Hypochlorous acid (HClO) serves as a critical biomarker in inflammatory diseases such as rheumatoid arthritis (RA), and its real-time imaging is essential for understanding its biological functions. In this study, we designed and synthesized a novel probe, RHMB, which ingeniously integrates rhodamine B and methylene blue fluorophores with HClO-specific responsive moieties into a single molecular framework. Upon exposure to HClO, RHMB exhibited significant dual-channel fluorescence enhancement characterized by high sensitivity (LODs of 2.55 nM and 14.08 nM), excellent selectivity, and rapid response time (within 5 s). Notably, RHMB enabled reliable imaging of both exogenous and endogenous HClO in living cells and in zebrafish, employing a unique duplex-imaging turn-on approach that highlighted its adaptability across various biological contexts. Furthermore, RHMB effectively monitored HClO fluctuations in an RA mouse model and assessed the therapeutic efficacy of diclofenac (Dic) in alleviating RA symptoms. These findings underscore the potential of RHMB as an invaluable tool for elucidating the biological roles of HClO in various diseases.

Wound infections, exacerbated by the prevalence of antibiotic-resistant bacterial pathogens, necessitate innovative antimicrobial approaches. Polymicrobial infections, often involving Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus (MRSA), present challenges due to biofilm formation and antibiotic resistance. Hypochlorous acid (HOCl), a potent antimicrobial agent, holds promise as an alternative therapy. An electrochemical bandage (e-bandage) that generates HOCl in situ via precise polarization controlled by a miniaturized potentiostat was evaluated for the treatment of murine wound biofilm infections containing both P. aeruginosa with \"difficult-to-treat\" resistance and MRSA. Previously, HOCl-producing e-bandage was shown to reduce murine wound biofilms containing P. aeruginosa alone. Here, in 5-mm excisional skin wounds containing 48-h biofilms comprising MRSA and P. aeruginosa combined, polarized e-bandage treatment reduced MRSA by 1.1 log10 CFU/g (P = 0.026) vs non-polarized e-bandage treatment (no HOCl production), and 1.4 log10 CFU/g (0.0015) vs Tegaderm only controls; P. aeruginosa was similarly reduced by 1.6 log10 CFU/g (P = 0.0032) and 1.6 log10 CFU/g (P = 0.0015), respectively. For wounds infected with MRSA alone, polarized e-bandage treatment reduced bacterial load by 1.1 log10 CFU/g (P = 0.0048) and 1.3 log10 CFU/g (P = 0.0048) compared with non-polarized e-bandage and Tegaderm only, respectively. The e-bandage treatment did not negatively impact wound healing or cause tissue toxicity. The addition of systemic antibiotics did not enhance the antimicrobial efficacy of e-bandages. This study provides additional evidence for the HOCl-producing e-bandage as a novel antimicrobial strategy for managing wound infections, including in the context of antibiotic resistance and polymicrobial infections.
OBJECTIVE: New approaches are needed to combat the rise of antimicrobial-resistant infections. The HOCl-producing electrochemical bandage (e-bandage) leverages in situ generation of HOCl, a natural biocide, for broad-spectrum killing of wound pathogens. Unlike traditional therapies that may exhibit limited activity against biofilms and antimicrobial-resistant organisms, the e-bandage offers a potent, standalone solution that does not contribute to further resistance or require adjunctive antibiotic therapy. Here, we show the ability of the e-bandage to address polymicrobial infection by antimicrobial resistant clinical isolates of Staphylococcus aureus and Pseudomonas aeruginosa, two commonly isolated, co-infecting wound pathogens. Effectiveness of the HOCl-producing e-bandage in reducing pathogen load while minimizing tissue toxicity and avoiding the need for systemic antibiotics underscores its potential as a tool in managing complex wound infections.

Atherosclerosis (AS) is the leading cause of cardiovascular disease. Foam cells, with elevated lipid droplets (LDs) and HClO levels, are the main components of the atherosclerotic plaques that are characteristic of AS. Super-resolution imaging can be used to visualize the distribution of LDs in foam cells at the nanometer level, facilitating the identification of LDs and HClO. In the present study, we report the development of a ratiometric fluorescent probe, SFL-HClO, for super-resolution imaging of LDs and HClO. Super-resolution imaging with this probe revealed the precise structure of LDs at the suborganelle level. Moreover, the fluorescence behavior of SFL-HClO on the surface of LDs verified its excellent performance in detecting HClO in the foam cells. SFL-HClO can sequentially and specifically respond to LDs and HClO via \"turn-on\" and ratiometric signal output, respectively, thus contributing to precise imaging of foam cells. Importantly, we demonstrate that SFL-HClO can be used to report on upregulated HClO in atherosclerotic plaques in the aorta of AS mice, providing a suitable fluorescent tool for early atherosclerotic disease assessment.

BACKGROUND: Bisulfite (HSO3-) serves as a bleaching agent, antioxidant, antimicrobial, and regulator of enzymatic reactions in biosystem. However, abnormal levels of bisulfite can be detrimental to health. Hypochlorous acid (HOCl), which acts as bioactive small molecules, is crucial for maintaining normal biological functions in living organisms. Disruption of its equilibrium can lead to oxidative stress and various diseases. Therefore, it\'s essential to monitor the fluctuations of HOCl and HSO3- at cellular and in vivo levels to study their physiological and pathological functions.
RESULTS: This study constructed a novel NIR bifunctional colorimetric fluorescent probe using thienocoumarin-indanedione structures to identify hypochlorite (ClO-) and bisulfite (HSO3-). By using CSO-IO to recognize HSO3- and HOCl, two distinct products were generated, displaying green and blue fluorescence, respectively. This property effectively allows for the simultaneous dual-functional detection of HSO3- (LOD: 113 nM) and HOCl (LOD: 43 nM).
CONCLUSIONS: In this work, the biocompatible molecule CSO-IO has been effectively designed to detect HOCl/HSO3- in living cells and zebrafish. As a result, the dual-functional fluorescent probe has the potential to be utilized as a molecular tool to detect HSO3- derived compounds and HOCl simultaneously within the complex biological system.

BACKGROUND: Photodynamic therapy (PDT) is a pioneering and effective anticancer modality with low adverse effects and high selectivity. Hypochlorous acid or hypochlorite (HClO/ClO-) is a type of inflammatory cytokine. The abnormal increase of ClO- in tumor cells is related to tumor pathogenesis and may be a \"friend\" for the design and synthesis of responsive phototherapy agents. However, preparing responsive phototherapy agents for all-in-one noninvasive diagnosis and simultaneous in situ therapy in a complex tumor environment is highly desirable but still remains an enormously demanding task.
RESULTS: An acceptor-π bridge-donor-π bridge-acceptor (A-π-D-π-A) type photosensitizer TPTPy was designed and synthesized based on the phenothiazine structure which was used as the donor moiety as well as a ClO- responsive group. TPTPy was a multifunctional mitochondria targeted aggregation-induced emission (AIE) photosensitizer which could quickly and sensitively respond to ClO- with fluorescence \"turn on\" performance (19-fold fluorescence enhancement) and enhanced type I reactive oxygen species (ROS) generation to effectively ablate hypoxic tumor cells. The detection limit of TPTPy to ClO- was calculated to be 185.38 nM. The well-tailored TPTPy anchoring to mitochondria and producing ROS in situ could disrupt mitochondria and promote cell apoptosis. TPTPy was able to image inflammatory cells and tumor cells through ClO- response. In vivo results revealed that TPTPy was successfully utilized for PDT in tumor bearing nude mice and exhibited excellent biological safety for major organs.
UNASSIGNED: A win-win integration strategy was proposed to design a tumor intracellular ClO- responsive photosensitizer TPTPy capable of both type I and type II ROS production to achieve photodynamic therapy of tumor. This work sheds light on the win-win integration design by taking full advantage of the characteristics of tumor microenvironment to build up responsive photosensitizer for in situ PDT of tumor.

BACKGROUND: Highly reactive oxygen species (ROS) could lead to serious damage in living cells and are associated with many diseases like cancers. Metal cluster with strong fluorescence has great potential in biosensing and many thiolate ligands-protected clusters have been applied in ROS sensing.
RESULTS: In this work, we synthesized levonorgestrel protected Au10 cluster with specific sensing ability for highly ROS via crystal transformation from Au8 cluster, demonstrating the significance of inner core structure on detecting performance. The detection limit of Au10 cluster for ClO- could reach as low as 0.1 μM. This fluorescent probe not only achieving detection of exogenous ClO- in living cells and zebrafish, but also successful imaging of endogenous ClO- in HeLa and HepG2 cells.
CONCLUSIONS: In comparison to previously reported cluster-based sensors for ROS, this work proposes a different reaction mechanism of metal nanoclusters for ROS detection (breakage of gold-alkynyl bond and oxidation of alkynyl group). This provides new directions for designing specific ROS probes and broadens the applications of metal clusters in disease diagnostics.

As a type of reactive oxygen species, hypochlorous acid (ClO-) plays an important role in sterilization, disinfection and protection in organisms. However, excessive production of ClO- is closely related to various diseases. In this work, we have designed a robust ratiometric fluorescent probe, RDB-ClO, using the excited-state intramolecular proton transfer (ESIPT) strategy. RDB-ClO was achieved by modifying 2-(2-(benzo[d]thiazol-2-yl)-6-(diethylamino)-3-oxo-3H-xanthen-9-yl) benzoic acid (RDB-OH) with a 1-naphthoyl chloride group, specifically for the sensitive detection of ClO-. In the presence of ClO-, RDB-ClO demonstrated relatively good performance, showing swift response time (35 s), low detection limit of 5.1 nM and high selectivity towards ClO-. Notably, the convenience and accessibility detection of ClO- has been implemented using test strip and agarose probe. RDB-ClO effectively tracked both endogenous and exogenous ClO- in HeLa cells, HepG2 cells and zebrafish. Additionally, it is successfully applied to detect changes of exogenous ClO- content in E. coli. and acetaminophen (APAP)-induced liver injury in mice. The development of RDB-ClO represents a promising molecular tool for studying the pathogenesis of DILI and biotransformation of ClO- in bacteria.

Hypochlorite (ClO-) and gallium (Ⅲ) ions (Ga3+) have extensive applications in various human industries and daily activities. However, their inherent toxicity poses significant risks to environmental preservation and human well-being. Hence, the development of reliable and handy detection tools for ClO- and Ga3+ in the environment and food is crucial. In this study, a ratiometric fluorescent probe was prepared based on benzothiazolaldehyde and pyridine-2-carboxylic acid hydrazide, which exhibited exceptional performance characteristics for the selective detection of ClO- and Ga3+. These features include high specificity, low detection limits (0.28 μM for ClO-, 0.13 μM for Ga3+), mild pH conditions (pH 4-11 for ClO-, pH 6-11 for Ga3+), fast response time (within 30 s), as well as versatile applicability across different matrices such as water, soil, food, and plant samples. Additionally, this probe can be used with a smartphone color recognition app. The probe offers a convenient and effective tool for the detection of ClO- and Ga3+, demonstrating its potential application value in environmental monitoring and food safety.

Since the onset of the SARS-CoV-2 pandemic in early 2020, there has been a notable rise in sodium hypochlorite disinfectants. Sodium hypochlorite undergoes hydrolysis to generate hypochlorous acid for virus eradication. This chlorine-based disinfectant is widely utilized for public disinfection due to its effectiveness. Although sodium hypochlorite disinfection is convenient, its excessive and indiscriminate use can harm the water environment and pose a risk to human health. Hypochlorous acid, a reactive oxygen species, plays a crucial role in the troposphere, stratospheric chemistry, and oxidizing capacity. Additionally, hypochlorous acid is vital as a reactive oxygen species in biological systems, and its irregular metabolism and level is associated with several illnesses. Thus, it is crucial to identify hypochlorous acid to comprehend its environmental and biological functions precisely. Here, we constructed a new fluorescent probe, utilizing the twisted intramolecular charge transfer mechanism to quickly and accurately detect hypochlorous acid in environmental water and biosystems. The probe showed a notable increase in fluorescence when exposed to hypochlorous acid, demonstrating its excellent selectivity, fast response time (less than 10 seconds), a large Stokes shift (∼ 102 nm), and a low detection limit of 15.5 nM.

Endogenous hypochlorous acid (HOCl) is one of the most important reactive oxygen species (ROS) and acts as a distinct biomarker that is involved in various inflammatory responses including rheumatoid arthritis (RA). Therefore, it\'s crucial to develop an efficient method for the tracking and analysis of HOCl levels in vivo. Natural products continue to be compounds of interest, because they not only offer diverse and specific molecular scaffolds but also provide invaluable sources for new drug discovery. Herein, we firstly demonstrated harmaline (HML), a natural alkaloid mainly found in Peganum harmala L, could be acted as a novel fluorescent probe for HOCl with exceptional precision and responsiveness. Remarkably, this probe not only specifically tracked HOCl levels in cells and inflammatory RA mouse models, but also exhibited effective anti-inflammatory effects on RAW264.7 cells and anti-proliferative effects on fibroblast-like synoviocytes. Furthermore, HML has the potential to alleviate LPS-induced inflammation by inhibiting the NF-κB signaling pathway. This study represents the first example of a natural product that can simultaneously act as a fluorescent probe for specific ROS and a promising therapeutic candidate for a specific disease, which will undoubtedly extend the application of fluorophore-rich natural products.