Wearable and implantable biosensors that can accurately detect biological molecules in a non- or minimally invasive manner have vast potential for monitoring patients' physiology and response to therapies. For example, wearable glucose monitors that measure blood glucose levels and convert these measurements into readily readable and continuously recorded electrical signals have become indispensable in the management of diabetes patients. Similar biosensors have been developed for the monitoring of electrolytes in sweat, biomarkers in interstitial fluid near the skin surface, and to report on the function of internal tissues.