Prostate-specific antigen (PSA) has long been the best biomarker available for early detection of prostate cancer, despite problems with over-diagnoses and false positives. As it turns out, the PSA blood test is also a potential biomarker for breast cancer, but levels are so small in women that it would take an ultrasensitive test to measure them. Taiwanese researcher Chien Chou and colleagues have found a way to make a test sensitive enough. They've built a fiber-optic biosensor using gold nanoparticles and PSA antibodies to detect and report PSA levels using a fluorescent signal. The researchers say that it's able to detect elevated PSA levels in breast cancer cases, although they also say that it avoids false positives at the same rate as those found in prostate cancer PSA tests. Story | Abstract