Professor Charles Lieber and his students have made wires whose thinness is measured in atoms instead of fractions of an inch. That allowed Lieber’s team to develop what is likely to be an important scientific tool, a coated wire capable of detecting low levels of a protein that marks the presence or recurrence of prostate cancer. “The device immediately senses levels of PSA (prostate-specific antigen) four times smaller than is now possible with blood tests that often take days,” says Lieber, Hyman Professor of Chemistry at Harvard University. Liber believes it will be possible to expand the use of such unimaginably small wires to sense the presence of malignancies, such as breast and ovarian cancers, as well as other types of diseases, and pathogens used in biological warfare. The sensor is so small it opens up the possibility of detectors implanted in the body to continuously monitor levels of insulin and other critical molecules. The nanowire, as it’s known, is a scant 10-billionths of a meter (10 nanometers) in diameter, or about five times smaller than a virus.