A microelectronic technology based amperometric immunosensor for α-fetoprotein using mixed self-assembled monolayers and gold nanoparticles

A novel amperometric immunosensor for the detection of α-fetoprotein (AFP) based on the integration of microelectronic technology, mixed self-assembled monolayers (mixed SAMs), gold nanoparticles (nanogold) and enzyme amplification has been developed. Using microelectronic technology, an immunosensor was fabricated which has an “Au, Pt, Pt” three-microelectrode system and two microwells constructed by SU-8 photoresist on silicon wafer. Using mixed SAMs and nanogold, a mixed monolayer comprising cysteamine and 1,6-hexanedithiol was formed on the working electrode surface to assemble nanogold and further to immobilize AFP antibody for detecting AFP in human serum samples. The stepwise mixed SAMs and nanogold based immobilization procedure was characterized by means of cyclic voltammetry. The factors influencing the performance of the resulting immunosensor were studied in detail. After the addition of H2O2 and KI to the immunosensor incubated with AFP and further with horseradish peroxidase-labeled AFP antibody, the cathodic current varied linearly in concentration range of AFP from 15 to 350 ng/ml with a detection limit of 5 ng/ml. Moreover, the studied immunosensor has attractive advantages, such as miniaturization, compatibility with the complementary metal oxide semiconductor (CMOS) techniques, high specificity, good reproducibility and long-term stability, which make it potentially attractive for clinical immunoassays.