Smartphone-assisted RGB color analysis of a paper-based vapochromic chemosensor for selective detection of pyridine vapors

The search for simple and effective optical chemosensors is an area of current and growing interest. In this work, a paper-based chemosensor of a vapochromic Zn(salen)-type complex is developed. It can selectively detect pyridine vapors, from those of the most common VOCs and other heterocyclic amines, over a wide concentration range from tens to thousands of ppm, requiring a simple fabrication method, films preparation by dip-coating, and enabling detection by using a smartphone-assisted color recognition app and a proper RGB color analysis. The latter includes normalization to the rgb values and the color difference ΔErgb, from the RGB color changes of the films before and after exposure. Reliability of this method is assessed by comparison with results of UV–vis reflectance spectra, and could represent a general approach for VOCs detection using vapochromic materials on films. These results are contrasted with those obtained using non-normalized RGB values, demonstrating that the latter can lead to unreliable and hardly repeatable results. Vapochromic paper-based films represent a simple, cost-effective, portable and disposable chemosensor that, combined with a proper RGB color analysis readout, is useful for the on-site detection of pyridine vapors in various industrial and environmental settings.