A novel label-free voltammetric immunosensor for the detection of α-fetoprotein using functional titanium dioxide nanoparticles

A highly sensitive label-free voltammetric immunosensor was developed based on the functional titanium dioxide nanoparticles (PV–NTiP), which was prepared by capping 1,1′-bis-(2-phosphonoethyl)-4,4′-bipyridinium dibromide (PV) on the surface of the titanium dioxide nanoparticles (NTiP) with covalent attachment. The PV–NTiP has prominent biocompatibility, good electron transfer ability, primarily excellent adsorption, large specific surface area and positively charged environment. As a result, the negatively charged gold nanoparticles (NGP) could be adsorbed on the PV–NTiP modified electrode surface by electrostatic adsorption, and then to immobilize α-1-fetoprotein antibody (anti-AFP) for the assay of α-1-fetoprotein (AFP). The fabricated procedures and electrochemical behaviors of the immunosensor were characterized by electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and cyclic voltammetry (CV). The anti-AFP/NGP/PV–NTiP modified electrode was sensitive to AFP in linear relation between 1.25 and 200 ng/mL with the correlation coefficient of 0.9982, and the detection limit (S/N = 3) is 0.6 ng/mL under the optimal conditions. In addition, the proposed immunosensor exhibits good sensitivity, selectivity, stability and long-term maintenance of bioactivity and it may be used to immobilize other biomoleculars to develop biosensor for the detection of other antigens or biocompounds.