2.6. Fabrication of biosensor

The glassy carbon working electrode (2 mm diameter) was carefully polished with 3 μM alumina powder and sonicated subsequently in ethanol and water in order to remove adsorbed particles. After that, 10 μL of GO/AuNPs /Ab₁ was dropped on the surface of electrode and left at room temperature for 10 min. Then, the modified electrode was incubated in 1 wt% BSA solution for 30 min to eliminate nonspecific binding between the antigen and the electrode surface. Subsequently, serum sample was added onto the electrode surface and incubated for 20 min at room temperature, and then the electrode was washed to remove unbounded PSA molecules. After washing, the electrode was electrochemically investigated. Subsequently, GO/AuNPs /Ab₂ was dropped onto the same electrode surface; then, incubated for another 20 min, and finally the electrochemical measurements were repeated.