Raman chemical imaging of chromate reduction sites in a single bacterium using intracellularly grown gold nanoislands.

Imaging live molecular events within micro-organisms at single-cell resolution would deliver valuable mechanistic information much needed in understanding key biological processes. We present a surface-enhanced Raman (SERS) chemical imaging strategy as a first step toward exploring the intracellular bioreduction pockets of toxic chromate in Shewanella. In order to achieve this, we take advantage of an innate reductive mechanism in bacteria of reducing gold ions into intracellular gold nanoislands, which provide the necessary enhancement for SERS imaging. We show that SERS has the sensitivity and selectivity not only to identify but also to differentiate between the two stable valence forms of chromate in cells. The imaging platform was used to understand intracellular metal reduction activities in a ubiquitous metal-reducing organism, Shewanella oneidensis MR-1, by mapping chromate reduction.