A “lab on a contact lens” can measure the neurotransmitter serotonin in tears, potentially offering a novel wearable method to noninvasively analyze levels of stress, a new study finds.“Tears could become a practical, noninvasive source of biochemical information that can be measured repeatedly over time,” says Yangzhi Zhu, director of the biomedical device center at the Terasaki Institute for Biomedical Innovation in Los Angeles. “Most biomarker testing today still relies on blood draws or isol...