Toward wearable patch for sweat analysis

•Flexible wearable electrochemical sensing platform for continuously monitoring of chloride ions in sweat is presented.•Highly sensitive chloride patch is fabricated by using low cost techniques: drop casting and screen printing.•Real-time monitoring of the chloride concentration in sweat of a test subject during treadmill exercise is demonstrated. This work presents an inexpensive and disposable miniaturized electrochemical sensing platform, which was fabricated on a polyethylene terephthalate substrate for continuously monitoring the ion composition of sweat. The sweat patch consisted of an area for sweat collection, integrated reference electrode and an array of screen printed AgCl electrodes for real-time monitoring chloride concentration in sweat. The printing process and thickness of the AgCl electrodes were optimized to enhance the stability of the electrode in fluid. The AgCl electrodes were stable for more than a week in fluid and had a chloride sensitivity of 58mV per decade. The reference electrode was successfully fabricated on the same patch by adding a polyhydroxyethylmethacrylate hydrogel layer on top of one of the AgCl electrode in the array and followed by conditioning in 3M KCl solution. The patch, which was worn on the chest of a test subject, was able to continuously monitor the chloride concentration in sweat of the test subject during an one hour treadmill exercise. Reasonable agreement was shown between the real-time measurements and control measurements of sweat samples, which were collected from the test subject and analyzed off-line.