A photonic crystal-hydrogel sensor for the monitoring of potassium ions in sweat

Sweat contains abundant physiological information critical for health monitoring, making wearable sweat sensors increasingly popular in exercise and training surveillance. Most of the existing sensors are designed to measure physical parameters such as heart rate, blood pressure, and respiration, relying on electronic instruments for biochemical analysis of body fluids. In this study, we present a wearable hydrogel band integrated with a photonic crystal array, for visual, non-invasive and in situ analysis of sweat for sports practitioners. The hydrogel sensor, inspired by the biological properties of onions, demonstrates excellent skin adhesion for efficient sweat collection. This innovative design allows for the development of a simple, reliable, and low-cost sensor capable of detecting potassium ion concentrations and pH levels in sweat. Under optimized conditions, the developed sensor can respond to potassium ion concentrations ranging from 1 mM to 150 mM, with a pH response range of 3 to 9 for human sweat. The dynamic cycling tests of potassium ion concentration and pH in sweat demonstrated that this sensor can effectively monitor electrolyte balance and dehydration during outdoor exercise.