A human serum albumin-assisted caged fluorophore probe for fluorescence turn-on detection of hypochlorous acid.

Fluorescence detection of hypochlorous acid (HOCl), a reactive oxidant that modulates immune responses and inflammation, can be complicated in serum due to nonspecific interactions between fluorescent probes and serum proteins. In particular, human serum albumin (HSA), the most abundant protein in serum, can alter the probe fluorescence by increasing background signals and distorting analyte-dependent responses. Rather than suppressing this protein-induced effect, we sought to convert albumin binding into a controlled signal-generation step. Here, we report DSH, an HSA-assisted caged fluorophore probe for HOCl detection in albumin-containing media. DSH was constructed by masking dansyl-sarcosine (DS) with a 2,4-dinitrophenyl caging group through a hydrazine-based linker that undergoes oxidative cleavage in response to HOCl. In the caged state, fluorescence is suppressed, and direct albumin-induced activation is minimised. Upon exposure to HOCl, oxidative cleavage of the linker releases DS, which subsequently binds to HSA and produces a fluorescence turn-on response. Thus, HSA binding, typically considered a source of matrix interference, is repurposed as a signal-amplifying step in the sensing mechanism. This DSH-based sensing strategy enables calibration-based quantitative detection of HOCl in phosphate-buffered saline supplemented with HSA and diluted human serum, supporting the feasibility of this caged-fluorophore design under controlled albumin-containing conditions.