Real-Time Detection of Burn Wound Infection via a Turn-On NIR-II Fluorescent Probe

Skin infections represent a major clinical challenge and are frequently associated with persistent bacterial colonization and delayed wound healing. The progression of these skin infections, particularly in burn wounds, is directly mirrored by an elevation in local pH, which serves as a critical physicochemical marker of bacterial metabolic activity. However, studies using pH as a biomarker for real-time, in situ monitoring of infection status remain relatively limited. Current pH-responsive probes are often restricted by shallow tissue penetration and significant background interference, which reduce sensitivity and imaging contrast in complex biological environments. Herein, using a difluoroboron (BF₂) formazanate scaffold, we designed a series of NIR-II probes that are selectively activated by elevated pH associated with bacterial infection. Within these probes, AlkaP-BF₂ exhibits strong NIR-II emission (> 1000 nm) and displays a "turn-on" fluorescence over the pH range of 7.26-9.23. The utility of AlkaP-BF₂ was demonstrated by monitoring intracellular pH changes in bacterial cells and visualizing infection-associated pH elevations within burn wounds using NIR-II fluorescence imaging. Collectively, these findings establish AlkaP-BF₂ as a powerful noninvasive tool that enables the precise, real-time visualization of infection-associated microenvironmental changes in skin tissues.