Development of a Rapid Fluorescence Probe for the Determination of Aqueous Hypochlorite

Chlorine interacts with the aqueous environment, including the mucosa and alveolar fluid in the lungs, causes the immediate transformation of chlorine to hypochlorous acid (HClO) and hydrochloric acid (HCl) which induces cellular damage and may produce systemic toxicity. There are multiple techniques to monitor hypochlorite (HClO/ClO^-) from various matrices, however, they each have significant disadvantages, including limited sensitivity, complexity, and slow response. In this study, we developed a water-soluble fluorescein-based probe, called fluorescein thioacid (FSH), for the rapid and sensitive detection of HClO/ClO^- in aqueous solutions via oxidation of FSH to produce fluorescein. FSH was synthesized via a simple, one-step procedure and exhibited excellent selectivity for ClO^-, maintaining 82% signal stability for 24 h. FSH performed well over a wide pH range (4 to 10; optimum pH of 4), produced a linear range from 1 to 100 μM, and had a detection limit of 100 nM. The probe was able to accurately quantify HClO/ClO^- concentrations in tap water (13.8 μM) and swimming pool water (56.9 μM) samples. Overall, FSH is simple to synthesize, highly selective, highly sensitive, has excellent water solubility, and produces a fast response for monitoring of aqueous ClO^- levels.