An Adaptable Porphyrin-Based pH-Responsive Ratiometric Fluorescent Nanoprobe for Rapid and Visual Acidity Detection

pH detection plays a critical role in human health monitoring, environmental protection and energy conservation. Herein, water-soluble porphyrin derivative nanoparticles (WSPD NPs) were successfully synthesized, exhibiting a ratiometric fluorescent response in acidic aqueous solutions with a significant fluorescence color change from red to orange as pH values decreased from 4 to 2. Notably, WSPD NPs displayed similar fluorescence behavior in various acidic organic solvents. The pH-responsive mechanism is attributed to the protonation of pyrrolic nitrogen, a process unaffected by solvent species. WSPD NPs possessed excellent biocompatibility with low cytotoxicity and efficient cellular uptake for intracellular pH imaging. Furthermore, their good solubility and photostability in battery electrolytes allowed for pH detection in sodium (Na) half-cells. The developed WSPD NPs test strips for convenient and visual pH sensing obtained satisfactory results in different acidic solvents, and the fluorescence messages could be stored for a week, while avoiding damage to the pH meter and addressing the short preservation time of commercial pH test strips. This WSPD NPs-based ratiometric fluorescent nanoprobe realized a rapid response for pH detection under various acidic conditions, accompanied by the fluorescence color changes discernible to the naked eye. Its versatility allows for applications in drinking beverage samples, pH sensing test strips, living cells, and battery electrolytes.