Over the last number of years a movement has taken place where conventional point-to-point grab sampling style sensors have slowly been phased out in favor of in situ autonomous sensors. Autonomous sensors provide a better insight into the monitored parameter delivering more data points in a less manual fashion. Over the next ten years, it’s predicted that gas sensors will become smaller, consume less power and exhibit much improved performance, and be of substantially reduced cost [1]. Optical sensors certainly are in pole position in terms of development having already met many of the criteria. The authors present a low cost (< €1) sensing platform. Two L.E.D’s are setup as a light sensor (emitter,detector), where the light passing from the emitter to detector L.E.D is modulated by a chemically selective colorimetric film, providing an indirect chemical measurement (this sensing setup is visible in Figure 1). Our presented experimental setup has exhibited a limit of detection in the p.p.b region (0.001145 mg/L or 12 ppb) [2], as well as demonstrating a 95% recovery within 30 seconds of contaminant exposure [2] (example exposures visible in Figure 2). This work has been done utilizing a bromophenol blue based dye, which was inkjet printed to created reproducible optical pH sensitive slides. However, the target of the device can be tuned by varying the colorimetric coating composition.