RU2320994C1 - Method for assay of biological toxins - Google Patents

Abstract

FIELD: medicine, analytical biochemistry.

SUBSTANCE: claimed method includes assay of various biological toxins by using biological microarray. Said biological microarray represents ordered array of three-dimensional hydrogel cells on solid support, obtained by photo- or chemically induced polymerization and containing immobilized antibodies against various bacterial, plant and animal originated toxins or biotoxins. Method of present invention makes it possible to analyze simultaneously several biotoxins in sample.

EFFECT: method of increased sensitivity.

8 cl, 3 dwg, 1 tbl, 6 ex

Description

FIELD OF THE INVENTION

The invention relates to analytical biochemistry and quantitative immunochemical analysis and for the quantitative detection of various biological toxins by the immunochemical method using three-dimensional microchips based on hydrogels.

The proposed method for the detection of biotoxins can be used in medicine, in the food industry, in environmental protection. Currently, the development of fast and sensitive methods for the analysis of biological toxins is becoming important due to the threat of bioterrorism, since many natural toxins can be used as components of biological weapons.

State of the art

Currently, many bacterial, plant and animal toxins that have a strong toxic effect on the human body are well known. The most powerful toxins produced by microorganisms include botulinum, tetanus and cholera toxins; of plant toxins, ricin and abrin are the most powerful. There are also many toxins secreted by poisonous animals: snakes, spiders, scorpions, etc. Most biotoxins are polypeptide in nature, however, low molecular weight compounds with high toxicity are also known, for example tetrodotoxin (acupuncture fish), T-2 toxin (fungi), blue-green algae toxins.

To identify and analyze both the toxins themselves and the organisms that produce them, various laboratory methods are currently used, including animal tests, microbiological methods, DNA analysis using PCR, immunological methods: direct and indirect radio immunological, immunofluorescence and enzyme immunoassay . The most sensitive, fast and convenient method of analyzing toxins is the immunochemical method using antibodies against toxins. The sensitivity of biotoxin immunoassay using the classic “spot” variant reaches 0.01-1 ng of substance in 1 ml of the test solution (for example, in the case of ricin [1], staphylococcal enterotoxin B [2], diphtheria toxin [3]).

[1] M.A. Poly, V. R. Rivera, J. F. Heevetson, G. A. Merril. Detection of ricin by colorimetric and chemiluminescence ELISA, Toxicon, 1994, 32, 1371-1377.

[2] M.A. Poly, V. R. Rivera, D. Neal. Sensitive and specific colorimetric ELISAs for Staphylococcus aureus enterotoxins A and B in urine and buffer, Toxicon, 2002, 40, 1723-1726.

[3] K.H. Engler, A. Efstratiou. Rapid enzyme immunoassay for determination of toxigenicity among clinical isolates of corynebacteria, J. Clin. Microbiol., 2004, 38, 1385-1389.

Traditional immunological methods do not allow a simultaneous test for the presence of several toxins in a sample, so there is a need to develop a quick, sensitive and effective method for simultaneous parallel analysis. Parallel analysis of samples for the presence of several compounds is achieved using microarrays - arrays of individual cells containing various probes (proteins, receptors, antibodies, antigens, etc.). Conducting a simultaneous analysis of the sample in many ways significantly increases the efficiency of the analysis, allows you to miniaturize the research and significantly reduces the amount of test material.

The use of chips of various designs for the detection of biological toxins is described. For the simultaneous immunological determination of biological toxins, a chip biosensor based on immobilized antibodies against biotoxins has been proposed [4].

[4] F. S. Ligler, C. R. Taitt, L. C. Shriver-Lake, K. E. Sapsford, Y.Shubin, J.P. Golden. Array biosensor for detection of toxins. Anal. Bioanal. Chem., 2003, 377, 469-477.

The biochip consisted of two elements (blocks). Channels with immobilized antibodies were located on the surface of the slide. Immobilization was carried out by the formation of a complex of avidin-biotinylated antibodies. Protein toxins were analyzed by sandwich analysis using a pair of appropriate antibodies. Solutions of antigens and fluorescently-labeled developing antibodies were supplied to the immobilized antibodies through channels on the second block, oriented perpendicular to the columns of immobilized antibodies. The fluorescent signals of the antibody-antigen-labeled antibody complexes were recorded using a confocal microscope. The limits of detection of toxins were 1.6 ng / ml for cholera toxin, 8 ng / ml for ricin, 40 ng / ml for botulinum toxin A, 4 ng / ml for staphylococcal enterotoxin B, 6.2 · 10 ⁴ CFU / ml for bacteria Bacillus globigii. This biosensor was also used for the detection of low molecular weight toxins by competitive immunoassay.

For direct immunoassay of fluorescein-labeled staphylococcal and cholera toxins, Nanogen (USA) has proposed electronic microarrays with immobilized antibodies [5].

[5] K. L. Ewalt, R. W. Haigis, R. Rooney, D. Axley, M. Krihak. Detection of biological toxins on an active electronic microchip, Anal. Biochem., 2001, 289, 162-172.

The biotinylated antibodies were immobilized on a microchip by the formation of avidin-biotin complexes on microsites containing avidin. Electrodes were connected to microsites, and biotinylated antibodies, as well as solutions of the analyzed toxins, were supplied under the influence of an electric field. In this case, the analysis experiments were carried out only with toxins into which a fluorescent label was previously introduced.

Biopraxis (USA) is developing a microarray technology in which Raman spectroscopy (Raman scattering) is used for signal detection [6].

[6] A. E. Grow, L. L. Wood, J. L. Claycomb, P. A. Thompson, New biochip technology for label-free detection of pathogens and their toxins, J. Microbiol. Methods, 2003, 53, 221-233.

Biomolecules, in particular anti-biotoxin antibodies, are immobilized on a metal surface at points with a diameter of about 1 micron. After processing the microchip with a solution containing the analyte, an antibody-antigen complex forms, which is detected by obtaining Raman spectra, from which the spectra of free antibodies are subtracted. The possibility of detecting B (1) and G (1) aflatoxins from a mixture is shown.

Three-dimensional microarrays based on polyacrylamide hydrogels were first developed at the IMB RAS [7].

[7] G.M. Ershov, A.D. Mirzabekov. Method of manufacturing a matrix for the detection of mismatches, US Patent No. 5770721.

At present, gel microarrays are obtained by copolymerization and polymerization immobilization methods [8, 9].

[8] A.D. Mirzabekov, A.Yu. Rubin, S.V. Pankov, B.K. Chernov. The method of immobilization of oligonucleotides containing unsaturated groups in polymer gels during the formation of a microchip. Patent N2175972, November 20, 2001 (B.I. 2001, N25).

[9] A.D. Mirzabekov, A.Yu. Rubin, S.V. Pankov. Method for polymerization immobilization of biological macromolecules and composition for its implementation. RF patent N2216547.

The technology for producing hydrogel microarrays includes preparing a substrate (glass, plastic, silicon) (1), applying a polymerization mixture containing gel components and immobilized substances in the form of droplets onto a substrate using a robot (2), photoinduced gel polymerization with the formation of gel elements containing immobilized probes (3). As a result, arrays of discrete gel elements are obtained, each of which contains an immobilized probe. Oligonucleotides, DNA, proteins, and various low molecular weight compounds can serve as probes [10-12]. It was shown that protein microarrays obtained by copolymerization can be used to study protein-protein interactions, in particular, antigen-antibody interactions, and immunochemical and enzymatic reactions [11, 12].

[10] A.YU.Rubina, S.V. Pankov, E.I. Dementieva, D.N. Penkov, A.V. Butygin, V.A. Vasiliskov, A.V. Chudinov, A.L. Mikheikin, V.M. Mikhailovich, A.D. Mirzabekov. Hydrogel drop microchips with immobilized DNA: properties and methods for large-scale production, Anal. Biochem., 2004, 325, 92-106.

[11] A.Yu. Rubina, S.V. Pankov, S.M. Ivanov, E.I. Dementieva, A.D. Mirzabekov. Protein microchips. Doc. Acad. Science, 2001, 381, 701-704.

[12] A.Yu.Rubina, EIDementieva, AAStomakhin, ELDarii, SVPan′kov, VEBarsky, SMIvanov, EVKonovalova, ADMirzabekov, Hydrogel-based protein microchips: manufacturing, properties, and applications, BioTechniques, 2003, 34, 1008-1022.

In the present invention, microchips based on three-dimensional hydrogels are used to develop a method for the quantitative detection of biological toxins.

disadvantages

The disadvantage of traditional immunological methods of analysis is the inability to simultaneously analyze several compounds, in particular biotoxins, in the sample. Multiple parallel analysis of several compounds is achieved using microchips.

The disadvantages of the methods for analyzing biological toxins on microchips described in the literature include the complex technology for manufacturing microchips: combining several blocks, connecting channels for supplying solutions, attaching electrodes. Signals are recorded using complex and expensive equipment: confocal microscope, Raman spectroscopy, etc. These disadvantages were overcome when developing a method for immunoassay of biological toxins using three-dimensional microchips based on hydrogels.

Disclosure of invention

The aim of the invention is to develop a method for the quantitative detection of biological toxins of bacterial, plant and animal origin, allowing simultaneous parallel analysis of several biotoxins in a sample with a sensitivity not equal to or greater than the sensitivity of standard immunological tests. This goal is achieved by developing a method for the quantitative detection of biological toxins using microchips based on hydrogels. Hydrogel elements with a diameter of 100-600 μm and a height of 30-100 μm, containing immobilized antibodies against biotoxins or biotoxins, were obtained by photo- or chemically induced polymerization and covalently attached to the surface of the substrate (glass, plastic or silicon). The proposed method includes the following stages:

a) the manufacture of a biological microchip, which is an ordered array of three-dimensional hydrogel cells on a solid substrate, containing immobilized antibodies to various biotoxins or biotoxins, wherein an antibody to an individual biotoxin or an individual biotoxin is immobilized in each individual cell;

b) incubation of the microchip in a reaction medium including a sample containing biotoxins to be analyzed for the formation of biotoxin-antibody immune complexes, which, if necessary, is carried out under stirring conditions;

c) detection of the resulting complex;

d) quantitative detection of the analyzed biotoxin.

When a reaction medium containing the analyzed sample (biotoxin) is applied to the microchip, the formation of immune complexes with specific ligands immobilized in the gel cells of the microchip occurs. Detection of the formed complex at stage c) and subsequent quantitative detection at stage d) are carried out in the format of direct, competitive or sandwich immunoassay.

For direct immunoassay, the reaction medium in step b) contains the analyzed biotoxin, which forms a specific complex with antibodies against this toxin immobilized on a chip.

Competitive analysis is carried out using a microchip with immobilized biotoxins or immobilized antibodies. In the first case, the reaction medium in stage b) additionally contains labeled antibodies to the analyzed biotoxin, and labeled antibodies compete for binding with biotoxin in solution and biotoxin immobilized on a microchip. In another embodiment of a competitive assay, the microchip contains immobilized antibodies, and the reaction medium in step b) additionally contains labeled biotoxin. There is a competition between labeled and unlabeled biotoxin for binding to immobilized antibodies.

In the case of a sandwich immunoassay, the microchip contains immobilized antibodies, the reaction medium in step b) contains the analyzed biotoxin, which forms a specific complex with antibodies immobilized on the chip. After complex formation, the microchip is developed with labeled antibodies specific for another epitope of the given biotoxin.

If necessary, stage b) is carried out under stirring conditions, which significantly reduces the analysis time.

Direct and competitive methods of analysis are possible both for protein toxins and for low molecular weight toxins. The sandwich variant of immunoassay is possible only for protein biotoxins, for which antibodies specific for different epitopes of the protein molecule can be obtained.

Immunoassay results are recorded using fluorescence, chemiluminescence, or mass spectrometry directly from the gel elements of the microchip. Antibodies or biotoxins may contain fluorescent labels or conjugates to proteins or other compounds capable of participating in reactions leading to light emission (chemiluminescence or bioluminescence). Mass spectral detection does not require the introduction of additional labels.

Quantitative detection of biotoxin is carried out by carrying out stages a) -c) with standard (reference) samples containing known concentrations of the analyzed biotoxin. The calibration dependence “microchip gel cell signal - biotoxin concentration” is built. After this stage a) -c) is carried out with the analyzed sample, and the concentration of the analyzed biotoxin in the sample is determined by the calibration dependence.

The proposed method allows simultaneous parallel analysis of several biotoxins in the sample. The microchip for parallel multiple analysis contains immobilized antibodies against several toxins and / or several immobilized biotoxins. An antibody to an individual biotoxin or an individual biotoxin is immobilized in each individual gel cell. After the microchip is incubated in a reaction medium including a sample containing several biotoxins to be analyzed, specific biotoxin-antibody immune complexes are formed. In the case of direct immunoassay, the reaction medium contains a sample comprising several toxins to be analyzed, and after incubation of the microchip with the sample, the signals of the microchip cells containing the corresponding immobilized antibody are recorded. For competitive analysis, the reaction medium in step b) further comprises a mixture of labeled antibodies to all of the analyzed biotoxins or a mixture of all of the analyzed labeled biotoxins. In the case of a sandwich immunoassay, the development of a microchip after incubation in a reaction medium including a sample is carried out with a mixture of labeled antibodies against all of the analyzed biotoxins.

The sensitivity of the proposed method for the detection of biological toxins is not inferior to the sensitivity of the spot version of the immunoassay, for example, the detection limit of ricin by sandwich immunoassay using gel microarrays was 0.1 ng / ml (Table 1).

The proposed method for the analysis of biotoxins based on the use of gel microarrays has a number of significant advantages over the microarrays described in the literature: the developed three-dimensional gel structure has a much greater capacity for immobilization compared to two-dimensional microarrays, which greatly increases the sensitivity of the analysis; in addition, immobilized proteins are in a hydrophilic environment and there is no contact with the hydrophobic surface of the substrate, which helps to preserve the biological activity of the immobilized molecules and ensures high storage stability.

Brief Description of the Figures

The invention is illustrated by the following figures, in which:

Figure 1 shows the results of ricin immunoassay on microarrays.

A. Direct immunoassay. The microchips contained gel elements with immobilized antibodies against ricin Rch1, 0.1 mg / ml. Dependence of the fluorescence intensity on the concentration of ricin labeled with Cy3 in solution.

B. Competitive analysis. Microchips contained gel elements with immobilized ricin, 0.05 mg / ml. Dependence of fluorescence intensity on the concentration of ricin in solution after incubation of ricin with a solution of Cy3-labeled antibodies 1RK2, 4 μg / ml.

B. Sandwich analysis with fluorescence registration. The microchips contained gel elements with immobilized antibodies against ricin Rch1, 0.1 mg / ml; microarrays after incubation with ricin solutions were developed with anti-ricin 1RK1 antibodies labeled with Cy3, 20 μg / ml. Dependence of fluorescence intensity on ricin concentration in solution. The box in FIG. 1B shows fluorescence signals at low ricin concentrations. The dashed line corresponds to fluorescence intensity 3 times higher than the scatter of the background signal; the ricin detection limit was 0.1 ng / ml.

G. Sandwich analysis with chemiluminescent registration. The microchips contained gel elements with immobilized antibodies against ricin 1RK2, 0.1 mg / ml; microarrays after incubation with ricin solutions showed biotinylated antibodies against ricin 2RK1 (40 μg / ml), an avidin peroxidase conjugate (45 μg / ml) and chemiluminescent peroxidase substrates. Dependence of the intensity of chemiluminescence on the concentration of ricin in solution.

Each point in the graphs is the average of four parallel measurements.

Figure 2 shows MALDI-TOF mass spectra of staphylococcal enterotoxin B obtained from gel cells of a microchip with immobilized monoclonal antibodies against this toxin S222, 0.1 mg / ml, after incubation of the microchip with a toxin solution. The concentration of biotoxin in a solution of 100 (A), 10 (B) and 1 (C) μg / ml.

Figure 3 presents the results of the simultaneous analysis of several biotoxins on one microchip. The microchips contained gel elements with immobilized monoclonal antibodies against staphylococcal toxin (S222), diphtheria toxin (7D9), tetanus toxin (3D2C6), lethal anthrax toxin factor (10EDG7), ricin (1RK1) and viscumin (TAS). Each antibody was immobilized in 4 gel cells at a concentration of 0.1 mg / ml. Fluorescence images were obtained after incubating the microchip with a solution of staphylococcal toxin (chip 1), diphtheria toxin (chip 2), tetanus toxin (chip 3), lethal factor anthrax toxin (chip 4), ricin (chip 5) and viscumin (chip 6) and manifestations with a mixture of Su3-labeled monoclonal antibodies against all 6 studied biotoxins (antibodies against staphylococcal enterotoxin B S643, antibodies against diphtheria toxin 2A3, antibodies against tetanus toxin 3D10B11, antibodies against lethal factor anthrax toxin 3B4 D9, antibodies against ricin Rch1, antibodies against viscumin MNA9). The concentration of biotoxins in a solution of 50 ng / ml (for each of the toxins), the concentration of each developing antibody in a mixture of 20 μg / ml, the total concentration of labeled antibodies in a mixture of 120 μg / ml.

The implementation of the invention

Hydrogel microchips for the quantitative detection of biological toxins are made by photo- or chemically induced radical polymerization using a patented technology [9]. The microchip is an ordered array of three-dimensional hydrogel cells on a solid substrate, containing immobilized antibodies to various biotoxins of bacterial, plant and animal origin, or immobilized biotoxins of various nature. An individual ligand is immobilized in each individual cell of the microchip. The binding of a ligand with a hydrogel matrix is possible both directly during its immobilization during gel formation, and through the formation of specific complexes of avidin (streptavidin) - biotin, for example, immobilized avidin - a biotinylated antibody, or immobilized nitrilotriacetic acid - a recombinant protein containing another recombinant protein .

As the ligands, antibodies of various types, all types of immunoglobulins (IgG, IgM, IgA, IgD, IgB), monoclonal antibodies, polyclonal antibodies, recombinant antibodies, various types of mini-antibodies, including Fab fragments and single chain antibodies (scFv and others), as well as low molecular weight biotoxins and biotoxins of protein nature. Ligands for the formation of a specific complex with the analyzed biotoxins can also be DNA or RNA aptamers capable of high-affinity interaction with the corresponding compound. For example, an RNA aptamer consisting of 31 nucleotides specific for ricin A chain [13] and DNA aptamers specific for cholera toxin and staphylococcal enterotoxin B [14] were obtained.

[13] J.R. Hesselberth, D. Miller, J. Robertus, A. D. Ellmgton. In vitro selection of RNA molecules that inhibit the activity of ricin A-chain, J. Biol Chem., 2000, 275, 4937-4942.

[14] J. G. Bruno, J. L. Kiel. Use of magnetic beads in selection and detection of biotoxin aptamers by electrochemiluminescence and enzymatic methods, Biotechniques, 2002, 32, 178-183.

The method of polymerization immobilization used for the manufacture of microchips allows one to obtain microchips containing immobilized DNA, RNA, and proteins [9-12].

The type of compounds used for immobilization depends on the analyzed object and the method of analysis (direct, competitive, sandwich analysis, etc.).

The method for quantitative detection of biotoxins using hydrogel microarrays includes the following steps:

a) the manufacture of a biological microchip, which is an ordered array of three-dimensional hydrogel cells on a solid substrate, obtained by photo- or chemically induced polymerization and containing immobilized antibodies to various biotoxins of bacterial, plant and animal origin or biotoxins, and an antibody to an individual is immobilized in each individual cell biotoxin or individual biotoxin;

b) incubation of the microchip in a reaction medium including a sample containing biotoxins to be analyzed for the formation of biotoxin-antibody immune complexes, which, if necessary, is carried out under stirring conditions;

c) detection of the resulting complex;

d) quantitative detection of the analyzed biotoxin.

As the reaction medium during the analysis, buffer solutions are used, which are usually used in immunoassays, for example, 0.01 M phosphate buffer, pH 7.2, containing 0.15 M NaCl, 0.05 M Tris-HCl, pH 7.4, and etc. To reduce nonspecific interactions, polyvinyl alcohol, bovine serum albumin and sucrose, milk powder proteins and others (the so-called "blocking buffers", which are well known to specialists in this field) are added to the reaction medium.

A method for the quantitative detection of biotoxins can be carried out in the form of various types of immunoassay, for example, direct, competitive and sandwich immunoassay (Example 1). For direct immunoassay, the microchip contains immobilized antibodies against the analyzed biotoxin, and the reaction medium in stage b) contains the analyzed biotoxin, which forms a specific immune complex with immobilized antibodies. In fluorescence registration, the analyzed biotoxin contains a fluorescent label; in chemiluminescent registration, biotoxin is a conjugate with a protein or other compound capable of participating in reactions leading to light emission (chemiluminescence or bioluminescence). The recorded fluorescent or chemiluminescent signal of the microchip cells with immobilized antibodies is proportional to the concentration of biotoxin (Example 1, Fig. 1A). Methods for introducing a fluorescent label or for conjugating to a protein or other compound are well known in the art. In particular, the procedures described in G. T. Hermanson, Bioconjugate Techniques, Academic Press, San Diego, 1996 can be used. In the case of mass spectral detection, no additional label is required.

Competitive analysis is carried out using a microchip with immobilized biotoxins or immobilized antibodies. In a first embodiment, the reaction medium in step b) further comprises fluorescently-labeled antibodies to the biotoxin to be analyzed (or corresponding antibody conjugates). The reaction mixture is incubated with a standard or assayed sample before application to the microchip. When the microchip is incubated with the reaction mixture, labeled antibodies compete for binding to the biotoxin in solution and the biotoxin immobilized on the microchip. The recorded fluorescent or chemiluminescent signal of the microchip cells with immobilized biotoxins is the higher, the lower the concentration of the analyzed toxin in the sample (Example 1, Fig.1B)

In another embodiment of a competitive assay, the microchip contains immobilized antibodies, and the reaction medium in step b) further contains a fluorescently-labeled biotoxin (or the corresponding biotoxin conjugate). There is a competition between labeled and unlabeled biotoxin for binding to immobilized antibodies. The recorded fluorescent or chemiluminescent signal of the microchip cells with immobilized antibodies is the higher, the lower the concentration of the analyzed toxin in the sample.

In the case of a sandwich immunoassay, the microchip contains immobilized antibodies, the reaction medium in step b) contains the analyzed biotoxin, which forms a specific complex with antibodies immobilized on the chip. After complex formation, the microchip is developed with fluorescently-labeled antibodies (or corresponding antibody conjugates) specific for another epitope of the given biotoxin. The recorded fluorescent or chemiluminescent signal of the microchill cells with immobilized antibodies is proportional to the concentration of biotoxin (Example 1, Fig. 1B, D).

Direct and competitive microchip assays can be performed for toxins of both protein nature and low molecular weight toxins. The sandwich variant of immunoassay is possible, as a rule, only for protein biotoxins, for which antibodies specific for different epitopes of the protein molecule can be obtained (immobilized binding antibodies and showing labeled antibodies).

Quantitative detection of biotoxins is carried out by carrying out stages a) -c) with known concentrations of the analyzed biotoxin and constructing a calibration dependence by which the amount of the analyzed biotoxin in the sample is determined. For all analysis options, a calibration graph is plotted for the intensity of the fluorescent or chemiluminescent signal of the corresponding gel cells of the microchip on the known concentrations of biotoxin in a standard (reference) solution. The unknown concentration of biotoxin in the sample is determined from the calibration curve by the value of the signal intensity obtained after the interaction of the analyzed sample with a microchip. The biotoxin detection limit is defined as the concentration corresponding to the intensity of the fluorescent / chemiluminescent signal, 3 times the spread of the background signal.

The results of the immunoassay of biotoxins using gel microarrays can be recorded by several methods: by fluorescence intensity; by chemiluminescence intensity; mass spectrometry directly from the gel elements of the microchip.

When recording results on the fluorescence intensity, antibodies against biotoxins and biotoxins labeled with fluorescent dyes, for example, such as Texas Red, tetramethylrodamine, fluorescein, cyanine 3 and 5 (Cy3, Cy5), are used, but not limited to them. The registration of fluorescence signals from the cells of the microchip is carried out using fluorescence microscopes or scanning microscopes of various types, allowing you to record the signal from the used fluorescent label.

When recording results on the intensity of chemiluminescence, conjugates of antibodies, biotoxins or avidin are used (for biotinylated proteins), for example, with such enzymes as horseradish peroxidase, alkaline phosphatase, β-galactosidase, luciferase, but not limited to them, giving chemiluminescent signals as a result of the corresponding enzyme reactions, for example, peroxidase-catalyzed oxidation of luminol by hydrogen peroxide. Chemiluminescent signals are recorded using CCD cameras or other recording devices, in particular fluorescence microscopes with the excitation light source turned off.

To register the results using MALDI-TOF mass spectrometry, a technique was developed for obtaining MALDI TOF mass spectra directly from the gel cells of the microchip. The procedure for recording the analysis results in this case includes processing the microchip with a solution that destroys the complex formed by the biotoxin under study with an antibody against this toxin immobilized on a chip (biotoxin is eluted from the microchip cell), direct mass spectral analysis directly from the gel element and identification of biotoxin by its molecular weight (Example 2, Figure 2).

Example 3 shows the results of an immunoassay of 6 different biological toxins on hydrogel microarrays. The method of quantitative detection of biotoxins using hydrogel microarrays is characterized by high sensitivity, not inferior to the sensitivity of standard immunological methods: for ricin, the detection limit was 0.1 ng / ml.

The proposed method for the quantitative detection of biotoxins using hydrogel microarrays allows simultaneous parallel analysis of samples for the presence of several toxins, which dramatically increases the detection efficiency and significantly reduces the amount of test material: 20 μl of the test sample is sufficient for analysis. The microchip for parallel multiple analysis contains immobilized antibodies against several toxins and / or several immobilized biotoxins. In the case of direct immunoassay, the reaction medium contains a sample comprising one or more of the analyzed toxins, and after incubation of the microchip with the sample, the signals of the microchip cells containing the corresponding immobilized antibodies are recorded. For competitive analysis, the reaction medium in step b) further comprises a mixture of labeled antibodies to all of the analyzed biotoxins or a mixture of all of the analyzed labeled biotoxins. In the case of a sandwich immunoassay, the manifestation of the microchip after incubation in the reaction medium containing the sample is carried out with a mixture of labeled antibodies against all of the analyzed biotoxins. Example 4 demonstrated the simultaneous sandwich analysis of 6 different biological toxins on a single microchip during the development of the microchip with a mixture of 6 fluorescently-labeled antibodies. The sensitivity of the parallel analysis was no less than the sensitivity for determining one toxin.

If necessary, the stage of incubation of the microchip in a reaction medium including a sample containing the biotoxins to be analyzed (stage b) is carried out under stirring conditions, which significantly reduces the analysis time (Example 5). Mixing can be carried out, for example, by switching the direction of flow of the reaction solution from direct to reverse using various types of pumps, ultrasound, electrophoresis, but not limited to these methods.

The advantage of hydrogel microchips in comparison with the two-dimensional chips described in the literature is the hydrophilic environment of molecules immobilized in the gel and the absence of contact with the hydrophobic surface of the substrate, which is especially important for protein molecules. The hydrophilic environment helps to preserve the biological activity of proteins and enzymes and ensures their stabilization during storage. Microchips with immobilized antibodies are stable for at least six months when stored in the presence of glycerol at 10 ° C (Example 6).

The invention is further illustrated by specific embodiments, which are provided for illustrative purposes only. The examples cited are not intended to be exhaustive or to limit the invention to the particular forms disclosed, and it is obvious that many modifications and variations are possible without departing from the spirit of the invention and without departing from the scope of the claims.

Example 1. Quantitative immunoassay of ricin using hydrogel microarrays

Hydrogel microarrays containing immobilized antibodies against ricin and ricin were obtained using the previously patented technology of polymerization immobilization [9]. To reduce nonspecific interactions in all assays, microarrays were preincubated in 0.01 M phosphate buffer, pH 7.2, containing 0.15 M NaCl, 1% polyvinyl alcohol (PVA-50) or 3% bovine serum albumin (BSA) and 4% sucrose (“blocking buffer”), 2 hours at room temperature. Before analysis, the solutions of ricin (sample) were diluted with 0.01 M phosphate buffer, pH 7.2, containing 0.15 M NaCl, 0.15% PVA-50 and 0.15% polyvinylpyrrolidone 360 (PVP-360).

Direct immunoassay. To microchips containing gel elements with immobilized monoclonal antibodies against ricin Rch1 and other biotoxins (antibodies against staphylococcal enterotoxin B S222, antibodies against tetanus toxin 3D2C6, antibodies against diphtheria toxin 7D9, 0.1 mg / g antibody immobilized to control cross-reactions in g ml), 20 μl of solutions of ricin labeled with Cy3 were added and kept at 10 ° С overnight. After washing the microchips with 0.01 M phosphate buffer, pH 7.2, 0.15 M NaCl, 0.1% Tween-20 (15 min, room temperature), the intensity of the fluorescent signals of the gel elements of the microchips was measured.

For competitive analysis, a microchip with immobilized ricin (0.1 mg / ml) was used. A solution containing detectable ricin was incubated with a solution of Cy3-labeled anti-ricin 1RK2 monoclonal antibody (4 μg / ml) for 2 hours at 37 ° C with stirring. The mixture (20 μl) after incubation was applied to the microchip and kept for 2 hours at 37 °. After washing (0.01 M phosphate buffer, pH 7.2, 0.15 M NaCl, 0.1% Tween-20, 15 min, room temperature), the intensity of the fluorescent signals was measured.

In the sandwich version of the immunoassay, microarrays were made with immobilized monoclonal antibodies against ricin 1RK2 and other biotoxins (antibodies against staphylococcal enterotoxin B S222, antibodies against tetanus toxin 3D2C6, antibodies against diphtheria toxin 7D9, for the control of cross-linking antibodies 0.1 g ( mg / ml), 20 μl of ricin solution was added and the chips were incubated at 10 ° C overnight After short-term (15 min) washing with 0.01 M phosphate buffer, pH 7.2, 0.15 M NaCl, 0.1% Twin-20, mic the plots showed Cy3-labeled 1RK1 antibodies specific for another epitope of antigen, 20 μg / ml (fluorescence detection), 40 min, room temperature. After washing (0.01 M phosphate buffer, pH 7.2, 0.15 M NaCl, 0.1% Tween-20, 15 min, room temperature), the intensity of the fluorescent signals was measured.With chemiluminescent detection, 20 μl of biotinylated anti-ricin 2RK1 antibodies with a concentration of 40 μg / ml were applied to the microchip after interaction with ricin, and then 20 μl of Avidin C conjugate horseradish peroxidase with a concentration of 45 μg / ml and chemiluminescent s substrates of peroxidase (luminol, H ₂ O _2); a chemiluminescent signal was detected for 60 seconds.

Antibodies against ricin and ricin labeled with Cy3, as well as biotinylated antibodies and the avidin peroxidase conjugate, were obtained by known methods described, for example, in [15].

[15] G. T. Hermanson, Bioconjugate Techniques, Academic Press, San Diego, 1996.

To measure fluorescent signals, a fluorescence microscope equipped with a CCD camera and computer programs for image visualization and processing of the obtained data was used, developed at the biochip laboratory of the IMB RAS [16].

[16] V. Barsky, A. Perov, S. Tokalov, A. Chudinov, E. Kreindlin, A. Sharonov, E. Kotova, A. Mirzabekov. Fluorescence data analysis on gel-based biochips, J. Biomol. Screening, 2002, 7, 247-257.

The microscope allows you to simultaneously analyze data from all elements of the microchip and to obtain two-dimensional and three-dimensional images of the fluorescent signal from the gel elements. The chemiluminescent signals were measured using the same fluorescence microscope with the excitation source turned off.

For all analysis options, a graph of the dependence of the fluorescence intensity or chemiluminescence on the concentration of ricin in solution was constructed (Figure 1). The ricin detection limit was calculated as the concentration corresponding to the signal intensity, 3 times the background signal spread.

For direct analysis of ricin, a dependence of the fluorescence intensity of the microarray gel cells on the concentration of Cy3-labeled ricin in the concentration range of 0.2-500 ng / ml was observed, a linear dependence was observed in the concentration range of 0.2-60 ng / ml (Fig. 1A), limit detection rate was 0.2 ng / ml.

In the case of competitive analysis, the fluorescence intensity of the gel cells of the microarray was inversely proportional to the concentration of ricin in the solution (Fig. 1B), and the detection limit was 4 ng / ml.

Calibration plots for ricin sandwich analysis with fluorescence and chemiluminescent detection are shown in Figs. 1B and D. The dependence of the fluorescence intensity and chemiluminescence of the microarray gel cells on the ricin concentration was observed in the range of ricin concentrations of 0.1-500 ng / ml (fluorescent 0 7-500 ng / ml (chemiluminescent detection). The inset in Fig. 1B illustrates the determination of the detection limit: the dashed line corresponds to a fluorescence intensity three times the background signal spread, so the lowest ricin concentration reliably determined by this method is 0.1 ng / ml. For enzyme-linked immunosorbent assay of ricin on a microchip with chemiluminescent detection, the detection limit was 0.7 ng / ml.

Under these conditions of the analysis, in particular, with the microchip blocking and washing procedures used by us, nonspecific signals, i.e., signals from microchip cells containing antibodies to other toxins, did not differ from background or from signals of empty gel elements.

Example 2. Identification of proteins on the gel element of the microarray by direct mass spectral analysis. Direct analysis of staphylococcal enterotoxin B on a microchip with mass spectral registration

A microchip was prepared containing immobilized monoclonal antibodies to staphylococcal enterotoxin B S222 in gel cells (0.1 μg of antibody / gel cell). After polymerization, the microchip was washed with 0.01 M phosphate buffer containing 0.15 M NaCl, 0.1% Tween-20, with stirring for 1 h (20 ° C). The microchip was incubated with a solution of staphylococcal enterotoxin in 0.01 M phosphate buffer, pH 7.2, containing 0.15 M NaCl (20 h, 20 ° C), and then washed from a protein that was not specifically bound to the gel, first by treatment with 0.01 M phosphate buffer, pH 7.2, containing 0.15 M NaCl, 0.1% Tween-20 (2 hours with stirring, 20 ° C), then with water. Prior to mass spectral analysis, the antigen-antibody complex was destroyed and the antigen was eluted onto the gel surface by adding 1 μl of a saturated MALDI monitoring matrix solution (sinapic acid) in a solution of 10% formic acid in 30% aqueous acetonitrile to each microarray cell. The microchip was kept for 20 min at room temperature in a humid chamber, then dried on a heating table at 40 ° C.

Mass spectra obtained directly from the gel elements of the microchip, after interaction with staphylococcal toxin solutions of various concentrations, are shown in FIG. 2. Staphylococcal enterotoxin B was identified by its molecular weight of 28,400 Da. As can be seen from the drawing, there is a quantitative correlation between the absolute intensity of the peaks of molecular ions and the concentration of enterotoxin in the concentration range of 1-100 μg / ml. Mass spectra from gel cells that did not contain antibodies to this toxin, but incubated with antigen solution, did not contain the above peaks.

Example 3. Quantitative immunoassay of various biological toxins using hydrogel microarrays

The results of the quantitative immunoassay of various biological toxins on gel microarrays obtained by polymerization immobilization are shown in Table 1. In addition to the immunoassay of ricin described in Example 1, an analysis was made of viscumin, staphylococcal enterotoxin B, tetanus toxin, diphtheria toxin and lethal factor sib. Direct, competitive and sandwich immunoassays with fluorescence and chemiluminescent registration were performed according to the methods described in Example 1 using the antibodies indicated in Table 1. Table 1 also shows the concentration range at which the dependence of the intensity of the fluorescent or chemiluminescent signal of the microarray gel cells was observed. on the concentration of biotoxin; the lower limit of the interval corresponds to the detection limit calculated as described in Example 1.

Example 4. Simultaneous analysis of several biotoxins on one microchip

The main advantage of microchips over traditional methods of immunoassay is the possibility of quantitative analysis of samples simultaneously for the presence of several antigens. Microchips were obtained with gel elements containing immobilized antibodies to 6 biotoxins (ricin, viscumin, staphylococcal enterotoxin B, tetanus toxin, diphtheria toxin, lethal factor of anthrax toxin). After incubation of the microchip with a solution containing one of the studied toxins, the microchip was developed with a mixture of Cy3-labeled secondary antibodies against all 6 toxins (Figure 3). Antibody pairs for parallel analysis of several toxins were selected so that non-specific interaction with other toxins and antibodies was minimal. For example, in the case of parallel analysis, anti-ricin antibodies 1RK1 were used as immobilized, and Rch1 antibodies were used as developing ones, and not vice versa, as in Example 1 for sandwich analysis, since the immobilized Rch1 antibodies gave nonspecific signals with Cy3-labeled antibodies against staphylococcal enterotoxin B SEB 643. Bright fluorescent signals were observed in gel elements containing the corresponding antibodies. The detection limits of biotoxins for parallel analysis were the same as in the determination of each toxin separately (Table 1).

Example 5. Acceleration of immunoassay of biotoxin when using the stirring of the analyzed sample

A ricin sandwich immunoassay was performed as described in Example 1, but microarrays were incubated with ricin solutions for 1 hour with stirring. Stirring was carried out using a peristaltic pump. For this, the microchip was placed in a flow chamber with a volume of 50 μl, equipped with tubes for supplying the sample. The chamber was attached to a peristaltic pump, and 100 μl of ricin solution was placed in the system. The sample was mixed by switching the flow direction from the forward to the reverse every 2 seconds; flow rate was 1.5 ml / min. Simultaneously, an analysis was carried out with stirring on 6 microchips, i.e. measurement of 6 samples with various ricin concentrations. After incubation, the microarrays were developed with Cy3-labeled secondary antibodies against ricin. The calibration schedule for determining ricin by a sandwich immunoassay method with stirring for 1 h was similar to the calibration schedule for a sandwich analysis with incubation overnight without stirring (Fig. 1B). Thus, the implementation of the mixing of the sample significantly reduced the time of immunoassay using microarrays.

Example 6. Stability of hydrogel microarrays with immobilized antibodies

Microchips with immobilized anti-ricin antibodies were made as described in Example 1. The microchips were stored at 10 ° C. in a humid chamber in the presence of 20% glycerol. A sandwich analysis of ricin with fluorescence registration was carried out, a calibration curve was constructed "fluorescence signal intensity - concentration of ricin in solution" and the detection limit of ricin was determined as described in Example 1. The detection limit of ricin on microchips after 6 months of storage was 0.1 ng / ml, i.e. the same as for microchips immediately after manufacture. Thus, microchips with immobilized antibodies fully retain their activity for at least 6 months of storage. The results of quantitative immunoassay of various biotoxins on a microchip are shown in the table.

Table
The results of quantitative immunoassay of various biotoxins on a microchip Biotoxin Type of analysis (signal recording) Antibodies The range of concentrations for analysis on microarrays, ng / ml Detection limit for standard test systems, ng / ml Ricin Direct analysis (fluorescence) Rch1 (immobilized) 0.2-500 0.1 Competitive analysis (fluorescence) 1RK2-Cu3 4-1000 Sandwich analysis (fluorescence) Rch1 (immobilized), 1RK1-Cy3 (developing) 0.1-500 Sandwich analysis (chemiluminescence) 1RK2 (immobilized), 2KK1-biotin + avidin-HRP (developing) 0.7-500 Viscumin Sandwich analysis (fluorescence) TAS (immobilized), MNA9-Cu3 (developing) 2-1000 0.08-5.0 Staphylococcal Enterotoxin B Direct analysis (fluorescence) S222 (immobilized) 50-20000 0.01-1.0 Sandwich analysis (fluorescence) S222 (immobilized), S643-Cu3 (developing) 1-300 Tetanus toxin Sandwich analysis (fluorescence) 3D2C6 (immobilized), 3D10B11-Cu3 (developing) 10-1000 one hundred Diphtheria toxin Direct analysis (fluorescence) 2A3 (immobilized) 12-25000 0.1-5.0 Sandwich analysis (fluorescence) 4C7 (immobilized), 2A3-Su3 (developing) 1-500 Lethal factor of anthrax toxin Direct analysis (fluorescence) 8D5B11 (immobilized) 20-20000 500 Sandwich analysis (fluorescence) 10EDG7 (immobilized), 3B4D9-Cy3 (developing) 4-4000 Sandwich analysis (chemiluminescence) 10EDG7 (immobilized), 3B409-biotin + avidin-HRP (developing) 6-1000

Claims (9)

1. A method for the quantitative detection of biotoxins in a sample, comprising a) the manufacture of a biological microchip, which is an ordered array of three-dimensional hydrogel cells on a solid substrate, obtained by photo- or chemically induced polymerization and containing immobilized antibodies to various biotoxins of bacterial, plant and animal origin or biotoxins, and an antibody to an individual is immobilized in each individual cell biotoxin or individual biotoxin; b) incubation of the microchip in a reaction medium including a sample containing biotoxins to be analyzed for the formation of biotoxin-antibody immune complexes, which, if necessary, is carried out under stirring conditions; c) detection of the resulting complex; d) quantitative detection of the analyzed biotoxin. 2. The method according to claim 1, in which the immobilized antibodies are antibodies selected from the group of antibodies to ricin, viscumin, staphylococcal enterotoxin B, tetanus toxin, diphtheria toxin, lethal factor anthrax toxin. 3. The method according to claim 1, in which the immobilized biotoxins are biotoxins selected from the group comprising ricin, viscumin, staphylococcal enterotoxin B, tetanus toxin, diphtheria toxin, lethal factor anthrax toxin. 4. The method according to claim 1, in which the detection of the formed complex in stage c) and subsequent quantitative detection in stage g) is carried out in the format of direct immunoassay. 5. The method according to claim 1, wherein the reaction medium in step b) further comprises antibodies to biotoxin, and the detection of the complex formed between the biotoxin immobilized on the microchip and the antibody against this biotoxin in step c) and subsequent quantitative detection in step d) are carried out in competitive immunoassay format. 6. The method according to claim 1, in which the reaction medium in stage b) additionally contains labeled biotoxin, and the detection of the formed complex between the antibody immobilized on a microchip and biotoxin in stage c) and subsequent quantitative detection in stage d) are carried out in the format of competitive immunoassay. 7. The method according to claim 1, in which the detection of the formed complex in stage c) and subsequent quantitative detection in stage g) is carried out in the format of a sandwich immunoassay. 8. The method according to claim 1, in which the quantitative detection of biotoxin is carried out by carrying out stages a) -c) with known concentrations of the analyzed biotoxin and constructing a calibration dependence by which the amount of the analyzed biotoxin in the sample is determined. 9. The method according to claim 1, in which at the stage c) the detection of the formed complex is carried out fluorimetrically, chemiluminometrically or mass spectrometrically.

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