Advancing fluoride (F–) detection: Exploring the potential of digital color analysis with a novel thiourea receptor

This study aimed to explore a novel colorimetric detection method for fluoride using spectroscopic and digital analysis techniques. Thiourea compound synthesized from p-phenylenediamine and 4-nitrophenyl isothiocyanate was used as a receptor, with the NH group playing the role of a binding site to enhance the colorimetric detection process. This method facilitated visual detection by the naked eye and offered selectivity for fluoride ions. The result showed that there was a significant color change response, shifting from colorless to orange when fluoride was detected using the thiourea receptor. In this context, the color change was characterized by a bathochromic shift observed with UV–Vis spectrophotometry and quantified through high Euclidean Distance (ΔE) value of RGB color characteristics in digital analysis. Furthermore, the thiourea-based fluoride detection method had a low detection limit of 1.4 µM for spectroscopic analysis and 1.7 µM for digital analysis, along with a high recovery rate. These results affirmed the significance of spectroscopic and digital analyses using the thiourea receptor as a promising alternative for the rapid on-site detection of fluoride in real environmental samples.