Quantifying Hypochlorous Acid Concentration in Environmental Water Using Smartphone Colorimetry

Fast and easy detection of hypochlorite by a smartphone-based fluorescent turn-on probe: Applications to water samples, zebrafish and plant imaging

We have developed a fluorescent probe DBT-Cl ((E)-2-(2-(4-(diphenylamino)benzylidene) hydrazinyl)-N,N,N-trimethyl-2-oxoethan-1-aminium chloride) for ClO- with an aggregation-induced emission (AIE) strategy depending on solvent polarity. DBT-Cl possessed a prominent solvatochromic emission property with intramolecular charge transfer (ICT) from the TPA (triphenylamine) to the amide group, which was studied by spectroscopic analysis and DFT calculations. These unique AIE properties of DBT-Cl led to the recognition of ClO- with high fluorescent selectivity. DBT-Cl quickly detected ClO- in less than 1 sec with a fluorescent color change from green to cyan. DBT-Cl had a low detection limit of 9.67 μM to ClO-. Detection mechanism of DBT-Cl toward ClO- was illustrated to be oxidative cleavage of DBT-Cl by 1H NMR titrations, ESI-mass, and DFT calculations. We established the viability for dependable detection of ClO- in actual water samples, as well as zebrafish and plant imaging. In particular, DBT-Cl was capable of easily monitoring ClO- through a smartphone application. Therefore, DBT-Cl assured a promising approach for a fast-responsive and multi-applicable ClO- probe in environmental and living organism systems.

A Photoelectrochemical Sensor for the Detection of Hypochlorous Acid with a Phenothiazine-Based Photosensitizer

This paper presents the development of a photoelectrochemical sensor for hypochlorous acid (HOCl) detection, employing a phenothiazine-based organic photosensitizer (Dye-PZ). The designed probe, Dye-PZ, follows a D-π-A structure with phenothiazine as the electron-donating group and a cyano-substituted pyridine unit as the electron-accepting group. A specific reaction of the phenothiazine sulfur atom with HOCl enables selective recognition. The covalent immobilization of Dye-PZ onto a titanium dioxide nanorod-coated fluorine-doped tin oxide electrode (FTO/TiO2) using bromo-silane coupling agent (BrPTMS) resulted in the fabrication of the photoanode FTO/TiO2/BrPTMS/Dye-PZ. The photoanode exhibited a significant photoresponse under visible-light irradiation, with a subsequent reduction in photocurrent upon reaction with HOCl. The oxidation of the phenothiazine sulfur atom to a sulfoxide diminished the internal charge transfer (ICT) effect. Leveraging this principle, the successful photoelectrochemical sensing of HOCl was achieved. The sensor showed high stability, excellent reproducibility, and selective sensitivity for HOCl detection. Our study provides a novel approach for the development of efficient photoelectrochemical sensors based on organic photosensitizers, with promising applications in water quality monitoring and biosensing.