JP2011027552A - Method for inhibition of fine particle aggregation, and preservative solution - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method that facilitates inhibiting aggregation which occurs during fine particles are preserved, and reduces variations in signal intensity caused by the aggregation. <P>SOLUTION: In the method, a solution of PEG having an average molecular weight of ≥2M is added to a fine particle suspension to inhibit the aggregation of fine particles. The fine particle preservative solution contains PEG having an average molecular weight of ≥2M. The fine particles are magnetic fine particles, and the particle diameter of the fine particles is ≤1 μm. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method and a storage solution for suppressing aggregation of fine particles, and more specifically to a method and a storage solution for suppressing aggregation of magnetic particles.

  For clinical tests and genetic tests, use clinical specimens such as blood, urine, and stool collected from patients as starting materials and measure the abundance and biochemical characteristics of the biological components to be tested to provide diagnostic indicators It is an object. However, clinical specimens contain a wide variety of contaminants, which may hinder the detection of the target component that is the subject of inspection and reduce the accuracy of the test results.

  Therefore, in recent years, in order to isolate and concentrate target components from clinical specimens, pretreatment techniques using magnetic fine particles in which molecules such as antibodies that specifically bind to target components are bound to the surface have been widely used. It is coming. Magnetic fine particles have a high contact frequency with a target component even in a liquid sample containing a large amount of impurities, and can efficiently adsorb and isolate the target component. In addition, magnetic fine particles can be separated by B / F by magnetism, and it is not necessary to use a large device such as a centrifuge, which is effective for application to an automation device. In the clinical laboratory field, aiming at the development of a highly sensitive assay, it is desired to reduce the reaction time and improve the sensitivity with fine particles. In general, the fine particles have a problem that the signal intensity decreases due to agglomeration of the particles during storage and a decrease in surface area. Further, since aggregation proceeds during storage, there is a problem that the degree of aggregation varies depending on the use time of the fine particles, the surface area of the aggregates varies, and a highly reproducible result cannot be obtained.

  As a means for solving the problems caused by aggregation of particles having a particle diameter of 0.01 to 100 μm, in Patent Document 1 (hereinafter referred to as Conventional Example 1), “Need to perform treatment to suppress non-specific reaction, natural aggregation, etc.” If there is a protein, such as bovine serum albumin (BSA), casein, gelatin, ovalbumin, or a salt thereof, on the inner wall surface or particle of the solution storage part of the container in which the specific binding substance for the substance to be measured is immobilized, It may be treated by a known method such as bringing a surfactant or nonfat dry milk into contact, and a blocking treatment (masking treatment) of a carrier on which a specific binding substance for the substance to be measured is immobilized may be performed. Is described.

  In Non-Patent Document 1 (hereinafter, Conventional Example 2), PEG having a molecular weight of 2000 to 5000 is modified on the surface of magnetic fine particles having a particle size of 2.2 μm to enhance the dispersibility of the particles.

  The conventional example 1 has the following problems. Conventional Example 1 shows the effect of blocking treatment on latex particles, but the effect on particles other than latex particles is unknown. Moreover, it is not disclosed how much aggregation is suppressed by the blocking treatment. Furthermore, in latex particles that have undergone blocking treatment, it is considered that the surface of the particles is covered with the blocking agent, and the latex particle surface is modified with an active group or linker for binding to biological substances, etc. However, there is a possibility that the formed coating acts to inhibit the binding reaction of biological substances and the like, and the surface active groups and linkers are apparently reduced.

  The dispersibility of the particles described in Conventional Example 2 is merely evaluated by the sedimentation of particles when the antigen is added in the immunoprecipitation reaction, and is evaluated for the aggregation that occurs during storage of the particles. Does not go. In addition, when using particles in which PEG is not modified on the surface, a step of modifying with PEG is necessary before using the particles. Compared to the case where the particles are simply added as in Conventional Example 1, the labor and time are reduced. It is not a simple method.

  In the case of fine particles having a particle size of 1 μm or less, the surface area per unit weight is larger than the particles having a particle size of more than 1 μm as shown in the conventional example, so that the number of contact between the fine particles is increased, and aggregation is likely to occur. . Therefore, development of a storage solution that suppresses aggregation of fine particles during storage and does not affect the reactivity of the fine particles is desired.

JP2006-227027

Nagasaki Y, Kobayashi H, Katsuyama Y, Jomura T, Sakura T .; Enhanced immunoresponse of antibody / mixed-PEG co-immobilized surface construction of high-performance immunomagnetic ELISA system, J Colloid Interface Sci, 309, 524-530, 2007

  An object of the present invention is to provide a method for efficiently suppressing aggregation occurring during storage of fine particles and maintaining the reactivity of the fine particles.

  The present inventors have found that aggregation occurring during storage of fine particles can be suppressed by adding polyethylene glycol (PEG) having a weight average molecular weight of 2,000,000 (2M), and have completed the present invention.

That is, the present invention includes the following inventions.
(1) A method for suppressing aggregation of fine particles, the method comprising adding a solution of polyethylene glycol having a weight average molecular weight of 2,000,000 or more to a suspension containing fine particles.
(2) The method according to (1), wherein the fine particles are magnetic fine particles.
(3) The method according to (1) or (2), wherein the particle diameter of the fine particles is 1 μm or less.
(4) The method according to any one of (1) to (3), wherein the final concentration of polyethylene glycol is 0.05 to 1 w / v%.
(5) A fine particle preservation solution for suppressing aggregation of fine particles, wherein the preservation solution contains polyethylene glycol having a weight average molecular weight of 2,000,000 or more.
(6) The preservation solution according to (5), wherein the fine particles are magnetic fine particles.
(7) The preservation solution according to (5) or (6), wherein the fine particles are fine particles having a particle diameter of 1 μm or less.
(8) The preservation solution according to any one of (5) to (7), wherein the polyethylene glycol concentration is 0.1 to 5.0 w / v%.
(9) A reaction method comprising a step of adding fine particles stored using the storage solution according to any one of (5) to (8) to the reaction solution.
(10) A step of washing the fine particles stored using the storage solution according to any one of (5) to (8) to remove the storage solution and a step of adding the fine particles from which the storage solution has been removed to the reaction solution. , Reaction method.
(11) A fine particle suspension containing fine particles and polyethylene glycol having a weight average molecular weight of 2,000,000 or more.
(12) The fine particle suspension according to (11), wherein the fine particles are magnetic fine particles.
(13) The fine particle suspension according to (11) or (12), wherein the particle diameter of the fine particles is 1 μm or less.
(14) The fine particle suspension according to any one of (11) to (13), wherein the polyethylene glycol concentration is 0.05 to 1 w / v%.
(15) The fine particle suspension according to any one of (11) to (14), wherein the fine particles have a surface modification for binding a biological substance.

  According to the present invention, aggregation occurring in fine particles can be easily suppressed, and furthermore, variation in measurement results caused by aggregation can be reduced.

It is a figure which shows the ratio of the monodispersed particle at the time of preserve | saving with the preservation | save liquid containing PEG. It is a schematic diagram of the immunoenzyme reaction which is one Embodiment of this invention. The experimental flow of Example 1 is shown. FIG. 2 is a graph showing the ratio of monodispersed fine particles used in Example 1. FIG. 3 shows the results of the immunoenzyme reaction of Example 1. The experimental flow of Example 2 is shown. 5 is a graph showing the proportion of finely dispersed monodispersed particles used in Example 2. FIG. FIG. 3 is a graph showing the results of the immunoenzymatic reaction of Example 2.

  The present invention relates to a method for suppressing aggregation of fine particles, and the method includes adding a solution of polyethylene glycol having a weight average molecular weight of 2,000,000 or more to a suspension containing fine particles. By adding a polyethylene glycol solution having a weight average molecular weight of 2,000,000 or more to a suspension containing fine particles, aggregation of the fine particles can be suppressed during storage of the fine particle suspension. Therefore, in other words, the present invention relates to a method for preserving a fine particle suspension, which comprises adding a solution of polyethylene glycol having a weight average molecular weight of 2,000,000 or more to a suspension containing fine particles.

  The target fine particles in the method of the present invention are not particularly limited, but those that are insoluble in water and do not melt during heat denaturation are preferred. Examples of the material include metals such as gold, silver, copper, iron, iron oxide, aluminum, tungsten, molybdenum, chromium, platinum, titanium, and nickel; alloys such as stainless steel, hastelloy, inconel, monel, and duralumin; Silicon: Glass materials such as glass, quartz glass, fused silica, synthetic quartz, alumina, sapphire, ceramics, forsterite and photosensitive glass; polyester resin, polystyrene, polyethylene resin, polypropylene resin, ABS resin (Acrylonitrile Butadiene Styrene resin), Plastics such as nylon, acrylic resin, fluororesin, polycarbonate resin, polyurethane resin, methylpentene resin, phenol resin, melamine resin, epoxy resin and vinyl chloride resin; agarose, dextran, cellulose, polyvinyl Examples include alcohol, nitrocellulose, chitin, and chitosan. In particular, the present invention is preferably directed to magnetic particles that can be collected from iron or iron oxide. When magnetic fine particles are used, fine particles can be recovered by magnetic separation, which is advantageous in terms of easy handling.

  The fine particles may have any shape, and examples thereof include a polyhedron, a polygonal column, a sphere, a cylinder, and a cone. The size of the fine particles is preferably 1 μm or less, more preferably 0.5 to 1.0 μm. Here, the particle diameter refers to the average particle diameter, and when the fine particles are not spherical, the particle diameter refers to the length of the longest side.

  The method of the present invention is particularly preferably used for fine particles for capturing biological substances. The microparticles for capturing the biological material preferably have a surface modification for binding the biological material. Biological substances include nucleic acids (including DNA and RNA), proteins, peptides, oligopeptides, polypeptides, sugars, cells, and the like. The surface modification on the microparticle is not particularly limited, and a biological substance can be covalently bonded, ionic bond, hydrogen bond, physical adsorption, biological bond (for example, binding of biotin and avidin or streptavidin, binding of antigen and antibody) Etc.) for surface binding. Specific examples include introduction of active groups that bind amino groups, hydroxyl groups, carboxyl groups, mercapto groups, etc., and coating with proteins such as protein A, protein G, monoclonal antibodies, polyclonal antibodies, avidin and streptavidin. It is done.

  For example, by introducing an active group such as an active ester group, an epoxy group, an aldehyde group, a carbodiimide group, an isothiocyanate group or an isocyanate group into the fine particles, a covalent bond can be formed with the amino group of the biological substance. In addition, by introducing an active group such as an active ester group, a maleimide group or a disulfide group into the fine particles, a covalent bond can be formed with a mercapto group of a biological material. Examples of the active ester group include a p-nitrophenyl group, an N-hydroxysuccinimide group, a succinimide group, a phthalimide group, and a 5-norbornene-2,3-dicarboximide group.

  One method for introducing an active group onto the surface of the fine particles is to treat the fine particles with a silane coupling agent having a desired active group. Examples of coupling agents include γ-aminopropyltriethoxysilane, N-β- (aminoethyl) -γ-aminopropyltrimethoxysilane, N-β- (aminoethyl) -β-aminopropylmethyldimethoxysilane, Alternatively, γ-glycidoxypropyltrimethoxysilane and the like can be mentioned. Another method for introducing the active group into the fine particles includes plasma treatment. By such plasma treatment, functional groups such as hydroxyl groups and amino groups can be introduced on the surfaces of the fine particles. The plasma treatment can be performed using an apparatus known to those skilled in the art.

  Examples of a method of binding a biological material to the fine particles by physical adsorption include a method of electrostatically binding the fine particles surface-treated with a polycation (polylysine, polyallylamine, polyethyleneimine, etc.) using the charge of the biological material. It is done.

  The method of the present invention is also suitably used for fine particles for use in biological material detection tests. The biological material detection test refers to a test for detecting a biological material contained in a sample such as a specimen, and preferably includes separating a specific biological material and / or detecting an interaction between biological materials. The interaction between biological materials includes interactions between biological materials and interactions between biological materials and other materials, such as interactions between proteins, interactions between proteins and polypeptides, interactions between nucleic acids. Effects, protein-nucleic acid interactions, protein-compound interactions, and the like, preferably specific interactions between biological materials. More specifically, hybridization between nucleic acid complementary strands, reaction between antigen and antibody or fragment thereof, binding reaction between enzyme and substrate or inhibitor, binding reaction between ligand and receptor, binding reaction between avidin and biotin, nucleic acid And transcription factor binding reaction, cell adhesion factor binding reaction, sugar chain and protein binding reaction, fatty chain and protein binding reaction, phosphate group and protein binding reaction, prosthetic factor and protein binding reaction, etc. .

  The weight average molecular weight of polyethylene glycol (PEG) is 2,000,000 (2M) or more, preferably 2 to 3.5M. Here, the weight average molecular weight of PEG refers to that measured by gel permeation chromatography (GPC) method using high performance liquid chromatography. Generally, PEG having a weight average molecular weight of 2M includes 1.5M to 2M PEG.

  Since PEG having a weight average molecular weight of less than 2M has no effect of suppressing the aggregation of fine particles, the average molecular weight of PEG used in the present invention is limited to 2M or more. Although the mechanism that exerts the aggregation-inhibiting effect is not clear, it is generally considered that PEG forms a network structure in solution, and the physical structure is caused by the network structure formed by PEG having an average molecular weight of 2M or more. It is considered that aggregation can be suppressed by reducing the contact frequency.

Polyethylene glycol (PEG) is a polymer of ethylene glycol and refers to a polymer having a structure represented by HO— (CH ₂ —CH ₂ —O) _n —H.

  When the PEG solution is added to the suspension containing fine particles, the final concentration of PEG, that is, the PEG concentration in the fine particle suspension after addition of the PEG solution is preferably 1 w / v% or less, more preferably 0.05 to 0.1 w / Try to be v%. By setting the final PEG concentration to 0.05 w / v% or more, the aggregation of the fine particles can be effectively suppressed. If the final PEG concentration is 1 w / v% or less, PEG is easily dissolved in the solvent.

  The solvent for dissolving PEG is not particularly limited, and examples thereof include phosphate buffer, glycine buffer, Tris-HCl buffer, Good buffer, and the like. The pH of the solvent is not particularly limited and is appropriately adjusted according to the subsequent steps. The PEG concentration in the PEG solution is appropriately selected so that the final concentration of PEG after addition to the fine particle suspension falls within the above concentration range, but is preferably 0.1 to 5.0 w / v%, more preferably 0.5 to 1 w / v%.

  The concentration of the microparticles during storage is not particularly limited and is appropriately adjusted according to the subsequent steps, but is usually 50 mg / mL or less, more preferably 1 to 10 mg / mL.

  The present invention also relates to a fine particle storage solution for suppressing aggregation of fine particles. The fine particle preservation solution of the present invention contains polyethylene glycol having a weight average molecular weight of 2,000,000 or more. The fine particles to be stored and polyethylene glycol are as described above. The concentration of polyethylene glycol in the fine particle preservation solution of the present invention is appropriately selected so that the final concentration of PEG after adding the preservation solution to the fine particle suspension is within the above concentration range, but preferably 0.1 to 5.0 w / v. %, More preferably 0.5 to 1 w / v%.

  The present invention also relates to a fine particle suspension containing fine particles and polyethylene glycol having a weight average molecular weight of 2,000,000 or more. The fine particles and polyethylene glycol are as described above. The PEG concentration in the fine particle suspension is preferably 1 w / v% or less, more preferably 0.05 to 0.1 w / v%. By setting the PEG concentration to 0.05 w / v% or more, the aggregation of the fine particles can be effectively suppressed. When the PEG concentration is 1 w / v% or less, PEG is easily dissolved in the solvent. The concentration of the fine particles in the fine particle suspension is not particularly limited, but is usually 50 mg / mL or less, more preferably 1 to 10 mg / mL.

  When using fine particles stored in a preservation solution containing the polyethylene glycol of the present invention, the fine particles may be used in a state suspended in the preservation solution, or washed before use to remove the preservation solution from the fine particles. May be. The solution in which the fine particles are suspended after washing is not particularly limited and is appropriately selected according to the intended use.

  The usage of the fine particles stored in the storage solution of the present invention is not particularly limited. By appropriately surface-modifying the microparticles, for example, it can be used for immunoenzyme reaction, immunoaggregation reaction, immunoprecipitation reaction, nucleic acid purification, protein purification, cell recovery, bacteria recovery and the like. For example, in the immunoenzymatic reaction, since the total surface area of all the microparticles decreases due to the aggregation of the microparticles, there may be a problem that the detected signal intensity varies depending on the degree of the microparticle aggregation. By using the storage method and storage solution, aggregation of fine particles can be suppressed, and variation in signal intensity can be suppressed.

  The microparticles stored using the storage solution of the present invention are, for example, a reaction solution for capturing a biological material or a reaction solution for interacting a biological material, preferably a reaction such as an immunoenzymatic reaction, an immunoagglutination reaction, an immunoprecipitation reaction, etc. The reaction can be carried out by adding to the liquid. Preferably, the fine particles stored using the preservation solution of the present invention are washed to remove the preservation solution, and then the reaction is carried out by adding the fine particles to the reaction solution as described above. By washing the microparticles before the reaction to remove the stock solution, the signal intensity of the reaction can be enhanced by the excluded volume effect of PEG.

  EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

Example 1
Examination of Aggregation Inhibition Effect by Addition of PEG Magnetic fine particles MyOne (Dynal) having a particle diameter of 1 μm were used as fine particles to be evaluated. In general, magnetic fine particles and the like are stored at a low temperature (about 4 ° C.), and it is considered that the magnetic particles aggregate and progress as the storage period becomes longer. In order to experimentally reproduce the agglomeration of magnetic fine particles after long-term storage, an accelerated test was performed to store the magnetic fine particles at 37 ° C for 2 weeks, which is estimated to be equivalent to the state of being stored at 4 ° C for 1 year. did. A PEG solution having a weight average molecular weight of 2M was added to a suspension containing magnetic fine particles and subjected to an acceleration test, and then the particle size distribution of the fine particles was determined. The particle size distribution was measured using forward scattering (FS) and side scattering (SS), which are proportional to the relative size of the particles, as indicators, and the proportion of monodispersed particles contained in the fine particles after the acceleration test was determined. The concentration of the magnetic fine particles was 1 mg / mL. The results are shown in FIG. Whereas the percentage of monodisperse particles is 67.7% when magnetic fine particles are suspended in a phosphate buffer solution (hereinafter referred to as PBS) that is normally used as a fine particle suspension and stored at 4 ° C for 2 weeks. When the accelerated test was conducted at 37 ° C. for 2 weeks, the proportion of monodisperse particles decreased to 31.8%, and the magnetic fine particles were aggregated. On the other hand, when PEG having a weight average molecular weight of 2M was added at a final concentration of 0.05 to 0.25 w / v%, the proportion of monodispersed particles after an accelerated test at 37 ° C. for 2 weeks was 78% or more, and the weight average molecular weight of 2M It became clear that the addition of PEG can suppress the aggregation of magnetic fine particles. As a comparative control, when PEG having a weight average molecular weight of 0.5 M was added at a final concentration of 2.5 or 0.25 w / v%, the proportion of monodispersed particles after an accelerated test at 37 ° C. for 2 weeks was 50% or less, PEG having an average molecular weight of 0.5 M could not suppress aggregation of magnetic fine particles. This result indicates that PEG having a weight average molecular weight of 2M is effective in suppressing aggregation of magnetic fine particles.

Evaluation of immunoenzyme reaction using microparticles The reactivity of magnetic microparticles after an accelerated test (stored at 37 ° C. for 2 weeks) was evaluated using the following method.
A sandwich ELISA system was used as a model system for the immunoenzymatic reaction (FIG. 2). Streptavidin 2 is modified to form fine particles 3 on the surface of the magnetic fine particles 1 used. Detection component 5 is α-fetoprotein (hereinafter referred to as AFP, Dako X0900), a tumor marker for liver cancer, biotin-labeled anti-AFP goat polyclonal antibody (NBT PA-011) as capture antibody 4, and alkaline phosphatase label as detection antibody 6. An anti-AFP rabbit polyclonal antibody (Dako A008) was used. 1.8 μL of capture antibody 4, 0.5 μL of detection component 5, 0.6 μL of detection antibody 6 and 180 μL of Wash Buffer (0.9% NaCl, 0.1% Tween20, hereinafter referred to as WB) are mixed to form complex 7. This was used for subsequent reactions. The reaction flow is shown in FIG. The concentration of magnetic fine particles in the preservation solution was 1 mg / mL. Using 14.4 μg of microparticles 3 that were accelerated in the stock solution shown in Fig. 3, 20 μL of complex 7 and 80 μL of WB were mixed in a white well plate and reacted at 37 ° C. Fine particles 3 were recovered by magnetic separation. After washing the microparticles twice with 80 μL of WB, 30 μL of luminescent substrate CDP-star (GE Healthcare Bioscience) was added and reacted at 37 ° C. for 5 minutes. Luminescence was measured with a plate reader (TECAN ULTRA).

  FIG. 4 shows the ratio of the monodispersed particles of the fine particles 3 subjected to the acceleration test in the preservation solution shown in FIG. The proportion of monodisperse particles is 78.5% at 0.1 w / v% PEG, which is higher than that of fine particles 3 subjected to an acceleration test in PBS, indicating that PEG has an effect of suppressing aggregation. It was done.

  Next, the results when the immunoenzymatic reaction was performed using the microparticles 3 subjected to the acceleration test in the preservation solution shown in FIG. 3 will be described with reference to FIG. The signal intensity in the case of using the microparticles 3 subjected to the acceleration test in PBS was reduced by about 30% compared to the case of using the microparticles 3 stored at 4 ° C. for 2 weeks. When using microparticles 3 that had been accelerated in a solution containing PEG with a weight average molecular weight of 2M, the signal intensity increased approximately twice compared to when microparticles 3 stored at 4 ° C for 2 weeks were used. . This result shows that from the viewpoints of both aggregation suppression and signal intensity enhancement, PEG with a weight average molecular weight of 2M is suitable as a component of the preservation solution for fine particles 3, and PEG with an average molecular weight of 2M is added to the fine particle suspension. This shows that aggregation of fine particles can be suppressed.

(Example 2)
After removing the PEG, the microparticles 3 subjected to the accelerated test (stored at 37 ° C. for 2 weeks) in a solution containing PEG having a weight average molecular weight of 2M as in Example 1 were washed immediately before the immunoenzymatic reaction. Used for immunoenzymatic reaction. The reaction flow is shown in FIG.

  FIG. 7 shows the ratio of the monodisperse particles of the fine particles 3 tested in the preservation solution shown in FIG. The proportion of monodisperse particles in which fine particles 3 are suspended in a preservation solution containing PEG is 79.1%, whereas the proportion of monodispersed particles of fine particles 3 from which PEG has been removed after the acceleration test is 87.3%. It was confirmed that the fine particles 3 did not agglomerate and maintained a dispersed state even when the was removed.

  Next, FIG. 8 shows the results when an immunoenzymatic reaction was performed using the microparticles 3 tested in the preservation solution shown in FIG. The signal intensity of the microparticles 3 from which PEG was removed after the acceleration test in a storage solution containing PEG was increased by approximately 30% compared to the microparticles stored in PBS at 4 ° C. for 2 weeks. This result shows that storage of the microparticles 3 in a PEG solution having a weight average molecular weight of 2M suppressed aggregation of the microparticles 3 and prevented a decrease in signal intensity. The difference between the signal intensity when the microparticles 3 were used in a preservation solution containing PEG and suspended in the preservation solution containing PEG, and the signal intensity when used after removing PEG was , Shows enhanced signal intensity due to the excluded volume effect of PEG. The difference between the signal intensity when microparticle 3 was suspended in PBS and stored at 4 ° C for 2 weeks and the signal intensity when PEG was removed and used after accelerating tests in a preservation solution containing PEG By adding, the aggregation of the fine particles 3 is suppressed, the reduction of the surface area is prevented, and the signal intensity is maintained.

  From the above, in terms of both aggregation suppression and signal intensity stabilization, PEG having a weight average molecular weight of 2M is suitable as a component of the preservation solution for the fine particles 3, and PEG having a weight average molecular weight of 2M is included in the suspension containing the fine particles 3. It was revealed that aggregation of the fine particles 3 can be suppressed by adding to the suspension. Also, according to the present invention, unlike the conventional example 2, the aggregation of the fine particles 3 can be easily suppressed by simply adding PEG to the preservation solution.

1… Magnetic particles
2 ... Streptavidin
3 ... fine particles
4… Capture antibody
5… Detection component
6… Detection antibody
7 ... complex

Claims (15)

  A method for suppressing aggregation of fine particles, comprising adding a solution of polyethylene glycol having a weight average molecular weight of 2,000,000 or more to a suspension containing fine particles.   The method according to claim 1, wherein the fine particles are magnetic fine particles.   The method according to claim 1 or 2, wherein the particle diameter of the fine particles is 1 µm or less.   The method according to any one of claims 1 to 3, wherein the final concentration of polyethylene glycol is 0.05 to 1 w / v%.   A fine particle preservation solution for suppressing aggregation of fine particles, the preservation solution containing polyethylene glycol having a weight average molecular weight of 2,000,000 or more.   The preservation solution according to claim 5, wherein the fine particles are magnetic fine particles.   The preservation solution according to claim 5 or 6, wherein the fine particles are fine particles having a particle diameter of 1 µm or less.   The preservation solution according to any one of claims 5 to 7, wherein the polyethylene glycol concentration is 0.1 to 5.0 w / v%.   The reaction method which has a step which adds the microparticles | fine-particles preserve | saved using the preservation | save liquid of any one of Claims 5-8 to a reaction liquid.   A reaction method comprising: washing fine particles stored using the preservation solution according to any one of claims 5 to 8 and removing the preservation solution; and adding the fine particles from which the preservation solution has been removed to the reaction solution. .   A fine particle suspension containing fine particles and polyethylene glycol having a weight average molecular weight of 2,000,000 or more.   The fine particle suspension according to claim 11, wherein the fine particles are magnetic fine particles.   The fine particle suspension according to claim 11 or 12, wherein the fine particles have a particle size of 1 µm or less.   The fine particle suspension according to any one of claims 11 to 13, wherein the polyethylene glycol concentration is 0.05 to 1 w / v%.   The fine particle suspension according to any one of claims 11 to 14, wherein the fine particles have a surface modification for binding a biological substance.

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