A novel fluorescent probe with large Stokes shift for accurate detection of HOCl in mitochondria and its imaging application

Rapid-response near-infrared fluorescence probe for colorimetric detection of HClO and its applications in environmental monitoring and biological imaging

As a crucial endogenous reactive oxygen species, hypochlorous acid (HClO) plays an indispensable role in numerous physiological and pathological processes. Additionally, it serves as a biomarker closely associated with inflammation and liver injury. The utilization of near-infrared fluorescence probes has surged in recent years for live biological imaging, owing to their minimal tissue damage and potent tissue penetration capabilities. In this work, a novel near-infrared fluorescence probe MB-HPD was synthesized to sensitively detect HClO. Probe MB-HPD exhibits remarkable selectivity, high sensitivity (14.3 nM), and rapid response towards HClO (20 s). Probe MB-HPD has demonstrated successful application in the imaging of HClO within cells and zebrafish. Remarkably, it has proven to be effective for detecting HClO within environmental samples, as well as imaging HClO in mice models of arthritis and APAP-induced liver injury. These findings indicate the broad applicability of probe MB-HPD, offering a promising avenue for designing highly selective near-infrared fluorescence probes suitable for real-time HClO monitoring.

Sulfur-based fluorescent probes for biological analysis: A review

The widespread adoption of small-molecule fluorescence detection methodologies in scientific research and industrial contexts can be ascribed to their inherent merits, including elevated sensitivity, exceptional selectivity, real-time detection capabilities, and non-destructive characteristics. In recent years, there has been a growing focus on small-molecule fluorescent probes engineered with sulfur elements, aiming to detect a diverse array of biologically active species. This review presents a comprehensive survey of sulfur-based fluorescent probes published from 2017 to 2023. The diverse repertoire of recognition sites, including but not limited to N, N-dimethylthiocarbamyl, disulfides, thioether, sulfonyls and sulfoxides, thiourea, thioester, thioacetal and thioketal, sulfhydryl, phenothiazine, thioamide, and others, inherent in these sulfur-based probes markedly amplifies their capacity for detecting a broad spectrum of analytes, such as metal ions, reactive oxygen species, reactive sulfur species, reactive nitrogen species, proteins, and beyond. Owing to the individual disparities in the molecular structures of the probes, analogous recognition units may be employed to discern diverse substrates. Subsequent to this classification, the review provides a concise summary and introduction to the design and biological applications of these probe molecules. Lastly, drawing upon a synthesis of published works, the review engages in a discussion regarding the merits and drawbacks of these fluorescent probes, offering guidance for future endeavors.

Development of Novel Fluorescent Probes for Specific Detection of Hypochlorous Acid

Hypochlorous acid (HClO) is widely used in everyday life for bleaching and disinfecting tap water, and also in human metabolism, where it plays an important role in destroying foreign bacterial invaders and pathogens as well as immune defense and cellular functioning maintenance. Abnormal levels of hypochlorous acid have the potential to cause joint inflammation, neuronal degeneration, and even life-threatening cancer. Specific identification and effective detection of hypochlorous acid are important for monitoring human health and the environment. In recent years, organic fluorescent probes have attracted much attention because of their simple synthesis, easy operation, high sensitivity, and high specificity, and a variety of hypochlorous acid fluorescent probes based on low-cost, easy-to-operate, and rapid identification have been developed. In this paper, we review the fluorescent probes that have been developed in the past five years for the specific recognition of hypochlorous acid based on different fluorophores, such as triphenylamine, coumarin, 1,8-naphthalize, etc., as well as recognition units, such as N-N dimethyl thiosemicarbazone, and describe how the probes and hypochlorous acid interact for identification in the same manner as other fluorescent probes. In addition, the reaction mechanism between the probe and hypochlorous acid, the fluorescence change of the probe, and the detection limit are described to illustrate the progress in the detection of hypochlorous acid in recent years and to provide ideas for the development of hypochlorous acid fluorescent probes in the future.

Ex Tenebris Lux: Illuminating Reactive Oxygen and Nitrogen Species with Small Molecule Probes

Reactive oxygen and nitrogen species are small reactive molecules derived from elements in the air─oxygen and nitrogen. They are produced in biological systems to mediate fundamental aspects of cellular signaling but must be very tightly balanced to prevent indiscriminate damage to biological molecules. Small molecule probes can transmute the specific nature of each reactive oxygen and nitrogen species into an observable luminescent signal (or even an acoustic wave) to offer sensitive and selective imaging in living cells and whole animals. This review focuses specifically on small molecule probes for superoxide, hydrogen peroxide, hypochlorite, nitric oxide, and peroxynitrite that provide a luminescent or photoacoustic signal. Important background information on general photophysical phenomena, common probe designs, mechanisms, and imaging modalities will be provided, and then, probes for each analyte will be thoroughly evaluated. A discussion of the successes of the field will be presented, followed by recommendations for improvement and a future outlook of emerging trends. Our objectives are to provide an informative, useful, and thorough field guide to small molecule probes for reactive oxygen and nitrogen species as well as important context to compare the ecosystem of chemistries and molecular scaffolds that has manifested within the field.

Ratiometric Fluorescent Probe for Super-Resolution Imaging of Lysosome HClO in Ferroptosis Cells

Ferroptosis is an iron-dependent programmed cell death that is characterized by the dysregulation of lipid reactive oxygen species (ROS) production, causing abnormal changes in hypochlorous acid (HClO) levels in lysosomes. Super-resolution imaging can observe the fine structure of the lysosome at the nanometer level; therefore, it can be used to detect lysosome HClO levels during ferroptosis at the suborganelle level. Herein, we utilize a ratiometric fluorescent probe, SRF-HClO, for super-resolution imaging of lysosome HClO. Structured-illumination microscopy (SIM) improves the accuracy of lysosome targeting and enables the probe SRF-HClO to be successfully applied to rapidly monitor the up-regulated lysosome HClO at the nanoscale during inflammation and ferroptosis. Importantly, the probe SRF-HClO can also detect HClO changes in inflammatory and ferroptosis mice and evaluate the inhibitory effect of ferroptosis on mice tumors.

Development of a Coumarin-derived Fluorescent Probe for Detection of HOCl and its Application in Cells and Zebrafish

We have prepared a simple, universal and efficient coumarin-derived fluorescent probe (XDS1) to detecting HOCl. The experimental findings revealed that the introduction of HOCl produced an obvious quenching effect on the probe with high selectivity and sensitivity. The calculated limit of detection (LOD) was as low as 0.02 μM. Furthermore, an impressive response time of less than 10 s was observed when XDS1 detecting HOCl. Importantly, the probe XDS1 exhibited negligible cytotoxicity, thereby facilitating its application for imaging HOCl within biological environment. The probe XDS1 had been successfully used for specific detection in cells.

Unraveling Ferroptosis Mechanisms: Tracking Cellular Viscosity with Small Molecular Fluorescent Probes

Ferroptosis is a recently identified form of regulated cell death characterized by iron accumulation and lipid peroxidation. Numerous functions for ferroptosis have been identified in physiological as well as pathological processes, most notably in the treatment of cancer. The intricate balance of redox homeostasis is profoundly altered during ferroptosis, leading to alteration in cellular microenvironment. One such microenvironment is viscosity among others such as pH, polarity, and temperature. Therefore, understanding the dynamics of ferroptosis associated viscosity levels within organelles is crucial. To date, there are a very few reviews that detects ferroptosis assessing reactive species. In this review, we have summarized organelle's specific fluorescent probes that detects dynamics of microviscosity during ferroptosis. Also, we offer the readers an insight of their design strategy, photophysics and associated bioimaging concluding with the future perspective and challenges in the related field.

A facile near-infrared xanthene fluorescence probe for visualizing of hypochlorous acid in vitro and in vivo

BACKGROUND

Hypochlorous acid (HClO) is an important biomarker for inflammation, cardiovascular disease, and even cancer. It is of great significance to accurately monitor and quantitatively analyze the fluctuations of HClO to better understand their physiological functions. Traditional HClO detection methods such as high-performance liquid chromatography (HPLC), and mass spectrometry are preferred, but are costly and unsuitable in vivo. Near-infrared (NIR) fluorescence imaging has the advantages of high sensitivity, high temporal and spatial resolutions, minimal autofluorescence, and deep tissue penetration, which facilitates its application in biological systems. Therefore, the development of sensitivity and simple NIR fluorescence monitoring HClO methods in vivo and in vitro is essential and desirable.

RESULTS

Herein, we present a NIR probe NOF3 by integrating the rhodamine scaffold and HClO-triggered moiety for the real-time detection of HClO in vitro and in vivo. NOF3 reacts with the HClO and releases the NOF-OH fluorophore of emitted signals at 730 nm, which is in the NIR region. The designed probe detected concentrations of HClO ranging from 0 to 17 μM with a low detection limit of 0.146 μM, presenting excellent sensitivity and selectivity toward HClO over other species. NOF3 manifests significantly turn-on NIR fluorescent signals in response to HClO concentration, which makes it favorable for monitoring dynamic HClO distribution in vivo. We exemplify NOF3 for the tracking of endogenously overexpressed HClO distribution in RAW 264.7 cells, and further realize real-time in vivo bioimaging of HClO activity in inflammation mice.

SIGNIFICANCE

The facile NIR NOF3 probe was successfully applied to visualize endogenous and exogenous HClO in living cells and mice. This study provides not only an effective tool for spatial and temporal resolution HClO bioimaging in vivo but also possesses great potential for use in future research on HClO-related biology and pathology.

Mitochondria-targetable small molecule fluorescent probes for the detection of cancer-associated biomarkers: A review

Cancer represents a global threat to human health, and effective strategies for improved cancer early diagnosis and treatment are urgently needed. The detection of tumor biomarkers has been one of the important auxiliary means for tumor screening and diagnosis. Mitochondria are crucial subcellular organelles that produce most chemical energy used by cells, control metabolic processes, and maintain cell function. Evidence suggests the close involvement of mitochondria with cancer development. As a consequence, the identification of cancer-associated biomarker expression levels in mitochondria holds significant importance in the diagnosis of early-stage diseases and the monitoring of therapy efficacy. Small-molecule fluorescent probes are effective for the identification and visualization of bioactive entities within biological systems, owing to their heightened sensitivity, expeditious non-invasive analysis and real-time detection capacities. The design principles and sensing mechanisms of mitochondrial targeted fluorescent probes are summarized in this review. Additionally, the biomedical applications of these probes for detecting cancer-associated biomarkers are highlighted. The limitations and challenges of fluorescent probes in vivo are also considered and some future perspectives are provided. This review is expected to provide valuable insights for the future development of novel fluorescent probes for clinical imaging, thereby contributing to the advancement of cancer diagnosis and treatment.

An ICT-switched fluorescent probe for visualizing lipid and HClO in lipid droplets during ferroptosis

Herein, we have designed and synthesized a fluorescent probe, LDs-ClO, which can detect hypochlorous acid and lipid accumulation simultaneously in lipid droplets of live RAW 264.7 cells. Cell ferroptosis was discovered to lead to an increase in HClO levels, and to possibly further stimulate accumulation of lipid. We expect the results of this work with LDs-ClO to promote the study of physiological and pathological processes related to lipid droplets and hypochlorite.

Exploring the Role of Mitochondrial Hydrogen Sulfide in Maintaining Polarity and mtDNA Integrity with a Multichannel Fluorescent Probe

Abnormal mitochondrial state has been implicated in the pathogenesis of various diseases including neurodegenerative disorders, myopathies, cardiovascular diseases, and cancers. Assessing mitochondrial functionality can be achieved by monitoring alterations in mitochondrial polarity and mitochondrial DNA (mtDNA) integrity, which serve as valuable biomarkers. Hydrogen sulfide (H2S), a gaseous signaling molecule, plays a regulatory role in mitochondrial respiratory chain activity, ATP synthesis, and calcium ion balance, thereby influencing cellular metabolism and signal transduction. Investigating the interplay between mitochondrial H2S, polarity, and mtDNA can enhance our understanding of the underlying regulatory mechanisms involved in H2S-mediated mitochondrial functions. To address this, we designed a mitochondria-targeted multichannel fluorescent probe, HNA, capable of cascaded detection of H2S and polarity, as well as parallel detection of mtDNA. The probe exhibited a significant turn-on response to H2S, emitting at approximately 604 nm, while the product HNAP demonstrated high sensitivity to polarity within the wavelength range of 526-591 nm. Additionally, the probe was able to bind to DNA, resulting in an enhanced long-wave emission at 668 nm. Facilitated by HNA, our study provides novel insights into the role of mitochondrial H2S in maintaining mitochondrial polarity and validates its protective effect on mtDNA through antioxidative mechanisms. Overall, this work proposes a potential therapeutic strategy for modulating the inflammatory process in mitochondrial-related diseases.

HClO imaging in vivo and drug-damaged liver tissues by a large Stokes shift fluorescent probe

Drug-induced liver injury (DILI), as a classic acute inflammation, has attracted widespread concern due to its unpredictability and severity. Among the various reactive oxygen species, HClO has been used as a marker for the detection of DILI process. Thus, we designed and synthesized a "turn-on" fluorescent probe FBC-DS by modifying 3'-formyl-4'-hydroxy-[1,1'-biphenyl]-4-carbonitrile (FBC-OH) with N, N-dimethylthiocarbamate group for sensitively sensing HClO. Probe FBC-DS showed a low detection limit (65 nM), fast response time (30 s), an enormous Stokes shift (183 nm) and 85-fold fluorescence enhancement at 508 nm in the detection of HClO. Probe FBC-DS could monitor exogenous and endogenous HClO in living HeLa cells, HepG2 cells and zebrafish. In addition, probe FBC-DS has been successfully utilized in biological vectors for imaging acetaminophen (APAP)-induced endogenous HClO. Moreover, DILI caused by APAP is evaluated by probe FBC-DS through imaging over-expression of endogenous HClO in the mice liver injury models. All in all, we have every reason to believe that probe FBC-DS can be a potential tool to study the complex biological relationship between HClO and drug-induced liver injury.

A "Turn-on" Fluorescent Probe Based on Phenothiazine for Selectively Recognizing ClO- and its Practical Applications

Hypochlorous acid (HClO), a highly reactive oxygen species, has important effects on human health. High selectivity and sensitivity remain challenges of fluorescent probes for detection of ClO- with a large Stokes shift. This work designed and synthesized a novel phenothiazine-based fluorescent probe TF which can detect ClO- by colorimetric and fluorescent dual signals. TF displayed turn-on fluorescence effect toward ClO- with high selectivity (≥ 28-folds) and sensitivity (LOD = 0.472 μM), fast response time (< 1 min) and large Stokes shift (150 nm) in PBS (pH = 7.4, 40% DMSO). Meanwhile, TF can visualize ClO- on the mung bean sprouts model and apply as testing strips for portable and rapid detecting ClO- by the naked eyes. A phenothiazine-based fluorescent probe with large Stokes shift was synthesized and its responding rapidly ability to detect ClO- was studied.

Fluorescent probes for lighting up ferroptotic cell death: A review

Ferroptosis is a newly discovered form of regulated cellular demise, characterized by the accumulation of intracellular oxidative stress that is dependent on iron. Ferroptosis plays a crucial role not only in the development and treatment of tumors but also in the pathogenesis of neurodegenerative diseases and illnesses related to ischemia-reperfusion injury. This mode of cell death possesses distinctive properties that differentiate it from other forms of cell death, including unique morphological changes at both the cellular and subcellular levels, as well as molecular features that can be detected using specific methods. The use of fluorescent probes has become an invaluable means of detecting ferroptosis, owing to their high sensitivity, real-time in situ monitoring capabilities, and minimal damage to biological samples. This review comprehensively elucidates the physiological mechanisms underlying ferroptosis, while also detailing the development of fluorescent probes capable of detecting ferroptosis-related active species across various cellular compartments, including organelles, the nucleus, and the cell membrane. Additionally, the review explores how the dynamic changes and location of active species from different cellular compartments can influence the ignition and execution of ferroptotic cell death. Finally, we discuss the future challenges and opportunities for imaging ferroptosis. We believe that this review will not only aid in the elucidation of ferroptosis's physiological mechanisms but also facilitate the identification of novel treatment targets and means of accurately diagnosing and treating ferroptosis-related diseases.

Fluorescent probes for ferroptosis bioimaging: advances, challenges, and prospects

Ferroptosis is a form of regulatory cell death distinct from caspase-dependent apoptosis and plays an important role in life entities. Since ferroptosis involves a variety of complex regulatory factors, the levels of certain biological species and microenvironments would change during this process. Thus, the investigation of the level fluctuation of key target analytes during ferroptosis is of great significance for disease treatment and drug design. Toward this aim, multiple organic fluorescent probes with simple preparation and non-destructive detection have been developed, and research over the past decade has uncovered a vast array of homeostasis and other physiological characteristics of ferroptosis. However, this significant and cutting-edge topic has not yet been reviewed. In this work, we aim to highlight the latest breakthrough results of fluorescent probes for monitoring various bio-related molecules and microenvironments during ferroptosis at the cellular, tissue and in vivo levels. Accordingly, this tutorial review has been organized according to the target molecules identified by the probes including ionic species, reactive sulfur species, reactive oxygen species, biomacromolecules, microenvironment, and others. In addition to providing new insights into the findings of each fluorescent probe in ferroptosis studies, we also discuss the defects and limitations of the probes developed, and highlight the potential challenges and further prospects in this domain. We anticipate that this review will convey profound implications for designing powerful fluorescent probes to decrypt changes in key molecules and microenvironments during ferroptosis.

Si-rhodamine fluorescent probe for monitoring of hypochlorous acid in the brains of mice afflicted with neuroinflammation

Neuroinflammation leads to a persistent oxidative stress in the brain, and is closely related to the pathology of various neurological disorders. Hypochlorous acid (HClO) is a reactive oxygen species (ROS) that, at high levels, can cause brain tissue damage and neurogenic apoptosis. Herein, we designed and synthesized a silicon-rhodamine (SiR)-based formohydrazide (FH)-containing fluorescent probe, denoted as SiR-FH, for sensing HClO. This probe showed good selectivity, rapid response and high sensitivity. SiR-FH was successfully used to detect endogenous and exogenous HClO in living cells. Moreover, SiR-FH realized real-time monitoring of change in HClO flux in the brains of mice with LPS-induced neuroinflammation. The probe provides a practical tool for the monitoring of oxidative stress related to neuroinflammation.

The Development of a 4-aminonaphthalimide-based Highly Selective Fluorescent Probe for Rapid Detection of HOCl

Recently, more and more evidence indicated that intracellular HOCl plays a crucial role in the regulation of inflammation and apoptosis, while excessive HOCl has an impact on human health problems. So, the development of methods for sensitive detection of HOCl is very vital to reveal its various physiological and pathological functions. In this paper, we have described a simple fluorescent probe for selective detection of HOCl, whereas for higher concentrations of other biological important substances, the probe almost does not respond. The experimental results show that the probe can quantitatively determine the range of 0-1 μM HOCl, the detection limit is 0.05 μM. In addition, the probe reacts quickly with HOCl (< 3 s), which is helpful to monitor HOCl in biological system because HOCl is highly reactive and short-lived. The ability of the probe to HOCl enables it to be used to track the HOCl levels in living systems.