Fe3+ and H+-triggered "Turn-on" Fluorescence Probe Based on Lysosomal-targeted RBH-EdC for Monitoring Intragastric Acidity.

The long-term visualization of intracellular Fe³⁺ dynamics and lysosomal activity is crucial for investigating the physiological roles and functions of lysosomes during the growth of organisms. The lysosome-targeted fluorescent probe (RBH-EdC), derived from rhodamine-nucleoside conjugates, demonstrates a sophisticated dual-activation design: one is Fe³⁺ response, triggering spirolactam ring-opening to form xanthine structures, resulting in ≥ 1000-fold fluorescence enhancement with visible colorimetric transition (colorless→pink). Another is pH sensitivity, demonstrating protonation-dependent fluorescence amplification at the dC at site N3 (pK_a = 2.9), achieving a 30-fold intensity increase at pH 2.5 within the 1.0-5.0 range. Remarkably, the RBH-EdC/Fe³⁺ complex showed a further significant 20-fold fluorescence enhancement at pH 3.0. This Fe³⁺/H⁺ co-activated "turn-on" system provides exceptional signal amplification for both in vitro and in vivo applications, enabling precise exploration of lysosome-related biological processes, including the response of the pH microenvironment, real-time monitoring of lysosomal pH dynamics, in situ measurement of gastric acidity levels, and potential application in gastric ulcer diagnostics.