Simultaneous Detection of Glutathione and Hydrogen Polysulfides from Different Emission Channels

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.

An aggregation induced emission chalcone fluorescent probe with large Stokes shift for biothiols detection

The homeostasis of biothiols is closely related to the health of organisms. In view of the important role of biothiols, a fluorescent probe (7HIN-D) for the detection of intracellular biothiols was developed based on a simple chalcone fluorophore 7HIN with "ESIPT + AIE" characteristics. The probe 7HIN-D was obtained by introducing a biothiols specific DNBS (2,4-dinitrobenzenesulfonyl) unit as a fluorescence quencher to the fluorophore 7HIN. The nucleophilic substitution reaction between biothiols and probe 7HIN-D will release the DNBS unit and the fluorophore 7HIN, which exhibits a "turn on" AIE fluorescence with a large Stokes shift of 113 nm. The probe 7HIN-D displays high sensitivity and good selectivity to biothiols, and the detection limits value of probe 7HIN-D for GSH, Cys and Hcy were 0.384 μmol/L, 0.471 μmol/L and 0.638 μmol/L, respectively. In addition, the probe has been successfully used for fluorescence detection of endogenous biothiols in living cells due to its excellent performance, good biocompatibility and low cytotoxicity.

Observing hydrogen sulfide in the endoplasmic reticulum of cancer cells and zebrafish by using an activity-based fluorescent probe

A crucial endogenous signaling chemical, hydrogen sulfide, is involved in many physiological actions. In this work, we created the fluorescent probe ER-Nap-NBD using a naphthalimide fluorophore as the signal reporter, a 7-nitro-1,2,3-benzoxadiazole amine as the responsive moiety, and a sulfonamide part for endoplasmic reticulum targeting. ER-Nap-NBD could be detected the H₂S levels in solution and in living systems (cells and zebrafish).

Visualizing MiRNA Regulation of Apoptosis for Investigating the Feasibility of MiRNA-Targeted Therapy Using a Fluorescent Nanoprobe

MiRNA-targeted therapy is an active research field in precision cancer therapy. Studying the effect of miRNA expression changes on apoptosis is important for evaluating miRNA-targeted therapy and realizing personalized precision therapy for cancer patients. Here, a new fluorescent nanoprobe was designed for the simultaneous imaging of miRNA-21 and apoptotic protein caspase-3 in cancer cells by using gold nanoparticles as the core and polydopamine as the shell. Confocal imaging indicated that the nanoprobe could be successfully applied for in situ monitoring of miRNA regulation of apoptosis. This design strategy is critical for investigating the feasibility of miRNA-targeted therapy, screening new anti-cancer drugs targeting miRNA, and developing personalized treatment plans.

General Applicability of High-Resolution Continuum-Source Graphite Furnace Molecular Absorption Spectrometry to the Quantification of Oligopeptides Using the Example of Glutathione

This communication introduces the first-time application of high-resolution continuum-source molecular absorption spectrometry (HR CS MAS) for the quantification of a peptide. The graphite furnace technique was employed and the tripeptide glutathione (GSH) served as a model compound. Based on measuring sulfur in terms of carbon monosulfide (CS), a method was elaborated to analyze aqueous solutions of GSH. The most prominent wavelength of the CS molecule occurred at 258.0560 nm and was adduced for monitoring. The methodological development covered the optimization of the pyrolysis and vaporization temperatures. These were found optimally to be 250 °C and 2250 °C, respectively. Moreover, the effect of modifiers (zirconium, calcium, magnesium, palladium) on the absorption signals was investigated. The best results were obtained after permanent coating of the graphite tube with zirconium (total amount of 400 μg) and adding a combination of palladium (10 µL, 10 g L−1) and calcium (2 µL, 1 g L−1) as a chemical modifier to the probes (10 µL). Aqueous standard samples of GSH were used for the calibration. It showed a linear range of 2.5–100 µg mL−1 sulfur contained in GSH with a correlation coefficient R2 > 0.997. The developed method exhibited a limit of detection (LOD) and quantification (LOQ) of 2.1 µg mL−1 and 4.3 µg mL−1 sulfur, respectively. The characteristic mass accounted for 5.9 ng sulfur. The method confirmed the general suitability of MAS for the analysis of an oligopeptide. Thus, this study serves as groundwork for further development in order to extend the application of classical atomic absorption spectrometry (AAS).

A novel fluorescent probe for the detection of sulfur dioxide derivatives and its application in biological imaging

A new probe CA-SO2 to efficiently and specifically detect SO2 was designed. The probe showed a fast response time (<50 s), low detection limit (LOD = 75 nM), large Stokes shift (129 nm) and was applied to detect SO2 in living cells and zebrafish.

The fabrication of transferrin-modified two-photon gold nanoclusters with near-infrared fluorescence and their application in bioimaging

Transferrin-modified AuNCs (Tf-AuNCs) with two photon-near infrared (TP-NIR) fluorescence were prepared. For the first time, a novel nanoprobe platform, Tf-AuNCs@MnO₂, was developed for the TP-NIR fluorescence imaging and magnetic resonance imaging of living cells and tissues. This platform had high spatiotemporal resolution and a tissue-penetration depth of 300 μm.

Highly sensitive fluorescent sensor based on coumarin organic dye for pyrophosphate ion turn-on biosensing in synovial fluid

Highly sensitive fluorescence detection of pyrophosphate ion (PPi) is in urgent demand but remains a great obstacle, ascribing to scarcity of high-performance materials with promising optical property and high affinity. Herein, we report the design and fabrication of a coumarin-based organic dye (DCCH-TPD) containing both hydrazide group and terpyridine moiety for PPi biosensing through Cu²⁺-induced photo-electron transfer (PET) effect and target analyte-switched competitive coordination reaction. Individual DCCH-TPD was found to be highly emissive, and displayed a turn-off response toward Cu²⁺ due to formation of Cu²⁺@DCCH-TPD and PET effect. The recognition of Cu²⁺@DCCH-TPD by PPi leads to generation of Cu²⁺@PPi complex, which greatly reduces the amount of Cu²⁺ coordinated with DCCH-TPD, subsequently decreasing PET effect. Significantly enhanced fluorescence is recorded and the fluorescence intensity is closely relied on PPi concentration. Thus, highly sensitive detection of PPi is achieved, and the detection limit was calculated to be 0.075 μM. Furthermore, the proposed sensor presented good selectivity, and excellent practical ability for application in arthritic fluid.

A bifunctional fluorescent probe for simultaneous detection of GSH and H2Sn (n > 1) from different channels with long-wavelength emission

In this work, we presented a long-wavelength emission fluorescent probe DCM-Cou-SePh that can discriminatively detect glutathione (GSH) and hydrogen polysulfides (H₂S_n, n > 1) from green and red emission channels, respectively. With the addition of GSH, probe DCM-Cou-SePh displayed green fluorescence emission (λ_ex/em = 430/530 nm). In the presence of H₂S_n, the probe exhibited a significant fluorescence enhancement in red channel (λ_ex/em = 560/680 nm). We also demonstrated that this probe was suitable to quantitatively detect GSH and H₂S_n with low detection limits (0.12 μM for GSH, 0.19 μM for H₂S_n). Furthermore, DCM-Cou-SePh can be used for sensing endogenous GSH and H₂S_n in living cells by dual-color fluorescence imaging.

A novel "off-on-off" fluorescent-nanoprobe based on B, N co-doped carbon dots and MnO2 nanosheets for sensitive detection of GSH and Ag. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2021;244:118831. [PMID: 32860994 DOI: 10.1016/j.saa.2020.118831]

In this study, a new "off-on-off" fluorescence strategy for detecting glutathione (GSH) and silver ions (Ag⁺) is presented. The constructed nanoprobe is composed of B, N co-doped carbon dots (B, N-CDs) and manganese dioxide nanosheets (MnO₂ nanosheets), where MnO₂ nanosheets serve as a kind of efficient fluorescence quencher. The sensing mechanism of the system is based on the inner filter effect (IFE) and destruction-protection strategy. The assay strategy includes three processes: fluorescence quenching of B, N-CDs by MnO₂ nanosheets, the deconstruction of MnO₂ nanosheets by GSH, the combination between GSH and Ag⁺. The MnO₂ nanosheets are reduced to Mn²⁺ because of the addition of GSH and restoring the fluorescence intensity of the system, while the formation of the complex between GSH and Ag⁺ inhibit the reduction of MnO₂ nanosheets on account of the addition of Ag⁺, leading to the decrease in fluorescence of the probe. This strategy allows the quantitative detection of GSH and Ag⁺ with detection limit of 0.32 μmol·L^-1 and 0.24 μmol·L^-1, respectively. Moreover, this approach displays good sensitivity, selectivity and broad linear range, which could be broadly applicable for practical applications.

Efficient β-Carboline Alkaloid-Based Probe for Highly Sensitive Imaging of Endogenous Glutathione in Wheat Germ Tissues

Discriminative detection of GSH is achieved by employing a highly sensitive and selective fluorescent probe (KL-DN) that bears β-carboline alkaloid as a potential fluorophore and an azide group as the recognition unit. A rapid fluorescence off-on change is caused by special redox reaction; KL-DN has the capability of monitoring endogenous GSH in wheat germ tissues, indicating that this probe holds great potential for biological applications in plant tissues.

A novel highly sensitive fluorescent probe for bioimaging biothiols and its applications in distinguishing cancer cells from normal cells

In recent years, targeting drugs made by physical loading or chemical bonding of drugs on small molecular carriers have shown a very wide application prospect in the field of tumor and cancer treatment. How to achieve the release of drugs in cancer cells has become the core of this research. One of the most important bases for drug localization is to use the difference of small molecular biothiol concentration between cancer cells and normal cells. Details of the changes of biothiol levels in the growth and reproduction of cancer cells are still poorly understood, and the main reason is the lack of sensitive real-time imaging tools for biothiols in cancer cells. In this work, we reasonably designed and synthesized the combination of 4-hydroxy-1,8-naphthalimide and NBD-Cl as a concise fluorescent probe HN-NBD for imaging biothiols in live cells and zebrafish. In addition, due to the advantages of HN-NBD design, it is sufficiently sensitive to biothiols, and further imaging can distinguish cancer cells from normal cells. Probe HN-NBD would be of great significance to biomedical researchers for the study of biothiol-related diseases, the screening of new anticancer drugs, and the early diagnosis and treatment of cancers.

Design and applications of a novel fluorescent probe for detecting glutathione in biological samples

This study aimed to develop a novel and practical fluorescent method for GSH detection in complex biological samples. To this end, a series of coumarin-based fluorescent probes was designed and synthesized using various aliphatic halogens as the sensing group. By using a new evaluation method of GSH/Cys/Hcy coexisting conditions, the probe with chloropropionate (CBF3) showed a high selectivity, excellent sensitivity, good stability for GSH detection. The reaction mechanism is proposed as nucleophilic substitution/cyclization and intramolecular charge transfer (ICT), which was confirmed by LC-MS and NMR analysis, as well as density functional theory calculations. In addition, CBF3 was demonstrated to be competent not only for the quantitative detection of GSH in real serum samples, but also for sensing GSH changes in different oxidative stress models in living cells and nematodes. This study showed a practical strategy for constructing GSH-specific fluorescent probes, and provided a sensitive tool for real-time sensing of GSH in real biological samples. The findings would greatly facilitate further investigations on GSH-associated clinical diagnosis and biomedical studies.

A highly selective fluorescent probe for hydrogen polysulfides in living cells based on a naphthalene derivative

Hydrogen polysulfides (H₂S_n, n > 1) are members of reactive sulfur species (RSS) and signaling molecules derived from hydrogen sulfide (H₂S). Recently, the functions of H₂S_n in physiological and pathological processes have been increasingly recognized. However, their biological effects and detailed mechanisms of action are still little known. Therefore, there is an urgent need to develop highly selective and sensitive techniques for monitoring hydrogen polysulfides (H₂S_n) in living cells. In this study, we designed and synthesized a fluorescent probe based on a naphthalene derivative for the detection of hydrogen polysulfides. A naphthalene derivative was applied as the fluorescent main structure and the 2-fluoro-5-nitrobenzoate group was chosen as the recognition unit. In the absence of hydrogen polysulfides, the fluorescent probe displayed almost no fluorescence. In the presence of hydrogen polysulfides, the fluorescent probe exhibited strong fluorescence. The sensing mechanism was based on H₂S_n-mediated aromatic substitution-cyclization reactions. The linear range of the response concentration of the probe to hydrogen polysulfide was acquired in a concentration range of H₂S_n from 7.5 × 10^-7 to 2.5 × 10^-5 mol L^-1. The detection limit was evaluated to be 5.0 × 10^-7 mol L^-1 for H₂S_n. The fluorescent probe can applied in a wide pH range including physiological condition pH. The fluorescent probe showed high specificity for H₂S_n over other reactive sulfur species (RSS). Moreover, the fluorescent probe has been successfully applied to confocal imaging of hydrogen polysulfides in HepG2 cells without cell cytotoxicity. All of such good qualities indicated that it could be used to detect H₂S_n in living cells.

A Simple Long-wavelength Fluorescent Probe for Simultaneous Discrimination of Cysteine/Homocysteine and Glutathione/Hydrogen Sulfide with Two Separated Fluorescence Emission Channels by Single Wavelength Excitation

Small molecular biothiols, such as cysteine (Cys), homocysteine (Hcy), reduced glutathione (GSH), and hydrogen sulfide (H₂S), play crucial parts in regulating the redox balance of life activities, regulating normal physiological activities and preventing various diseases. Quantitative analysis of these important small molecular substances is very important for revealing their diverse physiological and pathological effects. Although many fluorescent probes have been reported to detect biothiols in cells, it is still not sufficiently advanced to detect biothiols with separated fluorescence emission peak by same wavelength excitation. In our work, we designed a simple conjugate of Nile red and NBD (7-nitro-1,2,3-benzoxadiazole) as long-wavelength fluorescent probe NR-NBD for the simultaneous discrimination of these biothiols at single wavelength excitation. Probe NR-NBD could efficiently discriminate Cys/Hcy, GSH and H₂S by two separated fluorescence emission channels and absorption spectra. Importantly, probe NR-NBD has excellent specificity and sensitivity towards the monitoring of endogenous/exogenous Cys/Hcy and GSH/H₂S in living cells and zebrafish.

A rapid and sensitive fluorescent probe for detecting hydrogen polysulfides in living cells and zebra fish

Hydrogen polysulfides (H₂S_n, n>1) plays crucial roles in many biological processes, while it remains a challenge for rapid and selective detection of H₂S_n. We designed and synthesized a turn-on fluorescent probe (JCCF) for detecting H₂S_n based on a new julolidine-coumarinocoumarin scaffold. H₂S_n could trigger a dramatic fluorescence enhancement (52-fold) with a fast response time and a low detection limit of 98.3 nM (S/N = 3). Moreover, JCCF was successfully applied to image H₂S_n in living cells and zebra fish with low cytotoxicity.

A ratiometric fluorescent probe for simultaneous detection of Cys/Hcy and GSH

GSH, Cys and Hcy are the main intracellular thiols to play crucial roles in human pathologies. It is a great challenge to differentiate these three biothiols using single molecular fluorescent probes due to their close similarities in chemical structure and reactivity. In this work, based on the fluorescence resonance energy transfer (FRET) mechanism, a fluorescent probe CPR was constructed to simultaneously distinguish GSH and Cys/Hcy by means of ratiometric fluorescence changes: from red (584 nm) to green (542 nm) for GSH and from red (584 nm) to blue (472 nm) for Cys/Hcy. This probe showed high sensitivity and selectivity with low limits of detection (LOD = 12 nm, 13 nm and 30 nm for Cys, Hcy and GSH, respectively) and was capable of imaging GSH and Cys/Hcy in cells and zebrafish in a ratiometric manner with low toxicity.

Visualization of hydrogen polysulfides in living cells and in vivo via a near-infrared fluorescent probe

Hydrogen polysulfides (H₂S_n, n > 1), as the oxidized forms of H₂S, have attracted increasing attention these years due to their involvement in signaling transduction and cytoprotective processes. It is necessary to detect H₂S_n in living systems for the study of their functions. In this work, we report a BODIPY-based near-infrared emitting fluorescence probe NIR-PHS1, with "turn-on" response, rapid response rate (within 10 min), outstanding selectivity and excellent sensitivity (detection limit = 12 nM) response towards H₂S_n. The probe was successfully applied to the visualizing of endogenous H₂S_n in living cells. Moreover, it can be used for near-infrared in vivo imaging of H₂S_n in living mice. Therefore, NIR-PHS1 could be a potential imaging tool to study the biological roles of H₂S_n in living systems.

A simple highly specific fluorescent probe for simultaneous discrimination of cysteine/homocysteine and glutathione/hydrogen sulfide in living cells and zebrafish using two separated fluorescence channels under single wavelength excitation

Biothiols such as cysteine (Cys), homocysteine (Hcy), glutathione (GSH) and hydrogen sulfide (H₂S) are widely found in mammalian cells. They are closely related to the production and metabolic pathways and play very important roles in physiological and pathological activities. Therefore, the quantitative detection of these biothiols is of great significance. Although many fluorescent probes have been successfully used to track biothiols in biological samples, the fluorescence method for simultaneously detecting these biothiols using separated fluorescence emission channels under single wavelength excitation is still immature. In this work, we prepared the conjugate of seminaphthorhodafluor (SNARF) dye and 7-nitro-1,2,3-benzoxadiazole (NBD) using as a simple long-wavelength fluorescent probe SNARF-NBD for specific detection of biothiols. Cys/Hcy and GSH/H₂S were identified by two separated fluorescence emission channels under single wavelength excitation, which showed good selectivity and sensitivity. In addition, SNARF-NBD has low cytotoxicity and shows good imaging ability in living cells and zebrafish.

A new turn-on fluorescent probe with ultra-large fluorescence enhancement for detection of hydrogen polysulfides based on dual quenching strategy

Based on dual quenching strategy (ESIPT inhibited quenching and PET quenching), we have developed a new turn-on fluorescent probe 1. Combining 3-(benzo[d]thiazol-2-yl)-10-butyl-10H-phenothiazin-2-ol (dye 2) as the fluorophore and 2-fluoro-5-nitro-benzoic as the recognition moiety, probe 1 had feature of notable large Stokes shift, highly sensitivity and selective for monitoring H₂S_n with remarkable fluorescence enhancement (328-fold) response at 534 nm. Probe 1 exhibited excellent performance in the quantitative detection of H₂S_n with a 137 nm Stokes shift and a low detection limit of 26 nM in solution. Finally, probe 1 was successfully utilized to image H₂S_n in living A549 cells and zebrafish.

An endoplasmic reticulum-targetable fluorescent probe for highly selective detection of hydrogen sulfide

Hydrogen sulfide (H2S), a critical endogenous signaling molecule, is widely involved in many physiological processes. Endoplasmic reticulum, an important organelle with a sac-like structure, plays crucial roles in maintaining the normal function of cells. Accordingly, monitoring the H2S levels in endoplasmic reticulum is of great importance. Herein, we have developed an endoplasmic reticulum-targetable fluorescent probe, ER-CN, for H2S detection. ER-CN features excellent sensing properties, such as high sensitivity and selectivity. In addition, ER-CN exhibits low cytotoxicity and a fine endoplasmic reticulum targeting property (with a Pearson's colocalization coefficient of 0.95). Significantly, visualization of H2S in the endoplasmic reticulum of living HeLa cells by using ER-CN was successfully realized.

Functional synthetic probes for selective targeting and multi-analyte detection and imaging

In contrast to the classical design of a probe with one binding site to target one specific analyte, probes with multiple interaction sites or, alternatively, with single sites promoting tandem reactions to target one or multiple analytes, have been developed. They have been used in addressing the inherent challenges of selective targeting in the presence of structurally similar compounds and in complex matrices, as well as the visualization of the in vivo interaction or crosstalk between the analytes. Examples of analytes include reactive sulfur species, reactive oxygen species, nucleotides and enzymes. This review focuses on recent innovations in probe design, detection mechanisms and the investigation of biological processes. The vision is to promote the ongoing development of fluorescent probes to enable deeper insight into the physiology of bioactive analytes.

A near-infrared Nile red fluorescent probe for the discrimination of biothiols by dual-channel response and its bioimaging applications in living cells and animals

Biothiols, including cysteine (Cys), homocysteine (Hcy), glutathione (GSH) and H₂S, play important roles in human physiological processes.

A Turn-On Fluorescent Probe for Sensitive Detection of Cysteine in a Fully Aqueous Environment and in Living Cells

We reported here a turn-on fluorescent probe (1) for the detection of cysteine (Cys) by incorporating the recognition unit of 2,4-dinitrobenzenesulfonyl ester (DNBS) to a coumarin derivative. The structure of the obtained probe was confirmed by NMR and HRMS techniques. The probe shows a remarkable fluorescence off-on response (∼52-fold) by the reaction with Cys in 100% aqueous buffer. The sensing mechanism was verified by the HPLC test. Probe 1 also displays high selectivity towards Cys. The detection limit was calculated to be 23 nM. Moreover, cellular experiments demonstrated that the probe is highly biocompatible and can be used for monitoring intracellular Cys.

A low background D-A-D type fluorescent probe for imaging of biothiols in living cells

Two probes, structurally symmetric CBFB and asymmetric CBFM, constructed by a D-A-D (donor-acceptor-donor) type curcuminoid as the fluorophore and the DNBS (2,4-dinitrobenzenesulfonyl) group as the biothiol recognition site were designed and synthesized here. The DNBS group can quench the emission of the fluorophore by the PET (photoinduced electron transfer) process, and in the presence of biothiols, the emission of the probe was switched on as a result of the cleavage of the quencher by a nucleophilic aromatic substitution reaction. Experimental analyses and theoretical calculations revealed that two recognition moieties in the molecule can quench the fluorescence more efficiently, therefore, CBFB showed a much higher SNR (signal to noise ratio) than CBFM in biothiol detection with an emission maximum at 610 nm. This "low background" and "turn-on" fluorescent probe, CBFB, was successfully utilized to map endogenous biothiols in living cells.

A fluorescent τ-probe: quantitative imaging of ultra-trace endogenous hydrogen polysulfide in cells and in vivo

Hydrogen sulfide (H2S) has been recognized as an important endogenous gasotransmitter associated with biological signaling transduction. However, recent biological studies implied that the H2S-related cellular signaling might actually be mediated by hydrogen polysulfides (H2S n , n > 1), not H2S itself. Unraveling such a mystery strongly demanded the quantification of endogenous H2S n in living systems. However, endogenous H2S n has been undetectable thus far, due to its extremely low concentration within cells. Herein, we demonstrated a strategy to detect ultra-trace endogenous H2S nvia a fluorescent τ-probe, through changes of fluorescence lifetime instead of fluorescence intensity. This τ-probe exhibited an ultrasensitive response to H2S n , bringing about the lowest value of the detection limit (2 nM) and a lower limit of quantification (10 nM) to date. With such merits, we quantified and mapped endogenous H2S n within cells and zebrafish. The quantitative information about endogenous H2S n in cells and in vivo may have a significant implication for future research on the role of H2S n in biology. The methodology of the τ-probe established here might provide a general insight into the design and application of any fluorescent probes, beyond the limit of utilizing fluorescence intensity.

Polysulfide-triggered fluorescent indicator suitable for super-resolution microscopy and application in imaging

A new physiologically benign and cell membrane permeable BODIPY based molecular probe, MB-Sn, specifically senses intracellular hydrogen polysulfides (H₂S_n, n > 1) localized in the endoplasmic reticulum.