Sweat sensing in the smart wearables era: Towards integrative, multifunctional and body-compliant perspiration analysis

All life forms use a seamless integration of physical and chemical sensing mechanisms to enhance their performance and survival skills. To mimic the integrative sensing abilities found in nature, there is a significant interest in developing wearable devices that can smartly track the physiological and biochemical signals of the human body. Progress in wearable physical sensors has been remarkable giving rise to a number of consumer electronics products meant to measure parameters related to activity, posture, heart rate, respiration rate, and blood oxygen level. Comparatively, the progress in wearable chemical sensor development has been slower because of the inherent challenges in retrieving and processing bodily fluids. In this context, sweat provides a rich repository of biomarkers that is accessible continuously, on-the-go, and non-invasively. Here we provide a review of recent trends in the area of wearable sweat sensing with discussions on relevant topics of interest in material science, device development, sensing mechanisms, power generation, and data management. Exemplary wearable sweat sensors published in recent years are provided along with commercialization efforts in wearable sweat sensing. The review highlights the trends in multifunctional sensing platforms with flexible electronics that integrate data from both physical and biochemical sweat sensors.