Patent ID: 7632688

Claim:
A magnetic substance-encapsulated particle, which comprises an organic polymer material and a magnetic substance, wherein the magnetic substance has an average particle size of 1 to 30 nm, the magnetic substance being dispersed and encapsulated within the organic polymer material of said particle; wherein said organic polymer material comprises a monomer not having a hydrophilic group for forming a core of said particle and a monomer having a hydrophilic group for forming a shell of said particle and forming a particle having dispersion stability in water; and wherein an absolute deviation of a component ratio between a carbon element comprising the organic polymer material and a metal element comprising the magnetic substance is 0.27 or less, wherein the monomer not having a hydrophilic group comprises a monomer having a glycidyl group and a styrenic monomer and wherein the monomer having a hydrophilic group is polyethylene glycol (meth)acrylate represented by the following general formula (1) or a compound represented by the following general formula (2): CH 2 ═CR—COO—(CH 2 —CH 2 —O) n —H (1) in the formula, R represents H or CH 3 , and n represents an integer of 1 to 20, in the formula, X represents H or SO 3 − NH 4 + , and n represents an integer of 3 to 30.