Summary: A biosensor uses a biological molecule to measure a chemical reaction. Wearable biosensors that attach to the body externally, including tooth enamel biosensors, contact lens biosensors, sweat biosensors, and skin tattoo biosensors, are in development. Nanoparticle-based biosensors are being developed to allow for the early detection of cancerous biomarkers. Applications relevant to plastic surgery include the development of biosensors that can detect metastatic breast cancer cells, bioimpedance spectroscopy, and intraoperative point-of-care diagnostics.