Patent ID: 8084275

Claim:
A magnetic composite body comprising magnetic nanoparticles with a number average particle diameter of 1 to 50 nm and a compound represented by formula (I) fixed on surfaces of the magnetic nanoparticles: R 1 O—(CH(R 2 )CH 2 O) n -L-X Formula(I) wherein in formula (I), R 1 represents a hydrogen atom, an alkyl or alkenyl group having a carbon chain length of 1 to 20, or a substituted or unsubstituted, aryl or heterocyclic group; R 2 represents a hydrogen atom or a methyl group; L may be present or not present, and, when L is present, L represents an alkylene or alkenylene group having a carbon chain length of 1 to 10 which may have a branched chain or a substituent; X represents a hydrogen atom, a carboxylic acid group, a phosphoric acid group, or a sulfonic acid group; and n represents an integer of 1 to 10, wherein a compound selected from the group consisting of a polyvalent carboxylic acid, an amino acid, a protein, a peptide, and a polysaccharide is further fixed on the surfaces of the magnetic nanoparticles in the magnetic composite body.