U.S. patent application number 10/260369 was filed with the patent office on 2004-04-01 for colorimetric sensor.
Invention is credited to Lyons, Christopher Stewart, Maki, Stephen Paul, Rakow, Neal Anthony.
Application Number | 20040062682 10/260369 |
Document ID | / |
Family ID | 32029671 |
Filed Date | 2004-04-01 |
United States Patent
Application |
20040062682 |
Kind Code |
A1 |
Rakow, Neal Anthony ; et
al. |
April 1, 2004 |
Colorimetric sensor
Abstract
Disclosed herein are calorimetric sensor films comprising a
reflective layer, polymeric detection layer, and semi-reflective
layer. Also disclosed are devices comprising the colorimetric
sensor films and methods of making the films and devices.
Inventors: |
Rakow, Neal Anthony;
(Woodbury, MN) ; Lyons, Christopher Stewart;
(Saint Paul, MN) ; Maki, Stephen Paul; (North
Saint Paul, MN) |
Correspondence
Address: |
3M INNOVATIVE PROPERTIES COMPANY
PO BOX 33427
ST. PAUL
MN
55133-3427
US
|
Family ID: |
32029671 |
Appl. No.: |
10/260369 |
Filed: |
September 30, 2002 |
Current U.S.
Class: |
422/400 ;
422/82.05; 422/82.09; 422/86 |
Current CPC
Class: |
G01N 31/22 20130101;
G01N 21/78 20130101; G01N 33/525 20130101 |
Class at
Publication: |
422/055 ;
422/058; 422/060; 422/082.05; 422/082.09; 422/086 |
International
Class: |
G01N 021/00 |
Claims
What is claimed is:
1. A colorimetric sensor for measuring one or both of the presence
and concentration of an analyte comprising: a substantially
continuous reflective layer; a detection layer over the reflective
layer, the detection layer comprising at least one polymer
component, said layer being capable of a change in optical
thickness upon exposure to said analyte; and a substantially
continuous semi-reflective layer over the detection layer, the
semi-reflective layer having an index of refraction different from
the index of refraction of the detection layer.
2. The calorimetric sensor of claim 1 further comprising a
substrate layer under the reflective layer.
3. The calorimetric sensor of claim 1 wherein the detection layer
comprises a porous material.
4. The colorimetric sensor of claim 1 wherein the change in optical
thickness of the detection layer is due to a dimensional change of
said detection layer.
5. The colorimetric sensor of claim 1 wherein the change in optical
thickness of the detection layer is due to a change in the index of
refraction of said detection layer.
6. The calorimetric sensor of claim 1 wherein the change in optical
thickness of the detection layer is permanent.
7. The colorimetric sensor of claim 1 wherein the change in optical
thickness of the detection layer is reversible.
8. The colorimetric sensor of claim 1 wherein the detection layer
comprises two or more polymer components and wherein the optical
thickness of each polymer component will change in the presence of
a different analyte.
9. The sensor of claim 8 wherein the polymer components are
blended.
10. The sensor of claim 8 wherein different polymer components
comprise different areas of the detection layer.
11. The colorimetric sensor of claim 1 wherein the detection layer
comprises at least two polymers and wherein the optical thickness
of only one polymer will change in the presence of an analyte.
12. The colorimetric sensor of claim 11 wherein the at least two
polymers are arranged such that a visible pattern will form when
the sensor is exposed to the analyte.
13. The colorimetric sensor of claim 1 wherein at least one polymer
in the detection layer is at least partially crosslinked.
14. The colorimetric sensor of claim 1 wherein at least one polymer
in the detection layer is selected from the group consisting of
polymers or copolymers comprising acrylates and methacrylates.
15. The calorimetric sensor of claim 1 wherein at least one polymer
in the detection layer is a copolymer.
16. The colorimetric sensor of claim 1 wherein one or both of the
reflective and semi-reflective layer comprises a metal.
17. The colorimetric sensor of claim 1 wherein the semi-reflective
layer has a visible light transmittance of about 30 to about
70%.
18. An array comprising two or more of the calorimetric sensors of
claim 1.
19. The array of claim 18 wherein at least two sensors are on
opposite sides of a substrate.
20. The calorimetric sensor of claim 1 further comprising molecular
receptors in the detection layer.
21. The colorimetric sensor of claim 20 wherein the molecular
receptors are selected from the group consisting of calixarenes,
cyclodextrins, azacrowns, crown ethers, porphyrins,
metalloporphrins, peptides, proteins, nucleic acids, and
oligonucleotides.
22. A device comprising the calorimetric sensor of claim 1 and a
light source.
23. The device of claim 22 further comprising a photo-detector.
24. A method of detecting the presence or absence of an analyte
comprising providing the calorimetric sensor of claim 1, providing
a light source, contacting the sensor with a medium that may
contain an analyte, and monitoring the sensor for a change
inoptical properties.
25. The method of claim 24 wherein a photo-detector is used to
monitor the sensor for a change inoptical properties.
26. The method of claim 25 wherein the change in optical properties
produces a visible change.
27. The method of claim 24 wherein the medium is a gas.
28. The method of claim 24 wherein the medium is a liquid.
29. The method of claim 24 wherein the analyte is a gas.
30. The method of claim 24 wherein the analyte is a liquid.
31. A calorimetric sensor for measuring one or both of the presence
and concentration of an analyte comprising: a substantially
continuous reflective layer; a detection layer over the reflective
layer, the detection layer comprising at least one polymer
component; and a substantially continuous semi-reflective layer
over the detection layer, the semi-reflective layer having an index
of refraction different from the index of refraction of the
detection layer, said sensor being capable of a change in color
upon exposure to said analyte.
32. The colorimetric sensor of claim 31 wherein the change in color
is from a visible color to a lack of visible color.
33. The calorimetric sensor of claim 31 wherein the change in color
is due to delamination of the detection layer from an adjacent
layer.
Description
TECHNICAL FIELD
[0001] This disclosure relates to colorimetric sensor films.
BACKGROUND
[0002] The development of robust chemical sensors for a range of
analytes remains an important endeavor for applications such as
environmental monitoring, product quality control, and chemical
dosimetry. Among the many methods available for chemical sensing,
calorimetric techniques remain advantageous in that the human eye
can be used for signal transduction, rather than extensive
instrumentation.
[0003] Though calorimetric sensors currently exist for a range of
analytes, most are based upon employing dyes or colored chemical
indicators for detection. Such compounds are typically selective,
meaning arrays are necessary to enable detection of various classes
of compounds. Moreover, many of these systems have lifetime
limitation issues, due to photo-bleaching or undesirable side
reactions. Other optical sensing techniques, such as surface
plasmon resonance and spectral interferometry, require substantial
signal transduction hardware to provide response, and thus are not
useful for simple visual indication.
SUMMARY OF INVENTION
[0004] The present invention features novel multi-layered
colorimetric sensor films. The films typically constitute a highly
colored multi-layered interference filter whose hue shifts upon
analyte exposure. The multi-layered structure provides a versatile
platform for incorporating a variety of chemistries that can detect
a range of species. The films are flexible and robust, and can be
designed to provide fast, reversible (or, in some cases, permanent)
responses. As such, they are well-suited for application to the
areas mentioned above.
[0005] One aspect of the invention is a colorimetric sensor for
measuring one or both of the presence and concentration of an
analyte comprising a substantially continuous reflective layer; a
detection layer over the reflective layer, the detection layer
comprising at least one polymer component, said layer being capable
of a change in optical thickness upon exposure to said analyte; and
a substantially continuous semi-reflective layer over the detection
layer, the semi-reflective layer having an index of refraction
different from the index of refraction of the detection layer.
[0006] Another aspect of the invention is a device comprising the
colorimetric sensor and a light source. Another aspect of the
invention is a calorimetric sensor for measuring one or both of the
presence and concentration of an analyte comprising a substantially
continuous reflective layer; a detection layer over the reflective
layer, the detection layer comprising at least one polymer
component; and a substantially continuous semi-reflective layer
over the detection layer, the semi-reflective layer having an index
of refraction different from the index of refraction of the
detection layer, said sensor being capable of a change in color
upon exposure to said analyte.
[0007] Another aspect of the invention is a method of detecting the
presence or absence of an analyte comprising providing a
calorimetric sensor as described above, providing a light source,
contacting the sensor with a medium that may contain an analyte,
and monitoring the sensor for a change in optical properties.
[0008] As used in this invention:
[0009] "analyte" means the specific component that is being
detected in a chemical analysis;
[0010] "dimensional change" means a change of distance in a
direction normal to the surface of the detection layer surface;
[0011] "porous material" means a material containing a continuous
network of pores throughout its volume;
[0012] "reflective" means semi-reflective or fully reflective;
[0013] "semi-reflective" means neither fully reflective nor fully
transmissive, preferably about 30 to about 70% reflective, more
preferably about 40 to about 60%.
[0014] "substantially continuous" means a layer of material is
non-porous, but may have cracks, grain boundaries, or other
structures that create pathways through the layer of material.
[0015] An advantage of at least one embodiment of the present
invention is that the multi-layer sensor films can be constructed
so that water vapor does not create a change in the optical
properties.
[0016] Another advantage of at least one embodiment of the present
invention is that the films can be readily processed. The
reflective layers can be deposited via evaporative or sputter
coating, while the detection layer can be deposited via solvent
coating, plasma deposition, and vapor coating (as described in U.S.
Pat. No. 5,877,895).
[0017] Another advantage of at least one embodiment of the present
invention is that the change in appearance of the sensor can be
designed to be reversible or permanent.
[0018] Other features and advantages of the invention will be
apparent from the following drawings, detailed description, and
claims.
BRIEF DESCRIPTION OF DRAWINGS
[0019] FIG. 1 depicts a multi-layered film of the present
invention.
DETAILED DESCRIPTION
[0020] The multi-layered colorimetric sensor films of the present
invention may comprise colored films containing at least one
polymeric detection layer between a reflective and a
semi-reflective layer, which may both be metal layers. These
multi-layered films provide a general means for visual signal
transduction. The films function as interference filters, and thus
can be highly colored due to reflection of particular wavelengths
within the visible range. The coloration of the sensor films is
highly dependent upon the thickness of each layer within the
stack.
[0021] A general depiction of a multi-layered sensor film of the
present invention is shown in FIG. 1. In general, the films
comprise (optional) substrate layer 12, reflective layer 14,
detection layer 16, and semi-reflective layer 18.
[0022] The sensor films can be used for detecting the presence
and/or concentration of an analyte. The analyte may be a gas or a
liquid. The analyte may be present in a gaseous medium (such as
air) or liquid medium (such as water or other fluids). Typically
the analyte is an organic material.
[0023] In at least one embodiment, the analyte is detected by a
change in optical thickness of a polymer comprising a detection
layer upon exposure to the analyte. The analyte passes through an
outer semi-reflective layer and changes the optical thickness of
the detection layer. In one embodiment the analyte is absorbed into
at least a portion of the detection layer. Upon absorption, color
changes (often vivid) can indicate the presence of the analyte.
[0024] The change in optical thickness is typically observable in
the visible light range and can be detected by the unaided human
eye. However, sensors can be designed to show a change in optical
thickness when subjected to other light sources such as UV,
infrared, or near infra-red. Various detection mechanisms can also
be used. Examples of suitable detection mechanisms include
photo-detectors, e.g., charge coupled devices (ccd), digital
cameras, etc.
[0025] In another embodiment, the analyte is detected when its
presence causes the delamination of the detection layer from an
adjacent layer. Typically, delamination occurs when the analyte
wets the interface of the detection layer and an adjacent layer,
thereby reducing the interface adhesion. When delamination occurs,
optical interference is destroyed and the sensor loses perceptible
color. The presence of the analyte may also cause dewetting of one
or more polymers within the detection layer from an adjacent layer.
This process, which involves changes in the shape of the detection
layer that reduce the interfacial area with adjacent layers, causes
defects within the material which permanently change the optical
properties of the sensor film.
[0026] Substrate
[0027] The substrate is optional, but when present it may comprise
any suitable material capable of providing support for the
colorimetric sensor. It may be flexible or non-flexible. The
substrate material can be tailored to the application. Preferably,
it is suitable to use in a vacuum deposition process.
[0028] Reflective Layer
[0029] The reflective layer may comprise any material that can form
a fully reflective or semi-reflective layer. It is preferable that
the material is fully reflective at a thickness of about 20 to
about 200 nm. Thinner layers can typically be used to make the
reflective layer semi-reflective. Although the reflective layer is
typically made to be more reflective than the semi-reflective
layer, sometimes it is desirable to have the reflectivity of the
reflective layer and semi-reflective layer be the same so a
response to the presence of an analyte can be seen from either side
of the sensor film.
[0030] Suitable materials for the reflective layer include metals
such as aluminum, chromium, gold, nickel, silicon, and silver.
Other suitable materials include metal oxides such as chrome oxide
and titanium oxide.
[0031] In some embodiments, the reflective layer also acts as the
substrate, providing support for the sensor.
[0032] Detection Layer
[0033] The detection layer may comprise one or more polymers or
copolymers. In most embodiments, the detection layer comprises at
least one polymer whose optical thickness changes upon exposure to
an analyte. The change in optical thickness can be caused by a
dimensional change such as a change in physical thickness of the
polymer due to swelling or shrinkage or a change in refractive
index of the detection layer due to the presence or chemical
reaction of the analyte. The detection layer may change from one
color to another, from a color to no color, or from no color to a
color.
[0034] The detection layer may comprise two or more sub-layers. One
or more of the sub-layers may be discontinuous or patterned. The
sub-layers typically comprise different polymeric materials and may
absorb different analytes and/or may have different degrees of
sensitivity to one or more analytes. The sub-layers may have a
variety of configurations. For example, they may be stacked or may
be side by side.
[0035] The detection layer may comprise a pattern so as to create
colored images, words, or messages upon exposure to an analyte. A
sublayer may be patterned by having one or more portions that are
reactive to a particular analyte and one or more portions that are
non-reactive to the same analyte. Alternatively, a pattern of
reactive material may be deposited on a larger non-reactive
sublayer. In this case, it is preferable to make the patterned
layer very thin so that no difference in optical thickness is
apparent until an analyte is absorbed. The patterning can provide
easily identifiable warnings for a user upon exposure to an
analyte.
[0036] The thickness of the detection layer may be patterned, for
example as described in U.S. Pat. No. 6,010,751. This may be
desirable when the sensor is designed so that the presence of an
analyte causes the detection layer to swell or shrink, thereby
making a pattern disappear (for example when a thinner portion
swells to the same thickness as a thicker portion) or a appear (for
example, when an portion shrinks to a thinner thickness than an
adjacent portion).
[0037] The detection layer may comprise a blend of polymer
components. The blend may be homogeneous or heterogeneous. A blend
of polymer components in the detection layer can allow for large
number of analytes to be detected with the use of a relatively
small sensor.
[0038] The detection layer may be porous. This can boost the
sensitivity of detection due to the increase in surface area
exposed to an analyte. Porosity can be obtained by using porous
materials such as foams made from high internal phase emulsions,
such as those described in WO 01/21693, to form the detection
layer. Porosity may also be obtained via carbon dioxide foaming to
create bi-continuous, nanoporous material (see "Macromolecules",
2001, vol. 34, pp. 8792-8801), or by nanophase separation of
polymer blends (see "Science", 1999, vol. 283, p. 520). In general,
the pore diameters need to be smaller than the wavelength of the
light source used in the detection process. Nano-sized pores are
preferred.
[0039] One or more polymers comprising the detection layer may be
at least partially crosslinked. Crosslinking may be desirable in
some embodiments because it can increase mechanical stability and
sensitivity to certain analytes. Crosslinking can be achieved by
incorporating one or more multi-functional monomers into the
detection layer, or by subjecting the detection layer to, e.g.,
electron beam or gamma ray treatment.
[0040] For many applications, it is desirable that the polymer or
copolymer be hydrophobic. This will reduce the chance that water
vapor (or liquid water) will cause a change in optical thickness of
the polymer and interfere with the detection of an analyte, for
example, in the detection of organic solvent vapors.
[0041] For the detection of organic solvent vapors, polymeric
materials suitable for the detection layer include, but are not
limited to, polymers and copolymers prepared from classes of
monomers including hydrophobic acrylates and methacrylates,
difunctional monomers, vinyl monomers, hydrocarbon monomers
(olefins), silane monomers, and fluorinated monomers.
[0042] Examples of hydrophobic acrylates and methacrylates include
methyl(meth)acrylate, isodecyl(meth)acrylate,
2-ethylhexyl(meth)acrylate, cyclohexyl(meth)acrylate,
n-decyl(meth)acrylate, n-butyl(meth)acrylate,
isopropyl(meth)acrylate, lauryl(meth)acrylate, ethyl(meth)acrylate,
adamantyl(meth)acrylate, t-butyl(meth)acrylate, 2-phenoxyethyl
acrylate, isobornyl acrylate
[0043] Examples of multi-functional monomers include ethyleneglycol
di(meth)acrylate, diethyleneglycol di(meth)acrylate,
triethyleneglycol di(meth)acrylate, tetraethylene glycol
di(meth)acrylate, tripropylene glycol di(meth)acrylate,
polyethylene glycol di(meth)acrylate
1,6-hexanedioldi(meth)acrylate, trimethylol propane
di(meth)acrylate, neopentyl glycol di(meth)acrylate,
N,N-methylenebis(meth)acrylamide, diacrylates such as IRR-214 (UCB
Chemicals), pentaerythritol tri- and tetra-acrylate, and
trimethylol propane tri(meth)acrylate.
[0044] Examples of vinyl monomers include styrene,
.alpha.-methylstyrene, vinylacetate, vinylbutyrate, vinylstearate,
vinylchloride, and vinyl norbornene.
[0045] Examples of hydrocarbon monomers (olefins) include
isobutylene, ethylene, propylene, and norbornene.
[0046] Examples of silane monomers include organohydrosilanes,
alkoxysilanes, phenoxysilanes, and fluoroalkoxysilanes.
[0047] Examples of fluorinated monomers include
tetrafluoroethylene, vinylidene fluoride, and
hexafluoropropylene.
[0048] For detection in solution, detection of highly polar
analytes, and/or use in sensor arrays polymeric materials suitable
for the detection layer include, but are not limited to, polymers
and copolymers prepared from classes of monomers including
hydroxylated monomers, acrylamides, anhydrides,
aldehyde-functionalized monomers, amine or amine salt
functionalized monomers, acid functionalized monomers, epoxide
functionalized monomers, vinyl monomers, and other polymers.
[0049] Examples of hydroxylated monomers include
hydroxyalkyl(meth)acrylat- es.
[0050] Examples of acrylamides include (meth)acrylamide,
N-isopropyl (meth)acrylamide, N,N-dimethyl (meth)acrylamide.
[0051] Examples of anhydrides include (meth)acrylic anhydride.
[0052] Examples of aldehyde-functionalized monomers include
acrolein.
[0053] Examples of amine or amine salt functionalized monomers
include tbutylaminoethyl (meth)acrylate, diisopropylaminoethyl
(meth)acrylate, dimethylaminoethyl (meth)acrylate, vinylpyridine,
dimethylaminoethyl(meth- )acrylate-methyl chloride salt,
4-aminostyrene, and vinylimidazole.
[0054] Examples of acid functionalized monomers include
(meth)acrylic acid, carboxyethyl(meth)acrylate, (meth)acrylic
acid-metal salts, and styrene sulfonic acid.
[0055] Examples of epoxide functionalized monomers include
glycidyl(meth)acrylate.
[0056] Examples of vinyl monomers include N-vinylpyrrolidone,
vinyldimethylazalactone (VDM) and vinylidene chloride.
[0057] Examples of other polymers include poly(ethyleneoxide),
poly(caprolactone), poly(sulfone), poly(ethyleneglycol),
poly(urethanes), poly(carbonate), ethyl cellulose, fluoropolyol,
polyesters, polyamides, polyimides, and polyacetals. The polymer
component(s) of the detection layer may also have appropriate
functional groups or molecular receptors incorporated to detect
specific analytes. For example, acid-functionalized polymers, such
as poly(acrylic acid), enable detection of organic bases such as
ammonia gas. Incorporation of metal complexes, such as
metalloporphyrins, within the detection layer enables detection of
ligating species such as phosphines or mercaptans. Suitable
molecular receptors include calixarenes, cyclodextrins, azacrowns,
crown ethers, porphyrins, metalloporphyrins, peptides, proteins,
oligonucleotides, and nucleic acids.
[0058] By incorporating the appropriate chemistries within the
detection layer, it should be feasible to create sensors for a wide
range of analytes in solution. Either by initial deposition or by
post-functionalization of deposited materials, receptor molecules,
such as peptides or antibodies, may potentially be covalently
linked to the polymer. In such fashion, biosensors for selective
detection of bacteria, proteins, ions, etc. could be
fabricated.
[0059] The detection layer can have a thickness of more than about
50 nm, preferably in the range of about 100 to about 1000 nm.
[0060] Semi-Reflective Layer
[0061] The semi-reflective layer may comprise any material that can
form a permeable, substantially continuous, semi-reflective layer
and has a different index of refraction than the detection layer.
In most embodiments, it is preferable that the material is
semi-reflective at a thickness of about 5 nm because at this
thickness most analytes will be able to permeate through this layer
to the detection layer. Desired thicknesses will depend on the
material used to form the layer, the analyte to be detected, and
the medium that will carry the analyte.
[0062] Suitable materials include metals such as aluminum,
chromium, gold, nickel, silicon, and silver. Other suitable
materials include oxides such as aluminum oxide, titanium oxide,
and chromium oxide.
[0063] Additional Layers
[0064] The sensor film may comprise additional layers between any
of the previously described layers, as long as an additional layer
does not interfere with the optics of the sensor film. Additional
layers could include tie layers, structural layers, etc.
[0065] Method of Making
[0066] The multi-layered films of the present invention can be
created via methods such as the process described, e.g., in U.S.
Pat. No. 5,877,895. The detection layers may also be made by
spin-coating, solution coating, extrusion coating, or other
suitable techniques known in the art. The detection layer may also
be made by plasma deposition processes such as plasma
polymerization. The reflective and semi-reflective layers may also
be made by standard vapor coating techniques such as evaporation,
sputtering, chemical vapor deposition (CVD), plasma deposition, or
flame deposition. Another method for making the reflective and
semi-reflective layers is plating out of solution.
[0067] Uses
[0068] The film sensors may be used in a system comprising the
sensor, a light source, and, optionally, a means of monitoring the
sensor for a change of color. The light source could be a natural
or artificial light source. The monitoring could be done in a
variety of ways. It could be done visually, with a photo-detector,
or by other suitable means.
[0069] The analyte may be present in a vapor or liquid medium. For
example, an analyte may be present in the atmosphere or in a liquid
solvent.
[0070] Two or more film sensors may be used together to form an
array. The array may be in any suitable configuration. For example
an array may comprise two or more sensors side by side, or sensors
may be attached to, or constructed on, opposite sides of a
substrate. The sensors may be of the same type or may be different.
Arrays of multi-layered film sensors would be useful for
identification of analytes, as opposed to only detecting the
presence of a chemical agent.
[0071] The film sensors of the present invention have many useful
applications. They can be used, e.g., to detect a wide range of
organic vapors.
EXAMPLES
[0072] This invention may be illustrated by way of the following
examples.
[0073] Unless otherwise stated, the sensor film samples were viewed
from an angle normal to the surface of the film. Other viewing
angles may be used. The color observed can vary depending on the
angle of observation.
Example 1
[0074] A multi-layered calorimetric sensor film was produced via
the deposition method described in U.S. Pat. No. 5,877,895.
[0075] An aluminum reflective layer (100 nm) and polymeric
detection layer (500 nm) were sequentially deposited upon a
polyester substrate layer (50 .mu.m) in a single pass (15.24 m/min)
through a vacuum web system. The aluminum reflective layer was
thermally evaporated by feeding 0.1587 cm diameter aluminum wire
(Alcoa stock number 1199, Pittsburgh, Pa.) onto an electrically
heated (7V, 1250 amp) evaporation bar at a feed rate of 225 mm/min.
The polymeric detection layer (500 nm) was deposited followed by an
electron beam cure of 6.9 W-Sec. The monomer composition was a
48.5/48.5/3 by weight mixture of lauryl acrylate (available from
Sartomer, Exton, Pa.)/IRR214 (a proprietary hydrocarbon diacrylate,
available from UCB Chemicals, Drogenbos, Belgium)/Ebecryl170 (a
phosphoric acid monoacrylate compound also available from UCB
Chemicals). Chromium (Academy Precision Materials, Albuquerque, N.
Mex.) was then sputtered (2.95 W/cm2 DC power at 2 mTorr Argon
pressure), in a subsequent pass (15.24 m/min) through the vacuum
web system, onto the cured detection layer, to give a 5 nm thick
outer layer. The multi-layer sensor film had a green hue.
[0076] Sections of the multi-layered film (2.54 cm square) were
affixed on glass slides and exposed for one minute to saturated
vapors of various organic solvents in sealed jars. Within each jar,
the multi-layered film was suspended within the headspace above the
neat liquid analyte. As shown in Table 1, the exposures resulted in
vivid, visually detectable color changes. In each case, the color
changes were reversible upon removal from the solvent vapor within
tens of seconds, restoring the original green hue. Responses were
qualitatively reproducible, as repeat exposures produced the same
color changes.
1TABLE 1 Color Changes on Exposure to Various Compounds Solvent
Initial Color Color After Exposure Chloroform Green Red/Pink
Toluene Green Red/Pink Pyridine Green Red/Pink Ethanol Green Yellow
Acetone Green Red/Pink Water Green Green
Example 2
[0077] Visible reflectance spectra were taken of the multi-layered
films before and after exposure to a range of solvent vapors. Film
sections (2.54 cm square, from Example 1) were affixed on glass
slides and exposed to saturated organic vapors within sealed jars.
Once equilibrated, the exposed films were removed and covered
immediately with glass cover slides to prevent vapor desorption.
Reflectance spectra of the exposed materials were then taken using
a diffuse reflectance UV-VIS spectrometer. For all organic vapors
tested, substantial red-shifting of the reflectance maxima were
observed upon analyte exposure. The reflectance maximum centered at
524 nm (before exposure), for instance, exhibits shifts to higher
wavelengths (red shifts). The magnitudes of the shifts ranged from
22 nm (acetonitrile) to 116 nm (methylene chloride), as shown in
Table 2. This example shows that the multi-layered calorimetric
sensor films respond to organic vapors, exhibiting calorimetric
shifts for halocarbons, arenes, alcohols, ketones, nitrites, and
ethers. No shift was observed in the reflectance spectra on
exposure to saturated water vapor. Even upon submerging films in
liquid water, no color change was observed.
2TABLE 2 Reflectance Maxima Wavelength Shifts Upon Exposure to
Solvent Vapors Solvent Wavelength Shift (nm) Chloroform 65 Toluene
62 Methylene Chloride 116 Acetonitrile 22 Acetone 28.5 Ethanol 29
Diethyl Ether 35 Bromobenzene 81 3-pentanol 51 3-pentanone 46
Methyl Ethyl Ketone 62 Water 0
Example 3
[0078] In an effort to gauge the response sensitivity to different
analyte vapors, sensor film, made as described in Example 1, was
exposed to analytes at a range of concentrations using a simple
flow-through setup. Concentrations (as determined by partial
pressures) were controlled by bath temperatures. Air was bubbled
through neat liquid analytes, which were chilled using cold
temperature baths to control the vapor pressure. Mixtures of solid
carbon dioxide (dry ice) and 3-heptanone or ethylene glycol gave
bath temperatures of -38.degree. C. and -15.degree. C.
respectively. An ice water bath was used to give temperatures of
0.degree. C. Vapor pressures for each analyte were calculated at
these temperatures using data from the Handbook of Vapor Pressure
(Yaws, C. L. Gulf Publishing: Houston, 1994). Each air/vapor stream
was then flowed via a stainless steel cannula into a septum-sealed
vial containing the multi-layered film. The color changes of each
film on exposure were monitored visually, and multiple observations
were taken to ensure equilibrium. Table 3 presents the responses as
a function of concentration, with "green" indicating the unexposed
film color, "pink" indicating response for saturated vapors, and
"yellow" indicating an intermediate response. The results indicate
the ability to determine analyte concentration as well as the
qualitative presence of the vapor using the calorimetric sensor
films of this invention.
3TABLE 3 Film Colors as a Function of Solvent Vapor Concentration
Analyte Concentration (torr) Film Color (visual) Chloroform 5.1
Green/Yellow 25 Yellow/Yellow-pink 59 Pink 196 Pink Acetone 6.4
Green 30 Green/Yellow 69 Yellow/Yellow-pink 230 Pink Methylene
Chloride 15 Green/Yellow 63 Yellow-pink 141 Pink 430 Pink Toluene
0.37 Green 2.4 Yellow-pink 6.7 Pink 28 Pink Bromobenzene 0.028
Green/Green-yellow 0.24 Yellow-pink 0.79 Pink 4.2 Pink
Example 4
[0079] Sensor film (from Example 1) was used to detect organic
compounds in water. Submersion of the film within solution of
tetrahydrofuran (THF) in water (5% by volume) yielded a visual
change in color from green to yellow. Submersion into a solution of
acetone in water (25% by volume) produced a visible change in color
from green to yellow-green. This example shows that the multi-layer
calorimetric sensor films of this invention can detect the presence
of organic compounds in water. No change in color was observed upon
exposure of the film to plain water.
Example 5
[0080] Two multi-layered sensor films were prepared via
spin-coating of the detection layers. The structures were the same,
except for the polymer detection layers. To make each sensor film,
an aluminum reflective layer (100 nm) was deposited by electron
beam evaporation (2.5 nm/sec evaporation rate) in a batch system
vacuum coater onto a 50 .mu.m polyester substrate layer.
Poly(styrene) and poly(methylmethacrylate) detection layers were
each deposited onto one of the aluminum-coated substrates via
spin-coating. The polymers were coated via toluene solutions at
concentrations of 5% (w/w) and 9.4% (w/w) respectively. The
spin-coating was carried out at 3500 rpm for 25 seconds. The
resulting polymer thicknesses were 260 nm (poly(styrene)) and 500
nm (poly(methylmethacrylate)). Chromium layers (5 nm) were then
deposited onto each polymeric surface via sputtering conditions
identical to those in Example 1, to complete the multi-layered
sensor film constructions. Exposure of the sensor films to
saturated chloroform vapor yielded reversible color shifts from
purple to blue (poly(styrene)) and from pink to light green
(poly(methylmethacrylate)). Exposure of the films to toluene vapor
caused a permanent loss of interference-based color, as indicated
by the failure of the film to recover its original color upon
removal from the analyte. Transmission electron microscopy (TEM)
studies indicate that this irreversible change was caused by
delamination of the aluminum layer from the rest of the stack. This
example demonstrates the ability to create multi-layered
colorimetric sensors by spin-coating. It also demonstrates that a
permanent change in the appearance of a sensor of the invention can
be realized by the appropriate selection of materials and processes
used to make the sensors.
Example 6
[0081] Two different multi-layered films were constructed having
the same general structure and composition as that described in
Example 1 except that the detection layer thickness for Sample 6A
was 500 nm, while the thickness was 650 nm for Sample 6B. Both
films contained detection layers made via polymerization of lauryl
acrylate/IRR214/EB 170 mixtures, as in Example 1. Responses of the
two films to a series of vapors are shown in Table 4. While neither
individual sensor can identify every analyte (i.e., 6A does not
distinguish between toluene and acetone and 6B does not distinguish
between acetonitrile and acetone), the combined responses from both
sensors are unique to each species tested. The utility of sensor
arrays containing more than one unique multi-layered film for
analyte identification is demonstrated by this example.
4TABLE 4 Color Changes Upon Exposure to Various Solvents 6B 6A (650
nm (500 nm thick detection layer) thick detection layer) Solvent
Initial After Exposure Initial After Exposure Acetonitrile Green
Yellow Red Green Toluene Green Red/Pink Red Brown/Red Acetone Green
Red/Pink Red Green
[0082] Various modifications and alterations of this invention will
become apparent to those skilled in the art without departing from
the scope and spirit of this invention and it should be understood
that this invention is not to be unduly limited to the illustrative
embodiments set forth herein.
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