Abstract: Fe₃O₄/Au magnetic nanocomposites were synthesized, then the surface of the magnetic nanocomposites was amino-functionalized with thiourea to covalent immobilization of monoclona carcinoembryonic antibody(anti-CEA) using glutaraldehyde. The resulting magnetic bio-nanocomposites were attached onto the surface of solid paraffin carbon paste electrode with the help of a permanent magnet to construct a new amperometic immunosensor. The immunosensor was incubated with mixed solution of carcinoembryonic antigen(CEA) and horseradish peroxidase labeled carcinoembryonic antigen(HRP-CEA) for 30 min to perform the competitive immune reaction between CEA(or HRP-CEA) and anti-CEA immobilizated on the surface. The concentrations of CEA were determined indirectly by competitive immunoassay method via the changes of the H₂O₂ concentrations resulted from the catalytic degradation by HRP. The sensitivity for CEA determination was greatly improved due to the amplification effect of labeled HRP on the catalytic degradation of H₂O₂, which led to the change of the concentration of p-hydroquinone. There is a linear relation between response current and logarithm of concentrations of CEA in the concentration range of 2—160 ng/mL, with a detect limit of 0.57 ng/mL(on a 3σ basis). The simple manipulations of construction, low cost, high sensitivity, sharp specificity and easy regeneration of the sensing platform were main advantages of proposed immunosensor.

Key words: Fe₃O₄/Au magnetic nanoparticle, Amperometric immunosensor, Carcinoembryonic antigen