Effective immobilization of Au nanoparticles on TiO₂ loaded graphene for a novel sandwich-type immunosensor

A novel and sensitive sandwich immunosensor for amperometric determination of carcinoembryonic antigen (CEA) was designed using Au nanoparticles-titanium dioxide-graphene (AuNPs-TiO₂-graphene) nanocomposites. Dopamine-functionalized graphene was firstly prepared by π-stacking interaction, and TiO₂ was then attached to the surface of dopamine-graphene by the specificity and high affinity of enediol ligands to Ti (IV). Afterwards, AuNPs-TiO₂-graphene nanocomposites were synthesized with photo-reduction approach under ultraviolet irradiation. The morphology and conductivity of the as-prepared nanocomposites were characterized by transmission electron microscopy, Fourier transform infrared spectra, X-ray powder diffraction, cyclic voltammetry and electrochemical impedance spectroscopy. Taking the advantage of large specific surface area and excellent biocompatibility, AuNPs could covalently link horseradish peroxidase labeled secondary antibody (HRP-Ab₂) through the interaction between AuNPs and mercapto or primary amine groups of HRP-Ab₂ for sandwich-type immunosensor construction. Under optimum conditions, the modified electrode exhibited a linear current response to CEA concentration in a wide range of 0.005-200ngmL^-1 (R² = 0.994) with low detection limit of 3.33pgmL^-1 (S/N = 3).