Dual-Mode Protein Detection Based on Fe₃O₄–Au Hybrid Nanoparticles

A facile method of synthesizing Fe₃O₄–Au hybrid nanoparticles is reported utilizing the multifunctional nature of polyethyleneimine (PEI). An abundance of 5 nm gold nanoparticles were attached to 50 nm Fe₃O₄ nanoparticles via the covalent binding between the −NH₂ groups of the PEI and Au nanoparticles, as well as the electrostatic interaction between the negatively charged citrate-coated Au nanoparticles and the positively charged PEI-coated Fe₃O₄ nanoparticles. The as-prepared Fe₃O₄–Au hybrid nanoparticles, which combine the merits of magnetic materials and gold, were successfully employed for the first time in the dual-mode detection of carcinoembryonic antigen (CEA) via electrochemical and surface-enhanced Raman scattering (SERS) methods. Both methods make clever use of Fe₃O₄–Au nanoparticles and can accurately verify the presence of antigens. In particular, the electrochemical immunosensor detection displays a wide linear range (0.01–10 ng/mL) of response with a low detection limit (10 pg/mL), while the SERS method responds to even lower antigen concentrations with a wider detection range. The Fe₃O₄–Au hybrid nanoparticles therefore exhibit great potential for biomedical applications.