Down to the wires: A highly efficient artificial photosynthetic system employing hydrogen-terminated silicon nanowires is reported. The nanowires enable a cascading electron transfer from electron donor to NAD+ via a rhodium-based electron mediator. Approximately 80 % of NADH is photoregenerated from NAD+ by the nanowires during 2 h of light irradiation, and successfully coupled with the photoenzymatic synthesis of L-glutamate.