Cascade-activated fluorescent probe for temporal imaging of H2S and microviscosity dynamics under inflammatory stress.

Inflammation is a critical pathological process closely associated with redox imbalance, metabolic dysregulation, and microenvironment changes. Hydrogen sulfide (H2S) and microviscosity are both involved in inflammation stress, but their temporal relationship remains unclear. Existing H2S-viscosity dual-responsive probes mainly provide parallel readouts or are often limited by insufficient spectral separation. Herein, we developed a cascade-activated fluorescent probe PPAC-SNO2 for sequential detection of H2S and viscosity with a large spectral separation of 178 nm. Upon reaction with H2S, PPAC-SNO2 undergoes sulfonate cleavage to release PPAC-OH, producing red emission at 630 nm. Under high-viscosity conditions, the excited-state conformational evolution of PPAC-OH is restricted, generating blue-green emission at 452 nm. The large spectral separation minimizes channel crosstalk and enables accurate dual-channel imaging. In the lipopolysaccharide/aminooxyacetic acid group, where endogenous H2S biosynthesis was inhibited, delayed viscosity elevation was still observed, indicating that viscosity elevation is associated with inflammatory stress. In summary, PPAC-SNO2 enables dual-channel visualization of H2S and viscosity with large spectral separation and low crosstalk, providing a useful tool for probing time-dependent chemical signaling and microenvironment change during inflammatory stress.