Reversible spiropyran-based chemosensor with pH-switches and application for bioimaging in living cells, Pseudomonas aeruginosa and zebrafish

Intracellular pH was tightly regulated in many biological processes in which cells must control pH changes within a precise range. Hence, tracing intracellular pH variation was important for understanding the physiological and pathological processes. Although fluorescent probes can be a necessary tool for detecting changes in pH, there are many limitations to existing probes, such as background interference, large cytotoxicity, and poor permeability, which need to be urgently overcome. In this work, a ratiometric and colorimetric chemosensor based on spiropyran (SP-DCCH) was fabricated for monitoring pH change using fluorescence resonance energy transfer mechanism. SP-DCCH has demonstrated the advantages of high sensitivity and selectivity, outstanding permeability and hypotoxicity. Moreover, SP-DCCH displays a pH-sensitive response from 1.68 to 7.21 (pKa = 4.87) and a linear response from pH 3.81 to 6.01, which was desirable for detecting pH change in living biosystem. As expected, the results confirmed that the response signal was pH-dependent and regulated via switchable forms between spiropyran and merocyanine. Spectacularly, SP-DCCH has successfully realized sensing and mapping pH in living cells, P. aeruginosa and zebrafish. The above results exhibited that SP-DCCH could be a powerful tool for sensing and visualizing pH in living systems.