On page 62, Jenison et al. describe a biosensor for detecting nucleic acid targets present at only attomolar concentrations. The detector comprises a set of oligonucleotide probes bound to a silicon-based surface that can hybridize to specific nucleic acid targets. Bound nucleic acids are then detected by complementary probes labeled with biotin, which catalyzes an enzymatic reaction that deposits a thin film on the surface of the silicon. The color change that results on the biosensor's surface is detectable by the naked eye, suggesting potential applications in the clinic and field.