An Environmentally Applicable Thiourea-based Colorimetric Chemosensor for Monitoring ClO⁻

We developed a thiourea-based colorimetric chemosensor, NQH (N-(naphthalen-1-yl)-2-(quinoline-2-yl)hydrazine-1-carbothioamide), that could selectively recognize ClO⁻. NQH responded to ClO⁻ through a desulfurization reaction, resulting in a color change from colorless to yellow. Detection limit of NQH for ClO⁻ was 5.61 µM, and it functioned effectively over a wide pH range (3–10). The probe NQH showed low interference when combined with other analytes. NQH enabled practical detection in real water samples (tap, drinking, and river) and could be implemented in a test strip and smartphone-based quantitative systems for on-site analysis. NQH showed reliable recoveries for ClO⁻ quantification in real water samples by using a smartphone-based spike-and-recovery method. The desulfurization reaction mechanism for the colorimetric detection of ClO⁻ was elucidated using electrospray ionization mass spectrometry (ESI-MS), nuclear magnetic resonance (NMR) titration, and density functional theory (DFT) calculations.