Structure-Activity Relationship Guided Design of a Highly Sensitive Turn-on Fluorescent Probe for Imaging Inflammation-Associated-HOCl in Early Liver Fibrosis.

Early-stage liver fibrosis is potentially reversible, yet its timely diagnosis remains challenging due to the lack of sensitive molecular imaging tools. Hypochlorous acid (HOCl), an inflammation-associated reactive oxygen species has emerged as a key pathogenic mediator and early biomarker of fibrotic progression. Herein, guided by a structure-activity relationship (SAR) strategy, three donor-π-acceptor (D-π-A) fluorescent probes (PMBT, CMBT, and TMBT) were rationally designed and systematically evaluated for HOCl detection. Density functional theory calculations (DFT) and spectroscopic studies reveal donor-dependent electronic distributions and distinct HOCl-responsive behaviors. Among them, PMBT exhibits a rapid turn-on response (<10 s), naked-eye-detectable fluorescence enhancement, and a low detection limit of 11.38 nM, along with favorable mitochondrial localization. Benefiting from its high sensitivity and liver-targeting capability, PMBT enables effective imaging of endogenous HOCl and allows precise visualization of early-stage liver fibrosis in mouse models, highlighting its potential as a powerful diagnostic tool.