Fluorescent Probes for Hypochlorous Acid Detection in Biological Systems

Fluorescent probes are indispensable tools for the sensitive and selective detection of hypochlorous acid (HOCl) in living systems. HOCl, produced by the myeloperoxidase–chloride–hydrogen peroxide system in phagocytes, plays a dual role as a microbicidal agent and a mediator of inflammatory tissue damage. The capacity to visualise HOCl in real time has driven the development of probes featuring turn-on fluorescence, ratiometric output or time-gated luminescence. Many designs employ near-infrared (NIR) emission to minimise autofluorescence and enable deep-tissue penetration. Key sensing mechanisms include oxidative cleavage of recognitive linkers, deformylation reactions and selective quenching of lanthanide complexes. Advances in scaffold engineering—using ESIPT, FRET or hemicyanine frameworks—have delivered nanomolar detection limits, rapid response kinetics on the order of seconds and high selectivity over other reactive oxygen species. Incorporation of organelle-targeting moieties has permitted subcellular mapping of HOCl in mitochondria, lysosomes and phagosomes, shedding light on its roles in redox signalling, infection biology and disease progression. In vivo applications in models of rheumatoid arthritis, stroke and cancer underscore the translational potential of these probes for diagnosis, therapy monitoring and fundamental research. Emerging trends include multimodal sensors with logic-gate functions, paper-based test strips for point-of-care assays and nanoparticle-enabled ratiometric platforms aimed at clinical deployment.

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Fluorescent Probes for Hypochlorous Acid Detection in Biological Systems publication trend

The graph below shows the total number of articles in fluorescent probes for hypochlorous acid detection in biological systems across all publications each year (not limited to Nature Index journals).

Technical terms

Hypochlorous acid (HOCl): A potent oxidant generated by myeloperoxidase in phagocytes, involved in microbial killing and inflammatory damage.

Fluorescent probe: A molecule designed to produce a measurable fluorescence change upon interaction with a specific analyte.

Reactive oxygen species (ROS): Chemically reactive molecules containing oxygen, including HOCl, hydrogen peroxide and superoxide, with roles in cell signalling and oxidative stress.

Ratiometric detection: A sensing approach that measures the ratio of fluorescence intensities at two wavelengths to improve quantitative accuracy.

Near-infrared (NIR) emission: Fluorescence occurring in the 650–900 nm window, which offers reduced background autofluorescence and deeper tissue penetration.

Stokes shift: The difference in wavelength between a probe’s absorption peak and its emission peak, with larger shifts reducing spectral overlap.

References

1. Modeling the Reactions of Superoxide and Myeloperoxidase in the Neutrophil Phagosome IMPLICATIONS FOR MICROBIAL KILLING *. Journal of Biological Chemistry (2006).
2. Deformylation reaction-based probe for in vivo imaging of HOCl. Chemical Science (2018).
3. Rapid Response Fluorescence Probe Enabled In Vivo Diagnosis and Assessing Treatment Response of Hypochlorous Acid‐Mediated Rheumatoid Arthritis. Advanced Science (2018).
4. ESIPT-based fluorescence probe for the rapid detection of hypochlorite (HOCl/ClO − ). Chemical Communications (2018).
5. Dual-emissive nanoarchitecture of lanthanide-complex-modified silica particles for in vivo ratiometric time-gated luminescence imaging of hypochlorous acid. Chemical Science (2017).
6. A hemicyanine-based fluorescent probe for ratiometric detection of ClO- and turn-on detection of viscosity and its imaging application in mitochondria of living cells and zebrafish. Sensors and Actuators B Chemical (2023).
7. Imaging of hypochlorous acid in mitochondria using an asymmetric near-infrared fluorescent probe with large Stokes shift. Chemical Science (2022).