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 ΔE rgb , 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. • Development of a paper-based sensor for vapochromic detection of pyridine vapors. • Detection by smartphone-assisted color recognition app and RGB color analysis. • Proper RGB color analysis by color difference of normalized RGB values ( ΔE rgb ). • Assessment of the RGB color analysis through UV–vis reflectance measurements. • Detection of pyridine vapor concentration from tens to thousands of ppm.