The components of sweat provide an array of potential biomarkers for health and 
disease. Sweat chloride is of interest as a biomarker for cystic fibrosis, 
electrolyte metabolism disorders, electrolyte balance, and electrolyte loss 
during exercise. Developing wearable sensors for biomarkers in sweat is a major 
technological challenge. Potentiometric sensors provide a relatively simple 
technology for on-body sweat chloride measurement, however, equilibration 
between reference and test solutions has limited the time over which accurate 
measurements can be made. Here, we report on a wearable potentiometric chloride 
sweat sensor. We performed parametric studies to show how the salt bridge 
geometry determines equilibration between the reference and test solutions. From 
these results, we show a sweat chloride sensor can be designed to provide 
accurate measurements over extended times. We then performed on-body tests on 
healthy subjects while exercising to establish the feasibility of using this 
technology as a wearable device.