MIT researchers made progress using viruses to assemble microbatteries that are half the size of a human cell. Paula Hammond, Angela Belcher, and Yet-Ming Chiang and colleagues have already used the viral assembly method to make a battery's anode and electrolyte and hope to fabricate the cathode next, resulting in a complete device that could someday power biosensors or medical implants. (Seen below is an array of the battery electrodes, each one just four micrometers in diameter. There are one million micrometers in a meter.) From the MIT News Office:

First, on a clear, rubbery material the team used a common technique called soft lithography to create a pattern of tiny posts either four or eight millionths of a meter in diameter. On top of these posts, they then deposited several layers of two polymers that together act as the solid electrolyte and battery separator.

Next came viruses that preferentially self-assemble atop the polymer layers on the posts, ultimately forming the anode. In 2006, Hammond, Belcher, Chiang and colleagues reported in Science how to do this. Specifically, they altered the virus's genes so it makes protein coats that collect molecules of cobalt oxide to form ultrathin wires -- together, the anode.

The final result: a stamp of tiny posts, each covered with layers of electrolyte and the cobalt oxide anode.