This work demonstrates a low cost flexible sweat patch, which consists of a reference electrode and an array of chloride selective electrodes for real-time monitoring chloride concentration in sweat. The chloride sensitive electrodes were made by screen printing AgCl paste on polyethylene terephthalate (PET) substrate. The AgCl electrodes were stable for more than a week in liquid and showed a chloride sensitivity of 57 mV per decade. A reference electrode (RE) was successful developed on the

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... me patch by adding a polyhydroxyethylmethacrylate hydrogel layer on top of one of the AgCl electrode in the array and followed by conditioning in 3 M KCl solution. The sweat patch, which was worn on the chest of a test subject during an one hour treadmill exercise, was able to continuously detect the chloride ions in a small amount of sweat adsorbed in a gauze layer placed on top of the patch.