Microelectronic devices with biological components are typically used to analyze biological processes, but a group of bioengineers has shown that such devices can be used to control these processes as well. William E. Bentley of the University of Maryland and coworkers use a redox mediator to modulate the activity of enzymes covalently linked to a biocompatible scaffold on a chip-mounted gold electrode (Nat. Nanotechnol. 2014, DOI: 10.1038/nnano.2014.151). Their model system includes a fusion protein called HLPT, which consists of two enzymes involved in the synthesis of the bacterial signaling molecule autoinducer-2, and a redox mediator called acetosyringone. By applying a voltage to the gold electrode, they electrically oxidize acetosyringone, which chemically oxidizes HLPT and attenuates its activity. The extent of attenuation is linearly proportional to the amount of oxidized acetosyringone. By calculating the needed charge and applying a voltage for the appropriate length of time, Bentley and coworkers predictably control the amount of autoinducer-2 produced by HLPT. Such a strategy could be used in future chip-mounted devices to control biochemical processes in other biological systems, the researchers suggest.