Carboxyl-functionalized superparamagnetic Fe3O4/poly(St-co-MPS)/SiO2 composite particles for rapid and sensitive immunoassay.

: Superparamagnetic Fe3O4/poly(St-co-MPS)/SiO2 composite particles with the average size of 140 nm were functionalized with carboxyl group by emulsion polymerization. Functionalized particles with carboxyl contents of 13.6 and 136 micromol/mL were prepared by changing the amount of acrylic acid monomer used in the polymerization. After conjugation with human chorionic gonadotrophin (hCG) antibody, the particles were used to construct lateral flow immunoassays (LFIA) for the detection of hCG in solution. The quantitative analysis could be finished in 20 min by using the magnetic particles as labels. The detection limit of LFIA was determined to be 1 and 5 IU/L respectively for the magnetic particles with carboxyl contents of 13.6 and 136 micromol/mL.