Semiconducting nanowires have the potential to function as highly sensitive and selective sensors for label-free detection of biological and chemical species. In this paper, we describe the preparation and applications of oligopeptide-modified single crystal silicon nanowire (SiNW) arrays as multichannel metal ion sensors. Because these SiNW arrays were fabricated by using a "top-down" process, a very high density of individually addressable SiNW (180 SiNWs grouped into 36 clusters) can be manufactured on a single chip. Furthermore, after two different SiNW clusters are modified with Pb2+-selective and Cu2+-selective oligopeptide, respectively, concentrations of Pb2+ and Cu2+ in aqueous solutions can be detected simultaneously and selectively in two different channels. By using the SiNW arrays, we successfully achieved a detection limit of 1 nM for Pb2+ and 10 nM for Cu2+, respectively. These results demonstrate the potential utility of oligopeptide-modified SiNW arrays for highly sensitive and selective chemical and biological sensing applications. © 2009 Elsevier B.V. All rights reserved.