Abstract:
This invention embodies a method that can be used to increase the porosity of the gel substrate during the fabrication of microchips. This increase in gel porosity will allow larger molecules such as non-fragmented RNAs and DNA fragments greater then 100 base pairs in length, and proteins to be immobilized and introduced within the gel microchips.

Description:
[0001]    This application is based on a Feb. 5, 2001 Provisional Application having Ser. No. 60/266,656. 
     
    
     CONTRACTUAL ORIGIN OF INVENTION 
       [0002]    The United States Government has rights in this invention pursuant to Contract No. W-31-109-ENG-38 between the U.S. Department of Energy and the University of Chicago, representing Argonne National Laboratory. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    This invention relates to the manipulation and immobilization of macromolecules, and more specifically, this invention relates to a method to increase the efficiency of interaction between large macromolecules and a gel substrate. The gel substrate is used to manipulate, immobilize, and hybridize large RNA and DNA molecules and carry out different assays with protein molecules for subsequent study. 
         [0005]    2. Background of the Invention 
         [0006]    The development and application of arrays of immobilized biological compounds (biological microchips) has become a significant trend in modern biology, biotechnology and medicine. The main advantage of biological microchips over conventional analytical devices is the possibility of massive parallel analysis. Biological microchips are smaller than conventional testing systems and highly economical in the use of specimens and reagents. Major progress has been achieved in the manufacturing and application of biological microchips. 
         [0007]    Biological microchips exist in two major forms. The first is often referred to as a two-dimensional array, where the biological molecule of interest, e.g. DNA, is covalently attached to a solid glass substrate. The second form comprises an array of three dimensional gel pads, attached to a solid substrate, to which the biological molecule of interest is attached. (U.S. Pat. No. 5,552,270 to Khrapko, et al.) 
         [0008]    The main advantage of the use of a three-dimensional gel support for fixation of biological compounds is the larger capacity for immobilized compounds afforded by the three dimensional volume of the gel pad rather than the two dimensional area of a glass substrate. In addition, the gel pads in the array are chemically and physically separated from each other, for example by a hydrophobic surface. Therefore, the arrays of gel pads can be used as a large number of individual micro liter test tubes to carry out specific interactions and chemical and enzymatic procedures with microchip substances. 
         [0009]    U.S. Pat. No. 5,981,734 awarded to Mirzabekov et. al. on Nov. 9, 1999 discloses a method of manufacture of gel microchips using polyacrylamide gels of a particular formulation (including 5% concentration of the cross linking agent to the total formulation). Using this gel composition, immobilization and hybridization of small biological molecules occurs within the surface layers of the described gel pads. However, the described polyacrylamide gel does not provide a formulation which is highly efficient for the hybridization of large non-fragmented nucleic acid molecules (&gt;100 bases) or efficient immobilization and hybridization of large proteins, i.e., greater than 25 kilo-daltons (kD). As such the gel also does not provide a micro test tube environment in which protein assays such as immunoassays or enzyme assays can be carried out in parallel. One of the main reasons of this inaccessibility is the low porosity of the described polyacrylamide gel formulation. 
         [0010]    Generally there are several ways to increase the porosity of acrylamide-based gels, described in the literature. These include the increase in content of a cross-linker and decrease in total gel concentration. P. G. Righetti et al (1981)  J. Biochem Biophys Meth.  4 pp. 347-363, discusses limiting pore size of hydrophilic hydrogels for electrophoresis and isoelectric focusing. 
         [0011]    X. Wu, et al., (1992),  J. Polymer Sci.: Part A: Polymer Chem.,  30, 2121-2129 and R. Charlionet, R., Levasseur, L., and Malandain, J.-J. (1996),  Electrophoresis,  17, 58-66) discuss the use of pore forming agents. 
         [0012]    Other researchers have disclosed how changes in polymerization conditions can induce porous substrates. Such teachings include E. M. Belavtseva, (1984)  Colloid  &amp;  Polymer Sci.,  262, 775-779 and C. Gelfi, (1981)  Electrophoresis,  2, 220-228. 
         [0013]    M. Kozulic, et al. (1987)  Anal. Biochem.,  163, 506-512, and C. Gelfi, et al, (1992)  J. Chromatography,  608, 333-341) (IV) discuss how the substitution of acrylamide and methylene bis acrylamide with other mono- and bifunctional monomers induces porosity. 
         [0014]    A need exists in the art for a gel support with increased rates of diffusion for molecules contacting the gel. The gel should have extremely high hybridization capacities for large DNA fragments. Also, the gel should accommodate macromolecules, such as proteins and peptides, of up to 400,000 daltons (D) in size. 
       SUMMARY OF INVENTION 
       [0015]    An object of the present invention is to provide a gel formulation to immobilize and hybridize biological macromolecules that overcomes many of the disadvantages of the prior art. 
         [0016]    Another object of the present invention is to provide a high-capacity substrate to facilitate the immobilization and hybridization of large macromolecules A feature of the invention is that it provides greater accessibility of inner gel substrate volume to the macromolecules. An advantage of the invention is that the resulting higher capacity gel pads facilitates the immobilization of macromolecules having molecular weights of as much as 400 kilodaltons (400 kD wherein 1 kD=1000 daltons). 
         [0017]    Yet another feature of the present invention is providing a protocol for producing high capacity gels. A feature of the invention is the cleavage of the vicinal dihydroxy structure of certain cross-linkers of some of the polymers comprising the gels while other types of cross-linkers remain unscathed under cleavage conditions. An advantage of this protocol is that it prevents total gel substrate solubilization while simultaneously maintaining the geometrical configuration and/or the physical integrity of the gel pad shape. 
         [0018]    Another object of the present invention is to provide a method for producing a gel support with enhanced immobilization and hybridization efficiencies for large molecules. A feature of the invention is that the production of the gel support incorporates the use of a plurality of different types of cross-linkers. Another feature is that at least one type of cross linker, but not all of the cross linkers are subsequently cleaved after polymerization is complete. An advantage of the invention is that sufficient cross-linkers remain to provide a stable gel structure while also providing a gel having a higher capacity for hybridization of large non-fragmented nucleic acid molecules (100-300 bases) and immobilization and immunoassay with large proteins (25400 kD). 
         [0019]    Briefly, the invention provides a process for manufacturing hydrophilic open gels, the process comprising supplying acrylamide monomers, crosslinking them to each other with a first species of linking moiety and a second species of linking moiety so as to form a polymerized gel having cross-linkers with different properties, and cleaving one set of cross linkers thus changing the macromolecular binding properties of the gel. 
         [0020]    Also provided is a gel substrate comprising acrylamide moieties; a first linking agent connecting said acrylamide moieties to each other; and a second linking agent connecting said acrylamide moieties to each other, wherein the ratio of first linking agent to moiety ratio is less than the ratio of second linking agent to moiety ratio. 
     
    
     
       BRIEF DESCRIPTION OF DRAWING 
         [0021]    The invention together with the above and other objects and advantages will be best understood from the following detailed description of the preferred embodiment of the invention shown in the accompanying drawing, wherein: 
           [0022]      FIG. 1  depicts chemical formulas for mono- and bifunctional monomers used in the invented gel-polymerization method; 
           [0023]      FIG. 2  is a schematic diagram of the mechanisms of cross-linkage and cleavage of moieties comprising the invented gel substrate, in accordance with features of the present invention; 
           [0024]      FIG. 3  depict sequences of oligonucleotides and ssDNA used for diffusion studies and hybridization experiments; 
           [0025]      FIGS. 4A-B  illustrate the kinetics of binding goat anti-rabbit IgG to rabbit IgG on standard microchip and a microchip incorporating the invented gel, respectively, in accordance with features of the present invention; 
           [0026]      FIG. 5  illustrates the change of fluorescence intensity in an invented gel element before and after molecule loading, in accordance with features of the present invention; 
           [0027]      FIG. 6  illustrates the kinetics of diffusion of fluorescently labeled oligonucleotide or ssDNA out of invented gel substrates, in accordance with features of the present invention; 
           [0028]      FIGS. 7A-B  illustrate the kinetics of free diffusion of Texas Red labeled oligonucleotides into a standard micromatrix and the invented micromatrix, respectively, in accordance with features of the present invention; 
           [0029]      FIGS. 8A-B  illustrate the kinetics of free diffusion of Texas Red labeled oligonucleo-tides out of a standard micromatrix and a micromatrix comprising the invented porous gel, respectively, in accordance with features of the present invention; 
           [0030]      FIG. 9  illustrates the free diffusion of labeled ss DNA into standard micromatrix and invented micromatrix gel pads and out of invented the invented micromatrix gel pads, respectively, in accordance with features of the present invention; and 
           [0031]      FIGS. 10A-B  compares the kinetics of hybridization of ssDNA with complementary oligonucleotides on a standard microchip and on an invented Microchip II, respectively, in accordance with features of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0032]    As used herein, the following words and terms shall have the meaning ascribed below: 
         [0033]    “Micromatrix”: An array of gel pads after polymerization and activation on a solid support. 
         [0034]    “Microchip”: The gel pad array, further including molecules immobilized within each of the gel pads. 
         [0035]    “Standard” gel, substrate, matrix, microchip: This refers to the acrylamide-based gels, such as methylene bisacrylamide gel described in U.S. Pat. No. 5,981,734, awarded to Mirzabekov et. al. on Nov. 9, 1999, and incorporated herein by reference. 
         [0036]    The inventors present herewith a protocol for producing gel substrates capable of accommodating macromolecules having sizes up to 400 kD. These gel substrates provide volumes that are ten times the volume of state-of-the-art gel substrates. Generally, the invention provides for the utilization of high concentrations of cross linkers of the gel substrate material during gel polymerization, followed by periodate oxidation. This method produced gel porosities large enough to accommodate the sandwich complex of antibody-antigen-antibody constructs. Insertion of the macromolecules is further facilitated via electrophoresis, or else mixing the solutions within the polymerization with a micropump. 
         [0037]    An exemplary protocol for producing high capacity gel substrates for containment and manipulation of macromolecules is found in Arenkov et al.,  Analytical Biochemistry,  278, 123-131 (2000) and incorporated herein by reference. 
         [0038]    A feature of the protocol is the cleavage of some but not all of the cross links binding the polymers comprising the substrate. Generally, a gel having increased porosity occurs when some of the links between monomers comprising the gel are cleaved while others are left in place to maintain the gel pad shape. After the cleavage process, the gel pad must be activated in order to make it able to attach the biological macromolecule of interest. 
         [0039]    In a specific expression of the invented method, a more efficient gel formulation for immobilization of macromolecules is created by first forming a highly cross-linked gel composition from acrylamide (M) and N-acryloyl-tris(hydroxymethyl)aminomethane (NAT) (monofunctional monomers) and N,N′-diallyltartardiamide (DATD), N,N′-(1,2-dihydroxyethylene)bisacrylamide (DHEBA), and N,N′-methylenebisacrylamide (MBA) (bifunctional monomers) ( FIG. 1 ). 
         [0040]    Activation of the gel substrate is achieved via treatment of the gel with glutaraldehyde. If the monomer mixture contains DATD, aldehyde groups could be produced via gel treatment with sodium periodate ( FIG. 2 ). Oligonucleotides modified with amino groups and proteins could be immobilized through reductive coupling of their 5′-amino groups with the aldehyde groups of the compounds comprising the activated gel pad. An exemplary reductive coupling scenario is described in U.S. Pat. No. 5,981,734, and incorporated herein by reference. 
         [0041]    The gel pad substrate produced using the formulation described herein has several advantages over the prior art. For example, the rate of free diffusion (i.e., the velocity or speed) of long ssDNA fragments within the invented gel substrate is significantly higher than the rate of free diffusion of same DNA within the conventional gel substrate. It is also seen that the hybridization capacity for long DNA fragments is significantly higher on the invented gel substrate than that for conventional gel substrate. 
         [0042]    Additionally, macromolecules, in particular proteins and peptides, of a size up to 400 kD can be immobilized and manipulated using the invented gel pad substrate. The invented substrate also allows for several rounds of different immunoassays to be carried out successively on the same gel microchip with no loss in specificity. 
         [0043]    The invented gel formulation has also proved to be more efficient than the standard gel formulation during those reactions necessary for the polymerase chain reaction when carried out on a microchip. 
         [0044]    It is also possible to uses this formulation in the production of microchips using the method of co-polymerization manufacture. 
       Process Detail 
       [0045]    Gels of highly cross-linked compositions containing polyacrylamide and poly-N-acryloyl-tris(hydroxymethyl)aminomethane are utilized. In an exemplary gel composition, N,N′-(1,2-dihydroxyethylene)-bisacrylamide (DHEBA) and/or N,N′-diallyltartardiamide (DATD) as a first crosslinking species and N,N′-methylenebis-acrylamide (MBA) as a second crosslinking species are used as the cross-linking agents in these gels. 
         [0046]    Generally, all water soluble organic compounds containing two or more functional groups (acrylamide, methacrylamide, substituted acrylamide, substituted methacrylamide, acrylic, methacrylic, acrylate, methacrylate, allyl) and single or multiple diol groups within backbone hydrocarbon chain with different substituents could be used instead of DHEBA and DATD. All water soluble organic compounds containing two or more functional groups (acrylamide, methacrylamide, substituted acrylamide, substituted methacrylamide, acrylic, methacrylic, acrylate, methacrylate, allyl, etc) without a single diol group within backbone hydrocarbon chain with different substituents could be used instead of MBA. Any water soluble organic compound containing one functional group such as acrylamide, methacrylamide, acrylic, methacrylic, acrylate, methacrylate and their substituted analogs could be used instead of acrylamide and NAT. 
         [0047]    Generally, the first species is present in a weight percent with the second species in a range of between approximately 6:4 and 9:1, while total gel concentration is 3-5%. 
         [0048]    After gel polymerization, the accessibility of gel pad volume for large macromolecules and gel hydrophilicity are significantly increased by the cleavage of the vicinal diol structure of the DHEBA and/or DATD cross-linkers. Simultaneous with these cleavages is the prevention of gel solubilization by the presence of the MBA cross-linkers ( FIG. 2 ). 
         [0049]    Activation of the gel substrate is achieved via treatment of the gel with a compound which facilitates the attachment of proteins or modified oligonucleotides to gel substrate. This compound typically comprises a plurality of aldehyde moieties so as to facilitate the binding of one of the moieties with the amine group of the gel and another of the moieties with the amine group of the protein or modified oligonucleotide. An exemplary compound to facilitate such binding is glutaraldehyde. 
         [0050]    If the monomer mixture contains DATD, aldehyde groups could be produced via gel treatment with sodium periodate ( FIG. 2 ). Oligonucleotides modified with amino groups and proteins could be immobilized through reductive coupling of the 5′-amino group of with aldehyde group of the activated gel pad. 
         [0051]    It should be appreciated that the specific reagent and reactant volumes and concentrations presented infra are for illustrative purposes only and should not be construed as limiting the scope of the appended claims to these parameters. Rather, commercial-scale protocols will utilize reactant volumes and concentrations derived empirically after taking into consideration the efficiencies and accuracies desired. 
       EXAMPLE 1 
     Production of Gel Micromatrix I. 
       [0052]    A polymerization chamber consisted of a glass slide treated with Bind-Silane (LKB, Sweden) and a quartz plate mask of a specified topography: transparent 100×100 μm square windows spaced by 200 μm were arranged on a 1 μm thick chromium non-transparent layer. The slide and the mask were separated by 20 μm-thick teflon spacers. An exemplary polymerization chamber and a method for making same is disclosed in U.S. Pat. No. 5,770,721, incorporated herein by reference. 
         [0053]    Generally, the chamber was filled with a solution containing acrylamide, N,N′-(1,2-dihydroxyethylene)bis-acrylamide (DH EBA), N,N′-methylenebisacrylamide (Bis), glycerol, methylene blue, TEMED in sodium phosphate buffer (PB), pH 7.2. Preferable concentrations of the components of the solution are approximately 3% acrylamide, 0.8-0.9% N,N′-(1,2-dihydroxyethylene)bis-acrylamide (DHEBA), 0.13-0.15% N,N′-methylenebisacrylamide (Bis), between 30 and 50% glycerol, 1-2% (most preferably 1.3%) TEMED, and 2×10 −4 % methylene blue. The chamber was exposed to UV light in conditions to facilitate polymerization of the for a time. 
         [0054]    The matrix was then washed with water for 10 minutes to remove nonpolymerized monomers, dried, and kept at room temperature. 
         [0055]    The gel was treated with NaIO 4  in water (preferably 0.001 M to 0.1 M NaIO 4  for between 5-30 minutes at room temperature, and most preferably at 0.1 M for 20 minutes at room temperature). The treated gel was then washed with water and dried. The matrix was immersed into approximately 5 percent glutaraldehyde in 0.1 M PB, approximately neutral pH for about 48 hours at room temperature or 12 hours at 37° C. It was then washed in water, and dried. To minimize any chance for cross contamination of one gel pad entity with another, the matrix is treated with a compound to enhance the hydrophobic characteristics of the substrate onto which the individual gel units reside. An exemplary compound to enhance such hydrophobicity is Repel-Silane. After hydrophobic enhancing treatment, the matrix is rinsed with alcohol (such as ethanol) and water, and dried in a nitrogen atmosphere. 
         [0056]    Micromatrix I was used for immobilizing proteins and carrying out different immunoassays. 
       EXAMPLE 2 
     Production of Porous Gel Micromatrix II 
       [0057]    Same polymerization chamber as from Example 1 was used for fabrication of micro matrices for further hybridization experiments, while a chamber with a 1000×1000 μm mask with 40-μm spacers were used for preparation of micro matrices for diffusion experiments. For fabrication of this exemplary porous gel micromatrix, the chamber was filled with solution containing acrylamide, N-acryloyltris-(hydroxymethyl)-aminomethane (NAT) N,N′-(1,2-dihydroxyethylene)bisacrylamide (DHEBA), N,N′-diallyltartardiamide (DATD) N,N′-methylenebisacrylamide (Bis), glycerol, acetone, TEMED in sodium phosphate buffer, and at approximately neutral to slightly acidic pH. Preferable concentrations for the polymerization solution include approximately 1-2% (most preferably 1.5%) acrylamide, 1-2% (most preferably 1.5%) N-acryloyltris-(hydroxymethyl)-aminomethane (NAT), 0.65-0.75% (most preferably 0.70%) N,N′-(1,2-dihydroxyethylene)bisacrylamide (DHEBA), 0.15-0.25% (most preferably 0.20%) N,N′-diallyltartardiamide (DATD) (Bio-Rad), 0.08-0.12% (most preferably 0.1% N,N′-methylenebisacrylamide (Bis), 20-40% (most preferably 30%) glycerol, 1-3% (most preferably 2%) acetone, 1-2% (most preferably 1.3%) TEMED in approximately 0.1 sodium phosphate buffer, at approximately pH 6.8. 
         [0058]    The chamber was illuminated with 254-nm UV light. Then the matrix was washed with water to remove nonpolymerized monomers and glycerol, dried, and kept at room temperature. The gel micromatrix is treated with Repel Silane, repeatedly washed with ethanol and water, dried and then treated with 0.1 M NaIO 4 , washed with water and dried. 
       EXMAPLE 3 
     Immobilization of Proteins on Micromatrix I. 
       [0059]    The proteins are dissolved in any usual protein buffer, such as those buffers which do not contain amino groups. An exemplary buffer is a phosphate buffered solution such as a phosphate buffered saline (PBS) solution. One such PBS solution is disclosed in the Arenkov article above incorporated by reference. 
         [0060]    After the application of protein solutions onto the glutaraldehyde-activated gel pads, the microchip was incubated in a humid chamber. It then was washed successively in PBS with Tween-20, in PBS, and in PB. The microchip was treated at approximately 0 to 10 C (and preferably at 4° C.) in 0.1 M NaBH 4 , and washed briefly with water, then PBS with Tween-20, and finally in PB. The microchip was stored in sterile PBS at approximately 4° C. 
       EXAMPLE 4 
       [0061]    Preparation of Oligonucleotides and ssDNA 
         [0062]    Oligonucleotides for experiment ( FIG. 3 ) were synthesized on a 394 DNA/RNA synthesizer (Applied Biosystems) by standard phosphoramidite chemistry. Oligonucleotides for immobilization on microchips, long oligonucleotides (59 nt and 89 nt) for study of free diffusion, and reverse primer for DNA amplification contained 5′-amino groups introduced by use of 5′-Amino-Modifier C6 (Glen Research). Long oligonucleotides and reverse primer were labeled by Texas Red sulfonyl chloride (Molecular Probes) according to manufacturer protocol and then were purified by preparative denaturing PAGE. 
         [0063]    A 188 bp dsDNA ( FIG. 3 ) was prepared by PCR amplification from insert of cloned human carcinoma-associated antigen. 
       EXAMPLE 5  
       [0064]    Immobilization of Oligonucleotides with Modified Amino Groups on Micromatrix II 
         [0065]    Oligonucleotides were dissolved at different concentration in water. For application of oligonucleotides onto the gel matrix the same procedure as in example 3 was used. Prior to contact with the matrix, the oligonucleotides were modified pursuant to the teaching in U.S. Pat. No. 5,471,700, and incorporated herein by reference. 
         [0066]    After oligonucleotide application, the micromatrix was put into 0.1M freshly prepared solution of pyridine-borane complex in chloroform. Chloroform layer was covered with water; (approx ¼ inch). The micromatrix was incubated for 12 hours at room temperature. Then the microchip was washed microchip with distilled water and incubated in 0.1M sodium borohydride solution for 20 min. The microchip was washed with distilled water for 1 min and then incubated in distilled water at 60° C. 30 min to remove all unpolymerized components. Then the microchip was washed with distilled water and dried in the air. 
       EXAMPLE 6 
       [0067]    Kinetics of Immunobinding on Different Microchips with 100 μm×100 μm×20 μm Elements. 
         [0068]    Quantitative fluorescence measurements were carried out by use of a fluorescence microscope equipped with a cooled CCD camera (Princeton Instruments Inc.), a computer, and respective software. All experiments were carried out at room temperature. To study the time course of immunobinding and to compare microchips prepared using different gel compositions, the kinetics of binding of fluorescently labeled goat anti-rabbit IgG with rabbit IgG immobilized on different microchips was studied. Rabbit IgG (1.0, 0.2, 0.04 mg/ml) was immobilized on Micromatrix I and on a standard polyacrylamide gel micromatrix as described in Example 3, and in U.S. Pat. No. 5,552,270, incorporated herein by reference. The microchip was placed in an airtight chamber with quartz glass windows, and the chamber was filled with 30 μl of solution containing goat anti-rabbit IgG labeled with fluorescein isothiocyanate, and the kinetics of the interaction was recorded. 
         [0069]      FIG. 4  shows the time dependence of the intensity of the immuno-staining signal on the two different microchips.  FIG. 4  illustrates the kinetics of binding goat anti-rabbit IgG to rabbit IgG on standard microchip and the invented microchip (Microchip I) Rabbit IgG (1.0, 0.2, 0.04 micrograms/micro liter) was immobilized on standard (A) and the invented (B) microchips, and the kinetics of the interaction with FITC-labeled goat anti-rabbit IgG (dilution 1:100) was recorded, wherein the invented micromatrix is Micromatrix I as disclosed herein. 
         [0070]    The process of immunobinding proceeded slower on the standard microchip ( FIG. 4A ) than on the Microchip I ( FIG. 4B ), and the resulting signals on the standard microchip were 7-10 times lower than on Microchip I. Though the fluorescent signals on the microchip I reached a plateau within 7-25 h, the times required for 50% equilibrium signals were 0.2, 1, and 3 h for antibodies immobilized at 0.04, 0.2, and 1.0 mg/ml, respectively. This example demonstrates that the capacity of invented gel substrate for protein is significantly higher than on standard gel substrate. 
       EXAMPLE 7  
       [0071]    Comparison of Rates of Free Diffusion on Micromatrix II Containing 1000 μm×1000 μm×40 μm Elements. 
         [0072]    Quantitative fluorescence measurements were carried using a fluorescence microscope equipped with a cooled CCD camera, a computer, and respective software. All experiments were carried out at room temperature. Gel micro matrices were preliminary treated as described in Example 5. 
         [0073]    The experiments for monitoring of free diffusion kinetics were carried out in a chamber described in Example 6 but with 20-μm spacers. In a single experiment, a gel micromatrix was put into a chamber; then the chamber was filled with hybridization buffer [1 M NaCl, 10 mM sodium phosphate buffer (pH 7.2), 1 mM EDTA, 0.1% Triton X-100]. Under these conditions, we obtained gel pads with top surface “covered” with upper quartz window. Then the buffer were carefully removed from the chamber without chamber disassembling, and the chamber was filled with solution of Texas Red labeled oligonucleotide (1 pmol/μl) or ssDNA (0.5 pmol/μl) in hybridization buffer. 
         [0074]    The change of fluorescence intensity from a gel element was recorded, as illustrated in  FIG. 5 .  FIG. 5  is an image of a 1000×1000×40 micrometer (μm) element with covered top surface at different times of incubation with an 89-base Texas-Red labeled oligonucleotide. 
         [0075]    After the achievement of equilibrium, the sample-containing solution was removed from the chamber, and the chamber was washed 4 times with hybridization buffer. Then the kinetics of diffusion of fluorescently labeled oligonucleotide or ssDNA out of the gel element was recorded ( FIG. 6 ).  FIG. 6  is an image of a 1000×1000×40 μm element with covered top surface after incubation with 89-base Texas-Red labeled oligonucleotide and washing off of the probe. 
         [0076]      FIGS. 7-9  show experimental kinetic curves of free diffusion of 59 nt, 89 nt, and 188-base ssDNA on standard gel matrix and Matrix II. Though the kinetics of free diffusion of 59 nt and 89 nt oligonucleotides is nearly the same for both gels, 188-base ssDNA penetrates into the standard gel substrate very slowly in comparison to Matrix II gel substrate. 
         [0077]      FIG. 7  illustrates the kinetics of free diffusion of Texas Red labeled oligonucleotides (1 pmol/μl) into 1 mm×1 mm×40 μm standard micromatrix (A) and invented micromatrix (B) gel pads with covered top surface, wherein the invented micromatrix is Micromatrix II as disclosed herein. 
         [0078]      FIG. 8  illustrates the kinetics of free diffusion of Texas Red labeled oligonucleotides (1 pmol/μl) out of 1 mm×1 mm×40 μm standard micromatrix (A) and invented Micromatrix II (B) gel pads, with covered top surface. 
         [0079]      FIG. 9  illustrates the free diffusion of Texas Red labeled 188-based ss DNA (0.5 pmol/μl) into standard micromatrix and invented Micromatrix II gel pads (A) and out of invented Micromatrix II gel pad (B); 
         [0080]    This example demonstrates that accessibility of interior volume of for a standard gel substrate is comparable with that of invented substrate for single stranded nucleic acids with length lower than 100 base, but that the accessibility of interior volume of standard gel substrate is significantly lower than that of invented substrate for single stranded nucleic acids with length more than 100 base. 
       EXAMPLE 8 
       [0081]    Hybridization of 188-Base DNA on Standard Gel Microchip and Microchip II with 100 μm×100 μm×40 μm Gel Elements. 
         [0082]    The same 188-base ssDNA that was used for diffusion experiments was used for hybridization experiments. Hybridizations were carried out on standard microchip and microchip II with immobilized complementary oligonucleotides (see Example 5) of different length ( FIG. 3 ) and concentration 1 nmol/μl. The ssDNA concentration used for hybridization was 0.1 pmol/μl. The hybridizations were carried out in hybridization buffer used for diffusion experiments. The volume of hybridization chamber was 100 μl. Kinetic curves of hybridizations are shown on  FIG. 10 . The hybridization data confirm data obtained during study of free diffusion. The ssDNA hybridizes within the surface layers of standard gel pad. Therefore, we have here “surface” hybridization with rapid hybridization kinetics and low hybridization signals in comparison to microchip II. However, when hybridization is carried out on microchip II, the process proceeds much more slowly though final hybridization signals are 10-15 times higher ( FIG. 10 ). 
         [0083]      FIG. 10  compares the kinetics of hybridization of 188-base ssDNA with complementary oligonucleotides on a standard microchip (A) and on an invented Microchip II (B). 
         [0084]    Despite of lower rates of hybridization on microchip  11 , hybridization signals are significantly higher than on the standard microchip even after first several hours of hybridization. This phenomenon could be caused either by non-homogeneity of complementary oligonucleotide distribution within a gel pad or partial proceeding of hybridization which rate slows down as the ssDNA concentrates within a gel pad. This example demonstrates higher hybridization capacity of invented gel substrate for long DNA fragments. 
         [0085]    While the invention has been described with reference to the details of the illustrated embodiment, these details are not intended to limit the scope of the invention as defined in the appended claims.