Study of Single Antigen–Antibody Interactions on a Silicon Surface in Biosensors Based on Field-Effect Transistors with a Nanowire Channel

To develop highly sensitive biosensors based on field-effect transistors with a silicon nanowire channel (FET), single interactions of antibodies with prostate-specific antigen (PSA) on the surface of pure silicon modified with 5 nm gold nanoparticles were studied. A digital immunocomplex registration method using scanning electron microscopy was employed, where 25 nm gold nanoparticles served as antibody visualizing labels. A specialized algorithm was developed to calculate the nanoparticle density on the silicon surface. Various methods of chemical silicon modification using silanes (3-glycidoxypropyltrimethoxysilane (GOPS), 3-mercaptopropyltrimethoxysilane (GOPS-SH), and 3-aminopropyltriethoxysilane (APTES)), bifunctional reagents, and polyethylene glycol were applied to investigate covalent antibody immobilization. It has been shown that chemical modification methods using GOPS are characterized by a lower detection limit for prostate-specific antigen (PSA)—a biomarker of prostate tumors. Biosensor structures based on field-effect transistors with nanowire channels, whose surfaces were modified by two different methods using GOPS, were fabricated, and their pH sensitivity was studied. It has been demonstrated that the modification method using GOPS-SH is characterized by a maximum pH sensitivity of 70 mV/pH and is the most promising for the development of highly sensitive biosensors for biomarker detection.