An article in Technology Review takes a closer look at the nascent field of molecular imaging. Scientists at the NCI and the University of Tokyo designed a pH-sensitive fluorescent probe to seek out and grab on to specific receptors on a tumor's surface and light up only when the probe has made it inside a cancer cell. They tested the probe on HER2-positive tumors in mice and found that the probe detected tumors with 99 percent accuracy compared to an "always on" probe, which only detected 85 percent of the tumors.