Si nanowires (SiNWs) were modified by Au nanoparticles (AuNPs) using a self-assembled monolayer of aminopropyltriethoxysilane (APTES) and used for direct sensing of the bovine serum albumin (BSA). It was shown that repeated thermal treatment of the sensor greatly enhanced the reliability of the SiNW sensor by increasing the electrical conductivity largely from carbonization of the APTES molecules and from bringing the AuNPs in intimate contact with the SiNW surface. The AuNP-modified SiNW array sensor was able to detect 1-7 mu M of BSA. The sensor exhibited a good sensitivity over the tested concentration range and linear behavior. It is expected that the proposed label-free biosensor can be further developed to selectively detect and quantify biomolecules other than BSA. (C) 2010 Elsevier B.V. All rights reserved.