A novel low-cytotoxicity fluorescent probe applied to monitor pH in vivo and in vitro

Environmental pH plays an irreplaceable role in both cellular processes and production, and anomalous pH changes within cells may lead to various diseases. To tackle this issue, we designed and synthesized the novel low-cytotoxicity fluorescent probe called NAP-MP. The probe incorporates 1,8-naphthalimide as the fluorescence emitter, 1-methylpiperazine as the pH-sensitive moiety, and utilizes 3-aminopropyltriethoxysilane to improve its biocompatibility. The fluorescence of NAP-MP inhibits the photoinduced electron transfer (PET) process with the protonation of 1-methylpiperazine, resulting in the enhancement of fluorescence intensity. Density functional theory calculations have also confirmed the fluorescence mechanism. The probe demonstrates high selectivity, photostability and recyclability. The hydrogel prepared by the probe can detect different concentrations of ammonia in the air. In addition, due to its low toxicity and good biocompatibility, this probe has been successfully employed to observe pH changes in living HeLa cells. Overall, the development of this probe offers significant potential in the field of pH sensing, allowing for precise monitoring of pH levels in both environmental and biological systems. [Display omitted] •NAP-MP demonstrates excellent linear pH changes within the range of 6–8.•NAP-MP has excellent selectivity, photostability, and recyclability.•NAP-MP has low toxicity and good biocompatibility, which can be used to observe pH changes in living HeLa cells.•NAP-MP hydrogel can be utilized to the detection of environmental ammonia with a smartphone scanning application.