Determination of O2 using colour sensing from image processing with mobile devices

This paper presents a portable instrument designed and characterized for the determination of gaseous oxygen. It is based on quenching the luminescence intensity of the platinum octaethylporphyrin complex when it is excited, using a light-emitting diode (LED) with an emission peak at 380 nm. The luminescence emitted by the platinum complex is detected by taking an image with a colour CCD micro-camera integrated in the prototype which makes it possible to do a two-dimensional analysis of the luminescence. This image is processed by a microcontroller to obtain the red colour component of the RGB colour space, thus discarding any unnecessary colour information. The processing is carried out for the pixels over a large area of the sensing membrane, which allows for a statistical treatment of the obtained data. The measured R-value for the membrane can be directly related to the concentration of the surrounding oxygen. The resulting instrument has been fully characterized and calibrated, including drifts due to temperature and time. In addition, an application for Android camera devices such as smartphones was developed in order to use them as detectors and image processors to provide a prediction of the gaseous oxygen concentration.