Development of wrist-watch type biosensing system for real-time sweat lactate monitoring

A wrist-watch type biosensing system for real-time sweat lactic acid (LA) monitoring was fabricated and tested. The system consists of a microfluidic LA biosensor, a carrier-flow supplying device, and a sampling device for transporting whole secretions at the skin surface to the biosensor by continuous flow of phosphate-buffered saline (PBS). The perfusion test of PBS onto the skin surface by using the sampling device resulted in less than 1% leakage frequency at the collection site. The carrier-flow supplying device was able to feed PBS regardless of the body angle. When the subject wearing the device performed resistance training (lateral raise, 20 repetitions, 12.5 kg dumbbells), the LA secretion increased from 2 & mu;g/cm(2)/min to 16 & mu;g/cm(2)/min in response to the exercise, and then recovered to the baseline. The setup time for the measurement was less than 60 s. This indicates that the wrist-watch device can readily measure LA dynamics on the skin surface under conditions of the subject.