Voltammetric aptasensor for thrombin by using a gold microelectrode modified with graphene oxide decorated with silver nanoparticles

A sensitive electrochemical aptasensor was developed for the determination of thrombin. It is based on signal amplification by using graphene oxide (GO) decorated with silver nanoparticles (AgNP) and placed on a microelectrode. The graphene oxide decorated with silver nanoparticles (AgNP-GO) was synthesized by chemical reduction and then modified with a thrombin-binding aptamer 1 (TBA1; a 29-mer) carrying a 3'-terminal thiol group. It was immobilized on the AgNP-GO by self-assembled monolayer technique to form the signaling probe (TBA1-AgNP-G0). A capture thrombin-binding aptamer 2 (TBA-2; a 15-mer) carrying a 3'-terminal thiol group was self-assembled onto the surface of the gold electrode. After binding of thrombin and the signaling probe, a sandwich of type TBA2-thrombin-TBA1-AgNP-GO is formed. The square wave voltammetric signal of the AgNP is then recorded. The electrochemical oxidation signal (measured at 0.21 V vs. Ag/AgCI) increases linearly with the concentration of thrombin in the range from 0.05 nmol.L-1 to 5 nmol.L-1 with a detection limit of 0.03 nmol.L-1 (at S/N= 3). The aptasensor is highly specific and not affected by other proteins. It was successfully applied to the determination of thrombin in spiked human serum samples.