents may be neat or
may be binary or multi-component mixtures. For example, a solvent
may be pure chloroform or it may be a mixture of chloroform and
ethyl acetate (a binary mixture) or it can be a mixture of
chloroform, ethyl acetate and toluene (ternary or multi-component
mixture). Further, a solvent may be polar (aprotic or protic) or
non-polar. They are useful in applications where aqueous silver
compositions cannot be used. Non-aqueous compositions may be based
on solvents that have a range of boiling points from room
temperature to above 300.degree. C. for some thermal transfer
fluids.
[0048] An example of a non-aqueous composition comprises chloroform
as solvent. FIG. 2 shows the UV-VIS spectrum of such a composition
with a maximum peak--430-435 nm, a slight red shift in spectrum in
comparison to an aqueous composition occurs. In all other respects,
the spectrum is identical to that for an aqueous composition. The
small red shift of the absorption peak (<5 nm) have previously
been reported in published literature (Wang et. al., Langmuir, Vol.
14, pp 602 (1998)). However it is not attributed to an increase
average size of silver nanoparticles but more likely a result of
changes in polarity of the solvent that may shift the plasmon
resonance band to the right. Further a spontaneous change in
particle size is also not possible simply as a result of the
extraction operation to draw silver nanoparticles from aqueous
phase into the non-aqueous phase.
[0049] A TEM micrograph of silver nanoparticles is presented in
FIG. 3. The majority of silver nanoparticles in the compositions of
the present inventions are generally close to spherical though
occasionally some flat faces may be present. The silver
nanoparticles shown were prepared in aqueous medium utilizing
Polysorbate 20, silver saccharinate and TEMED. By measuring the
diameter of at least 100 particles in the TEM image, an estimate of
size distribution of the silver nanoparticles was obtained. The
corresponding particle size distribution of silver nanoparticles in
aqueous medium is presented in FIG. 4 and shows an average size of
.about.15 nm. FIG. 5 shows TEM image of silver nanoparticles from a
non-aqueous composition. The nanoparticles were first prepared in
aqueous medium and then extracted into a non-aqueous solvent,
chloroform. A few drops of chloroform solution comprising silver
nanoparticles were dried on a standard copper grid. The majority of
silver nanoparticles in the compositions of the present inventions
are generally close to spherical. FIG. 6 shows the size
distribution of silver nanoparticles in a non-aqueous medium with
an average size approximately 11-12 nm with all particles smaller
than 25 nm. The average size of silver nanoparticles in a
non-aqueous composition is quite close to the average size in an
aqueous medium. This fact is not surprising when it is noted that
the silver nanoparticles in the non-aqueous medium were extracted
from the aqueous solution.
[0050] To be commercially feasible, the antimicrobial compositions
of the present invention must exhibit reasonable shelf life. FIG. 7
compares the UV-VIS spectra of an aqueous composition made fresh
and after aging the composition at ambient temperature (25.degree.
C.) for nearly a year. There is almost no difference between the
two, suggesting no change in the particles size or particle size
distribution. The data clearly demonstrate that the aqueous
compositions of the present invention possess excellent shelf
life
[0051] Long term shelf life is not limited only to the aqueous
compositions of the present invention but extend to non-aqueous
compositions as well. The non-aqueous composition was tested in
chloroform for over 3 months by UV-VIS spectroscopy and found no
change in the spectrum shape or peak wavelength.
[0052] In addition to uses in rendering medical and non-medical
articles antimicrobial, both the aqueous and non-aqueous silver
nanoparticles compositions can be used to impart antimicrobial
properties to fluid based compositions. Non-limiting examples of
fluid compositions include adhesives, household sprays,
disinfecting solutions or compositions such as those disclosed in
U.S. Pat. No. 4,915,955 and incorporated by reference herein its
entirety, coating compositions for indoor and outdoor wood
products, and personal lubricants.
[0053] The nanoparticle compositions of the present invention may
comprise a wide range of amounts of silver or other metals,
referred to as silver or metal loading. Different amounts of silver
in the compositions can be achieved simply by using the desired
amounts of silver compounds during the production. For example, it
would be logical to expect a larger amount of silver nanoparticle
deposition when untreated articles or surfaces are treated with
nanoparticle compositions comprising a higher number of silver
nanoparticles and vice versa. Alternately, an incremental amount of
silver loading on a silver treated surface can be achieved by a
secondary treatment using a silver composition having a lower
amount of silver. Using nanoparticle composition having a
particular silver amount, one can spray or dip an article or
surface multiple times to effect higher silver loading on the
article. Each successive dip or spray would cause an incremental
increase in silver loading until the desired level is achieved. The
nanoparticle compositions of the present invention are generally
non-viscous or have low viscosities and allow for uniform coating
or contacting of surfaces, particular surfaces micron sized
features and rendering them antimicrobial or functional for other
purposes.
[0054] Silver or metal content of nanoparticle compositions can be
adjusted by a variety of methods. One can initially select the
desired amount of the metal compound or dilute a nanoparticle
composition having a known amount of metal nanoparticles. The
diluent added may comprise water and may or may not comprise other
components such as surfactant or other miscible solvents. The metal
content may be increased by concentrating the nanoparticle
compositions by removal of solvent by means known to those
ordinarily skilled in the art. One can remove most of the solvent
from the nanoparticle composition, and re-dilute to regenerate the
nanoparticle composition to a different volume or the original
volume, without causing the nanoparticles to agglomerate.
[0055] The metal nanoparticles of the present invention are formed
from weakly water soluble silver compounds formed with a variety of
anions both inorganic and organic. However, even highly
water-soluble compounds may be used in the practice of the present
invention. Metal compounds with imidic organic anions are useful,
and though many examples are given with silver saccharinate, the
invention comprises any metal compound that will form nanoparticles
in the methods disclosed herein. Metal compounds having imidic
organic anions are the subject of PCT/US2005/27260 incorporated by
reference herein in its entirety, and all the compounds taught
therein are included in the present invention. Metal compounds with
derivatives of saccharin can be suitably employed. Other metal
compounds, made by the reaction of soluble metal salts with
compounds with active methylene groups e.g. acetylacetonate and
derivatives may also be used.
[0056] In one embodiment of the invention, antimicrobial compounds
comprise compounds of silver as represented by: [0057]
M.sup.+X.sub.(n) wherein, M is a metal, such as silver, zinc
copper, platinum, rhodium, iridium or palladium, n is 1 or more X
is selected from A, B or C where R.sub.1 and R.sub.2 are --P or
--WP; and [0058] W is a linker of branched alkyl chain of 1-27
carbon atoms, straight alkyl chain of 1-27 carbon atoms, monoethers
containing 2-20 carbon atoms and polyethers containing 2-20 carbon
atoms; and
[0059] P is hydrogen, halogen atoms, haloalkyl, amide, sulfate,
phosphate, quarternary ammonium, hydroxyl, hydroxymethyl,
phosphonate, amino, carboxyl, carboxymethyl, carbonyl, acetyl,
succinimidyl ester, isothiocyanate, isocyanate, iodoacetamide,
maleimide, sulfonyl halide, phosphoramidite, alkylimidate,
arylimidate, acide halide, substituted hydrazines, substituted
hydroxylamines, carbodiimides, cyano, nitro, fluormethyl,
nitrophenyl, sulfonamide, alkenyl or alkynyl; and
[0060] R.sub.3 and R.sub.4 are hydrogen, straight alkyl with
C.sub.1-C.sub.3 carbon atoms, optionally terminating in aryl or
substituted aryl groups, branched alkyl with C.sub.1-C.sub.8 carbon
atoms, phenyl, substituted phenyl, benzyl, substituted benzyl and
fluoromethyl; and
A is one of the following:
##STR00001##
and B is one of the following
##STR00002##
[0061] R.sub.1 and R.sub.2 are --P and --WP as described above,
and
[0062] W is a linker as described above, and R.sub.3 and R.sub.4
are as described above.
C=behenate or bis(2-ethylhexyl) sulfosuccinate
[0063] Another embodiment of the invention comprises complexes of
silver
M.sup.+[Y.sup.-].sub.n
where M is a metal, such as silver, zinc copper, platinum, rhodium,
iridium or palladium, n is 1 or more; and Y is the following:
##STR00003##
where R.sub.1 and R.sub.2 are selected from the group consisting of
P and WP; as described above, and W is a linker as described above.
R.sub.3 and R.sub.4 are described above and Z is C6 or C8
alkyl.
[0064] Another embodiment of the present invention comprises the
following where
M.sup.+[Y'.sup.-]n
where M is a metal, such as silver, zinc copper, platinum, rhodium,
iridium or palladium, N is 1 or more and Y'- is the following:
##STR00004##
where R.sub.1 and R.sub.2 are selected from the group consisting of
--P and --WP; as described above, and W is a linker as described
above. R.sub.3 and R.sub.4 are described above and Z is amino,
alkylamino, chloro, or HNX, wherein X in HNX comprises aryl,
hydroxyl, amino, NHC.sub.6H.sub.5, or NHCONH.sub.2. Other ligands
that form silver compounds of the present invention comprise the
following shown in Table 1:
TABLE-US-00001 TABLE 1 ID Name Structure 1.01
1,1-Dioxo-1,2-dihydro- 1.lamda..sup.6-benzo[.alpha.]isothiazol-
3-one ##STR00005## 1.02 Pyrrolo[3,4-f]isoindole- 1,3,5,7-tetraone
##STR00006## 1.03 Aziridine ##STR00007## 1.04 Azetidine
##STR00008## 1.05 Isoindole-1,3-dione ##STR00009## 1.06
Pyrimidine-2,4,6-trione ##STR00010## 1.07 2-Thioxo-dihydro-
pyrimidine-4,6-dione ##STR00011## 1.08 Pyrrole-2,5-dione
##STR00012## 1.09 Imidazole-2,4-dione ##STR00013## 1.10
Benzo[de]isoquinoline- 1,3-dione ##STR00014##
[0065] The nanoparticles may be made from a single silver compound
or mixtures of silver compounds. For example, a mixture might
comprise silver compounds having high and low water solubilities.
Further the binary mixture might comprise a range of 0 to 100% the
weakly water-soluble silver compound. For example, when preparing
silver nanoparticles, sodium saccharinate may be added to only 80%
of the amount required to react with silver nitrate, then add TEMED
and so on. Therefore in the mixture, there is silver nitrate
(soluble salt) and silver saccharinate (weakly soluble salt)
together. Similarly one can weigh out powder forms of silver
nitrate and silver propionate in any desired proportions (0% silver
nitrate to 100%). Metal compounds for use in compositions or
devices of the present invention wherein the compound is X+Y-,
wherein X is a metal, such as silver, zinc copper, platinum,
rhodium, iridium or palladium, and Y is acesulfame, or derivatives
thereof.
##STR00015##
R.sub.1 and R.sub.2 are a hydrogen atom, optionally a branched
alkyl group having from one to 20, or up to 10 carbon atoms, an
aromatic hydrocarbon radical having up to 10 carbon atoms, or an
aliphatic acyl radical having from two to four carbon atoms,
R.sub.2 is an optionally branched alkyl group having up to 20
carbon atoms, or up to 10 carbon atoms, or an aromatic hydrocarbon
radical having up to 10 carbon atoms, and in which R.sub.1 and
R.sub.2 may also be linked to form an isocyclic ring which
optionally may be substituted by further hydrocarbon radicals . . .
. Also included are the salts of the compounds of this formula.
Additional compounds are shown in Table 2.
TABLE-US-00002 TABLE 2 Name Structure 3,4-dihydro-6- methyl-1,2,3-
oxathiazin-4- one-2,2-dioxide ##STR00016## 3,4-dihydro-6-n-
butyl-1,2,3- oxathiazin-4- one-2,2-dioxide ##STR00017##
3,4-dihydro-6- phenyl-1,2,3- oxathiazin-4- one-2,2-dioxide
##STR00018## 3,4-dihydro-5,6- dimethyl-1,2,3- oxathiazin-4-one-
2,2-dioxide ##STR00019## 3,4-dihydro-5- methyl-6-ethyl-
1,2,3-oxathiazin- 4-one-2,2-dioxide ##STR00020## 3,4-dihydro-5-
methyl-6-phenyl- 1,2,3-oxathiazin- 4-one-2,2-dioxide ##STR00021##
3,4-dihydro-5-ethyl- 6-methyl-1,2,3- oxathiazin-4- one-2,2,-dioxide
##STR00022## 3,4-dihydro-5-n- propyl-6-methyl- 1,2,3-oxathiazin-
4-one-2,2-dioxide ##STR00023## 3-Amino- benzenesulfonic acid
##STR00024## 3,4-dihydro-5,6- tetramethylene-1,2,3-
oxathiazin-4-one- 2,2-dioxide ##STR00025## 3,4-dihydro-5-
phenyl-6-methyl- 1,2,3-oxathiazin-4- one-2,2-dioxide ##STR00026##
3,4-dihydro-5-ethyl- 6-n-propyl-1,2,3- oxathiazin-4-
one-2,2-dioxide ##STR00027## 3,4-dihydro-5,6- [2,1-(3,4-dihydro-
)naptho]- 1,2,3-oxathiazin- 4-one-2,2-dioxide ##STR00028##
3,4-dihydro-5-n- propyl-6-n-butyl- 1,2,3-oxathiazin-
4-one-2,2-dioxide ##STR00029## 3,4-dihydro-5-n- butyl-6-n-amyl-
1,2,3-oxathiazin- 4-one-2,2-dioxide ##STR00030## 3,4-dihydro-5-
isopropyl-6-methyl- 1,2,3-oxathiazin- 4-one-2,2-dioxide
##STR00031## 3,4-dihydro-5-n-octyl- 6-methyl-1,2,3-
oxathiazin-4-one- 2,2-dioxide ##STR00032##
The present invention comprises metal compounds comprising a metal
and saccharincarboxylic acids or saccharincarboxylic acid esters of
the formula:
##STR00033##
wherein the substituents have the following meanings: L and M are
hydrogen, alkyl, alkoxy, cyano, alkylsulfonyl, nitro,
trifluoromethyl and chlorine; and, R is H or alkyl with 1-6 carbon
atoms. The present invention further relates to derivatives of
saccharin of the formula:
##STR00034##
wherein the L and M are independently selected from hydrogen,
alkyl, alkoxy, cyano, alkylsulfonyl, nitro, trifluoromethyl and
chlorine.
[0066] The present invention comprises metal compounds comprising a
metal and derivatives of saccharin of the formula:
##STR00035##
wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are independently
selected from hydrogen, alkyl, alkoxy, cyano, alkylsulfonyl, nitro,
trifluoromethyl and chlorine.
[0067] The compositions of the present invention comprise a
solvent, and the solvent may be water or a mixture of water and
known miscible organic solvents, a stabilizing agent which may be a
polymer and/or a surfactant, a metal compounds such as a silver
compound and a reducing agent. The solvent may be water or a
mixture. If the solvent is a mixture where the water content may
range between 55% v/v and 95% v/v, the mixture may be any water
miscible organic solvents including, but not limited to, lower
straight chain (C.sub.1-C.sub.6) or branched alcohols, acetone,
tetrahydrofuran, formamide, dimethyl formamide, acetamide and other
similar solvents. If the stabilizing agent used is a surfactant,
surfactants including, but not limited to, polysorbates or Tweens,
are useful. Any suitable surfactant may be used. The reducing
agent, the agent that is thought to trigger the formation of silver
nanoparticles in the solution includes, but is not limited to,
tertiary, secondary and primary amines, tertiary, secondary and
primary diamines, homopolymers or copolymers having primary amine,
secondary amine and tertiary amine moieties. Amine compounds may be
aliphatic or aromatic. Likewise, aliphatic and aromatic primary and
substituted amides and polymeric amide analogs also can be used. An
aromatic amide such as diethyl toluamide known as DEET also can be
used. Other reducing agents are triethanolamine and N,N,N',N'
tetramethyl ethylene diamine (TEMED). Polymeric compounds having
TEMED moiety or other amines in the pendant chain or in the main
chain may also be used as reducing agent.
[0068] The stabilizing agent may be a polymer, and a surfactant may
or may not be used in addition to the polymer. The polymer may be a
homopolymer or copolymer and can be synthetic or naturally derived.
Non-limiting examples of polymers or copolymer suitable for use as
stabilizers in the compositions include polymers formed from
acrylamide and its derivatives, methacrylamide and its derivatives,
polyamides, polyurethanes, polymers having no particular backbone
but with urethane segments or tertiary amine groups in the side
chains, other polymers predominantly polar in nature or co-polymers
having a portion that is derived from polar co-monomers. Examples
include, but are not limited to, acrylamide, methacrylamide,
substituted acrylamides (i.e. --CONH.sub.2 is replaced by
CON(R1).sub.2, substituted methacrylamides, acrylic acid,
methacrylic acid, hydroxyethyl methacrylate, acrylonitrile,
2-acrylamido-2-methylpropane sulfonic acid and its salts (sodium,
potassium, ammonium), 2-vinyl pyrrolidone, 2-vinyl oxazoline, vinyl
acetate, maleic anhydride and others. Though not wishing to be
bound by any particular belief, it is believed that stability is
achieved by steric hindrance due to the presence of polymer chains
in such a way that the particle agglomeration and growth is
suppressed.
[0069] The nanoparticle compositions of the present invention are
fairly stable at low pH as well as high pH. The acids that can be
added to antimicrobial silver compositions are organic acids
including polymeric analogs such as polyacrylic acid, acetic acid,
citric acid and similar acids though adding nitric acid >10%
will destroy the compositions by dissolving the silver
nanoparticles. Nitric acid at concentration below 10% will also
destroy the compositions over time. Adding 10% v/v ammonia solution
does not affect the silver nanoparticle compositions (i.e. no color
change is seen).
[0070] Silver content, as nanoparticles, of the compositions can be
adjusted by initially selecting the starting amount of the silver
compound in making the nanoparticles or by diluting the composition
after making the nanoparticles. The optical density of the silver
nanoparticles compositions obtained using Tow concentrations of
silver salt may not reach 2.0. However, the optical density of
compositions made with concentrated silver salt solutions may be
extremely high requiring very high dilution (>100 fold) for
absorbance readings below 2. Just as nitric acid can destroy the
silver nanoparticles compositions by dissolving, adding certain
water miscible solvents causes nanoparticles to agglomerate and
precipitate out. The silver content can be increased by
concentrating the compositions by removal of solvent by means known
to those ordinarily skilled in the art. In fact one can remove most
of the solvent from the compositions, re-dilute to regenerate the
composition to the original state without causing significant
silver nanoparticle agglomeration.
[0071] The compositions of the present invention comprise silver
nanoparticles and may also comprise weakly soluble silver
compounds. In the course of the preparation of nanoparticles, a
silver salt may formed in situ which may not be converted to silver
nanoparticles during the reaction period. Silver compositions where
the silver may or may not be present as unreacted trace of a salt
are still encompassed by the present invention.
[0072] Another embodiment of the antimicrobial silver compositions
of the present invention is a non-aqueous antimicrobial silver
composition. Those skilled in the art have recognized that it is
difficult to produce stable silver nanoparticles in a non-aqueous
medium (Zeiri and Efrima, J. Phys. Chem., Vol. 96, pp 5908-5917
(1992)). The non-aqueous silver nanoparticles compositions of the
present invention may be prepared by extracting the nanoparticles
from the aqueous compositions into a non-aqueous phase. While
non-aqueous solutions containing silver have been made, the studies
have not shown their antimicrobial efficacy. By non-aqueous we mean
organic media that are generally immiscible with water over a large
ratio between water and immiscible solvent. Non-aqueous solvents
used in preparing the compositions of the present invention are
methylene chloride, chloroform and other aliphatic and aromatic
chlorinated solvents, cyclohexane, diethyl ether, ethyl acetate and
mixtures thereof. The amount of silver content in non-aqueous
compositions can be adjusted by choosing the proper amount of
silver in the preparation of the aqueous composition followed by
extraction of the aqueous composition and by further appropriate
dilution if needed.
[0073] One embodiment of the present invention is compositions
comprising the mixtures of a surfactant, a silver compound
preferably a salt (that can ionize to a silver cation and an anion
in solution), TEMED and water. These compositions are precursor
compositions to the nanoparticle compositions of the present
invention. Precursor compositions are then subjected to certain
treatments to transform them into nanoparticle compositions of the
present invention. For example, precursor compositions wherein the
metal compound comprises silver can be heated to initiate the
silver nanoparticles formation which is indicated by a yellow
color. Heating can be achieved by direct or indirect contact with
electric heating element, by IR lamps, by microwave energy, by
acoustic energy or by the use of other electromagnetic radiation.
Precursor compositions also may be converted to nanoparticle
compositions by exposure to intense light energy (UV lamps,
strobes, mercury vapor lamps, halogen lamps, laser beams etc).
Precursor compositions may be employed to form silver nanoparticle
compositions where the nanoparticles may take different shape and
form. They may also be used in electroless plating applications in
the preparation of silver coated reflective coatings on glass
beads, plastic surfaces for improving the light reflectance of
signs at night, and other uses. Precursor compositions which are
aqueous in nature may be made and stored below ambient temperature
and used subsequently without any loss of performance.
Methods of Preparation of Nanoparticle Compositions
[0074] Different methods may be employed to prepare nanoparticle
compositions of the present invention. An example of a silver
nanoparticle preparation method comprises the following steps:
[0075] (i) preparing the aqueous solutions of a surfactant (and/or
polymer), of sodium saccharinate (or a suitable anion) and of
soluble silver salt solution, [0076] (ii) adding a sodium salt
solution to the surfactant solution under stirring, [0077] (iii)
further adding soluble silver salt solution to cause the
precipitation of weakly soluble silver salt, [0078] (iv) adding the
tertiary diamine (TEMED) and, [0079] (v) causing a temperature
increase of the resulting solution and maintaining the increase for
specific time period.
[0080] In another embodiment, after the temperature increase for a
specific duration in step (v), the solution temperature is returned
to room temperature. If desired, the solution temperature may also
be lowered to a temperature other than room temperature. The
temperature can be above or below the room temperature. The weakly
soluble silver salt may not immediately form a clear precipitate,
but this should not be considered as limiting the practice of the
invention. A variation of the above method involves reversing the
order of addition of sodium salt solution and soluble silver salt
solution. A further variation involves substituting the surfactant
with a water soluble polymer solution in step (i) with the other
steps remaining the same, or reversing the sodium salt solution and
the silver salt solution. The sodium salt solution and the silver
salt solution can be added in no particular order.
[0081] In one embodiment using polyacrylamide as the stabilizer in
one composition of the present invention, the preparation is as
follows. [0082] (a) preparing the polymer solution of desired
concentration, [0083] (b) adding in succession under mixing
appropriate quantities of the alkali metal solution of appropriate
anion such as saccharinate, soluble silver salt solution and the
reducing agent and, [0084] (c) causing a temperature increase and
maintaining the temperature increase for a specified time period to
form nanoparticles.
[0085] Optionally the solution may not be heated but left at room
temperature under ambient light over a period of 24 hours to 7 days
to complete the formation of silver nanoparticles. The temperature
increase can be caused by methods known to those ordinarily skilled
in the art. Alternately, light energy sources may be employed to
form silver nanoparticles.
[0086] In preparing non-aqueous silver compositions of the present
invention, a method comprises [0087] (a) preparing the aqueous
silver nanoparticles composition with desired silver content, as
described herein; [0088] (b) reducing its volume to concentrate the
aqueous composition, [0089] (c) extracting the said concentrate
with non-aqueous solvent or solvent mixture and [0090] (d)
recovering the non-aqueous solvent or solvent mixture comprising
the extracted silver nanoparticles.
[0091] The step (b) above is optional especially if the silver
content of the aqueous composition is significantly high. Likewise
the step (c) optionally may be carried out multiple times, each
time using a fresh portion of the non-aqueous medium. The
temperature may be room temperature in the practice of this method
of the present invention.
[0092] In the preparation of non-aqueous silver compositions of the
present invention, one can optionally add to the non-aqueous
solvent a compound that may be a liquid or a solid having at least
one double bond in its molecular structure. For example one may add
such a compound as an extraction aid in amounts up to 25% of the
non-aqueous solvent to improve the extraction efficiency.
[0093] In an embodiment for making non-aqueous silver compositions,
a double bond containing compound may also serve as a stabilizing
agent in the preparation of the aqueous silver compositions. A
double bond containing compound, such as an oleate or a sorbate,
may be added instead of the surfactant. In the second case, one may
form silver sorbate (in the presence of surfactant) and then
convert the salt to nanoparticles using TEMED. The sorbate anion
has two double bonds and the rationale is this organic anion may
get readily transferred into the non-aqueous phase. Such a compound
for example may be an oleate, sorbate, fumarate or cinnamate. The
compounds listed by no means should be construed as limiting. The
resulting aqueous silver compositions extract more readily with
non-aqueous solvent transferring silver nanoparticles to the
non-aqueous medium with greater efficiency and help to maintain the
stability in non-aqueous environment.
[0094] A modification of the method of preparation of non-aqueous
silver composition is to extract silver nanoparticles from aqueous
silver compositions into a non-aqueous solution and then add a
double bond compound to increase the stability of the compositions.
One may add no more than 25% by weight of the non-aqueous solvent
of this compound. Non-limiting examples of double bond compounds
are oleic acid, sorbic acid, cinnamic acid and their derivatives.
Polymeric compounds such as polyacetylenes, polyvinylenes and their
derivatives can also be used that have some solubility in
extracting the non-aqueous media.
[0095] Other compounds may be added to the compositions. For
example, in some applications of non-aqueous compositions, long
alkyl chain bearing thiols may be added to aid in the formation of
metal nanoparticles layers on silicon and similar semi-conducting
surfaces.
Effect of Process Conditions
[0096] Various parameters may affect the properties and performance
of the compositions, such as silver compounds with different
anions, the concentration effects of the silver salts, the
stabilizing agent and the reducing agent. A robust process for
producing silver nanoparticles can be used for nanoparticle
deposition on various substrates.
Silver Salts with Different Anions
[0097] The antimicrobial silver compositions of the present
invention are convenient to prepare. They were conveniently
prepared starting from a variety of silver salts formed in-situ
from corresponding sodium salts. Though one can also directly use
silver salts in dry form if available without departing from the
scope of the invention. The salts used may comprise organic or
inorganic anions. The salts were then reduced to silver
nanoparticles in the presence of a surfactant, Polysorbate 20, and
TEMED by heating the resulting mixture in a microwave for a brief
period. Stock solutions of Polysorbate 20 (.about.76 gm/L), silver
nitrate (0.1M) and sodium salts (0.125M) were prepared and were
used in a volume ratio of 1.2/4.0/3.0/1.2 for Tween.RTM. 20, sodium
salt solution, silver nitrate solution and TEMED. UV/VIS spectra of
silver nanoparticles compositions were measured on a Beckmann DU-20
spectrophotometer by diluting the composition with water (25 .mu.l
in 3 mL water) in a 1 cm path length cuvette. Deionized water was
used as a reference.
[0098] Table 3 lists the sodium salts that were used in preparing
corresponding silver salts in-situ. Of the 15 salts tested, only
about half of them failed to form clear and stable yellow brown
silver nanoparticles solution (FIG. 8). Silver chloride (from
sodium chloride) gave a red or flesh color precipitate that
immediately settled at the tube bottom. In addition, silver salts
with the following anions did not yield stable nanoparticles
solutions: borate, tartarate, carbonate, citrate, phosphate and
lauryl sulfate though their spectra indicated a peak .about.420 nm
suggesting the formation of silver nanoparticles in size .about.10
nm (FIG. 9). Of the silver salt yielding solutions of poor
stability, half were organic anions and the other half were
inorganic suggesting the inability to form stable nanoparticles
solutions was not related to their organic or inorganic nature.
While the use of the silver salts of anions borate, tartarate,
carbonate, citrate, phosphate and lauryl sulfate may not be
optimal, their use in the preparation of antimicrobial compositions
is encompassed by the present invention.
TABLE-US-00003 TABLE 3 Sodium salts with various inorganic &
organic anions used in preparing silver nanoparticles compositions
Precipitate Sodium salt Salt anion or debris NP Solution type type
formed? Appearance Chloride Inorganic Yes Red, flesh color
suspension, agglomeration Borate Inorganic Yes Dark green/grey
suspension, agglomeration Carbonate Inorganic Yes Green/grey
suspension, agglomeration Sulfate Inorganic no, silver Brown/yellow
deposit on tube clear Phosphate Inorganic yes Grey clear,
agglomeration Acesulfame Organic no Brown/yellow clear Oxalate
Organic no, silver Brown/yellow deposit on tube clear EDTA Di -
salt Organic no Brown clear Tartarate Organic yes, some Green/grey
silver deposit suspension, agglomeration Acetate Organic no, silver
Brown/yellow deposit on tube clear Citrate Organic yes Light
green/beige suspension, agglomeration Propionate Organic no, silver
Brown clear deposit on tube Dioctyl Organic no, no silver Brown
clear sulfosuccinate deposit on tube Lauryl Sulfate Organic yes
Grey/green suspension, agglomeration Oleate Organic no, no silver
Brown clear deposit on tube Note: The precipitate or debris are
filtered off or centrifuged to prevent interference during UV/VIS
spectral measurements
[0099] Another observation was the in situ formed salts that
readily formed silver nanoparticles did not show any precipitate or
debris formation. The embodiment that yielded no precipitate or
debris comprises a method comprising the following steps of, [0100]
(i) preparing the aqueous solutions of the surfactant, sodium
saccharinate (or a suitable anion) and silver salt solution, [0101]
(ii) adding the sodium salt solution and the tertiary diamine
(TEMED) to the surfactant solution under stirring, [0102] (iii)
further adding soluble silver salt solution and, [0103] (iv)
causing a temperature increase of the resulting solution briefly
and then returning the temperature to room temperature.
[0104] Therefore, the method of adding silver nitrate as the last
ingredient in solution to previous ingredients is one embodiment of
the present invention. Volume ratios of starting reagents of
1.2/4.0/3.0/1.2 for Tween.RTM. 20, sodium salt solution, silver
nitrate solution and TEMED respectively are elements of an
embodiment for making nanoparticles compositions.
[0105] Visually, the nanoparticle solutions prepared using sodium
oleate was the best. There was no debris or any metallic silver
deposits on the tube wall. This was somewhat expected because
published work have reported on the beneficial effect of oleate on
silver nanoparticles (Wang et. al., Langmuir, Vol. 14, pp 602
(1998)). The oleate stabilized nanoparticles solutions tend to be
very stable. Stabilizing effect of oleate has been attributed to
silver's interaction with pi electrons of the oleate double
bond.
[0106] FIGS. 8 and 9 show plots of absorbance (normalized to OD=1)
versus wavelength for various organic and inorganic anions. The
.lamda..sub.max for inorganic anions is 415 nm (FIG. 8) and their
full width half maximum (FWHM) are of similar magnitude though the
sulfate anion shows a tighter spectrum. Interestingly, the borate
and carbonate anions project a spectrum that is similar to sulfate
yet the nanoparticles solutions are not very stable. This indicates
that under the conditions, the nanoparticles of small size
.about.10 nm and narrow distribution are formed with these two
anions, but the ionic environment in those solutions is unable to
prevent their agglomeration.
[0107] In comparison, silver nanoparticle solutions prepared from
various organic anions more or less exhibit greater stability and
the characteristic yellow brown color indicating presence of
nanoparticles. Only a small difference in the spectral maximum
among them is observed but with a wide variation in their spectra
(FIG. 9). For example, the solution with EDTA anion shows a peak OD
at 390 nm and relatively sharp spectra. On the other hand, a
tartarate based solution while having a peak at 415 nm reveals a
practically flat spectra. Such spectra indicate a very broad silver
particle distribution.
[0108] In Table 4 wavelengths are listed where peak OD was observed
and FWHM values derived from the spectral data of solutions shown
in the figures. Like inorganic anions we see .lamda..sub.max around
415-425 nm for organic anions. The fact that we observed the same
.lamda..sub.max over so many different anions suggests the
mechanism of silver nanoparticle formation have little to do with
the type of anions present. But, the agglomeration behavior
suggests that the stability of silver nanoparticles formed very
much depend on the anion type. Without being bound to any theory,
the inventors are hypothesizing that the interaction of anions with
silver nanoparticles if thermodynamically favorable yield stable
solutions.
[0109] In the same table, the FWHM is listed for each spectrum. The
number is a measure of the width of the spectrum. Smaller the FWHM
number indicates sharpness of the spectrum. The FWHM value of 53 nm
for EDTA anion is the smallest seen so far and that includes
TABLE-US-00004 TABLE 4 .lamda..sub.max & FWHM values of UV-VIS
spectra of silver nanoparticles compositions prepared by using
different anions FWHM (nm) Salt anion Anion type .lamda..sub.max
(nm) (full width half max) Chloride Inorganic .sup. ND.sup.+ ND
Borate Inorganic 415 90 Carbonate Inorganic 415 92 Sulfate
Inorganic 415 65 Phosphate Inorganic ND ND Acesulfame Organic 415
92 Oxalate Organic 415 70 EDTA Di - salt Organic 400 53 Tartarate
Organic 415 ND Acetate Organic 415 67 Citrate Organic ND ND
Propionate Organic 420 72 Dioctyl sulfosuccinate Organic 425 66
Lauryl Sulfate Organic ND ND Oleate Organic 420 91 ND = Not
determined
published literature. The oleate FWHM value of 91 nm is fairly
close to the value of 88 nm reported in a published paper that
extensively examined oleate containing silver nanoparticle
solutions prepared from silver nitrate. The present work differs
from published accounts in that the FWHM values herein are for
solutions made from silver salts with concentrations 10 to 100
times higher than those previously tested. The fact that similar
FWHM was observed means practically no agglomeration of
nanoparticles in the solutions occur even when using high silver
concentrations.
Process Parameters
[0110] The effects of varying the stabilizer amount, reactants
ratio, concentration of the reducing agent and the order of reagent
addition on quality of the nanoparticle solutions were
examined.
[0111] Appropriate stock solutions of sodium saccharinate, silver
nitrate and Tween.RTM. 20 or Polysorbate 20 were prepared in
de-ionized water. Reducing agent was used as received. Two methods
to prepare silver nanoparticles were used. In Method A, a silver
saccharinate suspension was first formed in the presence of
surfactant by reacting silver nitrate and sodium saccharinate. To
the suspension, TEMED was added and the resulting turbid mixture
heated briefly in microwave oven to complete the nanoparticle
formation. Method B involved mixing surfactant Tween 20, sodium
saccharinate and TEMED in a capped vial to form a clear solution.
Silver nitrate solution was added last and the vial contents heated
in microwave oven to produce nanoparticles. In all experiments,
microwave heating time was 10 seconds on medium setting (Oven Make:
Quasar Instant Matic Cooking, 1500 W).
[0112] Nanoparticle solutions were characterized by recording
UV-VIS spectrum typically over 400 to 500 nm range on Beckman DU-20
Spectrophotometer. For the spectral scan, the nanoparticle solution
was diluted with water (25 .mu.l in 3 mL water) and transferred to
a 1 cm path length plastic cuvette. De-ionized water was used as
reference. The recording of the UV/VIS spectrum is a quick,
convenient and easy way to establish the formation of silver
nanoparticles. It takes advantage of strong absorption by silver
nanoparticles (<50 nm in size) in the visible range (390 to 500
nm). Strong absorption is the result of plasmon resonance band of
nanometer size silver particles. Such spectral evidence is indirect
evidence of silver nanoparticles.
[0113] Method A was used to investigate the effects of Tween 20
concentration, the molar ratio of silver nitrate to sodium
saccharinate, silver nitrate concentration and TEMED concentration
on nanoparticle formation. Tables 5 to 8 show the experimental
details. The surfactant, sodium saccharinate, silver nitrate
solution and TEMED volumes were in 10:10:10:1 ratio unless stated
otherwise. See FIG. 10 for measurements relating to Table 5. See
FIG. 11 for measurements relating to Table 6. See FIG. 12 for
measurements relating to Table 7. See FIG. 13 for measurements
relating to Table 8.
TABLE-US-00005 TABLE 5 Variation of Tween 20 Surfactant
Concentration Exp Tween 20 NaSac.sup.+ AgNO.sub.3 TEMED
Precipitate/ Solution No. (g/L) soln (M) soln (M) (ml) debris?
appearance 1 16.5 0.125 0.1 0.3 Yes Dark brown, no Ag deposit 2
11.0 0.125 0.1 0.3 Yes Dark brown, no Ag deposit 3 5.5 0.125 0.1
0.3 Yes Dark brown, no silver deposit 4 0 0.125 0.1 0.3 Yes Ash
green 5 0 0.0625 0.05 0.3 Yes Ash green 6 0 0.03125 0.025 0.3 Yes
Ash green .sup.+= Sodium saccharinate
TABLE-US-00006 TABLE 6 Variation of Sodium Saccharinate
Concentration Exp Tween 20 NaSac.sup.+ AgNO.sub.3 TEMED
Precipitate/ No. (g/L) soln (M) soln (M) (ml) debris? Solution
appearance 1 16.5 0.125 0.1 0.3 Yes Dark brown, no Ag deposit 2
16.5 0.110 0.1 0.3 Yes Dark brown 3 16.5 0.105 0.1 0.3 Yes Dark
brown 4 16.5 0.102 0.1 0.3 Yes Dark brown 5 16.5 0.100 0.1 0.3 Yes
Dark brown 6 16.5 0.075 0.1 0.3 Yes Dark brown 7 16.5 0.050 0.1 0.3
Yes Dark brown 8 16.5 0.025 0.1 0.3 Yes Dark brown
TABLE-US-00007 TABLE 7 Variation of Silver Nitrate Concentration
Exp Tween 20 NaSac.sup.+ AgNO.sub.3 TEMED Precipitate/ No. (g/L)
soln (M) soln (M) (ml) debris? Solution appearance 1 16.5 0.1250
0.1 0.3 Yes Dark brown, no Ag deposit 2 16.5 0.0625 0.05 0.3 Little
Brown/yellow, Ag debris deposit 3 16.5 0.03125 0.025 0.3 No
Brown/yellow
TABLE-US-00008 TABLE 8 Variation of TEMED Amount* Exp Tween 20
NaSac.sup.+ AgNO.sub.3 TEMED Precipitate/ No. (g/L) soln (M) soln
(M) (ml) debris? Solution appearance 1 16.5 0.125 0.1 0.6 Yes Dark
brown (purple tint) 2 16.5 0.125 0.1 0.9 Yes Dark brown (purple
tint) 3 16.5 0.125 0.1 1.2 Little Dark brown (purple debris tint)
*= The volume ratio was increased in favor of TEMED without
changing volumes of other reactants
Effect of Tween 20 Concentration
[0114] When the Tween 20 concentration was varied between
.about.5.5 gm/L and 16.5 gm/L little variation in the color and
consistency of the nanoparticle solutions was observed. All showed
characteristic yellow brown color. The white precipitate observed
in the solutions was the undissolved silver saccharinate. No debris
due to nanoparticle agglomerates, which normally would be black,
was seen.
[0115] FIG. 10 shows the normalized UV-VIS spectra of nanoparticle
solutions with different amounts of Tween 20. The spectra of
solutions without Tween 20 was not measured. All spectra are almost
identical indicating that all three nanoparticle solutions are
practically the same. The spectral wavelength maximum falls around
415 nm. A full width at half maximum (FWHM) .about.90 value can be
inferred (by extrapolating the curve between 350-400 nm maintaining
symmetry) and is consistent with published literature. No
agglomeration of nanoparticles was observed despite employing
silver salt concentrations that were 10 to 100 times higher than
used in published reports. This was unexpected because previous
researchers have reported their inability to obtain stable
nanoparticle solutions for silver concentration above 0.01M even
after employing surfactants.
[0116] It is clear that stabilized silver nanoparticle solutions
with a 0.1M silver concentration are achieved even with a low Tween
20 concentration of .about.0.2% w/v. The data underscore the
robustness of the preparation method. However, without Tween 20 in
the solution, the nanoparticles agglomerated to form ash green
colored precipitate. This was true regardless of the starting
silver concentration. All solutions without Tween 20 failed to
develop characteristic yellow brown coloration.
[0117] The Tween 20 concentration was also varied on the higher
side i.e. 33 gm/L, 49.5 gm/L and 66 gm/L with matching increase in
TEMED concentration. While we continued to see nanoparticle
formation from the solution color and the observation of some
debris that precipitated from the reaction mixture, the spectral
signature of the solutions with higher Tween 20 remained
essentially similar (data not shown) again verifying the process
robustness. The data suggested that there was no advantage from the
process point of view in raising surfactant content beyond the
nominal value of 16.5 gm/L. However, higher concentrations of
surfactant Tween 20 or other stabilizing agents can still b used
without departing from the scope of the invention.
Effect of Sodium Saccharinate Concentration
[0118] The silver nitrate concentration was held at 0.1M and the
sodium saccharinate concentration was varied to maintain ratios of
saccharinate to nitrate between 0.025M and 1.25 to test the effect
of modifying the saccharinate concentration (Table 6). Though,
higher non-limiting ratios of saccharinate salt or salts of other
anions can be used without departing from the scope of the
invention. Ratios other than specified here may also be used. In
all cases, whether the ratio was >1 or <1, yellow brown
colored silver nanoparticles solutions were obtained with the
debris primarily consisting of undissolved silver saccharinate. The
spectra were practically the same (see FIG. 11) indicating the
nanoparticles sizes and distribution were with an average size of
5-10 nm.
Effect of Silver Nitrate Concentration
[0119] Keeping all other conditions including the molar ratio of
saccharinate to nitrate unchanged but varying the silver nitrate
concentration did not affect silver nanoparticle spectra (FIG. 12).
The data once again indicated that the nanoparticle size and size
distribution essentially remained unchanged. The appearance of the
solution also stayed the same i.e. yellow brown with little or no
debris (Table 7). These results gave the basis to use silver
nitrate concentration to vary final silver nanoparticles count in
the liquid composition depending on the product specification.
Effect of TEMED Concentration
[0120] In the experiments above, the TEMED to silver nitrate
solution volume ratio 1:10. Here that ratio varied between 2:10 to
4:10 and looked for any changes in nanoparticle solutions formed
(Table 8). Visually, the solutions remained similar but we also
observed a purple tint on vial walls when we increased TEMED
concentration.
[0121] The silver nanoparticles character (size and distribution)
did not change as the spectra are identical (FIG. 13).
Effect of Order of Reagent Addition
[0122] In all experiments above, Method A was used where silver
saccharinate was formed first. In Method B, silver nitrate was
added last and in varying amounts. All resulting nanoparticles
solutions showed little or no debris indicating no agglomeration.
No undissolved saccharinate precipitate was seen. The test tube
walls also had no metallic silver deposition indicating that the
nanoparticles formed stayed in solution. Out of the 4 tests
performed, the one where nitrate and saccharinate solution was in
3:4 ratio (0.75 ml in FIG. 14) gave qualitatively the best
solution.
[0123] FIG. 14 shows spectra of four solutions prepared by reverse
addition. In each case the wavelength maximum was 415 nm and the
shape of the spectra over 400 to 500 nm range matched. For one
solution, OD below 400 nm up to 350 nm was measured to see if there
was spectral symmetry around the maximum. The graph does indicate
that the spectrum is symmetrical.
[0124] In comparison to known silver nanoparticle containing
compositions, the nanoparticle compositions of the present
invention comprise silver nanoparticles in concentrations almost 4
to 15 times or in some cases even higher based on the OD values as
measured by UV-VIS spectrophotometer. This higher silver
concentration gives added advantage to the compositions of the
present invention in its ability to impart higher silver loadings
on surfaces contacting the compositions.
[0125] During the process parametric study, in a large number of
the tests conducted there was the presence of precipitate or debris
in the reaction vessel and occasionally on treated devices.
However, this should not be construed as a limitation of the
present invention. The precipitate present in the compositions is
entirely due to the poorly soluble silver salt that is formed. By
adjusting the starting concentration of soluble silver salt or by
appropriate dilution, the amount of weakly soluble salt that may
stay behind as precipitate can be reduced or eliminated.
Stability of Silver Nanoparticles Solutions
[0126] Another important parameter from a process point of view is
the stability of silver nanoparticles solutions as a function of
time. Demonstrating at least a few weeks of stability is quite
important. One indirect measure of stability would be no change in
UV-VIS spectrum which can be easily monitored with time. In FIG. 7
the UV/VIS spectra of saccharinate based aqueous silver
nanoparticles composition made fresh and one of the same
composition after 11 months period is presented. During this time,
the sample vial was stored at ambient temperature (22 C-25 C). No
change in spectra was seen between a freshly prepared solution and
the stored one, even after nearly a year. This data support a
finding that the silver nanoparticles solutions possess excellent
room temperature stability. Similarly, though there is small
nominal change in the spectra, there was good stability of a
chloroform based non-aqueous silver nanoparticles composition at
4.degree. C. for over 3 months (FIG. 15). The overall shape of the
curve does not change much indicating the particles size and
distribution does not change.
Compositional Ranges
[0127] The nanoparticle compositions may be derived from metal
compounds formed in situ by anion exchange in an aqueous solution
when a soluble metal salt such as silver nitrate and the sodium
salt possessing the desired anion are mixed. For example, to form
silver barbiturate, an exchange could occur between silver nitrate
and sodium barbiturate. Silver compounds may be formed in situ or
may be provided as final silver compounds. Silver compounds
commercially available as powders or crystals can substitute the
in-situ formed silver compounds in the preparation of nanoparticle
compositions of the present invention. In the practice of the
present invention, silver compounds as a single compound or
mixtures including, but not limited to, acesulfame, alkyl
carbonates, acetylacetonates, acetates, ascorbates, barbiturates,
benzoates, bitartrates, bis(2ethylhexyl) sulfosuccinate borates,
bromides, carbonates, chlorides, citrates, folates, fumarates,
gluconates, halides, hydantoins, substituted hydantoins, iodates,
iodides, lactates, laurates, oxalates, oxides, palmitates,
perborates, phenosulfonates, phosphates, propionates, saccharin and
derivatives, salicylates, sorbates, stearates, succinates,
sulfadiazines, sulfates, sulfides, sulfonates, and tartrates.
Another feature of the method of preparation of the compositions of
the present invention is that the soluble silver salt is converted
to a less soluble silver salt in situ. In the formation of the less
soluble silver saccharinate in the methods of preparation of the
present invention, an excess of alkali metal alkaline earth metal
saccharinate is maintained. The molar excess of the saccharinate
ranges between ratios of 1 and 5, ratios between 1.05 and 2, and
ratios between 1.1 and 1.5. The anion exchanging metal salts must
possess cations higher in the electronegativity scale than silver.
Non-limiting examples of available metal cations are sodium,
potassium, calcium, and lithium. Non-limiting examples of soluble
silver salts are silver nitrate, silver citrate, and silver
acetate. Any soluble silver salt may be employed.
[0128] An important feature of the nanoparticle compositions of the
present invention is that compositions spanning wide ranges of
concentrations can be made without encountering compatibility or
formulation problems. Silver content of the nanoparticle
compositions can vary anywhere in the range of 0.0001% to 10%, 0.1%
to 2%, and 0.1 to 5%. When preparing nanoparticle compositions with
silver content such as >5%, silver may precipitate out as flakes
(agglomerated state) if a sufficient amount of surfactant or
stabilizer is not maintained. The precipitate can be removed by
filtration
[0129] The stabilizing agents are useful in maintaining the
nanoparticles compositions of the present invention and can be a
surfactant or a polymer. The surfactant can be of any type-anionic,
cationic, nonionic, or amphoteric. A large variety of surfactants
are commercially available. Non-limiting examples of stabilizers
for use in the antimicrobial silver compositions are anionic,
nonionic and amphoteric surfactants. Different classes of compounds
are commercially available under each type of surfactants. Among
polymers, polyacrylamide and derivatives (homo- and copolymers
having acrylamide moiety, acrylamide with one or two substituents
on the nitrogen atom), methacrylamide polymers and derivatives
(homo- and copolymers having methacrylamide moiety, methacrylamide
with one or two substituents on the nitrogen atom), polyamides and
derivatives, polyurethanes and derivatives, polyamines and
derivatives can be used. Surfactants for use as stabilizing agents
are nonionic known as Polysorbates or Tween NN where NN is an
integer equal to 20, 40, 60 and 80.
[0130] The surfactant or stabilizer concentration in the
compositions in relation to silver content may vary between the
weight ratio of 0.1 and 500 but the total stabilizer concentration
should not exceed 40% of the weight of the compositions. A ratio of
values of surfactant concentrations of Polysorbate type generally
lies below 5% w/v in the compositions. However, when using the
polymeric stabilizers the values may also be higher than 5% w/v.
Higher amount of stabilizer readily stabilizes silver compositions
with higher amounts of silver loadings.
[0131] In most published studies on the preparation of compositions
comprising silver nanoparticles a need for a reducing agent is
recognized. Inorganic reducing agents have been employed but due to
their strong reducing capacity, the formation of silver
nanoparticles does not proceed in a controlled fashion thus
yielding large size particles and often broad size distribution.
Not all organic bases, when used as reducing agents, necessarily
yield small and uniform size silver nanoparticles. Illustrative
examples though not limiting in any way of reducing agents for use
in the preparation of the antimicrobial silver compositions of the
present invention are tertiary, secondary and primary amines;
tertiary, secondary and primary diamines; homopolymers or
copolymers having primary amine, secondary amine and tertiary amine
moieties. Amine compounds may be aliphatic or aromatic. An aromatic
amide such as diethyl toluamide popularly known as DEET also can be
used. Useful reducing agents are tertiary minds or diamines,
including triethanolamine and N,N,N',N' tetramethyl ethylene
diamine (TEMED). Polymeric compounds having a TEMED moiety in the
pendant chain or in the main chain also may be employed as the
reducing agent. The amount of the reducing agent in the
compositions again in relation to silver can vary between the
weight ratios of 0.1 and 500, ratios between 2 and 50, and ratios
between 4 and 20. The reducing agent can be added neat or in a
diluted form. Both these variations are encompassed by the present
invention.
[0132] Non-limiting examples of the solvent bases for the
antimicrobial silver compositions are water or water based
solutions where water is at least the major component. Other
miscible solvents such as lower alcohols (C.sub.6 or less), lower
diols (C.sub.6 or less), THF, DMSO, DMF etc. can be used either
singly or as multi-component mixtures with water. Non-limiting
examples of non-aqueous solvents or mixtures thereof are
chloroform, methylene chloride, acetone, methyl ethyl ketone,
cyclohexane, ethyl acetate, diethyl ether, lower alcohols (C.sub.4
or less), lower diols (C.sub.4 or less), THF, DMSO and DMF. A
variety of solvents that are HAPS free as defined under the clean
air act of 1990 can be utilized in the preparation of non-aqueous
silver compositions of the present invention.
Antimicrobial Medical and Non-Medical Devices
[0133] One embodiment of the present invention comprises medical
devices that are rendered antimicrobial using methods comprising
contacting the surfaces of the devices with the nanoparticles
compositions. Medical devices, without limitation, include
catheters (venous, urinary, Foley or pain management or variations
thereof), stents, abdominal plugs, cotton gauzes, fibrous wound
dressings (sheet and rope made of alginates, CMC or mixtures
thereof, crosslinked or uncrosslinked cellulose), collagen or
protein matrices, hemostatic materials, adhesive films, contact
lenses, lens cases, bandages, sutures, hernia meshes, mesh based
wound coverings, ostomy and other wound products, breast implants,
hydrogels, creams, lotions, gels (water based or oil based),
emulsions, liposomes, ointments, adhesives, porous inorganic
supports such as titania and those described in U.S. Pat. No.
4,906,466, the patent incorporated herein in its entirety by
reference, chitosan or chitin powders, metal based orthopedic
implants, metal screws and plates etc. Synthetic fabrics, those
based on nylon or its blends with other fabric making materials
(silk, rayon, wool, bamboo, polyester, acrylic, acetate)
impregnated with silver nanoparticles are contemplated by the
present invention. Devices, medical including dental and veterinary
products and non-medical, made of silicone, polyurethanes,
polyamides, acrylates, ceramics etc., and other thermoplastic
materials used in medical device industry and impregnated with
silver nanoparticles using liquid compositions of the present
invention are encompassed by the present invention. Various coating
compositions for different polymeric or metal surfaces that can be
prepared from liquid compositions are also covered by the present
invention. Such coating compositions can be hardened by solvent
loss or cured by thermal or radiation exposure. Another aspect of
the present invention are the blends of antimicrobial liquid
compositions of the present invention and other antimicrobial
agents such as glasses and zeolites similar to those disclosed in
U.S. Pat. No. 6,248,342 and U.S. Pat. No. 5,049,139 and
incorporated in their entirety herein by their reference.
[0134] Antimicrobial medical and non-medical devices of the present
invention can be made by treating the devices with antimicrobial
silver compositions of the present invention by different methods.
One disclosed method of the present invention comprises steps of
making the said compositions in liquid form, contacting the said
compositions and the devices surfaces for a sufficient period of
time to allow accumulation of nanoparticles and then rinsing the
excess of said composition away and drying the device. A
modification of the disclosed method may involve drying the surface
of material first and then rinsing off the surface to remove
excess. The method of contact may be dipping the device in the said
compositions or spraying the compositions on the device or coating
blends of polymer solution and said compositions. A variation of
the disclosed method can be employed to deposit different loadings
of silver on the surface of tubing. For example, initially, one
level of silver loading can be applied over the entire length of
the tubing. Then, if needed, a second application can be made over
2/3.sup.rd length of the tubing and finally only a 1/3.sup.rd
portion of the tubing may be treated yielding a tubing with 1.0
three levels of silver loadings. Using this approach any particular
deposition pattern of silver loading can be achieved. A similar
approach can also be implemented over a flat material creating
different silver loadings pattern over the entire area. One
embodiment of the present invention having three levels of silver
loadings can be a bathroom product such as shower curtain. In such
a product, the lower portion can be loaded with the highest level,
the middle portion with intermediate level and the top portion with
smallest level of silver. Such silver based curtain will prevent
the mold and mildew formation on the curtain.
[0135] Yet another modification of the above disclosed method
comprises steps of pre-treating the device surface with an agent
that enhances the adhesion of silver nanoparticles to the surface
or primes the surface to catalyze the silver nanoparticles
formation by reduction of the silver salt amine complex that
adsorbs on the surface. For example, g-aminopropyl triethoxysilane
or similar type of adhesion improving agent, such as a polar
compound, can be used. In another situation, the surface can be
primed by treatment with an aqueous solution of tin chloride,
rinsed with water, dried and subsequently treated with the aqueous
silver nanoparticles composition, washed and dried to complete the
silver deposition on the surface. In place of tin chloride, other
agents such as gold, platinum, palladium, copper compounds can be
used.
[0136] An important feature of the method of the present invention
disclosed above is to deposit very small levels of silver loading
uniformly on a surface. The surface may comprise a flat area, or
belong to a sphere, cylinder (solid or hollow) and can possess
nanometer sized features or micron sized features. The surface
silver loading levels contemplated by the invention can be varied
to meet the intended use, and may generally range from 0.1
ug/cm.sup.2 to 100 ug/cm.sup.2, 0.5 ug/cm.sup.2 to 50 ug/cm.sup.2,
and 5 ug/cm.sup.2 to 30 ug/cm.sup.2.
[0137] A method of preparing antimicrobial medical devices such as
hydrophilic foams, sheet dressings, fabrics, gauzes comprises of
the following steps: immersing the dressing in antimicrobial
aqueous composition, draining the excess liquid or blotting it
away, then re-immersing in a second non-aqueous liquid such as
ethanol, isopropanol or THF for a period effective enough to
destabilize the silver nanoparticles, thereby depositing them
permanently on the substrate, blotting away excess liquids and
finally drying the substrate device. A modification of the method
may comprise adding the antimicrobial silver nanoparticle
composition to the starting mixture of ingredients to prepare a
device (e.g. a polyurethane based foam).
[0138] A method may comprise forming a liquid layer or film of the
pre-mixed composition (composition that is not yet subject to a
temperature increase) on the desired surface and then using known
means to rapidly cause a temperature increase of the liquid film or
layer to initiate silver nanoparticle formation in the vicinity of
the surface to which the nanoparticles irreversibly adhere to yield
an antimicrobial surface. The means to rapidly increase temperature
may include acoustic radiation, microwave radiation and IR
radiation or other electromagnetic radiation. Thermal energy can
also be provided by way of an oven-like environment.
[0139] Yet another method disclosed for rendering medical devices
antimicrobial particularly those that can withstand higher
temperatures (without losing dimensional integrity) comprise the
steps of preparing the pre-mix composition, heating the medical
device to uniform temperature, spraying or dipping the device with
the pre-mix composition to initiate rapid reduction of the silver
compound in the liquid film adhering the devices surface to silver
nanoparticles that irreversibly attach. If the device is dipped
then it can be removed from the bath to dry the liquid film and the
devices surfaces rinsed cleaned with water or other solvents. If
the warmed device is sprayed then the liquid will be evaporated off
from its surfaces. The surfaces can be rinsed with water or similar
solvents. The rinse solution may be plain water or may comprise
other additives such as surfactants, acids or complexing
agents.
[0140] Modifications of the methods of the present invention for
rendering certain hydrophobic polymers antimicrobial may be
required. For example, silicone polymer surfaces may not readily
becoming antimicrobial by immersion in aqueous silver compositions.
One disclosed embodiment comprises a method comprising the steps of
immersing the silicone polymer in a swelling solvent (that is also
miscible with water) to effectively fill the pores with swelling
solvent, transferring the swollen silicone polymer substrate
quickly and immersing it in the aqueous silver composition of the
present invention for a specified period to cause the exchange of
solvent within the pores. As a result, the silver nanoparticles
from the aqueous composition are drawn into the pores thus
rendering the silicone polymer surface antimicrobial.
[0141] Medical devices or non-medical devices of the present
invention can also be treated with non-aqueous silver compositions.
Often the devices comprising alginates or CMC either as fibers or
foam fibers are not suitable for treatment using aqueous
compositions as they are unusable after coming in contact with
water rich composition. Instead such devices can be conveniently
treated with non-aqueous silver compositions by dipping method or
spraying the compositions on the substrates. After removal of
solvent that occurs by evaporation under normal conditions or by
vacuum, the surfaces of the devices are impregnated with silver
nanoparticles and becoming antimicrobial. Non-aqueous compositions
can also be used to treat medical devices made from other polymers
so long as the non-aqueous solvent is a non-solvent for that
polymer or does not diffuse into the device and cause swelling.
Non-aqueous silver nanoparticle compositions can also be used in
situations where swelling is not detrimental. For instance, PTFE
films can be rendered antimicrobial by briefly dipping them in a
chloroform solution of silver nanoparticles. Such solution also can
be sprayed to yield pale yellow colored PTFE.
[0142] Yet another distinguishing feature of the present invention
is a method of forming silver nanoparticles in situ on the surface
of a medical device. For instance, one disclosed embodiment
comprises a method of yielding an antimicrobial surface comprising
the steps of providing a surface coating comprising finely
dispersed particles of the silver compound and treating the coated
surfaces with a reducing agent for a specified period or until all
of the silver compound is reduced to silver nanoparticles
predominantly monodisperse in size. An example of a silver compound
that can be used in such a method is silver saccharinate. A
reducing agent is TEMED and can be used to carry out the reduction
at room temperature. Though not limiting, room temperature is
preferable for this method though higher temperatures can be
employed without departing from the present invention. The silver
nanoparticle compositions can be formed in situ in a polymeric
coating or in porous matrices such as ceramics, clay, zeolites,
alumina, silica, silicates with finely divided silver compounds and
saccharinate in particular by reduction with TEMED or similarly
listed amine compounds.
[0143] Utilizing the methods of preparation of the present
invention rendering a device surface antimicrobial can yield
different amounts of silver loading depending upon the treatment
conditions. However, a commercial process requires that the silver
loading meet the specifications. In the instances where the silver
loading may exceed the upper specification limit, the product
batches may be rejected incurring significant costs. In such
instances, it is desirable that the product batch be re-treated to
bring the silver loading within the specification.
[0144] One disclosed method of the present invention to re-treat
the device surface impregnated with excess silver nanoparticles
comprises the steps of, [0145] (a) preparing a solution of 0.5% to
15% nitric acid, [0146] (b) treating the device surface with the
said nitric acid solution for a specified period by immersing the
surface in the solution and, [0147] (c) thoroughly rinsing the
device surface with deionized water and drying.
[0148] This method can remove the impregnated silver selectively in
small portions and also can be utilized to completely strip the
silver off the device surface or to clean production equipment.
This method also can be used to strip silver off of a treated
surface to create patterned surfaces bearing silver
nanoparticles.
[0149] Another embodiment of the present invention discloses a
method for altering the amber or yellow brown color of the
antimicrobial medical and non-medical devices deposited with silver
to improve their aesthetic appeal. Yet another feature of the
present inventive method is that it can cause uniform color loss of
amber color of the silver nanoparticles bearing surfaces without
loss of silver. Even very hard to reach surfaces typical of some
pre-formed micron sized objects can be readily treated as the
peroxide solution can readily penetrate and wet most surfaces. The
inventive method comprises following steps of, [0150] (i) preparing
an aqueous solution of hydrogen peroxide in appropriate
concentration, [0151] (ii) treating the amber colored surfaces
comprising silver nanoparticles for a specific period, [0152] (iii)
rinsing off the treating solution thoroughly with deionized water
and drying the surfaces.
[0153] The hydrogen peroxide concentration in the treating solution
can be varied from as low as 3% to 30% by weight. The time period
of contact of surfaces with the treating solution will be dictated
by the peroxide concentration in solution. For instance, the rate
of color loss of amber color is slower at low peroxide
concentration and vice a versa. The duration of contact also
depends upon the product specification. If a product needs to be
distinguishable as a silver containing product from non-silver
containing product one may want to terminate the peroxide treatment
to leave behind a faint yellow tint to the surface. In addition to
water as the solvent for peroxide solution, small quantities of
solvents miscible with water (but those non-reactive to peroxide)
may be added.
[0154] One may provide hydrogen peroxide as vapors with or without
an inert carrier such as nitrogen to cause contact with the
surfaces to be treated without departing from the scope of the
invention. The use of temperatures above and below room temperature
in the peroxide treatment of silver nanoparticles comprising
surfaces are also encompassed by the present invention. Other
methods such as the use of ultrasonic energy to increase the color
loss by peroxide treatment also can be employed. Patterning
surfaces bearing silver nanoparticles by the hydrogen peroxide
vapors or aqueous solutions by appropriate masking is covered by
the present invention.
[0155] Nanoparticles, such as silver nanoparticles, can be used to
create a nanoparticle coated foam or porous matrix that can be
simply added to non-potable water to disinfect it. Such a product
may be more appealing to campers over current iodine based products
as there water with trace amount of silver has no taste. In the
construction industry, for the control of mold and mildew in homes
the wooden structures during construction may be sprayed with
antimicrobial silver compositions of the present invention.
[0156] The present invention also contemplates antimicrobial
radioactive silver (.sup.110mAg) compositions and their methods of
preparation. In the use of these compositions, the antimicrobial
property can be a concomitant property. These compositions can be
used to prepare radioactive tracers comprising .sup.110mAg
nanoparticles. One potential use of these compositions is to
prepare labels with small amount of .sup.110mAg nanoparticles
adhering to them. Such labels can be readily prepared by spitting
tiny drops of the solution on the label surfaces by inkjet printing
methods. Such labels can then be used where a product has shelf
life equal to the half life of .sup.110mAg. Because the amount of
radioactive .sup.110mAg is so small there is practically no risk of
harm to consumer or to the product. They also may be used as
tracers in security applications e.g. in authentication.
[0157] One embodiment comprises a method of preparation of
antimicrobial radioactive .sup.110mAg nanoparticles composition
comprising the steps of, [0158] (i) preparing a stabilizer
solution, [0159] (ii) successively adding to it the sodium or
suitable metal saccharinate solution, .sup.110mAg nitrate solution,
reducing agent solution and, [0160] (iii) causing a temperature
increase to initiate reduction of in-situ formed weakly soluble
silver saccharinate to form silver nanoparticles.
[0161] Optionally the temperature increase may be for a brief
period or may be maintained for a specified period.
Mechanism of Silver Release from Solid Surfaces
[0162] An aspect of the nanoparticle compositions is their ability
to efficiently deposit metal on surfaces in the form of
nanoparticles that adhere to surfaces strongly. Not only does the
deposition of nanoparticles take place, simple handling will not
dislodge the nanoparticles from the surface. They even cannot be
readily removed by ultrasonication suggesting practically
irreversible binding of the nanoparticle to the surface. However,
the nanoparticles can be disrupted or dissolve away if chemically
treated.
[0163] While the presence of elemental silver on the surface would
generally make that surface at least bacteriostatic, it would not
necessarily make it bactericidal. Even if it did, it would be
extremely difficult to sustain such an action. Increasing silver
loading may increase sustained release but it also increases the
risk of cytoxicity in end use. The nanoparticles or nanoparticle
compositions of the present invention possess the ability to impart
antimicrobial characteristic to surfaces that can sustain the
activity for long periods without being cytotoxic to mammalian
cells. FIG. 16 shows the amount of silver released (as ions) each
day from a nylon surface treated with said antimicrobial silver
composition. There is sustained prolonged antimicrobial activity
because the only change taking place on the surface after treatment
with the compositions is the impregnation by silver nanoparticles.
As the activity is due to silver ions, it is clear that the only
source of silver ions is the silver nanoparticles. The results
indicate that an effective amount of silver ions is released on a
continuous basis over long periods. The results were also confirmed
by a test carried out using nylon tubing impregnated with
radioactive silver nanoparticles. The release characteristics of
radioactive silver (FIG. 16) at similar silver loading are
comparable to those observed earlier.
[0164] Because it is well established that it is the silver ions
(Ag.sup.+) that bring about the antimicrobial action not Ag.sup.0,
it is believed that the source of antimicrobial silver ions are the
silver nanoparticles residing on the surface. The present results
show, sustained release of ionic silver from nanoparticles made by
the methods taught herein. Theoretical estimates show that at the
observed rate of egress of silver from the surface, it would take
over 150 days to completely deplete the silver, which is
extraordinary.
Other Applications
[0165] The antimicrobial silver compositions of the present
invention can also be the starting material for producing dry
silver nanopowders suitable for material science and metallurgical
applications. Such compositions, aqueous or non-aqueous could be
atomized in high temperature environment to produce dry silver
nanopowder. The compositions of the present invention can be
produced on a large scale and, because they are prepared from
relatively inexpensive chemicals, a commercial process could be
quite feasible and could compete with other dry processes for
silver nanopowder. Another advantage of the compositions of the
present invention in producing dry silver nanopowders is that the
nanoparticles average size of .about.10 nm is small and the size
distribution is relatively tight--two factors that could offer
competitive edge over silver nanopowders with broad size
distribution produced by dry processes.
[0166] Other applications for silver nanoparticles comprising
compositions of the present invention are in the catalysis of
oxidation of olefins, separation of olefinic compounds, as
polishing slurries, dissipation of static charge from surfaces,
increasing thermal conductivity of liquids, increasing electrical
conductivity, in the preparation of radio frequency or similar
radiation shields, in analytical chemistry for surface enhanced
Raman spectroscopy.
[0167] In one aspect, the present invention provides a method of
depositing silver nanoparticles on elastomeric articles (e.g.,
those made of silicone) and optionally, rendering the elastomer
conductive, and the silver nanoparticles coated elastomeric
articles produced therewith. The term "conductive," as used herein,
refers to a conductivity of the order of about 0.1 Siemens/m or
more. A conductive article includes a semi-conducting article and
an article with metal-like conductivity.
[0168] Among noble metals, silver is quite versatile as its
antimicrobial properties finding widespread uses in biological and
medical applications and its high electrical conductivity and
thermal conductivity finds applications in electrical, electronics,
and thermal transfer fields.
[0169] One application utilizing high electrical conductivity of
silver is in making conductive elastomers. The term "elastomer" is
meant to encompass materials that can withstand strains of 1% to as
high as 1000%. Such elastomers (e.g., elastomeric sheets or
gaskets) may contain up to about 60% silver in the form of fine
powder to yield high conductivities. These elastomers typically can
maintain their conductivities even after being stretched by 300%.
In sheet forms, these elastomers may be applied to a surface to
absorb radio frequencies, for example, thus making the surface
invisible to radar detection, thereby making it potentially useful
for military applications. However, with 60% of the weight of the
sheet elastomers being silver, it will add considerable weight to
an aircraft if the sheet elastomers are to be used. Thus there is
need for silver based conductive elastomers that can provide radar
invisibility and yet not add much weight to the base weight of the
aircraft. In addition, the conductive elastomer may also be
stretched significantly, for example, 300%, without loss of
conductivity.
[0170] In one embodiment, the present invention provides methods
for the deposition of silver nanoparticles on to an elastomeric
article, comprising contacting an elastomeric article with a silver
composition under conditions suitable for reducing silver ions to
silver nanoparticles, thereby providing a silver nanoparticles
coating to at least one surface or a portion of a surface of the
elastomeric article. The silver composition may comprise a silver
salt, a solvent, a reducing agent, and a stabilizing agent. In
another embodiment, the silver composition may comprise silver
nanoparticles produced in accordance with methods of the present
invention. For example, a silicone-based elastomeric article may be
immersed in a silver nanoparticle solution under conditions
suitable for reducing silver ions to silver nanoparticles and for
depositing the silver nanoparticles to the article. Upon completion
of the silver deposition step, the article may be rinsed thoroughly
with deionized water, sonicated to dislodge loosely adhering silver
nanoparticles, and dried in an oven to eliminate moisture. The
deposition process may be repeated to obtain a conductive
elastomeric article with desired silver loading, i.e., the desired
amount of silver nanoparticles present. The conductive elastomeric
article of the present invention may also be treated with
compositions, such as, Tollens reagent or its variants, to change,
modify, or improve its physical or functional properties.
[0171] The present invention in a general sense comprises methods
of preparing conductive elastomeric articles. The present invention
also covers the compositions comprising silver that are employed in
said methods, articles prepared using the said methods and the
methods of using the said articles in various applications.
[0172] One embodiment of the methods of preparing flexible
conductive elastomers comprises of (i) cleaning the virgin
elastomer surface, (ii) depositing silver nanoparticles on the
flexible elastomer surfaces, (iii) rinsing the treated surface and,
(iv) drying to get rid of moisture or solvent. Optionally after
obtaining a dried silver deposited surface, it may be annealed to
increase the strength of the silver coating deposited. To improve
the adhesion of silver to the surface, optionally a wet or dry
chemical treatment step after cleaning step above but before the
silver deposition step may be included.
[0173] The purpose of cleaning virgin surface is to ensure a
baseline clean surface. However, this step can be omitted without
departing from the scope of the invention. Cleaning step can be
achieved by the use of known solvents such as high purity
de-ionized water, isopropanol, ethanol, glycol, acetone, toluene,
naphtha fractions, fluorinated solvents, acetate based solvents and
mixtures thereof. Aqueous solutions may optionally contain
surfactants, soaps, acids and detergents or be blends with organic
solvents. It is understood that cleaning solvents or solutions are
selected so that they don't damage the elastomers by swelling or
cracking the surfaces. The cleaning step may involve only a single
rinse or multiple rinses or single rinses using different types of
solvents or solutions. One can rinse with an organic solvent (that
is miscible with the follow on solvent) followed by a rinse with
another appropriate solvent (either aqueous or non-aqueous). A
variety of solvent combinations are possible with the overall
objective of achieving a clean surface. The type of cleaning
solvents and solvents listed above are presented for illustration
and by no means should be construed as limiting.
[0174] In addition to the wet cleaning step disclosed above, dry
processes may also be employed to complete the task. For example,
plasma based cleaning processes (oxygen or mixtures of gases) may
be used to clean surface. An additional benefit of plasma cleaning
is to introduce polar groups on the surface especially on
hydrophobic polymer based elastomers e.g. silicone. The plasma
treatment may actually perform two functions; it may clean the
surface and also increase surface polarity that would improve the
adhesion of nanosilver to the surface. Alternately, a wet chemical
treatment with appropriate solutions of
.quadrature.-aminopropyltriethoxysilane or with sulfur compounds
such as thiogylcerol or dodecanethiol may be carried out to improve
adhesion of silver nanoparticles to the flexible surfaces. The use
of binding layers known to those ordinarily skilled in the art for
improving adhesion is also contemplated by the present
invention.
[0175] The deposition of silver nanoparticles on elastomeric
surfaces is carried out by immersing the surfaces in a silver
containing solution. The silver containing solution may be aqueous
or non-aqueous. In one embodiment, the silver containing solution
is made and then elastomeric samples are immersed in and treated
for a pre-determined temperature and time. In another variation,
the elastomeric samples are pre-arranged in a bath or a container
and then the silver containing solution is poured over the samples
and maintained at desired temperature for a given period. The
surfaces to be coated may be flat or be vertical--both
configurations are encompassed by the present invention. In another
embodiment it may be desirable to deposit silver only one side of a
slab or sheet. In yet another embodiment it may be desirable to
deposit silver only in unmasked area to form traces. In yet another
embodiment, the silver can be deposited to conductive levels on
flexible or non-flexible substrates having channels and selectively
remove silver from non-channel area to form conductive channels.
All such variations are encompassed by the present invention.
[0176] The silver deposition step may be carried out at room
temperature or optionally below or above room temperature.
Different levels of silver coating on flexible surfaces can be
achieved by the methods of the present invention. By varying the
starting concentration of the silver in the treating composition or
alternately at a given concentration carrying out the treatment at
a higher temperature or for a longer period one can vary the level
of silver loading in the deposited layer. One can treat the
elastomeric substrate multiple times to increase silver loading
even further. But generally less than five silver treatments are
used. There are several embodiments on how the silver treatments
may be carried out. For example, one may choose to apply silver
coating by using silver nanoparticles compositions of the present
invention in only one step or multiple successive steps.
[0177] In another embodiment, one may employ one treatment with
silver nanoparticles composition and a second silver treatment such
as with Tollen's reagents or its variants. In yet another
embodiment, one may employ one or more silver treatments with
silver nanoparticles compositions and then one silver treatment
with Tollen's reagent or similar composition. It is understood by
those skilled in the art that optionally one may include a
sensitizing solution treatment before treatment with Tollen's
reagent. Thus it will apparent to those skilled in the art that the
methods of present invention allow for excellent flexibility in
loading from small amounts of silver (for semi-conducting surfaces)
to very high levels of silver to yield metal-like conducting
elastomers. Though the values of conductivity for conductive
elastomers of the present invention may be 0.1 .mu.m or more, one
can prepare conducting elastomers with values <0.1 .mu.m without
departing from the scope of the invention. Alternately, the
conductive elastomers may be characterized by the amount of metal
deposited or coated on the surface. It is logical to correlate less
or more amounts of silver per unit area with lower or greater
levels of electrical conductivity. A range for the amount of metal
in the electrical conductive layer of conductive elastomers of the
present invention may be 0.03 mg/cm.sup.2-50 mg/cm.sup.2, 0.1-20
mg/cm.sup.2, or 0.5-5 mg/cm.sup.2.
[0178] The compositions used for depositing silver on flexible
surfaces are not very different than those used for depositing
silver nanoparticles on hard surfaces. A large number of
compositions for preparing silver nanoparticles are disclosed in
PCT/US2005/027261 patent application which is incorporated in its
entirety by reference. Any of the compositions disclosed in that
application may be used in the deposition of silver. In one
composition, equal volumes of solutions of Tween 20, silver nitrate
and sodium saccharinate were mixed under stirring followed by
1/10th the volume of Tween 20 solution as TEMED and used to treat
flexible silicone substrate in the form of 3''.times.1'' strips
0.1'' thick. It may be apparent to those ordinarily skilled in the
art that during multiple treatments to achieve higher loadings of
silver, one may use a composition based on saccharinate as anion in
the first treatment and an acetate based composition in subsequent
treatments either once or more than once. Compositions based on the
use of mixture of anions are also contemplated for use in the
silver deposition step. Even the well known Tollen's reagent or its
variants may be employed after the first tier treatment is by
silver nanoparticles solution. In one embodiment of the present
invention, after multiple treatments with silver containing
composition, but before silver deposition with Tollen's reagent,
the surfaces were treated with tin chloride solution. The tin
chloride is used to "seed" the surface to accelerate silver
deposition during treatment with Tollen's reagents. Those skilled
in the art will recognize that salts of other noble metals such as
palladium, copper, etc., may also be used in place of tin.
[0179] Compositions comprising TEMED and triethanolamine are used
but compositions comprising any suitable initiators listed in the
co-pending application no. PCT/US2005/027261 may be used for
depositing silver on elastomeric substrates. Similarly, a variety
of surfactants may be used in preparing compositions for depositing
nanoparticles, such as polysorbates.
[0180] After the completion of the silver deposition, the surfaces
are rinsed to remove excess silver solution and to wash loose
silver particles. For rinsing, traditional rinsing methods may be
employed. Silver coated parts may be sprayed with a rinse solvent
which may be water. Parts may be rinsed by simply raising them up
and down in the bath. De-ionized water may be used but water from
municipal sources also may be employed to reduce costs. In such
cases, the final rinse may be of de-ionized water. Additional
rinsing with water miscible alcohol also may be carried out to
dehydrate and dry the surfaces. High energy water jets or
sonication bath also may be used to additionally remove any
residual loose particles.
[0181] Drying of silver coated surfaces may be carried out by
letting them dry under ambient conditions or by blowing hot air
over the parts. The use of IR lamps or acoustic energy may be
employed if the coated surface areas are relatively small.
[0182] Optionally, an annealing step may be carried out to fuse the
metal nanoparticles coating to increase its strength. In the case
of the annealing step the underlying substrate is not damaged by
it. The annealing step may be carried out to provide thermal energy
to the silver coating to cause its temperature to be at least
between 100.degree. C. and the melting point of the metal by any
known means. The precise temperature needed to effect proper
annealing is dictated by the thickness of the silver layer to be
annealed, the type of substrate used, the thickness of the article
etc.
[0183] For instance, annealing may be carried out by exposing the
silver coated surfaces to an open flame. An open flame that may be
controllable may be generated using propane, butane, acetylene or
similar gases. During annealing by flame, it is important that the
surfaces may be kept moving so as not to cause hot spots. The
silver coated substrates may be held in fixtures that would rapidly
move the coated surfaces over the open flame. The fixtures are
sufficiently flexible to allow for annealing of all surfaces with
minimum difficulty.
[0184] Alternately, annealing may be attempted by placing the
silver coated substrates in ovens or furnaces maintained at desired
annealing temperature. In another embodiment the parts to be
annealed may be placed on a conveyor belt that travels through a
controlled temperature environment. In yet another modification,
substrates may be held in a waffle iron type device to anneal
surfaces from both sides simultaneously. In yet another
modification, annealing may be carried out by exposing the
substrates with silver nanoparticles with steam. The steam may be
at low pressure or high pressure and may be dry or wet.
Alternately, the silver coated substrates may be squeezed between
hot rollers to bring about annealing of the silver coating. The use
of electromagnetic radiations such as IR, high energy e-beam,
x-ray, nuclear radiation, lasers etc in annealing step is also
contemplated by the present invention. For examples, a high power
laser beam can be traversed across a silver coated elastomeric
substrate to create a known pattern of electrically conductive
traces.
[0185] A variety of elastomeric substrates can be deposited by
silver using the methods of the present invention. A select few but
non-limiting examples include silicone, polyurethane, synthetic and
natural rubber. For that matter, the underlying polymer, which may
be a synthetic or natural polymer and may exhibit ability to
withstand low or high strain are encompassed by the present
invention. Flexible substrate may comprise all known synthetic and
natural film forming polymers. Non-limiting examples of polymers
include polyimides, polyamides, polyacetals, polysulfones, PBTs,
PBO's, ethylene and propylene based polymers, acetate polymers,
polyacrylates, polycarbonate, PET's, PEN's or blends thereof or
co-polymeric derivatives. Though the substrates comprising the
listed polymers may be flexible they may exhibit only low levels of
reversible strain. Still these substrates are encompassed by the
present invention.
[0186] Various embodiments of conducting elastomeric articles can
be made by the methods of the present invention. In its simplest
and perhaps the most useful form, elastomeric sheets or strips can
be treated to deposit silver coating by inventive method or its
variants disclosed above. An embodiment in the form a flexible
conductive strip having multiple layers of silver or any of the
other metals mentioned can be made as follows. A strip of flexible
substrate e.g. silicone is treated to deposit silver coating on
both sides with larger surfaces and optionally annealed to obtain
conductive silver coating. The strip is then treated with a
solution of .gamma.-aminopropyltriethoxysilane or a mixture
comprising it to deposit a thin layer of the silane. After curing
the silane layer, a viscous coating of silicone pre-polymer such as
Sylgard 184 is applied on both sides of the strip to obtain a
flexible conductive elastomeric article having two silver layers.
In a variation of this embodiment, one can coat silver on both
sides as before. Thereafter, one can use a silver dissolving
solution e.g. concentrated nitric acid to remove coating one side
of the strip. A layer of another metal then can be deposited on the
stripped surface. Optionally, after annealing, a conductive
elastomeric strip with metal layers of different kind is obtained.
Again by applying a silicone coating on top of the metallic layer
with or without a binder layer such as
.gamma.-aminopropyltriethoxysilane, a sandwich elastomeric article
have two different metal layers is obtained. Following the method
described, one can also make a conductive elastomer with more than
two metallic layers.
Measurements for Conductivity
[0187] To assess if the surfaces of the elastomeric substrates
after silver or metal deposition have enough conductivity,
measurements using a simple multi-meter were carried out. However,
there are more sophisticated techniques such as 4 point probe
method that are commonly practiced in semiconductor industry for
measuring conductivity values with which those ordinarily skilled
in the art are familiar. The unit for reporting conductivity is
siemens/mm or siemens/cm which is reciprocal of electrical
resistivity reported in ohm-cm or ohm-m. It is straightforward to
convert to one set of units from another set and vice versa. Other
common unit for reporting conductive coatings is ohms/square which
is related to bulk resistivity by the following equation.
R=rL/(tW)
Where, R is the resistance of the thin film coating with length L
and width W, r is the bulk resistivity in ohm-meter or ohm-cm and,
t is the thickness. For a square resistor, L=W and therefore R=r/t.
Thus if thickness of the coating is known, the bulk resistivity r
can be determined and hence conductivity can be calculated.
[0188] In the case of the examples disclosed in the application,
the resistance values were measured using a multi-meter and
reported. It is well understood in the art that when a measurable
resistance reading is observed by the multi-meter it is a good
indicator that an electrical continuity is established via the
metal coating on the elastomeric substrate. For various prototypes
disclosed in the application, the electrical continuity remained
established even after application of high axial, bending or
torsional strains as indicated by measurable readings of the
resistances by multi-meter.
[0189] The methods of preparing elastomeric conductive articles
comprising silver or other metals disclosed herein yield articles
that show conductivity under high strain conditions. Without being
bound to any particular theory, it is theorized that the
nanoparticles are deposited on the elastomeric substrate and fill
the surface voids densely, yielding an electrically conducting
layer. Further annealing of this layer increases its strength
modulus that allows this layer to stretch readily even under high
strain without failure. As a result electrical continuity is
maintained.
[0190] The present invention further provides methods of using
conductive silver elastomeric articles, such as, without
limitation, to provide fireproof capability, to reduce
electromagnetic interference, to shield devices and circuits
against electrostatic discharging, and to impart radar invisibility
to military aircraft or other vehicles. To provide fireproof
capability, it is not essential that the elastomers have to be
electrically conductive.
[0191] In one aspect, the present invention provides methods and
compositions comprising for forming anti-fouling coatings to an
article, and the anti-fouling coatings produced therewith.
Materials that are immersed for long periods of time in fresh or
marine water are commonly fouled by the growth of microscopic and
macroscopic organisms. The accumulation of these organisms is
unsightly and in many instances interferes with function. The
natural process of accumulated growth is often referred to as
fouling of the surface. There are a number of agents that may be
applied to the surfaces to inhibit this growth. These agents are
known in the art as anti-fouling agents. While these agents are
highly effective, they have a fundamental limitation in that they
contain extremely toxic agents that often leech from the surface of
the article and accumulate in the local environment. Tin, copper
and zinc are examples of the agents that cause such problems when
used to kill local biota. Silver has been proven to be well
tolerated by the biota in the surrounding area yet be an effective
way of eliminating fouling of treated surfaces. In one embodiment,
the present invention provide a surface functionalization process,
where an anti-fouling coating to an article may be formed in
accordance with a method comprising contacting the article with a
silver composition under conditions suitable for reducing silver
ions to silver nanoparticles, thereby providing an anti-fouling
coating to at least one surface of the article, wherein the silver
composition comprises a silver salt, a solvent, a reducing agent,
and a stabilizing agent. For example, a surface functionalization
process is taught herein for the formation of a silver salt of
saccharinate in water containing a stabilizer agent (e.g., Tween)
and a reducing agent (e.g., TEMED) which upon mild heating forms
silver nanoparticles. Different types of surfaces can be treated
using the surface functionalization process and such treatments and
surfaces are contemplated by the methods of the present invention,
including steel, stainless steel, glass, titanium, copper, gold,
and a variety of polymers, such as, polypropylene, polycarbonate,
polyurethane, polyvinyl chloride, polystyrene, polysulfone, and a
number of silicones, including HTV and RTV. In some embodiments,
the silver nanoparticles so formed are bound to the materials very
tightly, some are bound tightly so that they can not be dislodged
by even sonication.
[0192] The fouling of surfaces which are exposed to fresh and
marine water in nature is thought to be due to the formation of a
biofilm, the articles with the silver nanoparticle coatings of the
present invention were tested for their resistance to biofilm
formation. The experimental data indicates that such articles
coated with nanoparticles resist biofilm formation. For example,
the surfaces of stainless steel and plastics (e.g., polycarbonate
and polypropylene) may be contacted with silver or other metal
nanoparticles using methods in accordance with embodiments of the
present invention. Such materials may be widely used for food
processing or storage equipment, which is prone to the formation of
biofilms during use. The surfaces treated in accordance with the
present invention prevent or reduce biofilm formation and thus
minimize or reduce the likelihood of transmission of microorganisms
which may cause food spoilage and disease. Any article or surface
that contacts a fluid and which could have a biofilm attach or grow
can be treated by the methods and compositions taught herein.
Examples of such articles or surfaces include, but are not limited
to, food storage and preparation devices, laboratory equipment,
marine or water vehicles, hulls, propellers, anchors, ballast
tanks, motors, pilings, liquid filtering equipment, tubing, ropes,
chains, fish tanks, liquid containers, water bowls, cooling towers,
water tanks, canteens, fuel tanks, and storage bins.
[0193] Antimicrobial surface coatings, such as, the antimicrobial
silver coating of the present invention, may prevent transmission
of disease between persons and/or animals. Surfaces that are
touched by humans or animals may be treated by the methods and
compositions taught herein and thus are made resistant to
transmission of microbes. This lessens the risk of transmission of
microbes of the environment. For example, the surface of a golf
ball is very often cleaned by golf players either by licking or by
moistening with saliva. Therefore ample opportunity exists for the
transfer of organisms from the surface of golf balls to the buccal
cavity of the players. Many of the organisms that may reside on the
surface of a golf ball may post severe health risk to people. In
one embodiment, the present invention provide a method for forming
an antimicrobial coating on a golf ball, comprising contacting a
golf bail with a silver composition under conditions suitable for
reducing silver ions to silver nanoparticles, thereby providing an
antimicrobial coating to the golf ball, wherein the silver
composition comprises a silver salt, a solvent, a reducing agent,
and a stabilizing agent. Any common article having a surface that
may contact a human or animal can be treated using the methods
taught herein to provide an antimicrobial coating to the
article.
[0194] The present invention further provides a method for making
ultra-smooth surfaces for applications in a wide range of fields,
including, without limitation, electronics and medicine. In one
embodiment, the method comprises contacting an article with the
silver composition taught herein under conditions suitable for
reducing silver ions to silver nanoparticles and orderly binding
the silver nanoparticles to at least one surface of the article,
wherein the silver composition comprises a silver salt, a solvent,
a reducing agent, and a stabilizing agent. Under such conditions,
the silver nanoparticles formed will attach to the surface.
Electron microscope images of the location of the particles show
that they may be evenly distributed on the surface when the surface
is very smooth. When the surface is irregular or rough, such as,
containing pitting, grooving, depressions, and/or extrusions, the
deposition of particles is initially in the lower parts of such
depressions. As more particles become deposited there is a tendency
for the depressions (e.g., grooves and pits) to be filled first.
The remainder of the surface is then coated by a more even
distribution of the particles. This process may form a very smooth
surface coating, i.e., a new surface on top of the coated surface.
In the case of the silver nanoparticles the effect is the formation
of an ultra-smooth and highly reflective surface.
[0195] In more than one embodiment of the present invention, silver
nanoparticles with a diameter ranging from about 0.5 to about 100
nanometers may be attached to surfaces. The union with surface may
be independent among the particles so that the particles may be
relatively independent from their adjacent particles. Such an
application of silver nanoparticles may produce a beneficial effect
for the treatment of flexible materials, such as, without
limitation, balloons, and synthetic or natural polymers. Surfaces
so treated with silver nanoparticles, even to a sufficient density
to become reflective and conductive, may be flexed, stretched,
and/or relaxed multiple times without causing the applied silver
nanoparticles to fall or flake off of the surface. Such
characteristics make the methods of the present invention useful
for the production of, for example, flexible mirrors and
stretchable elastic conductive polymers.
Microbiological Testing
[0196] The antimicrobial activity of device prototypes made with
antimicrobial silver compositions was verified by standard zone of
inhibition microbiology assay using Staphyloccocus aureus ATCC 6538
bacteria. Disks of .about.5-7 mm size were cut from samples and
placed on a Mueller Hinton Agar (MHA) plates that were inoculated
with bacteria and incubated overnight at 37 C. Disk from which
silver ions were released showed a clear zone around them.
Untreated samples and Silvasorb served as negative and positive
control respectively. The results from zone of inhibition assays
are presented in Tables 9 and 10. Because the device prototypes
comprise silver nanoparticles and not silver salts, ZOI assay may
not be the most suitable screening assay for antimicrobial
activity. Therefore, often we employed a bacterial challenge test
to evaluate microbiocidal activity and sustained release
characteristics. In an 8 hour bacterial challenge assay, catheter
sample pieces were immersed in culture medium in tubes and
inoculated with bacteria. The tubes were incubated at 37 C for 8
hours after which aliquots of culture medium were diluted and
spread on MHA plates and the numbers of bacterial colonies grown
after 24 hours were counted to determine the kill rate.
[0197] Liquid compositions with slightly different compositions
(see descriptive examples) were prepared quite readily and used to
impregnate variety of substrates with silver nanoparticles
including cotton gauze, nylon fiber and contact lenses and hydrogel
sheet. All prototypes including amorphous talc powder showed zones
of inhibition and sustained release antimicrobial
TABLE-US-00009 TABLE 9 ZOI Assay using Staphylococcus Aureus (Zone
of inhibition + disk dia/disk dia) Example Substrate ZOI data A1
Cotton gauze 9.5/7.0 A2 Cotton gauze 9.0/6.5 A3 Contact lens
8.0/6.5 A4 Si catheter 4.5/4.0 A5 Hydrogel 16.0/8.5 A6 Contact lens
9.0/6.5 B1 Hyd* polymer 8.5/6.0 B2 Hyd. Poly w/copperCu 10.0/5.0 B4
Talc powder 7.5/7.0 A9 Catheter w/hyd. Poly. coating 6.0/4.5 A10
Contact lens 10.0/6.0 A11 Cotton gauze 4.0/1.0 A12 Cotton gauze
3.0/1.0 A13 Contact lens 11.0/7.0 A15 Nylon catheter 3.0/1.0 A16
Nylon catheter 7.0/1.0 B9 Lubricating jelly 6.0/5.0 B10 Alginate
beads 7.0/3.0 A18 Breast implant membrane 8.0/6.0 A7 Nylon fiber
4.0/1.0 B15 Polypropylene woven fabric 9.0/7.0 *Hydrophillic
activity against Staphylococcus aureus (see Table 9). In silver
nanoparticle containing articles, the antimicrobial activity is
also sustained for 4 days as evident from the results in Table 10.
In the case of some substrates such as fiber, catheter and lens,
the antimicrobial activity was tested by the bacterial challenge
test. In such a test, the substrates are challenged with known
bacterial count while immersed in medium for 24 h. The medium was
then appropriately diluted and plated on MHA plates to estimate the
surviving bacterial count. The challenges were continued until the
substrates are exhausted of an effective amount of silver. The
bacterial challenge test results (Table 11) show that silver ions
release from nanoparticles embedded in substrate surface occurring
over 11 challenges i.e. 11 days. In contrast, similar commercial
products (Bardex & Lubrisil I.C. catheters) lasted only 3
days.
TABLE-US-00010 TABLE 10 Examples of Serial Transfer Results Against
Staphylococcus Aureus Example Substrate Day 1 Day 2 Day 3 Day 4 Day
5 A6 Contact lens 13.5/6.5 9.0/6.5 7.0/6.5 6.5/6.5 -- B1
Hyd.polymer 13.5/5.5 8.5/6.0 6.0/5.5 -- -- B2 Hyd.polymer 12.0/5.0
10.0/5.0 8.0/5.0 7.0/5.5 5.5/5.5 w/ copper
[0198] Biocompatibility of medical devices with tissues is
important. The agarose overlay assay is used to quantify the
inherent level of cytotoxicity present in device. The results from
agarose overlay tests verified that silver nanoparticle containing
substrates are non-cytotoxic as well as non-irritating. The
sonication of silver treated nylon fiber had no effect on
antimicrobial activity and repeatedly washing of the gauze did not
result in loss of activity. The results summarized here clearly
demonstrate that liquid compositions containing silver
nanoparticles are stable, can be made very easily and cheaply and
can be used to make a host of devices' surfaces antimicrobial.
[0199] In general, the present invention comprises compositions
comprising nanoparticles. Nanoparticle compositions comprise a
solvent, a silver nanoparticle, and a stabilizing agent. After
formation of the nanoparticles, there may be residual or unreacted
reducing agent remaining in the composition. It is understood that
a large number of nanoparticles form in the composition. The
solution may aqueous or non-aqueous. Aqueous solvents include
water, and non-aqueous solvents include methylene chloride,
chloroform other aliphatic and aromatic chlorinated solvents,
cyclohexane, diethyl ether, ethyl acetate and mixtures thereof,
stabilizing agents, stabilizers, or other similar terms, which are
used interchangeably include a polymer, a surfactant or both.
Polymers include a homopolymer copolymer, synthetic or naturally
derived, polymers of acrylamide and its derivatives, methacrylamide
and its derivatives, polyamides, polyurethanes, polymers having no
particular backbone but with urethane segments or tertiary amine
groups in the side chains, other polymers predominantly polar in
nature or co-polymers having a portion that is derived from polar
co-monomers, methaacrylamide, substituted acrylamides, substituted
methaacrylamides, acrylic acid, methacrylic acid, hydroxyethyl
methacrylate, acrylonitrile, 2-acrylamido-2-methylpropane sulfonic
acid and its salts (sodium, potassium, ammonium), 2-vinyl
pyrrolidone, 2-vinyl oxazoline, vinyl acetate, maleic anhydride.
Surfactants may be anionic, nonionic, or amphoteric
surfactants.
[0200] Methods of making silver nanoparticles comprise a) adding in
no particular order, an aqueous solution of a stabilizing agent
solution, an anionic donating solution and a soluble silver salt
solution, and b) adding a tertiary diamine solution, and further c)
heating the final solution to increase the reaction. The method
further comprises forming the nanoparticles in situ on the surface
of an article. The articles may be a woven or nonwoven fiber
article article. The article may be a medical device, polymer, a
fiber, a metal, glass, ceramic, fabric or combination thereof.
[0201] The nanoparticles may be extracted into a non-aqueous
solution. The invention also comprises methods of treating a
surface with silver nanoparticles, comprising, a) contacting a
surface with a solution comprising silver nanoparticles for a time
sufficient for an effective amount of nanoparticles to bind to the
surface, and b) rinsing the solution from the surface. The steps of
contacting and rinsing may be repeated multiple times to increase
the number of nanoparticles adhering to the surface. The surface
contacted may be a medical device or any of the other articles or
surfaces taught herein. The method further comprises, contacting
the surface with nanoparticles adhered thereto with an aqueous
solution of hydrogen peroxide for a sufficient period of time, and,
rinsing the hydrogen peroxide solution from the surface, wherein
the surface contacted may be a medical device, polymer, a fiber, a
metal, glass, ceramic, fabric or combination thereof.
[0202] The present invention comprises methods of rendering an
elastomeric surface electrically conductive, comprising, a)
contacting an elastomeric surface with a solution comprising metal
nanoparticles for a time sufficient for an effective amount of the
nanoparticles to adhere to the surface, and b) rinsing the surface.
Such elastomeric surfaces may optionally be reflective. Such
elastomeric surfaces may be reflective and not electrically
conductive. Metal nanoparticles used in such methods may be made by
methods comprising, a) adding in no particular order, an aqueous
solution of a stabilizing agent solution, an anionic donating
solution and a soluble metal salt solution, and b) adding a
reducing solution. The metal nanoparticle may comprise silver,
gold, platinum, iridium, rhodium, palladium, copper or zinc. The
method for making the metal nanoparticle may further comprise
heating the final solution. The contacting and rinsing steps may be
repeated multiple times to increase the number of nanoparticles
adhering to the surface. The surface contacted may be silicone,
polyurethane, synthetic or natural rubber, a synthetic or natural
polymer, flexible polymers of polyimides, polyamides, polyacetals,
polysulfones, PBTs, PBO's, ethylene and propylene based polymers,
acetate polymers, polyacrylates, polycarbonate, PET's, PEN's or
blends thereof or co-polymeric derivatives. The elastomeric or
flexible surfaces may be further treated by c) contacting the
elastomeric surface with nanoparticles adhered thereto with an
aqueous solution of hydrogen peroxide for a sufficient period of
time, and, d) rinsing the hydrogen peroxide solution from the
surface.
[0203] The present invention comprises elastomeric surfaces and
articles made by such methods, wherein an article produced by a
method of rendering an elastomeric surface electrically conductive
or optionally, wherein the method comprises a) contacting an
elastomeric surface with a solution comprising metal nanoparticles
for a time sufficient for an effective amount of the nanoparticles
to adhere to the surface, and b) rinsing the surface. Such articles
or surfaces may comprise flexible mirrors, stretchable elastic
conductive polymers, articles used to reduce electromagnetic
interference, to shield devices and circuits against electrostatic
discharging, and to impart radar invisibility to aircraft or other
vehicles.
[0204] The present invention comprises methods of rendering an
article or surface contacting a fluid resistant to biofilm
formation, comprising, a) contacting the article or surface with a
solution comprising metal nanoparticles for a time sufficient for
an effective amount of the nanoparticles to adhere to the surface,
and b) rinsing the surface. Metal nanoparticles used in such
methods may be made by methods comprising, a) adding in no
particular order, an aqueous solution of a stabilizing agent
solution, an anionic donating solution and a soluble metal salt
solution, and b) adding a reducing solution. Metal nanoparticles
used in such methods may be made by methods comprising, a) adding
in no particular order, an aqueous solution of a stabilizing agent
solution, an anionic donating solution and a soluble metal salt
solution, and b) adding a reducing solution. The metal nanoparticle
may comprise silver, gold, platinum, iridium, rhodium, palladium,
copper or zinc. The method for making the metal nanoparticle may
further comprise heating the final solution. The contacting and
rinsing steps may be repeated multiple times to increase the number
of nanoparticles adhering to the surface. The article or surface
contacting a fluid that is contacted by the nanoparticles may be
made of steel, stainless steel, glass, titanium, copper, gold,
synthetic and natural polymers, polypropylene, polycarbonate,
polyurethane, polyvinyl chloride, polystyrene, polysulfone,
silicones, HTV, RTV, blends or co-polymeric derivatives. The
article or surface contacting a fluid to be made resistant to
biofilm formation may be further treated by c) contacting the
article or surface contacting a fluid with nanoparticles adhered
thereto with an aqueous solution of hydrogen peroxide for a
sufficient period of time, and, d) rinsing the hydrogen peroxide
solution from the surface. The present invention also comprises
articles produced by rendering an article or surface contacting a
fluid resistant to biofilm formation, wherein the method comprises
a) contacting an article or surface contacting a fluid with a
solution comprising metal nanoparticles for a time sufficient for
an effective amount of the nanoparticles to adhere to the article
or surface, and b) rinsing the article or surface. Such articles
include, but are not limited to, food storage and preparation
devices, laboratory equipment, marine or water vehicles, hulls,
propellers, anchors, ballast tanks, motors, pilings, liquid
filtering equipment, tubing, ropes, chains, fish tanks, liquid
containers, water bowls, cooling towers, water tanks, canteens,
fuel tanks, or storage bins.
[0205] The present invention comprises methods of making metal
nanoparticles comprising, a) adding in no particular order, an
aqueous solution of a stabilizing agent solution, an anionic
donating solution and a soluble metal salt solution, and, b) adding
a reducing solution. The stabilizing agent solution comprises a
surfactant, a polymer or both. The polymer is a homopolymer
copolymer, synthetic or naturally derived, polymers of acrylamide
and its derivatives, methacrylamide and its derivatives,
polyamides, polyurethanes, polymers having no particular backbone
but with urethane segments or tertiary amine groups in the side
chains, other polymers predominantly polar in nature or co-polymers
having a portion that is derived from polar co-monomers,
methacrylamide, substituted acrylamides, substituted
methaacrylamides, acrylic acid, methacrylic acid, hydroxyethyl
methacrylate, acrylonitrile, 2-acrylamido-2-methylpropane sulfonic
acid and its salts (sodium, potassium, ammonium), 2-vinyl
pyrrolidone, 2-vinyl oxazoline, vinyl acetate, maleic anhydride.
The metal nanoparticles may be formed in situ on a surface or the
surface of an article. The nanoparticles may be extracted into a
non-aqueous solution. The present invention also comprises metal
nanoparticles made by such methods.
[0206] It must be noted that, as used in this specification and the
appended claims, the singular forms "a", "an", and "the" include
plural referents unless the context clearly dictates otherwise.
[0207] All patents, patent applications and references included
herein are specifically incorporated by reference in their
entireties.
[0208] It should be understood, of course, that the foregoing
relates only to exemplary embodiments of the present invention and
that numerous modifications or alterations may be made therein
without departing from the spirit and the scope of the invention as
set forth in this disclosure.
[0209] Although the exemplary embodiments of the present invention
are provided herein, the present invention is not limited to these
embodiments. There are numerous modifications or alterations that
may suggest themselves to those skilled in the art.
[0210] The present invention is further illustrated by way of the
examples contained herein, which are provided for clarity of
understanding. The exemplary embodiments should not to be construed
in any way as imposing limitations upon the scope thereof. On the
contrary, it is to be clearly understood that resort may be had to
various other embodiments, modifications, and equivalents thereof
which, after reading the description herein, may suggest themselves
to those skilled in the art without departing from the spirit of
the present invention and/or the scope of the appended claims.
EXAMPLES
Antimicrobial Device Examples 1-37
Example 1
Cotton Gauze
[0211] Dimethyl formamide (5 ml) was heated in beaker to .about.60
C under stirring. After the stir bar was removed a 2''.times.2''
cotton gauze (Curity brand, The Kendall Company, Mansfield, Mass.)
was placed in DMF to soak up all solvent. Silver nitrate solution
(0.3 ml, 0.1M) was pipetted over the gauze. Within a minute the
gauze turned yellow. After 5 minutes, the beaker was removed from
the hot plate and cooled to room temperature. The pale yellow
colored gauze was thoroughly rinsed with de-ionized water, blotted
and dried in oven at 40 C.
TABLE-US-00011 TABLE 9 Examples of Sustained Release of Silver from
Bacterial Challenge Test Against Pseudomonas Aeruginosa ATCC
9027(Each challenge is 24 h) % Kill Rate of Pseudomonas Aeruginosa
Challenge Inoculation Example Example Example Example No. size
(cfu/ml) 15 16 14 13 1 6300 100 100 100 100 2 4600 100 100 100 100
3 8700 100 100 100 100 4 3000 66.67 100 100 100 5 7000 100 0 100
97.14 6 8000 100 0 100 100 7 4000 100 Stopped 100 100 8 7000 100
94.14 57.14 9 5000 100 100 100 10 9000 100 100 100 11 4000 100 100
100 12 8000 54.88 0 0 13 6000 0 0 0
Bio-Film Inhibition Test
[0212] For in-dwelling medical devices such as urinary or venous
catheters, having antimicrobial surface characteristics is very
helpful for minimizing infections. But, even more important is the
ability of such devices to prevent bio-film formation. Once
bacteria have formed bio-films, they use it as shield making it
difficult to get rid of them. Antibiotics or other drugs are not
effective. One important distinguishing feature of the
antimicrobial devices of the present invention is their ability to
inhibit bio-film formation. To examine the bio-film inhibition
characteristics of the antimicrobial nylon tubing, a method based
on following principle was employed.
[0213] Bio-film formation can be evaluated by immersing the test
article in test medium that has been inoculated with the challenge
organism. After appropriate incubation, bio-film formation is
assessed by determining the amount of carbohydrate specific dye
that is bound on the surface of the device. There is a quantitative
relationship between the extent of bio-film formation and residual
carbohydrate on the surface. This can be quantified by first
extracting the dye in a suitable solvent and then measuring the OD
on a spectrophotometer.
[0214] FIG. 17 summarizes the results of bio-film testing on nylon
tubing samples with silver loading (in the form of nanoparticles)
of .about.600 ppm (based on the tubing weight). The silver treated
samples strongly inhibit bio-film formation against, E. Coli,
methicillin resistant staphylococcus aureus, pseudomonas aeruginosa
and candida albicans. In comparison, untreated device samples show
no inhibition (high OD values). The results unequivocally show the
resistance of the device of the present invention to bio-film
formation.
Example 2
Cotton Gauze
[0215] Gauze was treated exactly as in example 1 except the silver
nitrate solution concentration was 1.0M.
Example 3
Contact Lens
[0216] Contact lens (SEES, CibaVision Corporation, Duluth, Ga.) was
rinsed clean off the preservative solution and immersed in hot DMF
solution as in example 1. Under gentle stirring, silver nitrate
(0.3 ml, 1.0M) was added drop-wise to the hot DMF. After 5-7
minutes, the beaker contents were cooled, lens removed and rinsed
thoroughly with de-ionized water, blotted over tissue paper and
dried in oven at 40.degree. C. The lens imparted pale yellow
tint.
Example 4
Catheter Segment
[0217] DMF solvent (10 ml) was heated to .about.100.degree. C. in a
beaker under stirring. Silver nitrate solution (0.25 ml, 0.02M) was
added to the hot solvent to yield silver nanoparticles as indicated
by yellow color (due to plasmon resonance band). A pre-cleaned
silicone catheter (14 Fr, Degania Silicone Ltd, Israel) segment
.about.1'' long was immersed in the yellow solution for 15 minutes.
The catheter segment was removed, rinsed with de-ionized water and
dried. A small level of discoloration of the catheter segment was
seen.
Example 5
Hydrogel Sheet--Method 1
[0218] To de-ionized water (13.3 ml) in a cup, acrylamide (1.482
g), bisacrylamide (0.018 g) and glycerol (1.5 g) were added under
stirring. Separately, in hot (.about.60.degree. C.) de-ionized
water (10 ml), isopropanol and guar gum (0.165 g) were dissolved
and the solution was allowed to cool to room temperature. The guar
gum and acrylamide monomer solutions were mixed. To the mixture,
silver nitrate (1 ml, 0.1M) and sodium saccharinate (1 ml, 0.125M)
were added. With the help of a spatula, the viscous mass was mixed.
Upon precipitation of silver saccharinate, the viscous mass turned
whitish opaque.
[0219] To the silver salt containing mass, ammonium persulfate
(0.05 g dissolved in 1 ml of water) was added followed by TEMED
(0.063 ml in 1 ml of water). After TEMED addition, the mass began
to slowly turn brown colored with no immediate polymerization.
After 8 days, the viscous mass had converted into a brown colored
hydrogel sheet.
Example 6
Contact Lens
[0220] Contact lens (SEES brand, CibaVision Corporation, Duluth,
Ga.) was rinsed with de-ionized water to rinse off the preservative
solution and then it was soaked with the silver nitrate solution
(0.15 ml, 0.1M) for 10 minutes. Excess solution was drained off and
sodium saccharinate (0.15 ml, 0.125M) was added to re-immerse the
lens. Lens turned opaque due to the in-situ formation of silver
saccharinate. Excess liquid and any loose solids were pipetted off
and the lens rinsed once again with de-ionized water. TEMED (0.1
ml) mixed with water (0.2 ml) were added to soak the lens and
initiate reduction. After 5 minutes, the liquid turned pale yellow.
At that point, all liquid was discarded and the Tens rinsed several
times with water and dried overnight under ambient conditions.
Example 7
Nylon Fiber
[0221] Several strands of fibers (.about.1 mm dia) made of nylon
(polyamide) were immersed in silver nanoparticles composition made
in example B6 (total liquid volume 10 ml) for 72 hours at room
temperature. The immersed fibers were rinsed thoroughly with 70%
aqueous IPA and water. The fibers were also gently wiped with
tissue soaked in IPA and dried for 15 minutes at 45.degree. C. The
soaked portion of the fibers was colored light yellow to brown.
Example 8
Silicone Catheter Segment
[0222] 4'' long 14 Fr silicone catheter segment (Degania Ltd,
Israel) was cleaned with TPA and dried. The segment was dipped in 5
ml THF solution of saccharin (0.5 gm) for 1 h. The shaft was
removed and rinsed quickly with acetone once and immersed in silver
nitrate solution (0.5 g silver nitrate, 5 ml 90% acetone/water) for
0.5 h. The shaft segment was removed and thoroughly rinsed with
water and finally dipped in 30% TEMED solution in IPA. The solution
was warmed to induce reduction and set aside overnight. The segment
had turned yellow indicating reduction reaction had progressed. The
shaft was rinsed with water and dried in oven at 125.degree. C. to
remove all traces of TEMED.
Example 9
Catheter with Hydrophilic Polymer Coating
[0223] A small catheter segment .about.3'' long with hydrophilic
polymer coating (2.7% GRAFT-COAT, STS Biopolymers, Henrietta, N.Y.)
was immersed in silver nanoparticles solution prepared in a manner
of example B4 for 2 h. The segment was removed and washed with
water and dried at 45.degree. C. Barely any color was seen
initially but after several days a uniform brown color developed in
the coating.
Example 10
Contact Lens
[0224] Single lens (SEES, CibaVision Corporation) was soaked in 7
ml of the stock solution prepared in example B7 at room temperature
for 12-16 h. The lens was rinsed with water and dried at room
temperature. The lens was covered with a uniform shiny transparent
silver coating.
Example 11
Cotton Gauze
[0225] Cotton gauze (Curity brand, The Kendall Company, Mansfield,
Mass.) about 3''.times.3'' in size was successively soaked in
silver nitrate (0.1M) and sodium saccharinate (0.125M) with
blotting after each soak and dried at 110.degree. C. for 10
minutes. The dried gauze with silver salt was re-soaked in 30%
TEMED solution in IPA for 72 h, rinsed thoroughly with water, left
to soak for 24 h in water to remove solvent traces and dried. The
gauze turned yellow after about 3 h soak in TEMED. The color did
not leach during the rinsing and water soak steps.
Example 12
Cotton Gauze
[0226] Cotton gauze identical to the one in example 15 was soaked
in PAA-silver nanoparticles solution (5 ml) prepared in a manner of
example 40 for 72 h. The gauze was rinsed with water and left to
soak in water for 24 h and dried. The gauze imparted orange yellow
shade and did not leach any color during rinsing and water soak
steps.
Example 13
Contact Lens
[0227] Clear contact lens with embedded silver nanoparticles was
prepared as follows. Silver nanoparticles containing composition
was prepared by dissolving Tween 20 in water (1 ml), followed by
the addition of sodium saccharinate (1 ml, 0.125 M), silver nitrate
(1 ml, 0.1M) and TEMED (0.1 ml). The solution (0.5 ml) after aging
for a week was diluted to 2 ml with water and a pre washed contact
lens was immersed in it overnight. The lens was washed with water,
gently blotted and dried in oven at 75.degree. C. for 0.5 h.
Example 14
Silicone Catheter
[0228] 16 Fr Silicone catheter segment (.about.6'' long) was washed
with isopropyl alcohol (IPA) and dried. It was soaked in THF for 1
h to cause swelling of its walls and then dipped overnight in 1
week old silver nanoparticles solution prepared as follows. Tween
20 (0.025 g) was dissolved in sodium saccharinate solution (5 ml,
0.125M) and silver nitrate (5 ml, 0.1M) and 0.5 ml TEMED added to
it. The resulting liquid was briefly heated (10 s) in microwave
oven causing the solution to become yellow brown. After overnight
soak, the catheter was rinsed with water, IPA and water again and
dried in oven.
Example 15
Nylon Catheter--Method 1
[0229] Nylon catheter piece .about.1 mm dia, 15'' long (IFLOW
Corporation, Lake Forest, Calif.) was cleaned with IPA and wiped
dry. Catheter was soaked overnight in silver nanoparticles stock
solution (90 ml) prepared according to the procedure of example 44,
washed with water, IPA and wiped dry and further dried in oven at
45.degree. C. After treatment, the catheter imparted a shade of
yellow.
Example 16
Nylon Catheter--Method 2
[0230] Nylon catheter segment .about.4'' long but otherwise similar
to example 15 was briefly (1 minute) dipped in THF solution of
.gamma.-aminopropyl triethoxy silane (0.1 ml silane/5 ml THF),
removed and dried in air for few minutes. The silane coated sample
was soaked in freshly prepared silver nanoparticles stock solution
(example 44) overnight. The catheter segment was washed with water,
IPA and wiped dry. The sample imparted more uniform and intense
yellow color than sample of example 15.
Example 17
Silicone Catheter--Bard
[0231] Catheter segment .about.3'' long (Lubrisil brand, BARD Inc.
Covington, Ga.) was wiped with IPA and soaked overnight in silver
nanoparticles stock solution prepared by method of example 14. The
segment was rinsed with water, IPA and dried in oven at 45.degree.
C. It imparted pale yellow brown color.
Example 18
Silicone Breast Implant Membrane
[0232] 3 pieces (.about.1''.times.1'') of breast implant membrane
(.about.0.5 to 1 mm thick) made of silicone were impregnated with
silver nanoparticles by first swelling it according to the step in
example 14 and soaking it overnight in silver nanoparticles
solution made by the method of example 44. The pieces were washed
with water, IPA and dried in oven at 75.degree. C. for few hours.
Each piece after treatment imparted pale yellow shade.
Example 19
Cyotoxicity of Nylon Fiber Strands
[0233] A silver nanoparticles solution was first prepared by mixing
0.2 gm Tween 20 in 4 ml water, adding 4 ml sodium saccharinate
(0.125M), then 4 ml silver nitrate (0.1M) followed by 0.4 ml TEMED
and heating in microwave oven (1500 W power) for 10 seconds and
then cooling to room temperature. Four nylon fiber strands
(.about.1 mm dia & 9'' long) were immersed in the solution
overnight. The strands were rinsed with water several times and
dried in air. After silver nanoparticles impregnation, the fiber
surface impart yellow brown color.
[0234] Using agarose overlay no cytoxicity to L929 fibroblast cells
was observed. The silver content of the fiber was .about.800
ppm.
Example 20
Cyotoxicity of Silicone Catheter of Example 14
[0235] Using agarose overlay no cytoxicity to L929 fibroblast cells
due to the silver treated catheter was observed. The silver content
of the catheter was estimated to be greater than 800 ppm.
Example 21
Effect of Sterilization Methods on Substrates with Silver
Nanoparticles
[0236] Silicone catheters of Example 14 and nylon fiber strands of
Example 19 were subjected to ethylene oxide (ETO) sterilization.
The samples saw ETO dose typical of high volume products such as
medical tubings and kits. After sterilization there was a small
visually detectable change after sterilization. Both samples turned
slightly darker than the original shade.
Examples 22
Attempt to "Bleach" Yellow Color of Silver Gauze Comprising Silver
Nanoparticles
[0237] Several pieces (3''.times.3'') of Curity (Kendall) cotton
gauze were dripped with 2 ml each of a solution comprising silver
nanoparticles prepared according to the following manner: 10 ml
each of stock solutions of Tween 20 (concn: 50 gm/L), sodium
saccharinate (0.125M) and silver nitrate (0.1M) were mixed on
vortex mixer and TEMED (1 mL) was added. The resulting solution was
heated in a microwave oven for 30 seconds to yield a yellow brown
solution that was cooled to room temperature.
[0238] The gauze pieces were blotted and dried in oven at 45 C
overnight. Upon drying some gauze color changed to light brown. The
gauzes were soaked in 10% hydrogen peroxide solution (25 mL). Not
color change was observed in first few minutes though after more
than an hour the brown color much lighter. After 24 h soak, the
gauze pieces had turned white. They were blotted and dried in oven
at 45.degree. C. for 1 hour and left under lab light for continuous
exposure for 36 h. Except slight discoloration in few spots, the
gauzes looked unchanged giving us another method of preparing
silver antimicrobial gauze material.
Examples 23
Impregnation of Silicone Catheter by Treatment with Non-Aqueous
Silver Nanoparticles Composition
[0239] An aqueous composition similar to the one in example 50 was
made and left undisturbed for over a week in a capped vial. The
composition was diluted with 25 mL deionized water and extracted
with .about.15 mL chloroform. A portion of silver nanoparticles
were extracted into the chloroform layer. A clean catheter stem
made of silicone (14 Fr, Degania Ltd, Israel) was dipped into
chloroform layer for 0.5 h. Immersed portion of catheter swelled
due to solvent absorption. The catheter was then removed and
without rinsing dried in oven at 45 C for 15-20 minutes. Following
treatment, it imparted faint yellow color that after 24 h turned to
orange red. The color change indicated the presence of silver
nanoparticles in the catheter walls. It was found to antimicrobial
in 24 h bacterial challenge test.
Example 24
Silver Treated PTFE
[0240] 10 ml each of stock solutions of Tween 20 (concn: 16.7
gm/L), sodium saccharinate (0.125M) and silver nitrate (0.1M) were
mixed on vortex mixer and TEMED (1 mL) was added. The resulting
solution was heated in a microwave oven for 60 seconds to yield a
yellow brown solution. PTFE thread seal tape 4'' long was wrapped
around a test tube and then this tube and placed inside a large
test tube and the silver nanoparticle solution was poured in both
tubes to submerge the tape for 24 h and maintained at 55.degree. C.
The tape was rinsed thoroughly with water several times and dried
for 0.5 h at 55.degree. C. After silver nanoparticles impregnation
the tape imparted pale yellow color. It was found to be
antimicrobial in a 24 h bacterial challenge test.
Example 25
Silver Treated PP
[0241] 10 ml each of stock solutions of Tween 20 (concn: 16.7
gm/L), sodium saccharinate (0.125M) and silver nitrate (0.1M) were
mixed on vortex mixer and TEMED (1 mL) was added. The resulting
solution was heated in a microwave oven for 60 seconds to yield a
yellow brown solution.
[0242] PP strip were surface treated to improve aqueous wettability
as follows: 4 polypropylene strips (3''.times.1/4'') were soaked in
a 80 mL 9M sulfuric acid under stirring for 40 h. Thereafter, the
strips were rinsed with water several times and patted dry on paper
and then air dried. Next, the strip were placed in a THF solution
of g-aminopropyl triethoxysilane made by adding the silane (0.2
mL), 0.1 mL water and 0.1 mL boron trifluoride etherate to 10 mL
THF. After soaking for 5 minutes, the strips were removed and air
dried briefly and then at 55.degree. C. for 0.5 h.
[0243] The silane treated strips were then immersed in silver
nanoparticles solution made above for 4 h, rinsed, blotted on paper
and air dried. Each strip imparted pale yellow color indicating
impregnation of silver nanoparticles.
Example 26
Effect of <1 Ratio of Sac/Ag on Deposition of Ag on Nylon
Fibers
[0244] Tween 20 solution (3 mL, 16.7 g/L), sodium saccharinate (3
mL, 0.025M) and silver nitrate (3 mL, 0.1M) were vortexed together.
TEMED (0.1 mL) was added and vortexed again. TEMED addition turned
the mixture pale yellow. The solution was briefly heated in
microwave to .about.55 C and 4 clean nylon fiber strands were
immersed in the hot solution for 4 h. The immersed portion of the
fibers had turned blue black. The fibers were cleaned thoroughly
and dried. The fibers were found to be antimicrobial in ZOI
assay.
Example 27
Silver Treated Polysulfone
[0245] Tween 20 solution (2 mL, 16.7 g/L), sodium saccharinate (2
mL, 0.125M) and silver nitrate (2 mL, 0.1M) were vortexed together.
TEMED (0.2 mL) was added and vortexed again. The solution was
briefly heated in microwave to .about.70-75 C cooled to 55.degree.
C. and then seven 6'' pieces of hollow polysulfone tubes (<0.5
mm dia) were immersed in the hot solution for 4 h. The tubes were
rinsed with water and centrifuged with the tubes immersed in water
to clean them from the inside. The white polysulfone tubes had
become yellow colored and in ZOI assay were found to be
antimicrobial.
Example 28
Method of Depositing Silver on Fabrics by Treatment with Fumarate
Based Composition of Example B33 and Acetic Acid
[0246] Several cotton gauze pieces (2''.times.2'' from Bulkee II
gauze roll) are treated with the silver nanoparticles composition
made in example 70 by soaking in the composition for few minutes,
followed by blotting and then re-soaking them in dilute acetic acid
(5 ml glacial acetic acid in 100 mL water) for few minutes to
precipitate out the silver nanoparticles stabilized with fumarate.
After blotting on paper and drying in oven at 55.degree. C. for 0.5
h, gauzes with silver are obtained as light yellow colored
material. The gauzes are expected to be antimicrobial.
Example 29
Effect of Ammonia on Catheters Made from PEBEX.RTM. Nylon Tubing
Stock
[0247] Silver nanoparticles impregnated catheters tubing pieces (2
pieces 2'' long, 1 mm outer diameter and 0.6 mm inside diameter,
made from tubing stock of PEBEX.RTM. grade polyamide polymer) were
soaked in dilute ammonia solution (2 mL 28% ammonia in 8 mL water)
in a test tube to examine if the silver nanoparticles can be
dissolved away. No change was observed in color after 16 h
suggesting no effect of .about.7% ammonia on silver nanoparticles
impregnated on a surface.
Example 30
Silver Treated PVC Drain
[0248] Polyvinyl chloride (PVC) tubing several feet long having
1/4'' OD was soaked overnight in silver nanoparticles solution
prepared from Tween 20 solution (160 mL, 16.7 g/L), sodium
saccharinate (160 mL, 0.125M) and silver nitrate (160 mL, 0.1M)
after mixing in succession and stirring together for 15 minutes.
TEMED (16 mL) was added and stirred. The solution was heated in
microwave to .about.70-75 C cooled to 55.degree. C. The tubing was
removed and quenched in de-ionized water, rinsed in running water
and air dried. The tubing colorless before treatment yellow and was
uniform in color. It was found to be antimicrobial in bacterial
challenge test.
Example 31
Silver Treated PEBEX.RTM. Grade Nylon Tubing Catheters--Conditions
Versus ppm
[0249] This example examines the effects of time, starting
concentration of silver nitrate and temperature on the amount of
silver deposited on small dia nylon tubing material made of
PEBEX.RTM. type of nylon grade. The tubing simulates a type of
material used in catheters. The tubing was comprised of .about.1 mm
OD and 0.6 mm ID and came 27'' in length.
[0250] Tween 20 solution (160 mL, 16.7 g/L), sodium saccharinate
(160 mL, 0.125M) and silver nitrate (160 mL, 0.1M) were mixed in
succession and stirred together for 15 minutes. TEMED (16 mL) was
added and stirred. The solution was heated in microwave to
.about.70-75.degree. C. cooled to 40-45.degree. C. A dozen or so
catheter pieces were placed in a pyrex dish and weighed down (to
prevent them from floating). The cooled silver nanoparticles
solution was poured over the catheters in the dish and one catheter
was removed at a given time point, thoroughly cleaned and air
dried. The nylon tubing imparted yellow color of increasing
intensity with time. The tubing samples were analyzed for silver
content by AAS.
[0251] The test was repeated at 55-60.degree. C. by cooling the
solution to that temperature before pouring it on the catheters The
silver content (as average of 3 portions--top, middle and bottom)
of the catheter) as function of the time of treatment at two
temperatures are tabulated in Table 12.
TABLE-US-00012 TABLE 10 Silver Content of Nylon Tubing in ppm
Treatment time(h) T~40-45.degree. C. T~55-60.degree. C. 0.25 51 110
1 122 230 2 130 440 4 179 1017 8 290 1897
Example 32
Effect of Silver Concentration on Loading on the Nylon Tubing
Material
[0252] To study the effect of concentration, the starting
concentration of silver nitrate in preparing the treating solution
was varied. For this experiment radioactive silver was used and
counts determined the silver content instead of AAS assay
technique.
[0253] Briefly, Tween 20 solution (13.3 mL, 16.7 g/L), sodium
saccharinate (1.3 mL, 0.125M) and 1.3 mL .sup.110mAg silver nitrate
(in different concentrations), water (24 mL) were mixed in
succession and stirred together for 15 minutes. TEMED (0.13 mL) was
added and stirred. The solution was heated in microwave to
.about.70-75.degree. C. cooled to 52.degree. C. To the solution
were added 33 pieces of tubing material 2 cm in length and
centrifuged briefly to remove air bubbles and incubated at
52.degree. C. for 16 hours. The catheters were thoroughly rinsed
clean and air dried.
[0254] From the counts measured and specific activity, the amount
of silver deposited on the tubing was determined. The results are
presented below in Table 13.
TABLE-US-00013 TABLE 13 .sup.110 mAg loading in nylon tubing
samples AgNO3 in treatment Ag content in tubing Sample No. solution
(g/L) (ppm) (n = 5) 1 0.755 1422 2 0.670 1330 3 0.548 1235 4 0.426
1019 5 0.296 876
Example 33
Silver Treated Nylon Tubing--Effect of Nitric Acid
[0255] A catheter nylon tubing (1 mm OD) made of PEBEX having
silver loading of .about.920 ppm was prepared by following
procedure of Example 31. The amber colored catheter piece 1'' long
was immersed in 5 ml dilute nitric acid (prepared from 0.5 mL tech
grade nitric acid and 4.5 mL water) overnight. The piece was washed
with de-ionized water twice, then with isopropanol and dried by
blowing nitrogen gas. After acid treatment, the piece was bleached
to faint yellow. Silver analysis by AAS showed a loading of 350 ppm
indicating a reduction of .about.62% from the original loading.
[0256] This example affords a method of altering the silver loading
of silver nanoparticles impregnated articles by treatment with
nitric acid if the actual loading exceeds a proposed target. During
the test, discoloration (indicating loss of silver) of the
substrate due to exposure to nitric acid vapors was observed. This
result affords a method to pattern a silver nanoparticles bearing
surface by exposing them to nitric acid vapors or of other acids
possessing similar characteristics.
Example 34
Silver Treated Nylon Tubing--Effect of H.sub.2O.sub.2
[0257] The nylon tubing samples deposited with .sup.110mAg after
the egress experiment of example 32 were in this example for
studying the effect of H.sub.2O.sub.2 to eliminate the amber color
from the tubing surface. Just before soaking the sample tubings in
H.sub.2O.sub.2, the silver loading in ppm was determined by
measuring the radioactivity. The samples in separate tubes were
then soaked in 2 mL 30% H.sub.2O.sub.2 solution for 24 hr at
ambient temperature. Bubble formation due to oxygen was observed at
the tubing surfaces often floating the tubing pieces. The next day,
all samples had changed in color from amber to colorless. The
radioactivity of the samples was again measured and from the
specific activity, the silver loading was calculated. The results
given below (Table 14) indicate the silver loss due to peroxide
treatment is equivalent to the loss during 24 h saline soak. The
amber color silver nanoparticle comprising surfaces become
colorless without loss of silver (or antimicrobial activity).
TABLE-US-00014 TABLE 14 .sup.110 mAg content of nylon tubing
samples before and after H.sub.2O.sub.2 treatment AgNO.sub.3 in Ag
content in Ag content in original tubing (ppm) tubing (ppm) Sample
treatment (n = 5) before (n = 5) after No. solution (g/L)
H.sub.2O.sub.2 H.sub.2O.sub.2 1 0.755 1181 .+-. 9 1173 .+-. 10 2
0.670 1095 .+-. 3 1088 .+-. 4 3 0.548 1015 .+-. 3 1009 .+-. 4 4
0.426 800 .+-. 6 795 .+-. 7 5 0.296 700 .+-. 5 696 .+-. 5
Example 35
Antimicrobial Metal Implants
[0258] 10 mL each of Tween 20 surfactant solution (16.7 g/L),
sodium saccharinate (0.125M), silver nitrate and 20 mL de-ionized
water were mixed under stirring in a beaker to yield a suspension
with white particles. To the suspension, TEMED (1.5 mL) was added
and briefly mixed. The content was heated for a minute in a
microwave oven and the hot solution was poured on three metal
implant parts placed in a glass petri-dish. The dish was covered
and heated to 70.degree. C. for 4 hours. Metal parts were removed
from the solution, rinsed with de-ionized water several times,
placed in a beaker with water and ultrasonicated for 15 minutes to
remove loose particles. The metal parts were then dried in air. The
implant with silver nanoparticle impregnated surface showed
antimicrobial activity against pseudomonas that sustained for 3
days. In contrast, untreated control metal part showed uncontrolled
bacterial growth.
Example 36
Antimicrobial Polyurethane Foams
[0259] Antimicrobial silver nanoparticle composition was prepared
by mixing 25.5 mL each of Tween 20 solution (5.2 g/L), sodium
saccahrinate (0.0125M) and silver nitrate (0.01M) followed by TEMED
(0.255 mL) addition and heating the mixture at 48.degree. C. for 16
h. The cooled solution was used in the preparation of foams. I''
squares of Supersoft S00-T foam from Lindell Manufacturing from
Michigan and Medical grade (Type 562-6) from Rynel Corporation of
Maine were soaked in the silver nanoparticle compositions and
blotted lightly and dried in oven at 45.degree. C. for 0.5 h. The
foams were found to be antimicrobial in a ZOI assay against
Staphylococcus aureus and Pseudomonas aeruginosa.
Example 37
Antimicrobial Silicone Catheter Stems--Effect of Different
Sterilization Processes
[0260] Several stems of isopropyl alcohol cleaned silicone catheter
(14 Fr, Degania Silicone Ltd., Israel) were soaked in THF for a
period of 15-30 minutes. Separately an antimicrobial silver
nanoparticle composition was prepared by mixing equal volumes of
Tween 20 (50 g/L), sodium saccharinate (0.125M) and silver nitrate
(0.1M) and then adding TEMED ( 1/10.sup.th the individual stock
solution volume). The resulting mixture was briefly heated in
microwave oven for 30 to 45 seconds until the solution turned
yellow. The solution was cooled to room temperature and then
catheter stems swollen in THF were placed in the silver
nanoparticle solution overnight to deposit the particles on the
silicone catheter surface. The stems were thoroughly rinsed with
water and dried in air. After silver impregnation the color changed
to yellow brown to grey brown. A few stems with silver
nanoparticles each were sterilized by steam sterilization at
122.degree. C. for 15 minutes, e-beam process (approx 30 kGy) and
commercial standard ETO process. Sterilized catheter stems with
silver were found to be equally antimicrobial over 7 bacterial
challenges (24 h) of Pseudomonas aeruginosa strains with
inoculation dose--5e3 cfu/mL with 100% kill rate. None of the
sterilization processes studied had adverse effect on the
antimicrobial property of the catheters.
Example 38
Hydrophilic Cross-Linked Polymer
[0261] To de-ionized water (13.3 ml) in a cup, acrylamide (1.482
g), bisacrylamide (0.018 g) and glycerol (1.5 g) were added under
stirring. To the mixture, silver nitrate (1 ml, 0.1M) and sodium
saccharinate (1 ml, 0.125M) were added. Upon precipitation of
silver saccharinate, the resulting liquid turned whitish
opaque.
[0262] To the silver salt containing mass, ammonium persulfate
(0.05 g dissolved in 1 ml of water) was added followed by TEMED
(0.113 ml in 1 ml of water). After TEMED addition, the mass began
to slowly turn brown and was set aside overnight to polymerize to
yield red brown colored brittle solid polymer.
Example 39
Copper Modified Hydrophilic Cross-Linked Polymer
[0263] A portion of solid polymer (.about.0.1 g) from Example 38
and cupric chloride solution (1 ml, 0.1M) were placed in a capped
vial and set aside several days. The brown color of the polymer had
changed to blue due to hydration by cupric chloride solution and
the conversion of the nanoparticles to silver chloride.
Example 40
Hydrogel Sheet--Method 2
[0264] A silver nanoparticles containing polymer solution was
prepared as follows. Acrylamide (0.5 gm) was dissolved in
de-ionized water (5 ml). To the solution under mixing, ammonium
persulfate (16 mg) and TEMED (0.02 ml) were added to form
polyacrylamide (PAA) polymer solution. In the PAA solution diluted
first with 5 ml water, silver saccharinate was precipitated by
successively adding sodium saccharinate (1 ml, 0.125M) and silver
nitrate (1 ml, 0.1M). Silver nanoparticle formation by reduction
was initiated by adding TEMED (0.05 ml) to the PAA solution
(indicated by the solution turning red brown). If needed, the
solution was warmed to initiate reduction reaction. The solution
was set aside for at least 1 day to complete the reduction.
[0265] To the PAA--silver nanoparticles solution prepared above,
acrylamide (1.482 g), bisacrylamide (0.018 g) and glycerol (1.5 g)
were added under stirring. Separately, to hot (.about.60.degree.
C.) de-ionized water (10 ml), isopropanol and guar gum (0.165 g)
were added to form solution that was cooled to room temperature.
The guar gum and the PAA-silver nanoparticles monomer solution were
mixed. To the mixture, hydrogen peroxide solution (2 ml, 10%) was
added causing the solution to pale from its original red brown
color. Soon after adding the initiator, ammonium persulfate (0.05
g), the monomer solution with silver nanoparticles formed a red
brown gel. The gel was transferred to a petri-dish and left to dry
overnight.
Example 41
Talc Powder
[0266] A silver nanoparticles containing composition was prepared
as follows. Surfactant Tween 20 (0.05 g) was dissolved in water
(2.5 ml). To the surfactant solution, sodium saccharinate (0.25 ml,
0.125M), silver nitrate (0.25 ml, 0.1M) and TEMED (0.1 ml) were
added one after another. The mixture was heated briefly in
microwave oven to initiate silver salt reduction and then cooled to
room temperature.
[0267] Separately, talc powder (0.5 g), IPA (1 ml) and water (4 ml)
were mixed in a cup to get a uniform suspension. To the suspension
0.5 ml of the silver nanoparticles composition prepared above was
added and mixed on a vortex mixer. The cream colored solids were
recovered by centrifugation and drying in the oven at 45 C for few
hours.
Example 42
Aqueous Silver Nanoparticles Containing Composition
[0268] Sodium saccharinate (0.25 ml, 0.125M) and silver nitrate
(0.25 ml, 0.1M) were added to water (1 ml) in a test tube. Tween 20
surfactant (0.05 g) was added to the resulting suspension followed
by TEMED (0.05 ml) to start the reduction reaction. Within few
minutes, yellow color appeared that intensified overnight.
Absorbance of a diluted solution in water (dilution 1 to 5) was
measured over 400 nm-550 nm range. The maximum OD was observed at
415 nm.
Example 43
Aqueous Silver Nanoparticles Containing Composition
[0269] A composition with silver nanoparticles was prepared exactly
as in example 42 except the volume of sodium saccharinate, silver
nitrate and TEMED was doubled. The resulting solution showed a OD
maximum at .about.415 nm.
Example 44
Aqueous Silver Nanoparticles Containing Stock Solution
[0270] In a cup, Tween 20 (0.5 g) was dissolved in water (10 ml).
To this sodium saccharinate (10 ml, 0.125M), silver nitrate (10 ml,
0.1M) and TEMED (1 ml) were successively added. The liquid mixture
was heated (30 seconds) briefly in microwave oven (Instamatic
Cooking by Quasar) on MEDIUM setting. It turned yellow after
heating due to the formation of silver nanoparticles.
Example 45
Polymer Stabilized Silver Nanoparticles Composition
[0271] Acrylamide (2.96 g) was dissolved in 25 ml of water. To the
solution, ammonium persulfate (0.1 g) and TEMED (0.125 ml) were
added, mixed to start polymerization. After 10 minutes, sodium
saccharinate (1.25 ml, 1M) and silver nitrate (1 ml, 1M) were added
to the viscous polymer solution. The solution color changed to
orange red within minutes. The solution was warmed for 30 seconds
in microwave oven if needed to speed up the reduction reaction. OD
value peaked at a wavelength of 440 nm.
Example 46
Lubricating Jelly
[0272] Lubricating jelly (BARD Inc., Covington, Ga.) with silver
nanoparticles was prepared as follows. First, the nanoparticles
solution was prepared and then blended with the jelly. CMC sodium
salt (0.05 g, high viscosity grade, Sigma) was dissolved in water
(10 mL). To the CMC solution (1 ml), sodium saccharinate (1 ml,
0.125M), silver nitrate (1 ml, 0.1M) and TEMED (0.1 ml) were added
in succession. The solution became yellow and imparted weak green
fluorescence. To the lubricating jelly (8 g) in a cup, CMC-AgNP
solution (0.2 ml) made above was added and mixed to uniformity with
a glass rod. The jelly with silver nanoparticles imparted pale
orange tint.
Example 47
Alginate Beads
[0273] PAA-silver nanoparticles solution was prepared according to
the method of example 40. The solution was added to sodium alginate
solution (1 g/50 ml water). The resulting solution was added
dropwise to a stirred 2% calcium chloride solution (400 ml) to form
alginate beads embedded with silver nanoparticles. The beads were
filtered and once washed with de-ionized water and stored wet. The
beads imparted yellow color with trace green fluorescence.
Examples 48
Nail Polish Composition
[0274] A polymer used in nail polish application, Avalure 120 (1
ml) was mixed with silver nanoparticles solution (1 ml) leftover
from a preparation similar to Example A19 and spread over a clean
glass slide and dried at 45.degree. C. The dried film on the glass
did not change color from initial yellow even after more than two
months indicating that there is no agglomeration of silver
nanoparticles in dried films by diffusion mechanism.
Examples 49
Silver Nanoparticles Composition from Potassium Acesulfame
[0275] A composition comprising silver nanoparticles was prepared
in a dram vial by mixing Tween 20 (0.3 ml, 65 g/L), potassium
acesulfame solution (1 ml, 0.125 M), TEMED (0.3 mL) and lastly
adding silver nitrate solution (0.75 mL, 0.1 M), vortexing after
adding each ingredient. The resulting mixture was heated in
microwave oven for 10 seconds, cooled and OD measured over 400 to
500 nm. The wave length maximum was found to be 415 nm.
Examples 50
Preparation of Composition Comprising Silver Nanoparticles from
Barbituric Acid
[0276] Barbituric acid (0.368 g) was weighed and added to 10 mL
deionized water. Sodium carbonate (0.105 g) was added to water to
convert the acid to its sodium salt as the solution became
clear.
[0277] Silver nitrate (1 mL, 1M) solution was added to precipitate
out silver barbiturate as fine suspension. To 1 mL silver salt
suspension, 0.3 mL Tween 20 (65 g/L) and 0.3 mL TEMED were added
and the mixture was heated for 10 seconds in microwave oven. A
reddish orange color appeared indicating formation of silver
nanoparticles. The wave length maximum was measured at 415 nm.
Examples 51
Silver Nanoparticles Composition from Sodium Saccharinate
[0278] A composition comprising silver nanoparticles was prepared
in a beaker by mixing Tween 20 (1 g) in 20 mL deionized water, then
adding sodium saccharinate solution (20 ml, 0.125 mL), silver
nitrate solution (20 mL, 0.1M) and finally TEMED (2.0 mL). The
resulting mixture was heated in on a hot plate under stirring to
60-70.degree. C. over 15 min. Around 45 C, the color change to
yellow and continued to become darker. Some white precipitate was
seen at the beaker bottom. The OD versus 1 curve measured over 400
to 500 nm was similar to a similarly made but microwaved solution.
The wave length maximum was found to be 415 nm. The mode of heating
did not alter the OD curve.
Examples 52
Non-Aqueous Silver Nanoparticles Composition from Sodium Oleate
[0279] An aqueous composition comprising silver nanoparticles was
prepared in a test tube by mixing Tween 20 (0.3 mL, 65 g/L), sodium
oleate (1 mL, 0.125M), TEMED (0.3 mL) and finally adding silver
nitrate solution (0.75 mL, 0.1M) and heating it microwave oven
briefly until the solution turned yellow. The OD maximum was
observed at 415 nm. To the aqueous composition was added, toluene
(2 to 3 mL) and vortexed to homogenize the contents that were left
undisturbed for 2-3 weeks when all toluene had evaporated.
[0280] To the aqueous composition in the test tube, chloroform (3
mL) was added and shaken to extract the silver nanoparticles into
non-aqueous chloroform layer. The chloroform layer turned amber
brown as it gained copious amount of silver nanoparticles. The OD
of the chloroform layer after dilution was measured over 300 to 550
nm. The maximum was seen at 420 nm and the shape of the curve was
identical to the curve of the aqueous composition (see FIG. 1). The
aqueous liquid still rich with silver nanoparticles was
re-extracted with a second portion of the chloroform (3 mL) to
harvest more silver nanoparticles. A 1''.times.1'' piece of a
fabric woven from polypropylene having satin like finish was dipped
in the 2.sup.nd chloroform layer and quickly removed and left to
dry in air for few minutes. The fabric color changed from white to
faint yellow/orange. In ZOI assay against Staphylococcus aureus it
was found to be antimicrobial.
Examples 53
Silver Nanoparticles Composition from Hydantoin
[0281] A composition comprising silver nanoparticles was prepared
from hydantoin as follows:
[0282] Silver hydantoinate was first prepared according to a method
disclosed in example 2 of US Patent Application No. 2003/0186955.
Next, silver hydantoinate (0.05 g), deionized water (6.7 mL), Tween
20 solution (3 mL, 16.7 g/L) were mixed in a test tube and TEMED
(0.3 mL) were added and contents vortexed and heated in microwave
oven for 30 seconds to yield a yellow brown mixture. OD maximum of
the mixture at 420 nm confirmed the presence of silver
nanoparticles.
Examples 54
Non-Aqueous Silver Nanoparticles Composition
[0283] A non aqueous composition comprising silver nanoparticles
was prepared as follows: Sodium oleate (3.3 mL, 4 g/L) was used as
stabilizer in place of Tween 20. It was mixed with sodium
saccharinate (0.3 mL, 0.125M) in a test tube. To this mixture,
silver nitrate (0.3 mL, 0.1M) was added followed by water (6 mL).
Finally TEMED (0.17 mL) was added. The resulting mixture was
microwaved for 20 seconds to warm it and initiate nanoparticles
formation. Only faint color was observed. The contents now in a
beaker were heated on a hot plate to evaporate all of the water.
After most of the water was evaporated the beaker was cooled and 25
mL of chloroform added to extract silver nanoparticles. The
chloroform imparted yellow color indicating the presence of silver
nanoparticles. OD max was observed at .about.430 nm.
Examples 55
Non-Aqueous Silver Nanoparticles Composition
[0284] A non aqueous composition comprising silver nanoparticles
was prepared as follows.
[0285] First an aqueous composition comprising silver nanoparticles
made in proportions similar to in Example 44 and allowed to
evaporate to a viscous brown mass. To this mass chloroform (2-3 mL)
was added to extract silver nanoparticles. At once the chloroform
layer became yellow brown. OD max was 415 nm and in shape the OD vs
wavelength curve was similar to that in example 52. Few drops of
chloroform layer obtained were spread on a glass slide. Upon drying
the film gave shiny appearance and imparted turquoise color.
Example 56
Aqueous Silver Nanoparticles Compositions with CMC as Stabilizing
Agent
[0286] CMC Na salt solution was prepared by dissolving 0.05 g
polymer in water (10 mL). In a test tube, CMC solution above (1
mL), sodium saccharinate (1 mL, 0.125M) and silver nitrate (1 mL,
0.1M) were mixed. Finally, TEMED (0.1 mL) was added and mixture
vortexed. Yellow color change to the solution was observed within
few minutes indicating nanoparticles formation. The solution color
intensity increased with time. The solution also imparted green
fluorescence. OD max was observed at 438 nm.
Example 57
Aqueous Silver Nanoparticles Compositions with CMC as Stabilizing
Agent
[0287] In the example 56 above, the sodium saccharinate was
replaced with potassium acesulfame salt solution and preparation
repeated. Again yellow brown color due to silver nanoparticles in
solution was observed. OD was not recorded. The preparation was
repeated with potassium acesulfame salt instead of sodium
saccharinate. The solution obtained once again imparted yellow
brown color indicating the presence of silver nanoparticles.
Example 58
Aqueous Silver Nanoparticles Compositions with Propylene Glycol
Alginate as Stabilizing Agent
[0288] In the example 56 above, the CMC Na salt was replaced by
propylene glycol alginate and preparation repeated. OD maximum was
found to be 440 nm. The solution also imparted green fluorescence
but less in intensity that in Example 56.
Example 59
Aqueous Silver Nanoparticles Compositions Using Various Surfactants
as Stabilizing Agents
[0289] Surfactant stock solutions were made at .about.65 g/L using
Tween 20, Tween 80 and Polyoxyethylene stearate. To prepare silver
nanoparticles comprising solutions, a given surfactant solution
(0.3 mL), acesulfame potassium salt solution (1 mL, 0.125M), silver
nitrate solution (0.75 mL, 0.1M) were mixed and then TEMED (0.3 mL)
were added. The solutions were heated in microwave oven briefly
until the solution became yellow. OD versus wavelength data was
recorded for each surfactant (FIG. 18). Though small different in
the maxima was seen all were in 415-425 nm range indicating
consistent nanoparticles size.
Example 60
Silver Nanoparticles Compositions Prepared Using
Triethanolamine
[0290] Silver saccharinate powder was prepared from equimolar
mixtures of silver nitrate and sodium saccharinate solutions.
Silver saccharinate powder (30-35 mg) was added to Tween 20
solution (1 mL, 16.7 g/L) and then water (4 mL) was added. To this
mixture, triethanolamine (0.225 g) was added and it was briefly
heated in microwave until the content became yellow.
[0291] Various articles with antimicrobial property were prepared
using this above composition. Nylon fibers were made by dipping for
2 hours at 55.degree. C. and rinsing them. Cotton gauze and satin
pieces (2''.times.2'') were prepared by dipping them in the above
composition for a minute, then blotting them and soaking them in
ethanol (10 mL) for 5 minutes, re-blotting them and drying at
55.degree. C. for 15 minutes.
Example 61
Silver Nanoparticles Compositions Prepared Using Poly Vinyl Alcohol
(PVA)
[0292] PVA solution was prepared in de-ionized water (0.02-00.03
g/10 mL). PVA solution (1 mL), sodium saccharinate (1 mL, 0.125M)
and silver nitrate (1 mL, 0.1M) were vortex together. TEMED (0.1
mL) was added and vortexed again. The contents were briefly heated
in microwave oven. The solution turned grey brown though the OD max
of the solution was 455 nm.
Example 62
Silver Nanoparticles Compositions Using Polyacrylamide (PAA) as
Stabilizer
[0293] An identical test to Example 61 was carried out but instead
of PVA, poly acrylamide was used. PAA was made as a concentrate and
0.05 g concentrate was added to 1 mL water. The OD maximum of the
composition was 450 nm and its color was brown.
Example 63
Silver Nanoparticles Compositions Using Polyvinyl Pyrrolidone (PVP)
as Stabilizer
[0294] In Example 61, PVP was replaced with PVP solution (0.25 g/10
mL water) and the test repeated. The resulting composition after
heating turned green instead of yellow. The OD max was seen at 435
nm with the spectrum being less sharp than in the case of use of
Tween 20 indicating a broad particle distribution.
Example 63
Silver Nanoparticles Compositions Using Potassium Sorbate as
Stabilizer
[0295] A solution of potassium sorbate (0.1M) was prepared. The
sorbate solution (1 mL) was mixed with Tween 20 (1 mL, 16.7 g/L),
and silver nitrate (1 mL, 0.1M) were vortex together. TEMED (0.05
mL) was further added and vortexed again. The contents in a test
tube were briefly heated when solution color changed to orange
yellow. The composition OD maximum was 410 nm. This example shows
that one can use a double bond containing molecule (silver sorbate)
as the source of silver.
Example 64
Silver Nanoparticles Composition Using Sodium Oleate w/o Tween
20
[0296] Sodium oleate (4-5 mg) was dissolved in 1 ml water in a test
tube. To which were added sodium saccharinate (1 mL, 0.105M) and
silver nitrate (1 mL, 0.1M) to give a chuncky white precipitate. To
the test tube TEMED (0.2 mL) was added and briefly microwaved to
heat the contents. Upon heating a color change to yellow took place
indicating formation of silver nanoparticles. OD of the maximum was
not recorded.
Example 66
Silver Composition Comprising Silver-TEMED Complex
[0297] Tween 20 solution (1 mL, 16.7 g/L) and silver nitrate (1 mL,
0.01M) were mixed in a test tube. Then TEMED (0.1 mL) was added to
briefly heat in microwave oven to deposit silver as metallic film
on tube walls. The area of the glass surface coated with purplish
metallic film became poorly water wetting as indicated by the flat
water-air interface instead of a curved interface.
Example 67
Silver Composition Comprising Sorbate--Effect of Ethanol on
Stability
[0298] Solutions of silver nanoparticles composition of Example B27
were prepared by diluting with water and 66% water-33% ethanol
mixture (1:100 dilution factor). The UV/VIS scans were recorded of
either solution fresh and of the water-ethanol based solution after
5 days. No change in the spectra was observed indicating tolerance
of silver nanoparticles to ethanol.
Example 68
Use of Different Amines as Reducing Agents
[0299] Tween 20 solution (1 mL, 16.7 g/L), sodium saccharinate (1
mL, 0.125M) and silver nitrate (1 mL, 0.1M) were vortexed together.
Different amines (0.1 mL) was added and vortexed again. If needed,
the contents were briefly heated in microwave oven. The OD maxima
of the solutions were recorded.
[0300] Following amines were tested: N,N,N'N' tetramethyl
butylenediamine, ethanolamine, cyccohexylamine, dipropylamine,
triethanolamine. Of these dipropylamine and triethanolamine
successfully gave yellow colored solution indicating the presence
of silver nanoparticles with identical solutions OD maxima at 415
nm and practically identical spectral shapes of the curves.
Example 69
Silver Composition Using Powder Form of Silver Saccharinate
[0301] Silver saccharinate powder (15-20 mg) was added to Tween 20
solution (1 mL, 16.7 g/L) and then water (2 mL) was added. To this
mixture, triethanolamine (0.1 g) was added and it was briefly
heated in microwave until the content became yellow. The OD max of
the solution was 420 nm and the shape of UV-VIS spectrum was
identical to a composition made by in-situ formation of silver
saccharinate.
[0302] Nylon fibers were made by dipping in silver nanoparticles
composition above for 2 hours at 55.degree. C. and rinsing them.
Cotton gauze and satin pieces (2''.times.2'') were prepared by
dipping them in the above composition for a minute, then blotting
them and soaking them in ethanol (10 mL) for 5 minutes, re-blotting
them and drying at 55.degree. C. for 15 minutes. The fibers
exhibited antimicrobial activity.
Example 70
Silver Composition Comprising Fumarate
[0303] Sodium fumarate was made as follows: 0.116 g of fumaric acid
was added to 10 ml water in a test tube. Further, 2 molar
equivalents of sodium carbonate were added to form sodium fumarate.
Without isolating sodium fumarate, 1 ml of the sodium fumarate
solution above, Tween 20 solution (1 mL, 16.7 g/L) and silver
nitrate (1 mL, 0.1M) were mixed in succession and then TEMED (0.1
mL) was added. The tube contents were heated briefly in microwave
to yield a yellow colored solution with OD max of 420 nm. Without
Tween 20, the solution color is purple.
Example 71
Silver Nanoparticles Comprising Gel
[0304] In a cup, glycerol (5.0 g) was weighed, carboxymethyl
cellulose (0.5 g) was added and hand mixed to coat cellulose
particles uniformly with glycerol. Warm de-ionized water (40 mL)
was added to the cup and the resulting mass mixed to yield smooth
gel. Silver nanoparticle composition made from triethanolamine (0.1
g) from example 60 was added and mixed to uniformity to give a
yellow colored gel. To a portion of the gel (10 g), 1 g each of
citric acid and water were added to provide an antimicrobial gel
that could be used in the treatment of onychomycosis.
Example 72
Silicone Based Conductive Elastomer
[0305] Twelve silicone test strips (Type BMSI-7Z or 72B, Meggitt
Silicone Products, McMinville, Oreg.) in the shape of a dog bone
(4.5'' long and '' wide at ends, 2.5'' long and 0.25'' wide in the
neck) were immersed in 99% isopropanol in a glass beaker and
sonicated for 10 minutes (Fisher Scientific Sonicator Model FS30),
excess liquid rinsed off, and dried in an oven at 45.degree. C. for
10-15 minutes. The test strips were then transferred to a container
with 450 ml 23% nitric acid and slowly shaked overnight (or for 24
hours) at 25.degree. C. on a see saw rocker. The strips were
thoroughly rinsed with deionized water until there was no trace of
acid in the rinse water. In another container silver nanoparticles
solution was prepared by mixing Tween 20 solution (160 ml, 16.7
g/L), sodium saccharinate solution (160 mL, 0.025M), and silver
nitrate solution (160 ml, 0.1M). The mixture was stirred for 5
minutes after each solution addition. The solution was heated in
microwave oven briefly and the heating was stopped when the
solution temperature reached .about.55.degree. C. In a shallow
Pyrex dish the strips were laid flat on a nylon screen and the hot
silver nanoparticles solution was poured over the strips to immerse
the strips completely. The strips were left in the oven at
55.degree. C. for 18 h. The treatment with silver nanoparticles was
repeated twice but the duration was increased to 24 h. Prior to the
second silver treatment, the test strips were washed first with 200
ml Tween 20 solution (4.2 g/L). After the second silver treatment,
the strips were rinsed once again with Tween 20 solution (4.2 g/L)
followed by tap water rinses and then dried in the oven at
45.degree. C. for 15-20 minutes. Four strips were removed and saved
for another experiment. A third silver treatment was carried out on
the remaining 8 strips using a silver nanoparticles solution made
from 100 mL each of Tween20 solution (16.7 g/L), sodium
saccharinate solution (0.025M), and silver nitrate solution (0.65M)
for 16 h at 55.degree. C.
[0306] Following the third silver treatment, the strips were rinsed
with deionized water, sonicated in water and in isopropanol for 10
minutes each and then left on paper towels to air dry. Each piece
imparted a greenish turquoise metallic shine that was fairly
uniform. When probed with a multi-meter (Extech Instruments), no
electrical continuity was observed on any of the strips. Each strip
was then flame annealed by passing the strip across over butane
flame from a Lenk butane flame burner (Model 65) several times.
Care was taken not to cause any burning of underlying silicone. The
strips were then cooled to room temperature and tested for
electrical continuity under zero strain and a maximum of
.about.300% strain. Electrical resistances in the ranges of 3 to 20
ohms were recorded when probed across the strip length. When
strained to 300%, resistance values of 1 to 3 kiloohms were
recorded. Not all 8 samples showed continuity at 300% strain but
all showed continuity up to varying degrees of strain. Even after
multiple strain cycles, electrical continuity was not lost in the
test samples suggesting robustness of the deposited silver layer.
Despite deposition of silver layer on the strips, increase in their
weight post silver treatment was negligible indicating very thin
layer of silver was deposited.
Example 73
Silicone Based Conductive Elastomer
[0307] The extra 4 test strips prepared in the Example 72 were
treated slightly differently. The strips were treated with Tollens
reagent to deposit silver at a much faster rate than the rate in
the third treatment in Example 72. The test strips were dipped for
10 sec in a solution made by dissolving stannous chloride
(SnCl.sub.2.2H.sub.2O, 2.5 gm) in 50 ml deionized water and 5 ml
concentrated HCl, then rinsed with water and air dried briefly.
Next the strips were immersed for 6 mins in Tollens reagent
solution at 25.degree. C. made by mixing silver nitrate (0.1M, 196
mL), sodium hydroxide (10%, 16 mL), ammonium hydroxide (25%, 112
mL) and glucose solution (0.1M, 48 mL). The strips were removed,
rinsed with water, air dried and flame annealed as in Example C1
over butane flame. When tested for electrical continuity under
strain, they registered electrical resistances higher than those
samples in Example 72.
Example 74
Silver Based Flexible Mirror
[0308] A flexible mirror was also constructed by the inventors. A
Kapton.RTM. polyimide adhesive tape (about 3' long and 0.5'' wide)
was applied to a clean glass slide. The glass slide was suspended
from a hook such that the tape was completely immersed in
.about.150 mL silver nanoparticles solution in a cup maintained at
55.degree. C. for 4 h. The solution was prepared by mixing 50 mL
each of Tween 20 solution (5.6 g/L), sodium saccharinate (0.025M),
silver nitrate (0.1M), and TEMED (5 mL). It was heated to
55.degree. C. in a microwave oven.
[0309] After silver treatment, the slide and the film was
thoroughly rinsed with water, sonicated in water for 10 minutes to
remove loose debris, dried with hot air gun. The polyimide was
deposited with a shiny reflecting mirror of silver. Half of the
mirror was flamed annealed as described in Example 72. The annealed
portion was found to adhere better to the underlying Kapton.RTM.
tape whereas the non-annealed region could be rubbed off. The
annealed portion could be bent without the silver mirror flaking
off indicating good adhesion.
Example 75
Kapton Film with Silver Coating
[0310] A Kapton strip was coated with nanosilver using as in
Example 74 above but was treated for 1 h at 55.degree. C. instead.
The resulting shiny reflective Kapton strip was taped to a glass
slide with Scotchgard.RTM. tape to keep it flat during annealing.
The silver coating was annealed by butane flame by running it
lengthwise (.about.1 min with pauses to cool the strip). The cooled
film was examined for conductivity by measuring its resistance
lengthwise (.about.a distance of 7-8 cm). A resistance ranging 100
to 3000 ohms was observed at several points, showing the silver
coating became conductive after annealing. The strip was wrapped
around the 2 mm thick glass slide and still read resistance values
observed before. The annealed silver coating showed bend
resistance.
Example 76
Coated Acrylic Sheet
[0311] A coated Acrylic polymer (supplied by Rohm & Haas Co.,
Philadelphia, Pa.) strip 1 cm wide and .about.8 cm long was
immersed in a solution identical to that in Example 74. After 1 h
at 55.degree. C., the strip was removed, rinsed with Tween 20
solution (4.3 gm/L) and de-ionized water. The strip was treated at
55.degree. C. for 1 h second time using freshly made identical
silver containing solution to deposit more silver. The sample was
flame annealed as in Example 2, cooled and tested for electrical
continuity. Lengthwise over 7-8 cm the silver coating was
conductive with resistance values measuring 30-34 kiloohms.
Example 77
Electrically Conductive Tulle Material
[0312] Tulle material made of polyamide polymer (purchased from a
local fabric store) in the form of 2''.times.2'' squares (total-10
samples) were immersed in a solution made from 200 mL Tween 20
(16.7 gm/L), 200 mL 0.075M sodium acetate and 200 mL silver nitrate
(0.1M) and TEMED (20 mL). The solution was heated to 55.degree. C.
and after 2, 4, 6, 9 and 12 h period two samples each were removed
rinsed with 10% ammonium hydroxide solution and then with
de-ionized water and dried. The samples treated for 6 h or more
showed a metallic shine with a purplish tint. The metallic silver
coating was uniform on the nylon thread making up the tulle
material.
[0313] Using banana clips on the nylon thread at the diagonal
corners of the samples, the electrical resistance of the samples
was measured. The samples treated for 6 h or more--all exhibited
resistance values in the range 5-15 ohms clearing showing them to
electrically conductive. Even after wrapping the sample piece
around sharp bend did not change the resistance readings. Even
sonication of pieces for 10 minutes immersed in water did not alter
the resistance values indicating extraordinary adhesion of the
resulting nanoparticle silver coating.
[0314] None of the samples treated for 6 h or more required
annealing for the silver coating to be electrically conductive.
Example 78
Electrically Conductive Fluorosilicone Elastomer
[0315] A strip 1'' wide and 3'' long made of fluorosilicone
elastomer were supplied by Meggitt Silicone Products of
McMinnville, Oreg. The strip was wiped with isopropanol and air
dried. The strip was deposited with nanosilver in 3 steps. In step
1, a solution was prepared by mixing 40 mL Tween 20 (16.7 gm/L), 20
mL 0.125M sodium saccharin, 20 mL 0.125M sodium acetate and 40 mL
0.15M silver nitrate solutions. To this solution, 12 gm
triethanolamine (TEA) was added to yield a clear solution. After
heating the solution in microwave oven to .about.55.degree. C., the
elastomer strip was immersed in it. The contents were maintained at
55.degree. C. for 21 h, then removed and rinsed with de-ionized
water. Next, step 2 was carried out which was a repeat of Step 1.
The silver coated strip was removed again and rinsed thoroughly
with water. It was cut into two identical pieces (1''.times.1.5'').
One piece was annealed on butane flame and tested for electrical
continuity. On multi-meter display (Extech Model MiniTec 26.TM.) we
did not get a measurable reading indicating the coating to be
insulating. The remaining piece was subjected to Step 3. The sample
was immersed in a solution made with 40 mL each of Tween 20 (16.7
gm/L), 0.025M sodium saccharin and 0.25M silver nitrate solutions.
Triethanolamine (2 gm) was also added. The tub bearing solution and
the sample (spaced from the tub bottom by a nylon screen mesh
piece) were kept at 55.degree. C. for 24 h. After the treatment,
the sample was rinsed thoroughly--first with Tween 20 (4.3 gm/L),
tap water and finally with de-ionized water. The initially sky blue
colored sample imparted silver ash color with matte finish. When
handled, the silver tended to flake off slightly. Before annealing,
we recorded resistance values of the silver coated fluorosilicone
elastomer. One surface of the sample, the values when measured with
probe leads diagonically across were between 2 and 5 ohms (the side
away from tub bottom) and the surface closer to the bottom had
higher values (200 to 500 ohms). The difference we surmise is due
to different rates of silver deposition on the top versus bottom
surfaces. Annealing the sample piece, did not alter the resistance
values very much, but the sample surface became silver grey with
increase in metallic shine. The conductivity of the fluorosilicone
sample had resistance values <5 ohms.
Example 79
6''.times.6'' Silicone Elastomer Slabs
[0316] A total of 50 6''.times.6'' silicone elastomer slabs were
coated with silver. To prepare the slabs for coating, they were
threaded with a strong fish line through two points each spaced 1''
from the top and respective side edges of the slab. This allowed
the slab to be suspended without touching the bottom of a
Sterilite.RTM. 1 gallon polypropylene pitcher. 17 slabs were
treated in two separate pitchers with the third holding 16 slabs.
The slabs suspended inside pitcher were rinsed with Tween 20
solution (4.3 gm/L) and then de-ionized water. Excess liquid was
drained off from the pitchers and the slabs were treated with
silver solution without further drying as follows.
[0317] The slabs were treated to three different levels of silver
loading--low, medium and high. Each level was to achieve different
level of conductivity (or resistance). Following steps were
involved in producing slabs with silver coating.
Stage 1 @ 55.degree. C. for 24 h
[0318] Treatment of the slabs with a solution made from 1 volume
part Tween 20 (16.7 gm/L); 1 volume part 0.025 M sodium saccharin;
1 volume part 0.1 M silver nitrate, and 0.1 volume part TEMED
(tetramethyl ethylene diamine). The slabs were rinsed with tap
water and once with de-ionized water.
Stage 2 @ 55.degree. C. for 18 h
[0319] Treatment of the slabs with a solution made from 1 volume
part Tween 20 (16.7 gm/L), 1 volume part 0.025 M sodium saccharin,
1 volume part 0.1 M silver nitrate, and 0.1 volume part TEMED. The
slabs were rinsed with tap water and once with de-ionized
water.
Stage 3 @ 55.degree. C. for 24 h
[0320] Treatment of the slabs with a solution made from 1 volume
part Tween 20 (16.7 gm/L), 1 volume part 0.025 M sodium saccharin,
1 volume part 0.25.degree.M silver nitrate, 0.1 volume part TEMED
The slabs were rinsed with tap water and once with de-ionized water
(and air dry if low level slabs were made)
Stage 4 @ 55.degree. C. for 4 h
[0321] Treatment of the slabs with a solution made from 1 volume
part Tween 20 (16.7 .mu.m/L), 1 volume part 0.025 M sodium
saccharin, 1 volume part 0.25 M silver nitrate, and 0.1 volume part
TEMED. The slabs were rinsed with tap water and once with
de-ionized water and air dried at room temperature
Stage 5 @ 55.degree. C. for 16 h
[0322] Treatment of the slabs with a solution made from 1 volume
part Tween 20 (16.7 gm/L), 1 volume part 0.025 M sodium saccharin,
1 volume part 0.25 M silver nitrate, and 0.1 volume part TEMED The
slabs were rinsed with tap water and once with de-ionized water and
air dry at room temperature
[0323] To produce slabs, the following protocols were followed: Low
level--Stages 1 to 3; Medium level--Stages 1 to 4; and High
level--Stages 1 to 3 and 5.
[0324] Finally, all slabs were flame annealed .about.15's on each
side on a propane heater and cooled to room temperature. The
resistance values were measured across the two diagonals on each
side and presented in tables below. The values typically are in
megaohms for low loading slabs; are of the order of kiloohms for
medium loading and are in tens of ohms for high loading. The
gradual decrease in resistance values indicated that the treatment
variation was achieving the desired goal of having different
thicknesses of silver coating. Random measurements of resistance
values with some slabs samples under bending strain showed
electrical continuity and registering only very small increase.
TABLE-US-00015 TABLE 15 Resistance Values in mega ohms of Silver
Coated Silicone Slabs (Low Loading) Side 1 Side 2 Sample No.
Diagonal 1 Diagonal 2 Diagonal 3 Diagonal 4 1 2.4 1.9 1.85e-4
5.3e-5 2 15.0 3.0 5.0 9.0 3 1.15e-4 3e-4 9.8e-5 1.3e-3 4 1.27e-4
1.53e-4 8.4 2.3e-3 5 8e-4 1.38e-4 2e-3 1.1e-3 6 12.5 10.0 22.0
5.5e-2
TABLE-US-00016 TABLE 16 Resistance Values in ohms of Silver Coated
Silicone Slabs (Medium Loading) Side 1 Side 2 Sample No. Diagonal 1
Diagonal 2 Diagonal 3 Diagonal 4 1 23 25 53 55 2 430 460 480 750 3
165 147 26 53 4 75 69 14 80 5 2500 242 100 89 6 8 13 16 14
TABLE-US-00017 TABLE 17 Resistance Values in ohms of Silver Coated
Silicone Slabs (High Loading) Side 1 Side 2 Sample No. Diagonal 1
Diagonal 2 Diagonal 3 Diagonal 4 1 7 8 12 5 2 3 16 124 32 3 5 4 7 9
4 30 20 90 46 5 8 9 9 8 6 30 22 18 7
Example 80
Silver Coated Fluorosilicone Elastomer
[0325] Three strips (1''.times.3'') of fluorosilicone similar to
the one used in example 79 were coated at low, medium and high
levels of silver following the method in example 80 except instead
of TEMED triethanolamine was used. This yielded one strip at low,
medium and high silver loading. The strips were annealed as in
example 8 and examined for electrical conductivity using
multi-meter. We observed no measurable resistance values for low
and medium coated samples but the high level samples showed reading
in the range of 20-30 megaohms.
[0326] To determine the amount of silver coated, we cut thin
slivers from the coated pieces and stripped them of silver by
treating them with a mixture of 30% Hydrogen peroxide and
concentration nitric acid. The solutions with dissolved silver were
analyzed for silver by FAAS. The amount of silver at low, medium
and high loading were found to be 0.33 mg/cm2, 0.8 mg/cm2 and 1.35
mg/cm2 respectively.
Example 82
Silver Coated Silicone Elastomer
[0327] Silicone elastomer in the shape of a dog bone
(.about.3.5''.times.1.0''.times.0.063'' with 0.25''wide and 1.5''
long stem in the center) was soaked in 23% nitric acid overnight
and rinsed with de-ionized water and dried. It was treated with
silver nanoparticles solution made by mixing equal volumes of Tween
20 (16.7 g/L, 70 mL), sodium saccharinate (0.025M) and silver
nitrate (0.1M) followed by TEMED addition (7 mL). The mixture was
warmed to 55.degree. C. in a microwave oven upon which it turned
clear dark brown. The dog bone was immersed in solution for 17 h at
55.degree. C., rinsed with water and dried. The initial light gray
piece turned light grey black in color after silver treatment.
[0328] It was re-treated using a fresh silver solution made the
same way for 24 h at 55.degree. C. Next, it was rinsed and
sonicated in water for 10 minutes at 25.degree. C. The initial
light gray piece now looked more silvery in color after 2nd silver
treatment.
[0329] A sensitizing solution was prepared by dissolving 0.5 g
SnCl2.2H20 and 0.5 g concentrated HCl in 10 mL de-ionized water. To
this solution, were added isopropanol (5 mL), concentrated HCl (4
mL) and de-ionized water (31 mL). The silver coated dog bone was
immersed in the sensitizing mixture for 10-15 s, rinsed thoroughly
with water and dried with a hot air gun. Yet another silver
containing solution (Tollen's reagent) was prepared as follows. To
silver nitrate solution (0.1M, 48 mL), sodium hydroxide solution
(10% w/v, 4 mL) was added to yield a brown precipitate. To the
precipitate was added ammonium hydroxide (7% v/v) in just enough
volume to get a clear colorless solution. To this silver-ammonia
complex solution, freshly made glucose solution (0.1M, 12 mL) was
added. Half amount of the total volume of the solution prepared was
transferred to a 50 mL polypropylene tube and the dog bone strip
immersed in it for 6 min at 25.degree. C. The strip was removed and
rinsed with water and air dried. The strip thus obtained was flame
annealed over butane flame. The dog bone strip was found to be
electrically conductive (resistance <5 ohms). Under stretching
to .about.300% the resistance value observed was in <10
kiloohms. The strip continued to show conductivity (R<5 ohms)
even after repeated strain fatigue cycles. Even after 3-4 twists,
the resistance measured lengthwise was <50 ohms. Even after 1
year, the same type of electrical conductivity behavior in the
sample was observed. The amount of silver deposited on the dog bone
was determined to be .about.2.9 mg/cm2.
Example 82
Golf Ball--Method 1
[0330] A golf ball was treated to deposit silver on its surface. An
aqueous mixture was made by mixing equal volumes (30 mL) of Tween
20 (16.7 gm/L), sodium saccharinate (0.1M) and silver nitrate
(0.1M). To the milky suspension, TEMED (3 mL) was added under
gentle stirring. The content were transferred to a 125 mL capacity
glass container containing the golf ball. Enough solution was
poured to keep the ball submerged. The container was capped with a
lid and placed in an oven at 55.degree. C. for 24 h. The treatment
was repeated to yield a golf ball surface impregnated with silver.
After the repeat treatment, the ball was rinsed thoroughly with
deionized water and left to air dry. The ball had a yellow brown
color that was very uniform.
Example 83
Golf Ball--Method 2
[0331] A golf ball was treated to deposit silver. The silver
containing solution was prepared by mixing .about.67 mL each of
Tween 20 (16.7 gm/L), sodium saccharinate (0.075M) and silver
nitrate followed by TEMED (6.7 mL). The solution was heated in
microwave to .about.60.degree. C. and poured over the golf ball,
which was placed in glass beaker, ensuring the ball remained
submerged. The beaker was covered to prevent the liquid from
evaporating. The beaker was placed in an oven set to 60.degree. C.
for .about.20 h. The ball was removed and rinsed with water and
left to air dry. The color of the ball turned yellow from the
initial white the intensity of which increased with time. In feel
the golf ball was no different than before. During the treatment,
there was no loss of the logo image. Though not tested, the silver
coated ball is expected to be bacteriostatic.
Example 84
Polycarbonate Film
[0332] A .about.8 cm.times.1 cm (.about.0.1 mm thick) film strip
made of polycarbonate was cut from a sheet and transferred to a
polystyrene tube with a cap. Separately, a silver containing
mixture was prepared in a glass test tube by mixing 2 mL each of
Tween 20 (16.7 gm/L), sodium saccharinate (0.075M) and silver
nitrate (0.1M) and TEMED (0.2 mL) in that order. The mixture was
heated in microwave oven to .about.55.degree. C. when its color
became light yellow. The hot mixture was transferred to PS tube
containing sample strip and the tube heated for 16 h at 55.degree.
C. in an oven. After the treatment, the sample was washed with
water and air dried. The portion of the strip that was immersed in
solution had turned uniformly amber colored. Iridescent shades of
magenta, blue and metal were observed on the strip surface. The
amber color indicated presence of silver nanoparticles on the
surface.
Example 85
Polycarbonate Film
[0333] A strip was prepared exactly as described in example 85. The
strip was sonicated for 10 minutes to remove loosely adhering
particles. The amber colored portion of the strip was treated a
mixture made with Tween 20 (16.7 g/L, 3 mL), silver nitrate (16.7
g/L, 3 mL) and TEMED (0.3 mL) for 1 h at 55.degree. C. The strip
color was much darker than before and its surface somewhat shiny.
The darker amber shade than before suggested the strip gained more
silver than in the sample in example 85.
Example 86
Polystyrene Substrates
[0334] This example describes the method of silver deposition on
various polystyrene based articles. For illustration tubes and well
plates were used, but the method described is applicable to all
types of polystyrene articles and surfaces. A polystyrene tube was
uniformly coated on the inside with silver. The coated surface had
metallic shine and in ambient lab light, the color of the coated
layer was reddish brown.
Example 87
Glass Substrates--Formation of a Silver Mirror
[0335] This example illustrates the use of glass slide but the
method is applicable to other articles made from glass. In a
petri-dish, a piece of nylon mesh was placed as spacer between the
dish surface and glass surface. A solution made from Tween 20 (16.7
g/L, 20 mL) and silver nitrate (0.1M, 20 mL) and TEMED (2 mL) was
poured over the slide. The petri-dish was sealed and place in an
oven at 55.degree. C. for 1-2 h. The solution was discarded and
glass slide was thoroughly was with de-ionized water and dried with
a heat gun. A very reflective shiny silver mirror was obtained.
When held to light, the silver mirror imparted purple blue color
and was transparent. The mirror was electrically conductive
registering a resistance value of 55-65 ohms along the length of
the glass slide.
Example 88
Polyurethane Tubing Stock
[0336] This example describes a method to deposit silver on
polyurethane class of materials. Though the illustrative example
uses tubing stock, the method is applicable to all polyurethane
based articles. Polyurethane tubing stock was cut in 30 inches long
sections. 6 tube segments were wrapped around a rod and zip-tied.
The tube segments were placed inside a tubular reactor containing a
silver solution made from equal volumes of Tween 20 (16.7 g/L, 120
mL), sodium saccharinate (0.075M) and silver nitrate (0.1M). The
contents were heated to 55.degree. C. under gentle rocking
(.about.10-12 oscillations/min). After 55.degree. C. was reached
the reactor was opened briefly and TEMED (12 mL) was introduced and
reactor lid closed. The contents were maintained at 55.degree. C.
for 3 h. The reactor was opened and the spent silver solution was
drained. Then 600 mL of 1:4 diluted ammonium hydroxide was poured
and the reactor rocked for 15 minutes. After draining ammonium
hydroxide, the samples were removed and washed thoroughly with lots
of de-ionized water, centrifuged to remove water inside lumen and
left to air drying on clean paper overnight. After silver
treatment, the catheter segments imparted yellow brown color.
Silver analysis by FAAS showed a loading in the range 7-10
.mu.g/cm2.
Example 89
Glass Prism
[0337] A glass prism (sides .about.1.5'' and height .about.1.0''
and .about.0.5'' deep) was washed in a sonicator (Fisher Scientific
Model FS 30) for 5 minutes each in, 10% nitric acid, 10% sodium
hydroxide solution, isopropanol and 1:10 diluted ammonium hydroxide
in succession and then placed directly in a solution made by mixing
Tween 20 (16.7 g/L, 50 mL), silver nitrate (0.15M, 50 mL) and TEMED
(5 mL) and heated to 55.degree. C. for 18 h. After treatment was
complete, the prism was removed and washed with Tween 20 solution
(16.7 g/L) followed by thorough rinsing with de-ionized water. The
measured reflectance of silverized glass prism was 88-90% for
>500 nm.
Example 90
Titanium Disks
[0338] This example describes silver nanoparticle deposition on
titanium disks (32 mm dia and 2 mm thick). The method is applicable
to titanium substrates of all kinds with minor variations as
needed. Twenty disks were placed in a warm solution (55.degree. C.)
obtained after heating a mixture of 1.3 liters each of Tween 20
(16.7/g/L), sodium acetate (0.075M) and silver nitrate (0.15M) and
TEMED (0.13 liter). The tub holding the solution and disk was
capped and placed on a shaker in an oven set at 55.degree. C. for
18 h. The tub was removed, liquid drained off and the disks quickly
placed in another container with 500 mL of wash solution (10% v/v
ammonium hydroxide) for 1 minute and then washed with de-ionized
water, patted dry with tissue paper and air dried. After the
treatment, there was very little visible difference. The silver
loading was estimated to be .about.20 .mu.g/cm2.
Example 91
Gold Screws
[0339] This example describes deposition of silver nanoparticles on
gold surfaces. For illustration gold screws that are commonly used
in dental medicine were used. Fifty screws with gold surface
(.about.0.35'' long, .about.0.08'' dia, 0.075'' screw head dia and
0.15'' threaded length) were treated with silver containing
solution at 55.degree. C. for 16 h. The treating solution was made
from Tween 20 (16.7 g/L, 125 mL), sodium saccharinate (0.125M, 75
mL), silver nitrate (0.1M, 50 mL), de-ionized water (125 mL) and
TEMED (12.5 mL). The screws were sealed in a nylon mesh satchel to
prevent their accidental loss and to expedite cleaning. After the
treatment, the satchel with screws was immersed in a beaker filled
with de-ionized water and rinsed thoroughly, and the screws were
then left to air dry on Paper. Deposition of silver on the gold
screws was evident from gold surface turning silver white in color.
The amount of silver deposited was determined by FAAS as .about.24
.mu.g/cm2.
Example 92
Copper Substrates
[0340] This example demonstrates the deposition of silver
nanoparticles on copper articles. For illustration, a US copper
penny coin was used. The method can be applied to all copper
surfaces. A solution of silver was prepared by mixing Tween 20
(16.7 g/L, 4 mL), sodium saccharinate (0.075M, 4 mL), silver
nitrate (0.1M, 4 mL) and TEMED (0.4 mL) in that order. The solution
in a 50 mL PP tube (Falcon Brand) was heated to 55.degree. C. in
microwave oven, cooled to room temperature and then poured over a
clean copper penny (bright colored) placed over a mesh in a Petri
dish. The penny was kept submerged in the liquid overnight. It was
rinsed, sonicated for 3 minutes in water, wiped dry gently to yield
silver coated ash grey penny.
Example 93
Silicone Tubing Stock
[0341] This example describes deposition of silver nanoparticles on
clear silicone tubing stock (OD: 3.1 mm and ID: 1.5 mm) that is
commonly used in urinary catheters. While the exemplary substrate
is tubing, the method of treatment can also be readily applied to
silicone based articles. A silver containing solution was prepared
by mixing 20 mL each of Tween 20 (16.7 g/L), sodium acetate (0.05M)
and silver nitrate (0.15M) followed by TEMED (2 mL). To 50 mL
capacity polypropylene (PP) tube (BD Falcon brand), 10 pieces of 1
cm long pieces of tubing were added and then 10.33 mL of the silver
solution pipetted. Three PP tubes in total were prepared and placed
on a shaker inside an oven at 55.degree. C. One tube was removed
after 2 h, the 2nd tube after 3 h and the 3rd tube after 4 h. Each
time, the sample pieces were poured in Tween 20 solution (4.2 g/L,
50 mL), then rinsed with de-ionized water and left to dry in air
overnight. The clear tubing pieces became yellow brown to dark
brown with increased treatment time. The silver loading on tubing
stock treated for 2, 3 and 4 h was determined as 8.4, 11.1 and 13.4
.mu.g/cm2 respectively.
Example 94
Luer Activated Device Composed on Polycarbonate and Silicone
[0342] This example describes the method of depositing silver
nanoparticles on polycarbonate and silicone surfaces of a Luer
activated device. The medical device consists of three
parts--polycarbonate based housing and base and a silicone gland
allows for needleless connection for introducing fluids into the
human body. While the device treated was chosen as illustration,
the treatments can be applied to any polycarbonate or silicone
based articles.
[0343] The housing was treated as follows. 2500 housing pieces were
placed a basket in a tank lined with polypropylene liner. A silver
containing solution was made using 5 liters each of Tween 20 (16.7
g/L), sodium acetate (0.05M) and silver nitrate (0.15M). To this
solution TEMED (0.5 liter) was added. The tank was heated to
55.degree. C. and the heating maintained for 24 h. The pieces were
removed, rinsed with Tween 20 (4.2 g/L), 10% ammonium hydroxide and
de-ionized water and allowed to air dry. Of the treated pieces, 400
were treated second time with the same silver solution for 1 h at
55.degree. C. maintaining the solution volume per piece to .about.6
ml.
[0344] The base was treated identically to housing as described in
the preceding paragraph. Both pieces turned shiny grey black after
treatment. Similarly, the silicone gland was treated using same
chemical recipe at 55.degree. C. but the treatment lasted
.about.9.5 h without the need for a re-treatment. The fluid volume
to part ratio remained the same. The silicone piece was turned
greenish grey with shiny but non-reflective surface.
[0345] The silver coated components were assembled into luer
activated devices and sterilized by gamma irradiation before use in
biofilm assay. The amount of silver on the housing base and gland
was estimated by FAAS as .about.36.6, 25.6 and 93.0 .mu.g/cm2.
Example 95
Biofilm Fouling Assay
[0346] Surfaces exposed to fresh and marine water over time will
foul i.e. form a slippery layer due to the formation of biofilm. It
is known free floating i.e. planktonic microorganisms generally
will not adhere to surfaces however some microorganisms develop an
ability to form polysaccharide film i.e. convert to biofilm forming
counterparts after they have adhered to surfaces. They colonize
this layer and continue to build and ultimately spread the film all
over the surface. Fouled surfaces may affect
hydrodynamics--increase resistance to flow and heat and may affect
the aesthetics of water conveyances such as boats.
[0347] The present invention eliminates the problem of biofilm
formation by deposition of nanoparticles, such as silver
nanoparticles, on surfaces. The assay was applied to evaluate
silver coated polycarbonate and silicone surfaces of a luer
activated device. However, its application to these surfaces is for
illustration and not to be construed as limiting. To the contrary
the assay with minor variations can be applied to assess biofilm
inhibition by nanoparticle coating on different polymers, metals
and ceramics. The principle of the assay involves allowing
microorganisms to form and grow biofilm of the surface and then
evaluate biofilm formation by sloughing off biofilm from the
surface using sonication and plating the sloughed off biofilm
containing fluid to enumerate surviving bacteria. Prior to
sonication, the surfaces on which biofilm is grown are rinsed
thoroughly to remove all planktonic bacteria. Rinsing is enough to
wash off free floating planktonic bacteria.
[0348] Day 0
[0349] 1. Bacteria inocula, Staphylococcus aureus, (ATCC: 6538),
(at 1.times.10.sup.8 cfu/ml) were diluted 1:10 into 4 ml saline,
and further diluted 1:100 into M103 media (M103 media filter
sterilized: 1% Serum, 0.25% Glucose, 0.1% Neopeptone) for starting
M103 inocula of approximately 1.times.10.sup.5 cfu/ml (t=0).
[0350] 2. T=0 inocula of the 1.times.10.sup.5 cfu/ml were plated on
TSA at 10.sup.-3, 10.sup.-4, 10.sup.-5, and 10.sup.-6 dilutions,
and plates were incubated overnight at 35.degree. C.
[0351] 3. 6 (3 treated and 3 untreated) Luer activated devices as
above were used. 2 ml saline was injected into each device, and
each device was actuated 25 times to simulate actual use.
[0352] 4. 2 ml of M103 inoculum (containing 1.times.10.sup.5 cfu/ml
bacteria) were pushed through each device, and devices with the
same treatment conditions were placed in 50 ml conical tubes.
[0353] 5. Tubes containing the devices were incubated overnight at
35.degree. C.
[0354] Day 1
[0355] 1. T=0 plates were counted.
[0356] 2. 2 ml of sterilized M103 media with a 10.sup.3 dilution of
bacteria was pushed through each device. This step was continued
for 6 successive days. Each device was actuated 25 times per day to
simulate actual use for a total of 175 actuations for samples in
168 h test.
[0357] Day 7
[0358] 1. To remove any non-adherent bacteria, 10 ml of saline+0.1%
Tween 80 were pushed through each device.
[0359] 2. To ensure only pure saline was in the device for
sonication, 2 ml saline was pushed through each device.
[0360] 3. All duplicate devices were placed in a 16.times.125 mm
glass test tube.
[0361] 4. All tubes are placed in a room temperature water bath in
the sonicator. The water in the bath was covering the heights of
the devices in the tubes.
[0362] 5. The tubes were sonicated for 1 min, and rested for 1 min,
alternating for 5 total times.
[0363] 6. 1 ml saline was passed through all devices, and collected
in a 24 well plate.
[0364] 7. 100 .mu.l was pipetted from the collected flow-through
for each device into the well of the first row of a 96 well-micro
titer plate. 180 .mu.l of 0.9% sterile saline is added in the wells
down each column.
[0365] 8. A serial ten fold dilution (100-10.sup.-4) was prepared
down each of the rows by transferring 20 .mu.l from each dilution
well.
[0366] 9. 100 .mu.l samples from the wells with 10.sup.-1,
10.sup.-3, and 10.sup.-5 dilutions were transferred to TSA plates
and spread for counting, for final dilutions of 10.sup.-2,
10.sup.-4, and 10.sup.-6.
[0367] 10. Incubated at 35.degree. C. overnight and the plates were
counted. Results follow.
TABLE-US-00018 TABLE 18 T = 0 plate count Plate count: Plate count
Dilution A B (-3) 152 224 (-4) 20 17 (-5) 1 1 (-6) 0 0 Starting CFU
of M103 bacteria: 1.58 .times. 10.sup.5
TABLE-US-00019 TABLE 19 Plate Count after 7 Days Treated Treated
Treated Sample Sample Sample Untreated Untreated Untreated Dilution
1 2 3 Sample 1 Sample 2 Sample 3 (-1) 1 0 0 TMTC TMTC TMTC (-3) 0 0
0 792 774 984 (-5) 0 0 0 26 20 12 (-7) -- -- -- 1 0 5 TMTC = too
many to count
TABLE-US-00020 TABLE 20 Average CFU and Log Reduction in Silver
Nanoparticle Coated Device Treated Untreated Ave. CFU 3.33
8.50*10.sup.5 Log CFU 0.52 5.93 Log Red 5.41 --
[0368] The results show that silver nanoparticle treated Luer
activated device having polycarbonate and silicone surfaces
exhibited strong inhibition of biofilm formation for 7 days. The
quantitative measure, the log reduction in bacterial count compared
to an untreated device is >5 log translating into a 99.999%
reduction.
Example 96
Preparation of Gold Nanoparticles
[0369] In a test tube, sodium oleate solution (0.125M, 1 mL),
aqueous hydrogen tetrachloroaurate trihydrate (1% w/v, 1 mL) and
disodium EDTA solution (0.125M, 0.2 mL) were added in succession.
The test tube was placed in microwave oven and heated briefly to
increase solution temperature to .about.45-50.degree. C. (color
change to blue black seen) and the test tube left to cool to room
temperature under lab light. After 4 h, the blue black color had
changed to wine red and color became much darker. The solution
remained red color for over a month at ambient temperature. The
UV/VIS absorption peak was around 530 nm.
Example 97
Gold Nanoparticles Preparation--Method--2
[0370] In a test tube, following solutions & chemicals were
added and tube heated briefly as described in example 97.
[0371] Sodium oleate solution (0.125M, 0.9 mL)
[0372] Hydrogen tetrachloroaurate trihydrate (1% w/v, 0.1 mL)
[0373] De-ionized water (0.9 mL)
[0374] Disodium EDTA solution (0.125M, 0.1 mL)
[0375] The color of tube contents changed to pale yellow and then
to wine red. No precipitation was observed and wavelength maximum
was 530 nm.
Example 98
Gold Nanoparticles Preparation--Method--3
[0376] In a test tube, sodium oleate solution (0.125M, 1 mL),
hydrogen tetrachloroaurate trihydrate (1% w/v, 1 mL) and TEMED (0.1
mL) were added in succession. The yellow colored solution changed
in intensity after TEMED addition. The test tube was placed in
microwave oven and heated briefly to increase solution temperature
to .about.45-50.degree. C. (color change to yellow brown seen) and
then as the test tube cooled to room temperature it finally turned
red in color. After 4 h, the blue black color had changed to wine
red and color intensity dark. No agglomeration of particles in
solution was seen. The UV/VIS absorption peak was around 530
nm.
Example 99
Gold Nanoparticles Preparation--Method--4
[0377] This example was carried out like example 99 except instead
of sodium oleate as stabilizer we used Novec.RTM. 4430 (a
fluorinated surfactant from 3M Company) solution (32 g/L). A clear
violet purple solution was obtained having wavelength maximum at
.about.580 nm.
[0378] These examples describe the preparation of gold
nanoparticles using methods of the present invention. In these
methods, such as where noble metals such as gold, copper, rhodium,
platinum or palladium are used, the use of an anion compound may be
optional. In addition, reducing agents such as sodium borate,
hydrazine hydrate, primary amines, lithium aluminum hydride and
others known to those skilled in the art may be used to initiate
nanoparticle synthesis.
[0379] Suitable stabilizers for such nanoparticles synthesis
include polyacrylamide, carboxymethyl cellulose, TritonX-100.RTM.,
T-MAZ.RTM., Span 800, Novec 4430, Novec 4432, PVA, PVP,
polyurethane diol, sodium dodecyl sulfate, dioctyl sulfosuccinate,
propylene glycol alginate, tartaric acid. Suitable initiators or
reducing agents for such nanoparticles may be TEMED,
triethanolamine (TEA) and TEA-water mixtures (0.1 to 90% TEA),
tetrabutyldiamine and its aqueous solution (0.1 to 90% amine),
tetradimethyldiaminomethane and its aqueous solution (0.1 to 90%
organic moiety), aldehydes such as formaldehyde, glutaraldehyde,
and dipropylamine and its aqueous mixtures (0.1 to 90% amine). A
suitable gold compound may be hydrogen tetrachloroaurate
trihydrate, but other gold compounds If available may be used
without departing from the scope of the invention.
* * * * *