An aptamer-functionalized silicon-nanowire (Si-NW) field effect transistor (FET) biosensor was successfully fabricated, characterized and applied to real-time electrical detection of binding with the target protein for biomedical applications. Surface modifications were carried out using 3-aminopropyl diethoxysilane and succinic anhydride to introduce amine and carboxyl groups onto Si substrates. Anti-thrombin aptamers with 5'-end amine groups were chemically grafted onto the surface-modified Si substrates through amide bond formation. Atomic force microscopic (AFM) analyses confirmed the successful immobilization of anti-thrombin aptamers on Si-NWs and their binding with thrombin samples. The anti-thrombin aptamers bound to Si-NWs through the linker appeared to have a mean height of approx. 4 nm and the thrombin/aptamer complex to have a mean height of approx. 8 nm. Fluorescence micrographs visualized the FITC-labeled thrombin after binding to anti-thrombin aptamers immobilized on Si-NWs. Furthermore, the anti-thrombin Si-NW FET biosensor was successfully applied to the real-time detection of electronic signals during and after binding with a thrombin sample at a concentration of approx. 330 pmol l(-1) and the thrombin in blood samples.