In this work the development of an autonomous, robust and wearable micro-fluidic platform capable of performing on-line analysis of pH in sweat is discussed. Through the means of an optical detection system based on a surface mount light emitting diode (smLED) and a photodiode as a detector, a wearable system was achieved in which realtime monitoring of sweat pH can be performed during sport activity. We show how through systems engineering, integrating miniaturised electrical components, and by improving the micro-fluidic chip characteristics, the wearability, reliability and performance of a sweat analysis platform has been significantly improved.