A microliter-scale microbial fuel cell array for bacterial electrogenic screening

We have developed an array of six MEMS (micro-electro-mechanical systems) microbial fuel cells (MFCs), a compact and reliable platform for rapid screening of electrochemically active bacteria. The MFC array contains vertically stacked 1.5 μL anode/cathode chambers separated by a proton exchange membrane (PEM), and represents the smallest MEMS MFC array currently available. Each layer, except for the PEM, was micro-patterned by using laser micromachining and was precisely aligned. Within just 5 h, we successfully determined the electricity generation capacity of two known bacterial electrogens (wild-type S. oneidensis and P. aeruginosa) and another metabolically more voracious organism with 4 isogenic mutants constructed with the hypothesis that such mutations could alter their electrogenic properties. Genetically engineered genes in P. aeruginosa including nirS (nitrite reductase), lasl (N-(3-oxododecanoyl)-l-homoserine lactone synthase), bdlA (biofiilm dispersion locus) and pilT (controls the number of Type IV pili on the poles of the bacteria) sensitively showed different efficiencies of extracellular electron transfer to the anode in the significantly reduced micro-chambers. In addition, the percent deviation of all six MFC units was less than 1.4% from their open circuit voltages recorded, which is far less than that of mL-sized MFC arrays (25%) and even MEMS MFC arrays (>8%). This analytical platform would provide the practical tools for fundamental study and characterization of the behavior and physiology of microorganisms and their interaction with MFCs with a greater level of insight and productivity.