Microfluidic biofuel cells: Series-connection with superhydrophobic air valves

We report the construction of microfluidic biofuel cells connected in series by semiautomatic air valves, in which a lotus leaf-like superhydrophobic structure (a micropillar array) traps air and ionically isolates each biofuel cell aligned within the channel. The micropillar array was prepared by conventional photolithography and reactive ion etching (RIE) techniques, and the structural parameters of the micropillars (size and spacing) were optimized as to obtain the highest degree of hydrophobicity. The open-circuit voltage measured at the ends of three aligned biofuel cells was three times larger than that of a single cell using the semiautomatic air valve system.