Construct a lysosome-targeting and highly selective fluorescent probe for imaging of hydrogen sulfide in living cells and inflamed tissues

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.

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 Turn-On Fluorescent Probe for Highly Selective Detection and Visualization of Hydrogen Sulfide in Fungi

Hydrogen sulfide (H2S) is a significant actor in the virulence and pathogenicity of fungi. The analysis of endogenous H2S in fungi benefits the prevention and treatment of pathogenic infections. Herein, a H2S-activated turn-on fluorescent probe named DDX-DNP was developed for the sensitive and selective detection of H2S. Using DDX-DNP, the ability of several oral fungi strains to produce H2S was identified, which was also validated using a typical chromogenic medium. In addition, DDX-DNP was successfully used for the visual sensing of endogenous H2S in fungal cells via microscope, flow cytometry, and colony imaging, along with a specific validation with the co-incubation of H2S production inhibitors in living cells. Above all, DDX-DNP could be used for H2S detection, the fluorescent imaging of fungi, and even the identification of related fungi.

A robust NIR fluorescence-activated probe for peroxynitrite imaging in cells and mice osteoarthritis models

Osteoarthritis (OA) is the most common type of joint disease, which is difficult to treat, but early standardized diagnosis and treatment can effectively alleviate the pain and symptoms of patients. Therefore, it is important to construct an effective tool to assist in the early diagnosis and evaluation of the therapeutic effect of OA. In this work, a near-infrared (NIR) fluorescence-activated fluorescent probe, YB-1, was constructed for the evaluation of the diagnostic and therapeutic efficacy of OA via detection and imaging of the biomarker of ONOO- in inflammatory cells and mice osteoarthritis models. YB-1 exhibited high selectivity, high sensitivity, and a high ratio yield (I668/I0) fluorescence increasing (∼30 folds). Besides, YB-1 can be used effectively to image endogenous and exogenous ONOO- in living human chondrocytes cells (TC28a2), as well as to evaluate the effect of drug (Chrysosplenol D, CD) treatment in IL-1β-induced inflammatory cells model. Interestingly, YB-1 was available for OONO- imaging analysis in the collagenase-induced mice OA models and assessment of the effect of CD treatment in mice OA models, with good results. Thus, the newly constructed YB-1 is a powerful molecular tool for the diagnosis and treatment of OA-related diseases.

A turn-on fluorescent nanosensor for H2S detection and imaging in inflammatory cells and mice

Hydrogen sulfide (H₂S) is an endogenously generated gaseous signaling molecule and is known to be involved in the occurrence and development of inflammation. To better understand its physiological and pathological process of inflammation, reliable tools for H₂S detection in living inflammatory models are desired. Although a number of fluorescent sensors have been reported for H₂S detection and imaging, water-soluble and biocompatibility nanosensors are more useful for imaging in vivo. Herein, we developed a novel biological imaging nanosensor, XNP1, for inflammation-targeted imaging of H₂S. XNP1 was obtained by self-assembly of amphiphilic XNP1, which was constructed by the condensation reaction of the hydrophobic, H₂S response and deep red-emitting fluorophore with hydrophilic biopolymer glycol chitosan (GC). Without H₂S, XNP1 showed very low background fluorescence, while a significant enhancement in the fluorescence intensity of XNP1 was observed in the presence of H₂S, resulting in a high sensitivity toward H₂S in aqueous solution with a practical detection limit as low as 32.3 nM, which could be meet the detection of H₂S in vivo. XNP1 also has a good linear response concentration range (0-1 μM) toward H₂S with high selectivity over other competing species. These characteristics facilitate direct H₂S detection of the complex living inflammatory cells and drug-induced inflammatory mice, demonstrating its practical application in biosystems.

Development and application of a novel β-diketone difluoroboron-derivatized fluorescent probe for sensitively detecting H2S

Hydrogen sulfide{Wang, 2018 #4}{Wang, 2018 #4}{Zhong, 2020 #9} (H₂S) is a poisonous and harmful gas molecule. Certain concentrations of H₂S{Liu, 2021 #8} can irritate the eyes, respiratory system, and central nervous system of human beings. Therefore, it was an urgent need for highly selective, anti-interference, and sensitive detection technology for hydrogen sulfide. Herein, a novel "turn-on" fluorescent probe 1-(2-(6,6-dimethylbicyclo[3.1.1]heptyl-2-ene-2-yl))-9-(4-(dimethylaminophenyl))non-1,6,8-triene-3,5-dione boron difluoride complex (MCBF) was designed and synthesized for detecting H₂S sensitively. MCBF displayed a remarkable fluorescence enhancement response to H₂S with a large Stokes shift of 220 nm. The sensitive detection of MCBF towards H₂S owned good selectivity, fast response time (6 min), excellent photostability, and low detection limit (0.44 μM). The sensing mechanism of MCBF towards H₂S was well confirmed by HRMS analysis, ¹H NMR titration, and density functional theory (DFT) calculations. What's more, probe MCBF was successfully applied to detect the contained H₂S in red wine, which showed the potential practicability of MCBF in real samples analysis.

Lysosome-targetable brightly green fluorescence carbon dots for real-time monitoring in cell and highly efficient removal in environment of hypochlorite

Due to the lacks of lysosome localization group and reaction/interaction site for hypochlorite (ClO^-) on the surface of the carbon dots (C-dots), no C-dots-based lysosome-targeted fluorescence probes have, so far, been reported for real-time monitoring intracellular ClO^-. In this work, 1,3,6-trinitropyrene (TNP) was used as a precursor to prepare C-dots with maximum excitation and emission wavelengths at 485 and 532 nm, respectively, and quantum yield ∼ 27% by a hydrothermal approach at 196 °C for 6 h under a reductive atmosphere. The brightly green C-dots can sensitively and quickly respond to ClO^- in aqueous solution through surface chemical reaction, showing a linear relationship in the range of 0.5-120 μΜ ClO^- with 0.27 μΜ of limit of detection (LOD). Most significantly, the C-dots can localize at intracellular lysosome to image ClO^- in lysosomes. Also, the magnetic nanocomposites (C-dots@Fe₃O₄ MNCs) were fabricated via a simple electrostatic self-assembly between Fe₃O₄ magnetic nanoparticles (Fe₃O₄ MNPs) and C-dots for highly efficient removal of ClO^- in real samples. Therefore, lysosome-targetable C-dots-based probes for real-time monitoring ClO^- were successfully constructed, opening up a promising door to investigate the biological functions and pathological roles of ClO^- at organelle levels.

Construction of novel coumarin-carbazole-based fluorescent probe for tracking of endogenous and exogenous H2S in vivo with yellow-emission and large Stokes shift

Recent medical studies have confirmed that endogenous H₂S serves as the third gas-messenger besides nitric oxide (NO) and carbon monoxide (CO), which is produced by enzyme-catalyzed metabolism of cysteine and takes part in multiple physiological processes. The abnormal levels induced by H₂S overproduction in mammals can destroy tissues and organ systems, which lead to certain serious diseases, such as neurodegenerative diseases, cardiovascular diseases, and various cancers. In this work, we developed a novel coumarin-carbazole fluorescent probe COZ-DNB with yellow emission and a large Stokes shift for H₂S detection. In probe COZ-DNB, the newly dye COZ-OH as a luminophore and the 2,4-dinitrophenyl ether moiety was chosen as a trigger group for H₂S. Probe COZ-DNB itself displayed nearly non-fluorescent. However, COZ-DNB gave the remarkable fluorescence with an 83-fold enhancement in the yellow region after interaction with H₂S. The sensing mechanism of COZ-DNB toward H₂S was checked by means of UHPLC, HRMS and DFT/TD-DFT calculations. What's more, probe COZ-DNB also exhibited fast response (2.0 min), high sensitivity (65.0 nM), a large Stokes shift (161.0 nm), high stability and excellent selectivity. Furthermore, COZ-DNB was applied for imaging of exogenous and endogenous H₂S in living HeLa cells and zebrafish with satisfactory performances. We anticipate COZ-DNB would be served as a potential tool for investigating the biological functions of H₂S in pathological processes.

Novel near-infrared spectroscopic probe for visualizing hydrogen sulfide in lysosomes

Considering the scarcity of hydrogen sulfide (H₂S) probes with subcellular organelle targeting, especially probes with near-infrared (NIR) emission wavelengths fluorophores, our group has been working to overcome this problem and looking forward to providing potential practical tools for exploring the relationship between the physiology and pathology of H₂S at subcellular level. In this paper, a novel colorimetric and NIR fluorescent probe SHCy-H₂S for the specific detection of H₂S in lysosome over other biological thiols was designed and synthesized. The xanthene-benzothiozolium fluorophore was chosen to provide fluorescence emission maxima over 735 nm, and 2,4-dinitrophenyl group was chosen as fluorescence quenching group and specific H₂S response site. Impressively, SHCy-H₂S exhibited high selectivity, fast response and detection limit as low as 0.116 μM for H₂S, marked obvious color changes in naked-eye and fluorescence. Specially, SHCy-H₂S was capable of specifically imaging endogenous lysosomal hydrogen sulfide, providing a potential tool for exploring the function of H₂S at subcellular level.

A ratiometric fluorescent probe for hydrogen sulfide in neat aqueous solution and its application in lysosome-targetable cell imaging

Hydrogen sulfide (H₂S) has been recently regarded as one of the most important gasotransmitters in the metabolic system, while abnormal H₂S concentration is associated with various diseases. Although numerous fluorescent probes have been developed for the detection of cellular H₂S, only a few of them can monitor lysosomal H₂S with ratiometric fluorescent output. Here, we developed a water-soluble probe 1 toward H₂S by introducing 2,4-dinitrophenyl ether into a novel merocyanine-based dye. As expected, H₂S induced an obvious red-shift of the probe from 520 nm to 580 nm in neat aqueous solution, and this fluorescent ratiometric response is highly selective and sensitive (with the detection limit of 0.81 nM), rapid (within 10 s), and effective in a wide pH range (2.0-10.0). In particular, the probe was successfully applied for tracing H₂S in the lysosomes of living cells and in zebrafish.

A naphthimide fluorescent probe for the detection of selenols in selenium-enriched Tan sheep

An "off-on" fluorescent probe, Nap-DNB, which is based on naphthimide, was designed and developed for the detection of biological selenols in vitro. We have adopted a combination of a low-pH detection environment and reaction sites that are more difficult to destroy to avoid the interference of a large number of biological thiols in biological samples. Nap-DNB can completely respond to selenocysteine within 15 mins, with a detection limit of 92 nM. Nap-DNB was successfully used for the detection of selenols in the serum, liver, and longissimus dorsi of selenium-enriched Tan sheep. Through comparison, we found that the detection of selenols by the Nap-DNB is similar to that by thioredoxin reductase and glutathione peroxidase in a commercial kit method. Nap-DNB can be used for the detection of selenols in selenium-enriched Tan sheep.

Simultaneous Discrimination of Cys/Hcy and GSH With Simple Fluorescent Probe Under a Single-Wavelength Excitation and its Application in Living Cells, Tumor Tissues, and Zebrafish

Owing to the important physiological sits of biothiols (Cys, Hcy, and GSH), developing accurate detection methods capable of qualitative and quantitative analysis of biothiols in living systems is needed for understanding the biological profile of biothiols. In this work, we have designed and synthesized a 4′-hydroxy-[1,1′-biphenyl]-4-carbonitrile modified with NBD group-based fluorescent probe, BPN-NBD, for sensitive detection of Cys/Hcy and GSH by dual emission signals via a single-wavelength excitation. BPN-NBD exhibited an obvious blue fluorescence (λmaxem = 475 nm) upon the treatment with GSH and reacted with Cys/Hcy to give a mixed blue-green fluorescence (λmaxem = 475 and 545 nm). Meanwhile, BPN-NDB performed sufficient selectivity, rapid detection (150 s), high sensitivity (0.011 µM for Cys, 0.015 µM for Hcy, and 0.003 µM for GSH) and could work via a single-wavelength excitation to analytes and had the ability to image Cys/Hcy from GSH in living MCF-7 cells, tumor tissues, and zebrafish by exhibiting different fluorescence signals. Overall, this work provided a powerful tool for thiols visualization in biological and medical applications.

A novel lysosome-located fluorescent probe for highly selective determination of hydrogen polysulfides based on a naphthalimide derivative

Hydrogen polysulfides (H₂S_n, n > 1) belongs to sulfane sulfur in the reactive sulfur species (RSS) family and plays a significant regulatory role in organisms. Highly selective and lysosome-located probes for detecting hydrogen polysulfides are rare. Thus, it is important to develop a technique to detect the changes of H₂S_n level in lysosomes. In this work, a lysosome-targeting fluorescent probe for H₂S_n was designed and developed based on a naphthalimide derivative. 4-Hydroxynaphthalimide was selected as the fluorescent group and 2-chloro-5-nitrobenzoate group was used as a specific recognition unit for H₂S_n. A morpholine unit was chosen as a lysosome-located group. In the absence of H₂S_n, the fluorescent probe exhibited almost no fluorescence. In the presence of H₂S_n, the fluorescent probe showed strong fluorescence owing to H₂S_n-mediated aromatic substitution-cyclization reactions. The fluorescence emission intensity at 548 nm of the probe showed a good linear relationship toward H₂S_n in the range of 2.0 × 10^-7 - 9.0 × 10^-5 mol·L^-1, and the detection limit was found to be 1.5 × 10^-7 mol·L^-1. The probe possessed a wide work range of pH, including the pH of physiological environment, and high selectivity for H₂S_n. There are almost no cytotoxicity and the ability of detecting endogenous and exogenous H₂S_n in lysosomes. These results indicate that the fluorescent probe can provide a good tool for intracellular and extracellular detection of H₂S_n.

Progress on the reaction-based methods for detection of endogenous hydrogen sulfide

Hydrogen sulfide (H₂S) is a biologically signaling molecule that mediates a wide range of physiological functions, which is frequently misregulated in numerous pathological processes. As such, measurement of H₂S holds great attention due to its unique physiological and pathophysiological roles. Currently, a variety of methods based on the H₂S-involved reactions have been reported for detection of endogenous H₂S, bearing the advantages of good specificity and high sensitivity. This review describes in detail the types of reactions, their mechanisms, and their applications in biological research, thus hopefully providing some guidelines to the researchers in this field for further investigation.

Construction of DCM-based NIR fluorescent probe for visualization detection of H2S in solution and nanofibrous film

Hydrogen sulfide (H₂S) played crucial roles in biological processes and daily life, and the abnormal level of H₂S was associated with many physiological processes. In this paper, we designed and developed a dicyanomethylene-4H-chromene (DCM)-based near-infrared (NIR) fluorescent probe DCM-NO guided by theoretical calculation. The probe displayed excellent selectivity towards H₂S with a fast response time (3 min) and low detection limit (fluorescence 25.3 nM/absorption 6.61 nM) in Hela cells and real water samples. Furthermore, the probe-doped solid sensing materials (test strips and nanofibrous films) exhibited specific visualization of H₂S under ambient light or hand-held UV lamp, providing great potential for on-site and real-time application in environmental and biological systems.