Development of Digital Colorimetric-Based Thiourea Receptor for Highly Sensitive Detection of Dihydrogen Phosphate

This study aimed to synthesize a new chemosensor, namely 1,1’-(1,4-phenylene)bis(3-(4-nitrophenyl)thiourea), specifically designed for detection of H2PO4−. The compound was characterized using FTIR, LC-MS, 1H NMR, and 13C NMR, while the colorimetric sensing abilities were validated through various analyses. These include linearity, limit of detection (LOD), limit of quantification (LOQ), precision, and accuracy using UV-Vis spectrophotometry, RGB, and HSV color components. Digital images of color changes were captured using a smartphone camera and Color Grab app was used to quantify color components. Subsequently, anions test (NO3−, Cl–, HSO4−, and H2PO4−) were conducted in acetonitrile, where the addition of H2PO4− induced a distinct color change from colorless to yellow. The results showed that detection of H2PO4− depended on pH of the solution, with no color change observed at pH 1-3 due to anions converting to acidic species. At pH 5, H2PO4− was detected as a yellow color change, and alkaline conditions led to different color responses. Furthermore, UV-Vis detection showed recovery values of 99.80% to 100.6%, indicating high accuracy. RGB and HSV color component-based sensors showed recovery values of 101.6% to 114.4% and 92.50% to 110.2%, respectively. The LOD of the UV-Vis, RGB, and HSV methods were 0.16 µM, 0.46 µM, and 0.18 µM, while LOQ values were 0.54 µM,1.52 µM, and 0.61 µM, respectively. In conclusion, the synthesized chemosensor showed potential for accurate and sensitive detection of H2PO4− using UV-Vis spectrophotometry and digital colorimetric-based image