Bifunctional Bile Acid-Salicylaldehyde Based Fluorescent Probe for Excellent Detection of Hydrazine and pH, and Multiple Applications in Environmental Samples, Smartphone-Assisted System, Paper Strips, and Living Cells.

A new cholic acid-salicylaldehyde conjugate, probe CASA, was facilely constructed through one-step esterification. The probe sensitively and selectively detected both N2H4 and pH, with the salicylaldehyde group as the sensing site. Based on the combined AIE/ESIPT mechanism, the probe exhibited a yellow-green turn-on fluorescent response to N2H4 with a low detection limit of 26 nM and a rapid detection time of 10 min. Through the ICT process, the probe displayed a light blue turn-on fluorescence signal for neutral pH variations in a linear range of 5.0-7.8 with a pKa value of 6.26. The microstructural attributes of the probe during assembly could elucidate the recognition processes. Probe CASA enabled quantitative analysis of N2H4 and pH in real environmental samples. A smartphone-assisted sensing system and probe-coated portable test strips were developed to facilitate convenient and on-site testing. Additionally, the probe possessed excellent biocompatibility and low cytotoxicity, making it possible to monitor the changes of N2H4 and pH within living cells. This dual-channel N2H4-pH independent detection can prevent spectral crosstalk, facilitate instrument simplification, and provide a more intelligent and reliable analytical toolkit for complex systems. The findings are anticipated to provide more innovative strategies of highly efficient fluorescent probes for multi-analyte detection.