U.S. patent application number 11/125749 was filed with the patent office on 2005-10-20 for electrophoresis gels with incorporated indicia.
This patent application is currently assigned to Bio-Rad Laboratories, Inc.. Invention is credited to Gueffroy, Donald E., Panattoni, Cory M., Provost, Roger S..
Application Number | 20050230256 11/125749 |
Document ID | / |
Family ID | 33097808 |
Filed Date | 2005-10-20 |
United States Patent
Application |
20050230256 |
Kind Code |
A1 |
Panattoni, Cory M. ; et
al. |
October 20, 2005 |
Electrophoresis gels with incorporated indicia
Abstract
PATENT An electrophoresis gel is prepared with indicia
incorporated into the gel itself rather than on a label or backing
that is adhered to the gel. According to one method, the indicia
are applied by first coating a solid surface that will be used as
one internal surface of a gel mold with a solution of a
water-permeable polymer, allowing the coating to dry, imprinting
indicia in ink on the dry coating, and then forming the gel over
the coating. In a variation on this method, the indicia are applied
to a sheet which is then placed against the mold surface, the sheet
being either a liner that is separable from the gel yet coated with
the polymer or a sheet of the polymer itself. Alternatively, the
indicia are printed directly on the mold surface without first
coating the surface. This is achieved by using as a printing
composition a mixture of an ink and a solution of a water-permeable
polymer, then forming the gel over the imprinted indicia.
Inventors: |
Panattoni, Cory M.;
(Winters, CA) ; Gueffroy, Donald E.; (Davis,
CA) ; Provost, Roger S.; (Napa, CA) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW, LLP
TWO EMBARCADERO CENTER
EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Assignee: |
Bio-Rad Laboratories, Inc.
Hercules
CA
|
Family ID: |
33097808 |
Appl. No.: |
11/125749 |
Filed: |
May 9, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11125749 |
May 9, 2005 |
|
|
|
10408835 |
Apr 3, 2003 |
|
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Current U.S.
Class: |
204/615 ;
204/616 |
Current CPC
Class: |
G01N 27/44747
20130101 |
Class at
Publication: |
204/615 ;
204/616 |
International
Class: |
G01N 027/27 |
Claims
1-48. (canceled)
1. A kit for applying indicia to an electrophoresis gel, said kit
comprising: a solid flexible sheet having a coating of a
water-permeable polymer on one side, said polymer being one that is
capable of receiving ink but is not bonded to said sheet; and an
ink that is capable of being retained by said polymer.
2. A kit in accordance with claim 1 in which said solid flexible
sheet has first and second sides, said coating of water-permeable
polymer is on said first side and said second side is coated with
an adhesive that will adhere said sheet to a glass or plastic
plate.
3. A kit in accordance with claim 1 in which said solid flexible
sheet has first and second sides, said coating of water-permeable
polymer is on said first side and said second side is not coated
with an adhesive that will adhere said sheet to a glass or plastic
plate.
4. A kit in accordance with claim 1 in which said water-permeable
polymer is a member selected from the group consisting of linear
polyacrylamide, linear polyacrylamide derivatives, poly(vinyl
alcohol), poly(vinyl pyrrolidone), poly(ethylene glycol),
poly(ethylene oxide), dextrans, water-soluble celluloses, starch,
and agarose.
5. A kit in accordance with claim 1 in which said water-permeable
polymer is linear polyacrylamide.
6. A kit in accordance with claim 1 in which said ink is a visible
pigment.
7. A kit in accordance with claim 1 in which said ink is a
fluorescent dye.
8. A kit in accordance with claim 1 in which said ink is an
ultraviolet dye.
9. A kit in accordance with claim 1 in which said ink is a
luminescent dye.
10. A kit in accordance with claim 1 in which said ink is contained
in a writing implement.
11. A kit for applying indicia to an electrophoresis gel, said kit
comprising: a solid water-soluble polymeric sheet that is capable
of receiving ink; and an ink that is capable of being retained by
said sheet.
12. A kit in accordance with claim 11 in which said water-soluble
polymeric sheet comprises a polymer selected from the group
consisting of linear polyacrylamide, linear polyacrylamide
derivatives, poly(vinyl alcohol), poly(vinyl pyrrolidone),
poly(ethylene glycol), poly(ethylene oxide), dextrans,
water-soluble celluloses, starch, and agarose.
13. A kit in accordance with claim 12 in which said polymer is
linear polyacrylamide.
14. A kit in accordance with claim 11 in which said ink is a
visible pigment.
15. A kit in accordance with claim 11 in which said ink is a
fluorescent dye.
16. A kit in accordance with claim 11 in which said ink is an
ultraviolet dye.
17. A kit in accordance with claim 11 in which said ink is a
luminescent dye.
18. A gel marking combination comprising: an ink composition
comprising a pigment dispersed in a solution of a water-soluble
polymer in a solvent, and a writing implement capable of retaining
said ink composition and of depositing said ink composition on a
solid surface upon contact.
19. A gel marking combination in accordance with claim 18 in which
said pigment is a pigment that when dry is insoluble in a
polyacrylamide gel.
20. A gel marking combination in accordance with claim 18 in which
said pigment is a visible pigment.
21. A gel marking combination in accordance with claim 18 in which
said pigment is a fluorescent dye.
22. A gel marking combination in accordance with claim 18 in which
said pigment is an ultraviolet dye.
23. A gel marking combination in accordance with claim 18 in which
said pigment is a luminescent dye.
24. A gel marking combination in accordance with claim 18 in which
said water-soluble polymer is a member selected from the group
consisting of linear polyacrylamide, linear polyacrylamide
derivatives, poly(vinyl alcohol), poly(vinyl pyrrolidone),
poly(ethylene glycol), poly(ethylene oxide), dextrans,
water-soluble celluloses, starch, and agarose.
25. A gel marking combination in accordance with claim 18 in which
said water-soluble polymer is a member selected from the group
consisting of linear polyacrylamide, poly(vinyl alcohol),
poly(vinyl pyrrolidone), poly(ethylene glycol), poly(ethylene
oxide), dextran, water-soluble celluloses, starch, and agarose.
26. A gel marking combination in accordance with claim 18 in which
said water-soluble polymer is linear polyacrylamide.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention resides in the field of gel electrophoresis,
and addresses in particular the concerns and difficulties
associated with attaching labels, markings and other indicia to
slab gels for various purposes.
[0003] 2. Description of the Prior Art
[0004] Gel electrophoresis is one of the most widely used
analytical procedures in biotechnology for the separation of both
proteins and nucleic acids from complex samples. Gel
electrophoresis offers a sensitive, rapid means of separating,
identifying and quantifying biologically relevant molecules. The
configuration and size of the gel can vary, depending on the type
of separation. Slab gels, for example, are particularly useful
since they permit separations to be performed in either one or two
dimensions, and the resulting bands or spots can be observed
directly or visualized, recorded and analyzed by instrumentation.
In one-dimensional slab gel separations, a large number of samples
can be separated side-by-side in a single gel and analyzed
simultaneously. In two-dimensional slab gel separations, thousands
of proteins from a single sample can be resolved in a single gel
typically by first using isoelectric focusing to separate the
proteins into bands in one dimension and then using sodium
dodecylsulfate polyacrylamide gel electrophoresis to further
separate the proteins in each band in the second dimension. Tube
gels or strip gels are typically used for the first dimension
separation. Once separated, the molecules of interest can be
detected and identified or quantified directly by comparison to
standards, or interrogated further by diverse methods such as
hybridization to tagged probes, immunochemical detection or
analysis by mass spectrometry.
[0005] The reading of a gel can be performed either visually by the
user or by automated detection systems. Certain indicia are often
included in the reading procedure to assist in the identification
of the sample components and to minimize the occurrence of errors.
These indicia may consist of gel orientation guides, migration
distance indicators, lane indicators, sample identifiers, the
supplier's catalog numbers, and even the supplier's logo. Barcodes
may be used to provide some of these indicia, while others may be
simple letters, numbers or grid lines and similar markings. Indicia
can also help avoid mistaking one gel for another when different
gels have been simultaneously stained and washed, as is typically
done prior to the reading of a gel to make the bands or spots
readily detectable. Many of these concerns are present in tube gels
as well, particularly those that serve as the first dimension in a
two-dimensional separation. Tube gels would benefit not only from
identifying indicia, but also from alignment markings that would
alert the technician when a portion of the gel has been stretched
or otherwise distorted.
[0006] Indicia can thus be useful in many ways, but to be
effective, the indicia must not interfere with the electrophoretic
separation or impose limitations on the processing and handling of
the gel that occur after the separation is completed. These needs
have presented a challenge to gel manufacturers and users.
[0007] A common means of applying indicia in the prior art is the
embedding of a paper label in the gel. As the gel becomes enlarged
during processing, however, paper labels often curl and tear, and
even when they remain intact, paper labels tend to become stained,
obscuring the indicia. A gel labeling method that does not involve
the use of paper labels is disclosed in United States Patent
Application Publication No. US 2003/0038030 A1, publication date
Feb. 27, 2003, filing date Sep. 20, 2002. The method in this
publication involves the use of a backing consisting of a solid
transparent sheet on one side of the gel. The gel is chemically
bonded to the backing to assure secure adherence, and the desired
indicia are imprinted on the backing sheet. The gel is formed over
the backing by polymerizing the gel from a monomer solution that is
in direct contact with the backing while forming covalent bonds
between the gel and functional groups on the backing. Other backing
sheets are disclosed in U.S. Pat. No. 4,415,428, issued Nov. 15,
1988, on an application filed Jan. 27, 1982.
[0008] Backing sheets have also been used that adhere to the gel by
means other than covalent bonds. Unfortunately, backing sheets that
are not bonded to the gel are susceptible to detachment from the
gel, particularly during the handling or processing of the gel
after electrophoresis, which results in loss of the indicia.
Regardless of how the backing sheet is made to adhere to the gel,
the sheet itself presents problems during the staining of the gel.
Staining is typically performed by immersing the gel in a staining
solution and allowing the solution to penetrate the gel from all
sides. When this is done with gels that have a backing sheet,
penetration occurs only from the exposed side, and this requires
more time for proper staining to occur. This results in low
efficiency, sensitivity and reliability.
[0009] It would seem that some of these problems could be
eliminated by using only a partial backing sheet or a label of
smaller dimensions than the gel, leaving the remainder of the gel
exposed on both sides. This would not be suitable for all types of
indicia, but for those for which a small label would suffice,
further problems would arise. When a gel to which a small label is
attached is removed from a gel cassette for staining and analysis,
for example, the chances that the gel will break are particularly
high. One reason is that the gel in the area adhering to the label
is less flexible and less able to stretch than areas of the gel
that are not constricted by the label, and this difference makes
the gel particularly vulnerable to breakage at locations close to
the edges of the label. This vulnerability is made even greater
when the gel is immersed in solutions for applying stains and for
removing excess stain, since these solutions can cause a gel to
enlarge or shrink by as much as 30%. Gels with small labels are
also susceptible to the formation of extensive cracks emanating
from the label when the gels are dried for long-term storage.
SUMMARY OF THE INVENTION
[0010] These and other concerns are addressed by the present
invention, which resides in a method for forming an electrophoresis
gel with indicia that are incorporated directly in the gel, that do
not interfere with solute migration or become distorted during
electrophoresis, and that do not impose dimensional restriction to
the gel, i.e., do not prevent the gel from expanding, contracting,
or stretching during the staining, washing, drying, or handling
that typically occur in the processing steps that follow an
electrophoretic separation. The invention also resides in gels
bearing indicia incorporated by this method and in various
components used in forming gels bearing these indicia.
[0011] The indicia are incorporated in the gel by any of several
methods in accordance with this invention. According to one method,
a coating or film of water-permeable polymer is applied over the
internal surface of a gel mold, the coating or film if applied wet
is allowed to dry, and the indicia are applied to the coating or
film with a suitable ink. A gel is then cast in the mold over the
imprinted coating or film without becoming bonded to the surface of
the mold. The surface to which the indicia are applied in this
manner can be any inside surface of the mold cavity wetted by the
gel-forming reagents. For slab gels, the surface can be one of the
two flat plates of a cassette or the flat bottom plate of an open
casting tray for a slab gel, while for tube gels, strip gels, or
gels of other configurations that are cast in two-part molds, the
coated surface can be the internal surface of any single part of
the mold. Since neither the gel nor the water-permeable polymer are
bonded to the surface of the mold, the gel, which incorporates the
water-permeable polymer, can be removed from the mold with the
indicia remaining intact in the gel.
[0012] In a second method, the indicia are applied to a flexible
solid sheet that has been coated on one side with a water-permeable
polymer. The solid sheet itself is not water-permeable, and the
indicia are placed on the coated side of the sheet. The flexible
sheet is placed over the surface of a glass or plastic plate or
mold part, either before or after the indicia have been applied,
with the polymer coating and indicia facing away from the glass or
plastic. The sheet can be simply placed against the glass or
plastic or is adhered to the glass or plastic by an adhesive.
Either way, the gel is cast in the mold with the sheet as a liner,
and electrophoresis is performed in the cast gel. Following
electrophoresis, the gel, which incorporates both the polymer from
the coating and the indicia and is not bonded to the flexible
sheet, is removed from the mold and readily separated from the
flexible sheet or liner. The liner will generally remain adhered to
the mold surface although the adherence can be strengthened by the
use of an adhesive between the liner and the surface.
[0013] In a third method, the indicia are applied to a dry film of
the water-permeable polymer which has been previously prepared
outside the mold, and the indicia are applied before the film is
placed in contact with the mold surface. The indicia-bearing film
is then placed over the mold surface and the gel is cast in the
mold. Here again, the resulting gel incorporates the
water-permeable polymer and the indicia, and is readily removable
from the mold after electrophoresis is performed since neither the
gel, the polymer, nor the indicia are bonded to the mold
surface.
[0014] In a fourth method, the indicia are imprinted directly on
the internal surface of the mold by applying a printing medium
consisting of a solution or suspension of the ink or pigment in a
liquid solution of a water-soluble polymer. The indicia are then
allowed to dry by evaporation of the solvent or suspending agent,
and the gel is then cast over the dried indicia. Electrophoresis is
then performed, and the gel is removed from the mold with the
polymer and indicia as part of the gel.
[0015] In the typical electrophoretic procedure, the mold in which
the gel is cast also serves as the enclosure in which the gel is
retained during electrophoresis. In slab gels, for example, the
plates of a gel cassette serve as both the mold and the retaining
walls during electrophoresis. In two-dimensional electrophoresis,
the tube or strip gel used in the first-dimension separation is an
exception, since the second dimension separation is performed by
first removing the tube or strip gel from its enclosure and then
placing it along the edge of a slab gel before performing the
second dimension separation.
[0016] This invention further resides in electrophoresis gels
prepared by any of the methods described above and in kits for use
in applying indicia to gels by these methods. One type of kit
includes a flexible solid sheet of water-impermeable material
coated on one side with a dry water-permeable polymer ready for the
application of indicia, plus an appropriate ink that the
water-permeable polymer will retain, or a writing or printing
implement that can transfer the ink to the polymer surface
according to the desired indicia. Another type of kit includes a
sheet of the water-permeable polymer itself in dry form ready for
the application of indicia, plus the same type of ink or writing or
printing implement.
[0017] In embodiments of this invention that involve the
application of indicia over a sheet of polymer or a polymer
coating, suitable inks are those that adhere to the sheet or
coating, whereas in embodiments of this invention where the ink is
combined with a solution or suspension of the polymer to form an
ink composition, suitable inks are those that are readily dissolved
or suspended in the composition and compatible with the polymer. In
all of these variations, preferred inks are those that neither
dissolve in the gel-forming reagents during the casting of the gel
nor inhibit polymerization of the gel, and that remain stable in
the gel for the shelf life of the gel.
[0018] These and other features, objects, and advantages of the
invention and its preferred embodiments are described in more
detail below.
DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS
[0019] Gels to which this invention are most readily applicable are
those that are cast in a mold that can be opened to expose its
internal surfaces. Examples are slab gels that are cast in
cassettes constructed of two flat plates separated by spacers,
cylindrical gels that are cast in the annular space between two
concentric cylinders, and strip gels that are cast in two-part
molds. Descriptions of slab gel cassettes are found in U.S. Pat.
No. 4,572,040, entitled "Apparatus for Vertical Gel
Electrophoresis," issued Mar. 4, 1986, on an application filed Sep.
26, 1984, and U.S. Pat. No. 6,162,342, entitled "Rapid Assembly
Casting System for Slab Gels," issued Dec. 19, 2000, on an
application filed Feb. 12, 1999. A description of cylindrical gels
cast in the annular space between two cylinders is found in U.S.
Pat. No. 5,938,909, entitled "Cup-Shaped Vertical Slab Gel
Electrophoresis Apparatus," issued Aug. 117, 1999, on an
application filed Mar. 14, 1997. A description of strip gels cast
in two-part molds is found in co-pending U.S. patent application
Ser. No. 10/095,563, filed Mar. 11, 2002, entitled "Assembly for
casting and use of an isoelectric focusing strip." The molds
described in application Ser. No. 10/095,563 are rod-shaped molds
split longitudinally into two halves, each half having a
half-circle profile and a flat contacting surface with a groove of
rectangular cross section in each contacting surface. The contents
of each of the patents cited in this paragraph and elsewhere
throughout this specification are incorporated herein by reference
in their entirety. For slab gels or cup-shaped gels, the indicia
are applied to the internal surface of one of the two flat plates,
and for strip gels formed in two-part molds, the indicia are
applied in one of the grooves.
[0020] In embodiments of the invention in which the indicia are
applied to an intermediary liner sheet that does not become part of
the gel, the liner sheet can be made of any inert, flexible, and
preferably transparent material that can be coated with a
water-permeable polymer on one side and will not bond to the gel as
the gel is formed. While the coating material is a water-permeable
polymer, the sheet itself is preferably not water-permeable.
Examples of materials from which the sheet can be made are
MYLAR.RTM. and other polyesters, polymethylpentene, polystyrene,
polypropylene, polyethylene, styrene-acrylonitrile copolymers
(SAN), polycarbonate, cellulose acetate propionate, cellulose
acetate butyrate, nitrile-acrylonitrile-styrene copolymers,
acrylics (thermoplastic polymers and copolymers of acrylic acids),
poly(ethylene terephthalate) (PET), polymethacrylate, methyl
methacrylate copolymers (NAS), and acrylonitrile-butadiene-styrene
copolymers. The thickness of the sheet is not critical and can vary
provided that the sheet remains flexible. Best results will
generally be achieved with thicknesses ranging from about 0.05 mm
to about 0.5 mm. If desired, adhesion of the sheet to the mold
surface when the gel is removed can be improved by coating the
sheet with an adhesive on the side opposite the side bearing the
water-permeable polymer. Any conventional adhesive can be used,
preferably a pressure-sensitive adhesive which generally includes
an elastomeric polymer and a tackifying agent. Typical elastomeric
polymers are butyl rubbers, poly(vinyl ether)s, acrylics, and
silicones.
[0021] In embodiments of the invention in which the indicia are
applied to a dry sheet of water-permeable polymer before the sheet
is applied to the mold surface, the dry sheet can be formed by the
simple casting of a sheet from a solution or suspension of the
polymer and allowing the solvent or suspending agent to evaporate.
Once the indicia are applied and the sheet is placed over the mold
surface, the polymer then functions in the same manner as the
polymer in the coatings that are applied to the mold surface before
indicia are applied, i.e., the sheet becomes is incorporated into
the gel.
[0022] In embodiments of the invention in which the mold surface,
or a liner that adheres to the mold surface when the gel is
removed, is coated with a polymer before the indicia are applied,
as well as embodiments in which the indicia are applied to a sheet
of the polymer itself rather than to a liner with a polymer
coating, the polymer may be the same as or different than the
polymer used to form the bulk of the gel. As noted above, the
polymer is one which when dry is permeable by water and whose
chains are compatible with the polymer chains of the gel once the
gel is formed. Examples of polymers that can be used for these
embodiments are linear polyacrylamide, linear polyacrylamide
derivatives, poly(vinyl alcohol), poly(vinyl pyrrolidone),
poly(ethylene glycol), poly(ethylene oxide), dextran, water-soluble
celluloses, starch, and agarose. In this specification and the
appended claims, "linear polyacrylamide derivatives" include
polyacrylamides bearing substituent groups that improve the water
permeability and/or water solubility of the polyacrylamide.
Examples are poly(methacrylamide), poly(N-acryloylaminopropanol),
and poly(N-acryloylamino-ethoxyethanol). The term "water-soluble
celluloses" likewise includes modified celluloses such as those
known in the art and have properties similar to cellulose. Examples
are methylcellulose, ethylcellulose, hydroxymethylcellulose, and
hydroxyethylcellulose.
[0023] The term "water-permeable polymer" refers to a polymer which
when dry and placed in contact with water or an aqueous solution
will allow the water or the solution to penetrate the polymer
network. The term includes polymers that are soluble in water,
i.e., those that dissolve readily in water as well as those that
dissolve slowly or only with agitation. The term also includes
polymers that swell and/or become gelatinous upon absorption of
water.
[0024] The water-permeable polymer can be either a crosslinked
polymer or a linear polymer (not crosslinked). When the gel is
formed over the polymer, the polymer is incorporated into the gel
rather than forming a solid skin over the gel surface. The bulk gel
and the polymer together form a continuous gel with no physical
discontinuity or interface at the gel depth where the surface of
the polymer when dry was originally located. For gels whose bulk
composition is a crosslinked polymer, a particularly preferred
water-permeable polymer is one that is formed of a linear version
of the same polymer used in crosslinked form in the bulk of the
gel. When a linear polymer is used and is applied as a coating on
the mold surface, the coating can be formed from a solution of the
polymer or from a solution of a monomer and any additive(s)
necessary to effect polymerization of the monomer once it has been
applied to the surface. When a monomer solution is used, the
monomer solution can contain a catalyst, an initiator, or both, if
necessary to achieve polymerization, without a crosslinking agent,
and polymerization of the monomer into a linear polymer can occur
in the coating itself. Preferably, however, the coating is formed
by applying a liquid solution of a pre-polymerized linear polymer,
and the coating is dried by simply allowing the solvent to
evaporate.
[0025] When the gel to be formed is a polyacrylamide gel, for
example, a coating of linear polyacrylamide can be formed by
applying linear polyacrylamide in solution, aqueous or otherwise,
to the solid surface and allowing the solvent to evaporate.
Preferred linear polyacrylamides are those having a weight-average
molecular weight of from about 1,000 to about 10,000,000. The
concentration of the linear polyacrylamide can vary and is not
critical to the invention. The optimal concentration may depend on
the molecular weight of the polymer. A low molecular weight linear
polyacrylamide, such as one whose molecular weight is 1,500, may be
used at a high concentration such as 50% by weight, while a high
molecular weight linear polyacrylamide, one with a molecular weight
of 5,000,000 to 6,000,000 for example, may be used at a low
concentration such as 2% by weight. In some cases, a mixture of
both high and low molecular weight linear polyacrylamides will be
beneficial. Once the linear polyacrylamide coating is formed,
regardless of its molecular weight, the bulk gel can then be cast
over the coating from a solution of acrylamide monomer and a
crosslinking agent, in the concentration ranges listed above,
together with other additives as needed. Polymerization of the
monomer and crosslinking agent will result in a polymeric network
that is integral with and inseparable from the film. Although not
to be bound by any particular theory, one explanation for the
integral character of the resulting gel is that during the
polymerization reaction, the monomer penetrates the network of
linear polyacrylamide chains in the film and polymerizes around the
chains to form an intertwined network of chains, including those
that are crosslinked and those that are not crosslinked.
[0026] For gels that are formed by means other than polymerization,
such as agarose which gels upon cooling from a warm aqueous
solution, the film or sheet and the bulk of the gel can be formed
from solutions of the same materials. When the film is first
applied as a coating over the mold surface, the coating is allowed
to dry before the indicia are applied, and the entire gel is cooled
after the gel solution forming the bulk of the gel has been
added.
[0027] The application of a coating in the practice of this
invention can be achieved by conventional methods, such as by the
use of a brush or a pad or by spraying or dipping.
[0028] In embodiments in which the indicia are applied as a
solution or suspension of the ink in a liquid polymer solution, and
application is made directly to the mold surface or to a liner that
has been adhered to the surface, the polymer is preferably a
water-soluble polymer. As noted above, certain polymers will meet
both the definition of a water-permeable polymer and the definition
of a water-soluble polymer. When there is a difference, it may be
simply a matter of the rate of dissolving or the consistency or
viscosity of the resulting solution. When the ink is suspended or
dissolved in the liquid polymer solution, the composition will be
sufficiently fluid (i.e., of sufficiently low viscosity) that it
can function as an ink and is thereby capable of being applied with
a writing or printing implement. The polymer in these embodiments
may be the same as or different than the polymer used to form the
bulk of the gel. The considerations discussed above regarding
compatibility of the polymer with the gel apply here as well, i.e.,
the polymer in the ink formulation should be compatible with the
polymer forming the bulk of the gel. Here again, preferred polymers
for the ink formulation are linear polymers that dry readily by
evaporation of the solvent or suspending agent.
[0029] The term "gel-forming liquid" is used herein to denote
conventional liquid preparations that are poured, pumped, or
otherwise placed inside gel molds where they are allowed to
solidify into gels suitable for electrophoresis. As noted above,
the mold for a slab gel typically consists of two flat plates
separated by spacers that define the thickness or depth of the gel.
Molds for gels of other configurations, such as tube gels, gel
strips, and continuous closed cylindrical gels, are shaped
accordingly. The gel-forming liquid may be a monomer solution that
is allowed to polymerize in the mold cavity. Alternatively, the
gel-forming liquid may be a solution of a polymer or other material
that is placed in the cavity and then exposed to heat or any other
form of energy that will cause the material to solidify into a gel.
A further alternative is a gel solution that is hot when added to
the cavity and then gels upon cooling.
[0030] The most notable examples of gel materials are
polyacrylamide, polyacrylamide derivatives, agarose and starch. The
liquid from which the gel is typically formed is a solution of
monomer or other gel-forming material, and the gel is prepared by
filling the gel mold, enclosure, or cassette with the solution and
allowing the solution to solidify into a gel. The components used
in forming the gels and the procedures are well known among those
skilled in gel electrophoresis. Preferred gels are those made of
crosslinked polyacrylamide, and are typically formed from an
aqueous solution containing acrylamide monomer, a crosslinking
agent, a catalyst and an initiator. The amounts of each of these
components can vary widely, and the choice will depend on the
concentrations and molecular weights of the solutes to be
separated, as well as the type of electrophoretic separation, i.e.,
isoelectric focusing, a two-dimensional separation, a gradient gel
separation, a pulsed or oscillating field separation,
isotachophoresis, or any of the various electrophoretic procedures
that are known in the art. For polyacrylamide gels, the monomer
concentration in the starting solution may range from about 3% to
about 30% by weight of the solution itself, while the crosslinker
may constitute from about 0.5% to about 10% of the
monomer/crosslinker combination.
[0031] Inks that can be used in the practice of this invention
include any conventional ink or pigment formulation that when dried
is insoluble in the gel-forming liquid used to form the bulk of the
gel and therefore does not "run," "bleed," or otherwise produce
indicia that become distorted when placed in contact with the bulk
gel liquid. Since gel-forming liquids are typically aqueous
solutions, preferred inks are those that when dried are insoluble
in water and therefore will not diffuse into the bulk of the gel.
Inks that contain a solid pigment dispersed in water or in an
organic liquid that is miscible with water, such as aqueous or
alcohol-based solutions or suspensions, can be used provided that
the ink is a permanent ink that once dried will not diffuse into
the gel solution. Other inks suitable for use are fluorescent inks,
inks that are visible only in ultraviolet light, and inks that are
visible in both visible light and ultraviolet light.
[0032] In embodiments in which the ink is applied as a mixture with
a solution of polymer directly to the mold surface without first
coating the solid surface with a water-permeable polymer, the
relative amounts of ink and polymer solution may vary and are not
critical to the success of the invention. For certain inks, higher
proportions of ink will generally produce darker indicia, and the
proportion of ink to polymer may affect the viscosity of the
mixture and hence the ease with which it can be applied. Viscosity
limitations may be imposed by the implement used to apply to the
mixture to the plate, i.e., whether a pen or a stamp is used, the
fineness of the lines, and similar considerations. Certain inks,
such as those that are readable by instrumentation, require only
very small amounts, while those that are read visually will benefit
from higher amounts. Fluorescent inks, for example, can be used
effectively in concentrations substantially less than 1% by weight.
User-visible inks, on the other hand, are preferably used in
concentrations exceeding 5% by weight. Some will read best at
concentrations ranging from about 20% to about 80% ink by weight,
preferably from about 35% to about 65%. In one embodiment
successfully tested by the inventors herein, a 50% mixture was
used. The optimum amount for each ink is readily determinable by
routine experimentation using simple trial and error.
[0033] When the ink is applied over a coating of the dried
gel-forming material, application (i.e., the formation of the
indicia) can be made by hand using an implement such as a felt-tip
pen, a capillary pen, a stylus, or a brush. Mechanical printing
techniques, such as offset printing, lithography, or inkjet
printing, can also be used. Inkjet printing can be performed using
convention inkjet printers and inks, such as a VIDEOJET EXCEL 273SE
Inkjet Printer (Videojet Technologies, Inc., Wood Dale, Ill., USA)
with HR W/16-5600 ink. The same techniques can be used When the ink
is applied directly to the plate as a mixture with the gel-forming
liquid.
[0034] The term "indicia" is used herein to denote markings of any
kind. If the gel is a precast gel, the indicia may be the type of
information that might be incorporated by the manufacturer,
including, but not limited to, a barcode, a set of grid lines
across the entire gel, length indicators (i.e., "rulers" ) along
the edge of the gel, lane numbers, reference points for manual or
automated detection, a supplier catalog number, a supplier logo, or
information regarding the gel composition such as its gel type or
gel percentage. Alternatively, the indicia may be markings that can
be applied by the user for gels that are prepared at the user site,
such as a sample code number or other identifiers, the name of the
user, the date on which the gel was prepared or the separation was
performed, and the composition of the gel, including information
relating to concentrations or gradients.
[0035] In those embodiments of the invention in which a polymer
coating is first applied to the mold surface, or to one plate or
one internal face of the mold, the coating can be applied to the
entire plate or internal face or to only the portion where indicia
are needed. The choice will often depend on the type of indicia to
be applied. When the indicia are grid lines, for example, the
coating preferably covers the entire plate. When the indicia are a
bar code, the coating is only needed in the region where the bar
code will reside. Coating areas for other indicia will be readily
apparent to those skilled in the manufacture or use of
electrophoresis gels.
[0036] Once the indicia are applied, either to a coating, a coated
liner, or a sheet of the coating material, or directly to the
internal surface of the gel mold, the mold is closed and filled
with the gel-forming liquid. For slab gels, indicia are applied to
one of the two flat plates of the mold and the mold is closed by
combining the imprinted plate with the remaining plate and
appropriate spacers as needed to form a conventional slab gel
enclosure or cassette. For gels of other configurations, the molds
are formed appropriately, as will be evident to those skilled in
the use of these molds and the formation of electrophoresis gels in
general. Cassettes, plates and gel enclosures of various kinds are
well known in the art and widely available from commercial
suppliers.
[0037] The solid surfaces to which the indicia are applied, either
directly, through a coating, or through a coating on a liner, can
be formed of any material that is known for use as a structural
material for a gel mold. Examples are glass and various plastics
such as acrylics (thermoplastic polymers and copolymers of acrylic
acids), polystyrene, polycarbonate, poly(ethylene naphthalate)
(PEN), poly(ethylene terephthalate) (PET), poly(ethylene
terephthalate glycolate) (PETG), styrene-acrylonitrile copolymer
(SAN), and methyl methacrylate-styrene copolymers (NAS).
[0038] The following examples are offered only as illustration.
EXAMPLE 1
[0039] This example illustrates the application of indicia by hand
to a glass plate whose entire surface on one side is coated with
linear polyacrylamide, the indicia being formed in ink from common
ink pens and also in india ink.
[0040] A flat glass plate was coated with a 2% aqueous solution of
linear polyacrylamide having a weight-average molecular weight of
5,000,000 to 6,000,000, and the coating was allowed to dry. (All
percents in these examples are by weight unless otherwise noted.)
Markings were then applied by hand to the dry coating in separate
lines with different common writing pens--three Sanford Sharpies
(Series 35000 porous tip permanent markers, one black, one blue and
one red; supplier: PenCity, Ellijay, Ga., USA), one standard
ballpoint pen, and one Stanford Rolling Writer. India ink was
applied by a wooden rod dipped in the ink. Each ink was allowed to
dry before proceeding further.
[0041] Thus marked, the plate was combined with other cassette
components to form a gel cassette with a gap width of 1.0 mm. A
polyacrylamide gel was then cast in the cassette from an aqueous
acrylamide monomer solution consisting of 12% T, 2.6% C (i.e.,
monomer and crosslinker combined at a total concentration of 12%,
with the crosslinker constituting 2.5% of the monomer/crosslinker
combination), and catalyst and initiator in appropriate quantities.
As polymerization proceeded, the coating and the markings became
one with the gel and remained a part of the gel after the gel was
removed from the cassette. By visual observation, the indicia
written by the three Sanford Sharpie pens and the ball point pen
were all clear, sharp and easily readable. The indicia applied by
the Rolling Writer inhibited polymerization, and the indicia
applied by the india ink had smeared.
EXAMPLE 2
[0042] This example is a further illustration of the application of
indicia by a common ink pen to a glass plate coated with linear
polyacrylamide, using two different concentrations of linear
polyacrylamide in separate tests.
[0043] A flat glass plate was coated with a 2% aqueous solution of
linear polyacrylamide having a weight-average molecular weight of
5,000,000 to 6,000,000. A separate glass plate was coated with a
50% aqueous solution of linear polyacrylamide with a weight-average
molecular weight of 1,500. Both plates were allowed to dry.
Markings were then applied by hand to the coated sides of each
plate using a black permanent marker (Stanford Sharpie).
[0044] Each plate was then combined with other cassette components
to form a gel cassette with a gap width of 1.0 mm. A polyacrylamide
gel was then cast in the cassette from a monomer solution identical
to that of Example 1. As polymerization proceeded, each coating and
the markings applied to the coatings became part of the respective
gel and remained so after the gel was removed from the cassette.
Visual observations indicated that the markings on both gels were
clear and sharp and easily readable.
EXAMPLE 3
[0045] This example illustrates the application of indicia by an
inkjet printer to a glass plate coated with linear
polyacrylamide.
[0046] A flat glass plate identical to that of Example 1 was coated
with a 2% aqueous solution of linear polyacrylamide having a
weight-average molecular weight of 5,000,000 to 6,000,000. The
coating was allowed to dry and was then imprinted with a barcode
using a VIDEOJET EXCEL 273 SE Ink Jet printer with HT W/16-5600
ink. A polyacrylamide gel was then cast in a cassette of which the
plate formed one side, using a monomer solution identical to that
of the preceding examples. The resulting gel was then removed from
the cassette. The barcode remained intact on the gel upon removal
of the gel from the cassette. Even after the gel was dried
according to typical procedure following electrophoresis, the
barcode remained intact and readable.
EXAMPLE 4
[0047] This example illustrates the application of indicia to a
glass plate by marking the bare plate with india ink mixed with an
aqueous solution of linear polyacrylamide.
[0048] A glass plate that was not precoated with linear
polyacrylamide was used. Two ink/polyacrylamide mixtures were
prepared, both formed by combining equal volumes of india ink and
aqueous linear polyacrylamide. The linear polyacrylamide used in
the first mixture was a 0.75% aqueous solution and that used in the
second was a 2% aqueous solution, both by weight and both prior to
addition of the india ink. The ink/polyacrylamide mixtures were
applied as markings to separate areas of the plate by a wooden
stick dipped in each mixture. The markings were then allowed to dry
and a cassette was assembled from the plate. A gel was formed in
the cassette, using a monomer solution identical to those of the
preceding examples. The gel was then removed form the cassette.
[0049] The markings from both mixtures were present on the gel even
after removal from the cassette. Smearing of the markings occurred
but the markings were still readable. The smearing occurred during
the polymerization and did not continue after polymerization was
complete. The least amount of smearing occurred with the higher
concentration of linear polyacrylamide.
EXAMPLE 5
[0050] This example illustrates the application of indicia to a
flexible liner sheet coated with linear polyacrylamide.
[0051] A sheet of polypropylene was coated on one side with the
same 2% linear polyacrylamide solution used in Example 1 above, and
the coating was allowed to dry. The coated sheet, which did not
have an adhesive on its uncoated side, was then placed against a
flat glass plate, and markings were placed on the sheet by hand
using a black Stanford sharpie as described in Example 1. The plate
was then combined with another plate and spacers to form a slab gel
cassette, and a 12% polyacrylamide gel was cast in the cassette.
Upon subsequent removal of the gel from the cassette, the
polypropylene sheet remained adhered to the glass plate while the
linear polyacrylamide coating and the markings were incorporated in
the gel.
[0052] The foregoing description is offered primarily for purposes
of illustration. Further modifications, substitutions and
variations will be apparent to those skilled in the art and will be
included within the scope of the invention.
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