A Versatile pH-Dependent Fluorometric, Colorimetric, and Electrochemical Sensor for H₂S Monitoring in Water

Hydrogen sulfide (H₂S) is a colorless, foul smelling, toxic substance that can be found in water bodies and waste waters, especially in occupational susceptible environments, and can lead to harmful effects in humans at higher concentrations. An H₂S monitoring probe NNAP is synthesized, which displays pH-dependent electrochemical, colorimetric, and fluorescence responses. NNAP functions as a fluorometric sensor at pH 7.4, with a limit of detection (LOD) of 0.70 mM, and as a colorimetric sensor at pH 12, where visible color changes are discernible to the naked eye, with an LOD of 4.28 mM. Additionally, it demonstrates utility in electrochemical sensing at pH 2, with a LOD of 2.5 mM. Furthermore, NNAP-coated paper strips have been successfully utilized for real-time H₂S monitoring applications.