A nanosized mechanical device built from DNA can controllably “walk” in either direction along a track in response to light pulses, a team of researchers in the U.S. and China report in ACS Nano (DOI: 10.1021/nn302388e). UV light causes the nanostructure to walk in one direction, and visible light, the other direction. The study demonstrates that light-induced isomerization can serve as the basis of mobility in synthetic molecular motors. Such devices, which mimic the actions of natural motor proteins, may lead to construction of nanosized robots capable of ferrying molecular cargo to and from cells and mediating other biological processes. Chemist Weihong Tan of the University of Florida, Gainesville, and Hunan University and coworkers prepared a DNA-azobenzene complex (a two-legged walker) and a track featuring nucleotide binding sites that extend from the track and are complementary to segments of the nucleotide sequences in the walker’s legs. By exploiting UV-light-induced trans-to-cis isomerization of the azobenzene moiety, the team causes the walker to undergo a DNA strand displacement reaction and step along the track in one direction. Visible light reverses the isomerization, causing the complex to step in the other direction.