A pH-responsive probe for sulfide ion detection and intracellular pH/sulfide sensing

Sul-pH is a pH-sensitive fluorescent probe designed to detect mildly alkaline environments through a protonation-deprotonation mechanism. The probe is constructed using an ICT-based molecular design, with a cyclic chalcone serving as the parent fluorophore. Sul-pH exhibits a pH response range of 7-10, during which its fluorescence intensity at 601 nm increases by nearly 250-fold as the pH shifts from neutral to alkaline, accompanied by a pronounced visual color change. Moreover, the pH-responsive behavior of Sul-pH was correlated with the alkalinity generated during the hydrolysis of sulfide ions, enabling its application in the quantitative detection of S^2-. The probe responds specifically to the alkaline conditions produced by S^2- hydrolysis, thereby eliminating interference from HS^- during sulfide detection. Impressively, Sul-pH displays a rapid response within 6 s and demonstrates excellent pH cycling stability as well as photostability. Sul-pH also shows good performance in detecting S^2- in real water samples. Furthermore, Sul-pH can detect both S^2- and pH in living cells, providing a reliable tool for monitoring intracellular pH dynamics and sulfide ion fluctuations within biological systems.