Here we report a new microfluidic microbial fuel cell (MFC) platform built by soft-lithography techniques. The MFC design includes a unique sub-5 mu L polydimethylsiloxane soft chamber featuring carbon cloth electrodes and microfluidic delivery of electrolytes. Bioelectricity was generated using Shewanella oneidensis MR-1 cultivated on either complex organic substrates or lactate-based minimal medium. These micro-MFCs exhibited fast start-ups, reproducible current generation, and enhanced power densities up to 62.5 W m(-3) that represents the best result for sub-100 mu L MFCs. Systematic comparisons of custom-made MFC reactors having different chamber sizes indicate volumetric power density is inversely correlated with chamber size in our systems: i.e., the smaller the chamber, the higher the power density is achieved. Published by Elsevier Ltd.