Fluorescent Detection of Dynamic H2O2/H2S Redox Event in Living Cells and Organisms

A fluorescent probe for detecting H2O2 and delivering H2S in lysosomes and its application in maintaining the redox environments

Hydrogen peroxide (H2O2) is a reactive oxygen species (ROS) that can be used as a marker for the occurrence of oxidative stress in the organism. Lysosomes serve as intracellular digestive sites, and when the concentration of H2O2 in them is abnormal, lysosomal function is often impaired, leading to the development of diseases. Hydrogen sulfide (H2S) acts as a gaseous signaling molecule that scavenges H2O2 from cells and tissues, thereby maintaining the redox environment of the body. However, most of the reported hydrogen peroxide fluorescent probes so far can only detect H2O2, but cannot maintain the intracellular redox environment. In this paper, an H2O2 fluorescent probe LN-HOD with lysosomal targeting properties was designed and synthesized by combining the H2O2 recognition site with a naphthylamine fluorophore via a thiocarbamate moiety. The probe has the advantages of large Stokes shift (110 nm), high sensitivity and good H2S release capability. The probe LN-HOD can be used to detect H2O2 in cells, zebrafish and plant roots. In addition, LN-HOD detects changes in the concentration of H2O2 in plant roots when Arabidopsis is stressed by cadmium ion (Cd2+). And through its ability to release H2S, it can help to remove excess H2O2 and maintain the redox environment in cells, zebrafish and plant roots. The present work provides new ideas for the detection and assisted removal of H2O2, which contributes to the in-depth study of the cellular microenvironment in organisms.

Activity-Based Fluorescent Probes for Hydrogen Sulfide and Related Reactive Sulfur Species

Hydrogen sulfide (H2S) is not only a well-established toxic gas but also an important small molecule bioregulator in all kingdoms of life. In contemporary biology, H2S is often classified as a "gasotransmitter," meaning that it is an endogenously produced membrane permeable gas that carries out essential cellular processes. Fluorescent probes for H2S and related reactive sulfur species (RSS) detection provide an important cornerstone for investigating the multifaceted roles of these important small molecules in complex biological systems. A now common approach to develop such tools is to develop "activity-based probes" that couple a specific H2S-mediated chemical reaction to a fluorescent output. This Review covers the different types of such probes and also highlights the chemical mechanisms by which each probe type is activated by specific RSS. Common examples include reduction of oxidized nitrogen motifs, disulfide exchange, electrophilic reactions, metal precipitation, and metal coordination. In addition, we also outline complementary activity-based probes for imaging reductant-labile and sulfane sulfur species, including persulfides and polysulfides. For probes highlighted in this Review, we focus on small molecule systems with demonstrated compatibility in cellular systems or related applications. Building from breadth of reported activity-based strategies and application, we also highlight key unmet challenges and future opportunities for advancing activity-based probes for H2S and related RSS.

Small Molecule Optical Probes for Detection of H2S in Water Samples: A Review

Hydrogen sulfide (H2S) is closely linked to not only environmental hazards, but also it affects human health due to its toxic nature and the exposure risks associated with several occupational settings. Therefore, detection of this pollutant in water sources has garnered immense importance in the analytical research arena. Several research groups have devoted great efforts to explore the selective as well as sensitive methods to detect H2S concentrations in water. Recent studies describe different strategies for sensing this ubiquitous gas in real-life water samples. Though many of the designed and developed H2S detection approaches based on the use of organic small molecules facilitate qualitative/quantitative detection of the toxic contaminant in water, optical detection has been acknowledged as one of the best, attributed to the simple, highly sensitive, selective, and good repeatability features of the technique. Therefore, this review is an attempt to offer a general perspective of easy-to-use and fast response optical detection techniques for H2S, fluorimetry and colorimetry, over a wide variety of other instrumental platforms. The review affords a concise summary of the various design strategies adopted by various researchers in constructing small organic molecules as H2S sensors and offers insight into their mechanistic pathways. Moreover, it collates the salient aspects of optical detection techniques and highlights the future scope for prospective exploration in this field based on the limitations of the existing H2S probes.

Construction of smartphone-adapted signal visualization platform for dual-mode detection of H2S based on integrated metal-organic framework nanoprobes

Hydrogen sulfide (H2S) is a toxic contaminant and has great influence on many physiological processes. Due to various pathophysiological roles and environmental pollution problems, it is necessary to construct and develop simple and portable monitoring sensors for the precise detection of H2S. Herein, we developed a smartphone-adapted dual-mode detection platform by integrating the colorimetric and photothermal imaging analysis into a metal-organic framework-based chip (ZIF-8/Cu). Due to the nanoconfinement effect of ZIF-8, small-sized plasmonic CuS could be in-situ formed during the detection procedure of H2S and endowed the chips with excellent photothermal properties. By constructing a smartphone-adapted photothermal imager, the metal-organic framework-based chip could achieve a portable photothermal imaging analysis of H2S. Moreover, as the formed CuS was a good peroxidase-like nanozyme, the chips could also be used to trigger the enzymic catalytic reaction toward the chromogenic reaction of 3,3',5,5'-tetramethylbenzidine (TMB)-H2O2, thus providing another colorimetric sensing mode by using a smartphone App. In this smartphone-adapted visualization platform, the portable chemosensors could simultaneously achieve double detection modes at one electrode, which provided a new pathway for the accurate detection of H2S and circumvented the false-positive or negative errors during the detection process. Besides, by using the finite difference time domain (FDTD) simulation method, the in-depth mechanism, including the plasmonic effect and spatial electromagnetic field distribution, was explored to provide a possible reason for the excellent sensing performance of the dual-mode visualization platform. This work provides a new insight into the construction of the accurate, portable and smart sensing platform in the visual screening of H2S.

A Novel DNBS-based Fluorescent Probe for the Detection of H2S in Cells and on Test Strips

Hydrogen sulfide (H2S) plays a key role in the physiology and pathology of organisms, and H2S in the environment is easily absorbed and harmful to health. It is of great significance to develop a probe with good selectivity, high sensitivity and good stability that can detect hydrogen sulfide inside and outside organisms. In this work, we designed a novel "turn-on" fluorescent probe CIM-SDB for the detection of H2S. The probe CIM-SDB used indene-carbazole as the fluorophore and 2,4-dinitrobenzenesulfonyl as the recognition site. The probe CIM-SDB exhibited high selectivity and sensitivity to H2S (detection limit as low as 123 nM). Moreover, the probe CIM-SDB was successfully applied to the detection of intracellular exogenous and endogenous H2S, and the test strips prepared by the probe CIM-SDB could realize the convenient and rapid detection of H2S.

Peroxidase-like activity and mechanism of gold nanoparticle-modified Ti3C2 MXenes for the construction of H2O2 and ampicillin colorimetric sensors

Transition metal carbides modified by Au nanoparticles (Au/Ti3C2) were synthesized and developed as a colorimetric sensor for the determination of H2O2 and ampicillin. The surface electrical properties of Ti3C2 were changed, and Au nanoparticles (AuNPs) and gold growth solution were synthesized simultaneously. Au/Ti3C2 was obtained by seed growth method with AuNPs modified on the surface of transition metal carbides, nitrides or carbon-nitrides (Ti3C2 MXenes). The synthesized AuNPs and Ti3C2 had no peroxidase-like activity, but Au/Ti3C2 had. The peroxidase catalytic mechanism was due to electron transfer. The peroxidase activity of Au/Ti3C2 can be utilized for the determination of H2O2. The linear range of Au/Ti3C2 for H2O2 was 1-60 µM, and the detection limit was 0.12 µM (S/N = 3). A colometric sensor for ampicillin detection based on Au/Ti3C2 was further constructed since S in ampicillin formed an Au-S bond with Au/Ti3C2, leading to the weakening of its peroxidase-like property. The change of peroxidase-like property attenuated oxidation of TMB, and the ampicillin content was inversely proportional to the concentration of oxidized TMB, and the blue color of solution faded, which enabled the determination of ampicillin. The linear range for ampicillin was 0.005-0.5 µg mL- 1, and the detection limit was 1.1 ng mL- 1 (S/N = 3). The sensor was applied to the detection of ampicillin in milk and human serum.

A Benzil- and BODIPY-Based Turn-On Fluorescent Probe for Detection of Hydrogen Peroxide

Faced with rising threats of terrorism, environmental and health risks, achieving sensitive and selective detection of peroxide-based explosives (PEs) has become a global focus. In this study, a turn-on fluorescent probe (BOD) based on benzil (H2O2-recognition element) and 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) derivative (fluorophore) was developed to sensitively and specifically detect hydrogen peroxide (H2O2). The synthesized BOD had a very weak fluorescence due to intramolecular donor-excited photo-induced electron transfer (d-PET) effect; however, it could emit a strong fluorescence since H2O2 selectively oxidized the benzil moiety and released free BODIPY fluorophore (BOD-COOH). As a result, the proposed BOD detected H2O2 in linear detection ranged from 25 to 125 µM with a detection limit of 4.41 µM. Meanwhile, the proposed BOD showed good selectivity toward H2O2, which is not affected by other common reactive oxygen species (ROS) and ions from explosive residues. In addition, a blue shift from 508 to 498 nm was observed in the absorption spectra upon addition of H2O2. More importantly, the BOD was successfully applied for rapid detection of H2O2 vapor with good sensitivity (down to 7 ppb), which holds great potential for practical use in public safety, forensic analysis and environmental monitoring.

Recent progress in the development of fluorescent probes for imaging pathological oxidative stress

Oxidative stress is closely related to the physiopathology of numerous diseases. Reactive oxygen species (ROS), reactive nitrogen species (RNS), and reactive sulfur species (RSS) are direct participants and important biomarkers of oxidative stress. A comprehensive understanding of their changes can help us evaluate disease pathogenesis and progression and facilitate early diagnosis and drug development. In recent years, fluorescent probes have been developed for real-time monitoring of ROS, RNS and RSS levels in vitro and in vivo. In this review, conventional design strategies of fluorescent probes for ROS, RNS, and RSS detection are discussed from three aspects: fluorophores, linkers, and recognition groups. We introduce representative fluorescent probes for ROS, RNS, and RSS detection in cells, physiological/pathological processes (e.g., Inflammation, Drug Induced Organ Injury and Ischemia/Reperfusion Injury etc.), and specific diseases (e.g., neurodegenerative diseases, epilepsy, depression, diabetes and cancer, etc.). We then highlight the achievements, current challenges, and prospects for fluorescent probes in the pathophysiology of oxidative stress-related diseases.

A long-wavelength mitochondria-targeted fluorescent probe for imaging of peroxynitrite during dexamethasone treatment

Peroxynitrite (ONOO^-), as a strong oxidizing reactive nitrogen substance (RNS), is generated endogenously by cells. Its visualization research is crucial to understand relevant disease processes. Herein, we reported a long-wavelength mitochondria-targeted fluorescence "turn on" probe TL. The probe TL could react with ONOO^- by using 4-(Bromomethyl)benzeneboronic as a reactive site, which exhibited outstanding characteristics for detection of ONOO^-, thus improving response time (about 50 s), sensitivity (DL, 10.1 nM), and emission wavelength (667 nm). Besides, TL displayed well mitochondria targeting and biological visualizing of exogenous and endogenous ONOO^- in biological systems. Finally, TL was used to monitor high concentration of dexamethasone-induced an up-regulation of ONOO^-. This indicated that TL has excellent potential to study the fluctuation of ONOO^- in the physiological and pathological system.

H2S-based fluorescent imaging for pathophysiological processes

Hydrogen sulfide (H₂S), as an important endogenous signaling molecule, plays a vital role in many physiological processes. The abnormal behaviors of hydrogen sulfide in organisms may lead to various pathophysiological processes. Monitoring the changes in hydrogen sulfide is helpful for pre-warning and treating these pathophysiological processes. Fluorescence imaging techniques can be used to observe changes in the concentration of analytes in organisms in real-time. Therefore, employing fluorescent probes imaging to investigate the behaviors of hydrogen sulfide in pathophysiological processes is vital. This paper reviews the design strategy and sensing mechanisms of hydrogen sulfide-based fluorescent probes, focusing on imaging applications in various pathophysiological processes, including neurodegenerative diseases, inflammation, apoptosis, oxidative stress, organ injury, and diabetes. This review not only demonstrates the specific value of hydrogen sulfide fluorescent probes in preclinical studies but also illuminates the potential application in clinical diagnostics.

Activity-Based Sensing for Chemistry-Enabled Biology: Illuminating Principles, Probes, and Prospects for Boronate Reagents for Studying Hydrogen Peroxide

Activity-based sensing (ABS) offers a general approach that exploits chemical reactivity as a method for selective detection and manipulation of biological analytes. Here, we illustrate the value of this chemical platform to enable new biological discovery through a case study in the design and application of ABS reagents for studying hydrogen peroxide (H2O2), a major type of reactive oxygen species (ROS) that regulates a diverse array of vital cellular signaling processes to sustain life. Specifically, we summarize advances in the use of activity-based boronate probes for the detection of H2O2 featuring high molecular selectivity over other ROS, with an emphasis on tailoring designs in chemical structure to promote new biological principles of redox signaling.

A novel near-infrared fluorescent probe for visualization of intracellular hydrogen peroxide

Hydrogen peroxide (H₂O₂) as a crucial reactive oxygen species (ROS) plays a crucial role in redox signaling in physiological and pathological processes of living cells. Its normal production is closely related to signal transduction of living cells. Overproduction of H₂O₂in vivo has been proved to be related to many diseases. Some were developed to reveal the roles of H₂O₂. However, current fluorescent probes for the detection of H₂O₂ are restricted in their short emission wavelengths and small Stokes shifts that significantly decrease the sensitivity of detection and cellular visualization. In this work, a novel fluorescent probe BC-B was designed and synthesized with pinacol phenylboronic acid ester as a recognition group and near-infrared fluorophore BC-OH as a reporter group. BC-B probe exhibits a large Stokes shift (122 nm) and near-infrared emission (672 nm), showing an excellent selectivity and sensitivity in detection of H₂O₂ with the limit of 0.003 μmol/L. Confocal fluorescence imaging further demonstrates that BC-B can be used for detecting endogenous H₂O₂ in living cells.

Recent Progress in Organic Small-Molecule Fluorescent Probe Detection of Hydrogen Peroxide

The fluorescent probe has become an important method for accurate detection of H2O2, with advantages of simple operation, high sensitivity, good selectivity, and real-time dynamic monitoring. This paper reviews the research progress in organic small-molecule fluorescent probe H2O2 detection methods that are based on different recognition reactions. In addition, the application prospect of fluorescent probes in the detection of trace H2O2 is anticipated.

Target-Binding Accelerated Response for Sensitive Detection of Basal H2O2 in Tumor Cells and Tissues via a Dual-Functional Fluorescence Probe

Aberrant production of H₂O₂ is involved in cancer. The levels of H₂O₂ are significantly higher in tumor cells than in normal cells. It is important to develop fluorescent probes to image basal H₂O₂ selectively in tumor cells. So far, a cancer cell-targeting probe to image basal H₂O₂ has not been reported. Thus, we developed a fluorescent probe, BBHP, which contains benzil as a H₂O₂-recognition site and biotin as a target binding motif for the selective and sufficient detection of H₂O₂ in tumor cells. BBHP enables a selective fluorescence turn-on response to H₂O₂. The binding of the probe with biotin receptors can greatly accelerate the fluorescence response to H₂O₂. As a result, BBHP can sufficiently image basal H₂O₂ in biotin receptor-positive cancer cells and tumor tissues. Finally, BBHP was successfully applied to discriminate between cancerous and normal tissues.

Rational design of a fluorescent probe and its applications of imaging and distinguishing between exogenous and endogenous H2S in living cells

Hydrogen sulfide (H₂S), a recognized environmental pollutant, comes from a wide range of sources. For example, H₂S will be produced in the process of plant protein corruption, the decomposition of domestic sewage and garbage, food processing (wine brewing), etc. and once the concentration is too high, it will cause significant damage of environment and human body. Besides H₂S is an important gas signal molecule in vivo, which can be transferred through lipid membrane. Its existence level is closely related to many diseases. If we can "visually" trace the transmembrane transmission of hydrogen sulfide, it will be very helpful for the study of oxidative stress processes, cell protection, signal transduction and related diseases closely related to H₂S. Although some probes can detect H₂S in environment, cytoplasm and organelles, there are few reports on the release and internalization of H₂S. In this work, we report a H₂S fluorescence probe that can retain on the cell membrane, named PCM. The probe PCM can not only detect endogenous and exogenous H₂S, but also distinguish them, this provides a general strategy for the construction of probes to detect other biomarkers. In addition, PCM has been successfully applied to the detection of endogenous and exogenous H₂S in zebrafish, which has the potential to become a new chemical tool and provide help for the research of H₂S-related diseases.

Sequential detection of hypochlorous acid and sulfur dioxide derivatives by a red-emitting fluorescent probe and bioimaging applications in vitro and in vivo

A red-emitting fluorescence probe (DP) has been successfully developed for the sequential detection of hypochlorous acid (HOCl) and sulfur dioxide derivatives (SO32−/HSO3−) in vitro and in vivo.

Preparation of a nonenzymatic electrochemical sensor based on g-C3N4/MWO4 (M: Cu, Mn, ‎Co, Ni) composite for the determination of H2O2‎

‎ Hydrogen peroxide (H2O2) has a significant effect on physiological proceedings. In the ‎present research, a g-C3N4-based nanocomposite g-C3N4/MWO4(M: Cu, Mn, Co, Ni) was ‎prepared via the precipitation-calcination method. A...

Manipulating Intratumoral Fenton Chemistry for Enhanced Chemodynamic and Chemodynamic-Synergized Multimodal Therapy

Chemodynamic therapy (CDT) uses the tumor microenvironment-assisted intratumoral Fenton reaction for generating highly toxic hydroxyl free radicals (•OH) to achieve selective tumor treatment. However, the limited intratumoral Fenton reaction efficiency restricts the therapeutic efficacy of CDT. Recent years have witnessed the impressive development of various strategies to increase the efficiency of intratumoral Fenton reaction. The introduction of these reinforcement strategies can dramatically improve the treatment efficiency of CDT and further promote the development of enhanced CDT (ECDT)-based multimodal anticancer treatments. In this review, the authors systematically introduce these reinforcement strategies, from their basic working principles, reinforcement mechanisms to their representative clinical applications. Then, ECDT-based multimodal anticancer therapy is discussed, including how to integrate these emerging Fenton reinforcement strategies for accelerating the development of multimodal anticancer therapy, as well as the synergistic mechanisms of ECDT and other treatment methods. Eventually, future direction and challenges of ECDT and ECDT-based multimodal synergistic therapies are elaborated, highlighting the key scientific problems and unsolved technical bottlenecks to facilitate clinical translation.

A Highly Selective and Sensitive Colorimetric Chemosensor for the Detection of Hydrogen Sulfide: Real-time Applications in Multiple Platforms

Calorimetric chemosensors are found to be advantageous sensing systems due to their simplicity and favorable responsive properties. Although some colorimetric probes have been reported to detect hydrogen sulfide (H₂ S), the creation of rapid, highly selective, and sensitive probes for the detection of H₂ S remains a challenging target. In this work, we established dinitrosulphonamide decorated phenanthridine, 2,4-dinitro-N-(4-(7,8,13,14-tetrahydrodibenzo[a, i]phenanthridin-5-yl)phenyl)benzenesulfonamide (PHSH), for the calorimetric detection of H₂ S. H₂ S triggered thiolysis of PHSH resulted in a marked absorption enhancement alongside a visual color change from colorless to dark yellow. The result indicated that the chemosensor showed high sensitivity and selectivity with a fast response of less than 10 s with a detection limit as low as 6.5 nM. The chemosensor reaction mechanism with H₂ S was studied by UV-vis, ¹ H NMR, mass and HPLC analysis. In addition, the chemosensor has been used for the determination of H₂ S in many real-time samples.

Mitochondria-targeted NIR fluorescent probe for sensing Hg2+/HSO3- and its intracellular applications

Mercury and sulfur dioxide (SO₂) are common pollutants in the ecological environment, which are important factors causing many diseases of organisms. The lack of appropriate analytical tools has limited the further understanding of the relationship between ionic mercury (Hg²⁺) and SO₂. Herein, a bifunctional fluorescent probe LJ was designed and explored to simultaneously detect Hg²⁺ and SO₂ via desulfurization reaction and Michael addition reaction, respectively. Probe LJ showed distinct fluorescence responses which a large near-infrared fluorescence enhancement towards Hg²⁺ at λ_em = 713 nm and a blue shift at λ_em = 450 nm towards SO₂ without any spectral cross interferences. To the best of our knowledge, this is the first fluorescent probe with dual fluorescent emission channels to detect Hg²⁺ and SO₂ with the detection limit of 187 nM and 354 nM, respectively. Moreover, cell fluorescent imaging experiments indicated that the probe was mitochondria targetable and provided evidence that SO₂ could be used as an antidote to attenuate the toxicity of Hg²⁺ in living cells.

MACA Fast and Efficient Method for Detecting H2O2 by a Dual-Locked Model Chemosensor

A pentafluorobenzene-containing fluorescent probe GW-1 was designed and synthesized for monitoring hydrogen peroxide. The probe's fluorescence was activated by a dual-locked model system that consists of a spiro location and a target analyte, which avoids the "alkalizing effect." The smart GW-1 exhibited high selectivity toward hydrogen peroxide over other reactive oxygen species (ROS) by a dual-controlled molecular switch. These features are favorable for H2O2 sensing and pH changes in bioanalytical and biomedical applications.

A Single Fluorescent pH Probe for Simultaneous Two-Color Visualization of Nuclei and Mitochondria and Monitoring Cell Apoptosis

Subcellular organelles play indispensable roles in diverse biological processes by their precise mutual cooperation. Thus, the development of a single fluorescent probe (SF-probe) for simultaneous and discriminable visualization of different organelles and their dynamics during certain bioprocess is significant, yet remains greatly challenging. Herein, for the first time, we rationally prepared a pH-sensitive SF-probe (named HMBI) for the simultaneous two-color visualization of nuclei and mitochondria and monitoring cell apoptosis. HMBI shows remarkable ratiometric fluorescence changes toward pH changes. Due to different pH environments in subcellular organelles, HMBI can image nuclei and mitochondria with green and red emission, respectively. HMBI can monitor drug-induced cell apoptosis with dramatically decreased red emission in mitochondria but almost unchanged green emission in nuclei, and the shrinking and pyknotic nuclei are also observed during cell apoptosis. HMBI possesses tremendous potential in two-color biomedical imaging of the dynamic changes of nuclei and mitochondria in many physiological processes.

Fabrication of small-structure red-emissive fluorescent probes for plasma membrane enables quantification of nuclear to cytoplasmic ratio in live cells and tissues

Nuclear to cytoplasmic ratio is one of the vital parameters in diagnosis of cancer by means of hematoxylin-eosin (HE) stained histopathology. However, HE histopathology dependent on mechanical tissue slice damages biosamples and exhibits insufficient accuracy. Herein, we rationally prepared two small-molecule plasma membrane fluorescent probes with red-emitting fluorescence for visualizing plasma membrane in living cells and tissues. Their fluorescence intensities are strongly affected by environmental viscosity, which enables the exclusive imaging of plasma membrane in high fidelity. The probes can visualize plasma membrane in SiHa and rat blood red cells. Particularly, the probes are able to visualize T-tubule (transverse tubule) in skeletal muscle tissues successfully, suggesting their ability to image plasma membrane in tissues. In cooperation with Hoechst 33342, the nuclear to cytoplasmic ratio was successfully qualified in live cells and tissues. We believe these probes may have potential applications in facilitating the study on histopathology and the related areas.

A reversible near-infrared fluorescence probe for the monitoring of HSO3−/H2O2-regulated cycles in vivo

A near-infrared (NIR) fluorescent probe (XC) was constructed for the reversible detection of HSO3−/H2O2 in biosystems. The practical applications of XC were also demonstrated by the quantitative analysis of HSO3− in white wine and sugar samples.