Patent ID: 7732158

Claim:
A method to detect an analyte in an aqueous solution with use of an agglutination reaction of polymer-based fine particles dispersed in said solution, which comprises contacting the analyte with the polymer-based fine particle, wherein: (a) said fine particle has, as a core, a polymer chain segment with a chargeable group-carrying recurring unit, and has, as plural brushes on said core or as a shell, a hydrophilic polymer chain or segment of the hydrophilic polymer chain, wherein a member of a biologically specific bond which forms a counterpart to the analyte is bound to at least a part of free terminals of said hydrophilic polymer chain, (b) the agglutination reaction is conducted under a condition of a suitable pH under which the chargeable group is in a charged state and the fine particles can be bonded to the analyte or absorb the analyte to form agglutinated matter, and, subsequently, the agglutinated matter is treated under a condition of a raised ionic intensity, under which, although the biologically specific bond between the fine particles is not cleaved, a bond made by electrostatic interaction can be cleaved, and (c) the existence of agglutinated matter which remains after the treatment of step (b) is detected by a method capable of distinguishing a state in which the biologically specific bond is not cleaved, and a state in which the bond by electrostatic interaction is cleaved, the results being used as an index of the presence of analyte, wherein the hydrophilic polymer chain in the polymer-based fine particles is formed from a poly(ethylene glycol) macro monomer having formula (M): wherein X denotes a hydrogen atom, —COOM group (M denotes a hydrogen atom or an organic group), —CHR 1 R 2 (R 1 and R 2 either independently denote a C 1-6 alkyloxy group, phenyloxy group or a phenyl-C 1 - 3 alkyloxy group, or, taken together, denote —OCHR′—CH 2 O— wherein R′ denotes a hydrogen atom or a C 1-6 alkyl group) or —CH═O, R a denotes a hydrogen atom or a C 1-6 alkyl group, L 1 denotes a methylene group or a carbonyl group, L 2 denotes a carbonyl group, a C 1-3 alkylene group or a C 1-3 alkylphenylene group, n denotes an integer of 2 to 10,000, and p denotes an integer of 1 to 5; and wherein the polymer chain with a recurring unit carrying a chargeable group in the polymer-based fine particles is formed from a monomer having a formula (A): wherein R 1a denotes a hydrogen atom or a C 1-6 alkyl group, R 2a and R 3a either, independently, denote a C 1-6 alkyl group or, taken together, may form, with the nitrogen atom to which they are bound, a five- or six-membered heterocycle which may contain further one or two nitrogen atoms, an oxygen atom or a sulfur atom, X denotes —O— or —NH—, and p denotes an integer of 2 to 6; and wherein said two monomers are copolymerized with a crosslinking agent and/or an ethylenically polymerizable group-containing diluting monomer to give a random copolymer, said crosslinking agent and diluting monomer being allowed, where necessary, to be mixed with each other before crosslinked.