This work presents the construction of an ethanol microfluidic biofuel cell based on a biocathode and a bioanode, and operating in a Y-shaped microfluidic channel. At the anode, ethanol was oxidized by alcohol dehydrogenase, whereas at the cathode, the oxygen was reduced by laccase. Fuel and oxidant streams moved in parallel laminar flow without turbulent mixing into a microchannel fabricated using soft lithography methods. The enzymes were immobilized in the presence of reactive species at gold electrode surfaces. Bioelectrocatalytic processes were enhanced by combination of enzymes and carbon nanoparticles, attributed to appropriate electron transport and high amount enzyme loading. The benefit of the nanoparticles with higher surface porosity was explained by the high porous structure that offered a closer proximity to the reactive species and improved diffusion of the substrates within the enzyme films. The microfluidic BFC was optimized as function of electrode patterns, showing that higher current and power densities were achieved for shorter and wider electrodes that allow for thinner boundary layer depletion at the electrodes surface resulting in efficient catalytic consumption of fuel and oxidant. This miniaturized device generated maximum power density of 90 mu W cm(-2) at 0.6 V for a flow rate 16 mu L min(-1). (C) 2014 Elsevier B.V. All rights reserved.