A direct electron transfer single wall carbon nanotube (SWNT)-based biofuel cell on a gold-coated porous silicon (pSi) substrate shows a peak power density of 12 microwatts/cm2 in 4 mM glucose (corresponding to normal blood sugar concentration) with an average power of 1 microwatt over 48 hours of operation. An interesting feature of this biofuel cell is that it can be re-activated to operate with an average power output of 1 microwatt/cm 2 after storage for 3 months at 4°C. Gold particles were electrolessly self-assembled on each pSi substrate from HAuCl4 solution in alcohol after similarly depositing an adhesion-promoting Cr layer. The hierarchy of pores on pSi enables nanoscale transport during fuel cell operation via capillary and wicking effects. Carboxylated SWNTs were deposited by an electrophoretic process, followed by electrochemically-induced covalent immobilization of anodic glucose oxidase and cathodic laccase enzymes on the nanotubes to form the biofuel cell structure.