Hydrogen sulfide deactivates common nitrobenzofurazan-based fluorescent thiol labeling reagents

An ESIPT + AIE based dual-response fluorescent probe for continuous detection of PhSH and HClO and visualization of PhSH-induced oxidative stress in living cells

As a valuable industrial chemical, thiophenol (PhSH) is poisonous, which can be easily absorbed by the human body, leading to many serious health issues. In addition, PhSH-triggered oxidative stress is considered to be related with the pathogenesis and toxicity of PhSH. Therefore, efficient methods for monitoring PhSH and ROS production induced by PhSH in living systems are very meaningful and desired. Herein, we reasonably developed a facile dual-response fluorescent probe (HDB-DNP) by incorporating the dinitrophenyl (DNP) group into a novel methylthio-substituted salicylaldehyde azine (HDB) with AIE and ESIPT features. The probe itself was non-fluorescent owing to the strong quenching effect of DNP group. In the presence of PhSH, HDB-DNP gave an intense red fluorescence (610 nm), which can rapidly switch to green fluorescence (510 nm) upon further addition of HClO, allowing the successive detection of PhSH and HClO in two well-separated channels. HDB-DNP proved to be a very promising dual-functional probe for rapid (PhSH: < 17 min; HClO: 10 s) and selective detection of PhSH and HClO in physiological conditions with low detection limit (PhSH: 13.8 nM; HClO: 88.6 nM). Inspired by its excellent recognition properties and low cytotoxicity, HDB-DNP was successfully applied for monitoring PhSH and PhSH-induced HClO generation in living cells with satisfactory results, which may help to better understand the pathogenesis of PhSH-related diseases.

Specific imaging of intracellular hydrogen sulfide by a positively charged NIR fluorescent probe

The poor water solubility of traditional activatable organic molecular probes usually limits their detection ability in physiological environment. In this work, a positively charged H2S probe was designed, which exhibited a significantly enhanced responsiveness to H2S in the aggregated state due to the increased positive charge density on the aggregate surface. Under physiological conditions, the probe could be activated by H2S with specificity and sensitivity to release near-infrared fluorescence signal. Moreover, endogenous H2S levels in living cells were successfully monitored by using this probe. We expect that this probe can provide a new strategy for the design of activatable probes to break the limitation of poor water solubility of conventional organic molecular probes.

Construction of Coumarin-Based Bioorthogonal Macromolecular Probes for Photoactivation

Photoactivatable fluorescence imaging is one of the most valuable methods for visualizing protein localization, trafficking, and interactions. Here, we designed four bioorthogonal fluorescent probes K1-K4 by installing photoactive cages and HaloTag ligands onto the different positions of the coumarin fluorophore. Although K1-K4 all exhibited rapid photostimulated responses in aqueous solution, only K3 was found to have an obvious aggregation-induced emission (AIE). Next, macromolecular fluorescent probes Kn=1/2/3/4_POIs were obtained by covalently attaching K1-K4 to HaloTag-fused proteins of interest (POIs). Kn=3/4_POIs exhibited a higher fluorescence increase than that of Kn=1/2_POIs upon photoactivation in both liquid and solid phases. Moreover, K3_GFP_Halo and K4_GFP_Halo presented the fluorescence resonance energy transfer (FRET) from photocleaved K3 and K4 to GFP in the protein complex. We further examined the fluorescence labeling ability of K1-K4 to intracellular IRE1_Halo protein and found that K3 and K4 containing the HaloTag ligand on the C4 position of coumarin could be retained in cells for long-term tracking of the IRE1_Halo protein. Hence, we established a platform of novel bioorthogonal fluorescent probes conjugating onto Halo-tagged POIs for rapid photoactivation in vitro and in cells.

Precise Spatiotemporal Identification of Mitochondrial H2S Fluctuations through Exploiting an On-Demand Photoactivated Probe

Various signal molecules participate in complex biological processes in mitochondria. However, most currently available probes have problems in elucidating the functions of these active species in mitochondria due to the inability to light up these probes exclusively at the desired mitochondrial location, thereby compromising the specificity and accuracy. In this study, we present an on-demand photoactivation approach to the molecular design of optimized probes for precise spatiotemporal identification of mitochondrial H2S fluctuations. The designed probe with native yellow fluorescence can monitor the process into mitochondria but maintains nonfluorescent response to H2S during cellular delivery, providing the accurate timing of accumulation in mitochondria. On-demand photoactivation exclusively at the desired mitochondrial location affords a significant aggregation-enhanced and emissive response to H2S with lighting up red fluorescence at 690 nm, which is the only way to get such an emissive phenomenon and greatly improves the specificity and accuracy of targeting mitochondrial H2S. By using this photocontrolled fluorescence responsiveness to H2S, precise spatiotemporal identification of mitochondrial H2S fluctuations is successfully performed. Our work could facilitate advances toward interrogating the physiological and pathological consequences of mitochondrial H2S in various biological events.

Construction of a novel ESIPT and AIE-based fluorescent sensor for sequentially detecting Cu2+ and H2S in both living cells and zebrafish

The development of effective methods for tracking Cu²⁺ and H₂S in living organisms is urgently required due to their vital function in a variety of pathophysiological processes. In this work, a new fluorescent sensor BDF with excited-state intramolecular proton transfer (ESIPT) and aggregation-induced emission (AIE) features for the successive detection of Cu²⁺ and H₂S was constructed by introducing 3,5-bis(trifluoromethyl)phenylacetonitrile into the benzothiazole skeleton. BDF showed a fast, selective and sensitive fluorescence "turn off" response to Cu²⁺ in physiological media, and the situ-formed complex can serve as a fluorescence "turn on" sensor for highly selective detection of H₂S through the Cu²⁺ displacement approach. In addition, the detection limits of BDF for Cu²⁺ and H₂S were determined to be 0.05 and 1.95 μM, respectively. Encouraged by its favourable features, including strong red fluorescence from the AIE effect, large Stokes shift (285 nm), high anti-interference ability and good function at physiological pH as well as a low toxicity, BDF was successfully applied for the consequent imaging of Cu²⁺ and H₂S in both living cells and zebrafish, making it an ideal candidate for detecting and imaging of Cu²⁺ and H₂S in live systems.

Water-Stable Eu6-Cluster-Based fcu-MOF with Exposed Vinyl Groups for Ratiometric and Fluorescent Visual Sensing of Hydrogen Sulfide

Detection of H₂S in the biological system has attracted enormous attention in recent years. In this work, a new vinyl-functionalized metal-organic framework (MOF), [(Me₂NH₂)₂] [Eu₆(μ₃-OH)₈(BDC-CH═CH₂)₆(H₂O)₆] (Eu-BDC-CH═CH₂, BDC-CH═CH₂ = 2-vinylterephthalic acid), was synthesized under solvothermal conditions. The vinyl groups in the ligands can not only modulate the "antenna effect" of the ligand on Eu³⁺ ions but also serve as an exposed reactive site to allow for the quantitative detection of H₂S by Eu-BDC-CH═CH₂. The ratiometric fluorescent probe has the advantages of water stability, acid-base stability (pH = 2-11), fast response (<2 min), high selectivity, and sensitivity (LOD = 38.4 μM). We also used Eu-BDC-CH═CH₂ to detect and analyze H₂S in tap and lake waters, demonstrating the potential of the probe for biological and environmental applications. In addition, the MOF-based agarose hydrogel film allows for the visual detection of H₂S via a smartphone by identifying the RGB values. The vinyl-functionalized MOF can thus be a powerful sensing platform for H₂S.

An ESIPT-based fluorescent probe with fast-response for detection of hydrogen sulfide in mitochondria

Excited-state intramolecular proton transfer (ESIPT) has recently received considerable attention due to its dual fluorescent changes and large Stokes shift. Hydrogen sulfide (H₂S) is a gas signal molecule that plays important roles in modulating the functions of different systems. Herein, by modifying 2-(2́-hydroxyphenyl) benzothiazole (HBT) scaffold, a novel near-infrared mitochondria-targeted fluorescent probe HBTP-H₂S has been rationally designed based on excited-state intramolecular proton transfer (ESIPT) effect. The nucleophilic addition reaction of the H₂S with probe HBTP-H₂S caused the break of the conjugated skeleton, resulting the shifting of maximum emission peak from 658 nm to 470 nm. HBTP-H₂S showed fast-response response time, good selectivity and a large Stokes shift (188 nm) toward H₂S. Most importantly, inspired by the inherent advantages of the probe, HBTP-H₂S was successfully employed to monitor mitochondrial H₂S in HepG2 cells.

NBD-based synthetic probes for sensing small molecules and proteins: design, sensing mechanisms and biological applications

Compounds with a nitrobenzoxadiazole (NBD) skeleton exhibit prominent useful properties including environmental sensitivity, high reactivity toward amines and biothiols (including H2S) accompanied by distinct colorimetric and fluorescent changes, fluorescence-quenching ability, and small size, all of which facilitate biomolecular sensing and self-assembly. Amines are important biological nucleophiles, and the unique activity of NBD ethers with amines has allowed for site-specific protein labelling and for the detection of enzyme activities. Both H2S and biothiols are involved in a wide range of physiological processes in mammals, and misregulation of these small molecules is associated with numerous diseases including cancers. In this review, we focus on NBD-based synthetic probes as advanced chemical tools for biomolecular sensing. Specifically, we discuss the sensing mechanisms and selectivity of the probes, the design strategies for multi-reactable multi-quenching probes, and the associated biological applications of these important constructs. We also highlight self-assembled NBD-based probes and outline future directions for NBD-based chemosensors. We hope that this comprehensive review will facilitate the development of future probes for investigating and understanding different biological processes and aid the development of potential theranostic agents.

Development of a piperazinyl-NBD-based fluorescent probe and its dual-channel detection for hydrogen sulfide

To selectively detect H₂S based on the thiolysis reaction of 7-nitro-1,2,3-benzoxadiazole (NBD), amines attracted increasing attention since NBD amine is regarded as a new H₂S reaction site. Herein, a novel fluorescent probe, triphenylamine piperazine NBD (TPA-Pz-NBD), was developed. The results showed that it exhibited high selectivity towards H₂S via fluorescence spectroscopy and solution color. Furthermore, TPA-Pz-NBD not only detected H₂S by a dual-channel, turn-on fluorescence signal at 500 nm and turn-off fluorescence signal at 545 nm, respectively, but also displayed a wide detection range of 0-125 μM. In addition, living cell imaging results indicated that TPA-Pz-NBD holds potential for the detection of intracellular H₂S.

A Paper-Based Ultrasensitive Optical Sensor for the Selective Detection of H2S Vapors

A selective and inexpensive chemical paper-based sensor for the detection of gaseous H2S is presented. The triggering of the sensing mechanism is based on an arene-derivative dye which undergoes specific reactions in the presence of H2S, allowing for colorimetric analysis. The dye is embedded into a porous cellulose matrix. We passively exposed the paper strips to H2S generated in situ, while the absorbance was monitored via an optic fiber connected to a spectrophotometer. The kinetics of the emerging absorbance at 534 nm constitute the sensor response and maintain a very stable calibration signal in both concentration and time dimensions for quantitative applications. The time and concentration dependence of the calibration function allows the extraction of unusual analytical information that expands the potential comparability with other sensors in the literature, as the limit of detection admissible within a given exposure time. The use of this specific reaction ensures a very high selectivity against saturated vapors of primary interferents and typical volatile compounds, including alkanethiols. The specific performance of the proposed sensor was explicitly compared with other colorimetric alternatives, including standard lead acetate strips. Additionally, the use of a smartphone camera to follow the color change in the sensing reaction was also tested. With this straightforward method, also affordable for miniature photodiode devices, a limit of detection below the ppm scale was reached in both colorimetric approaches.

Fluorescent probes based on nucleophilic aromatic substitution reactions for reactive sulfur and selenium species: Recent progress, applications, and design strategies

Reactive sulfur species (RSS) and reactive selenium species (RSeS) are important substances for the maintenance of physiological balance. Imbalance of RSS and RSeS is closely related to a series of human diseases, so it is considered to be an important biomarker in early diagnosis, treatment, and stage monitoring. Fast and accurate quantitative analysis of different RSS and RSeS in complex biological systems may promote the development of personalized diagnosis and treatment in the future. One way to explore the physiological function of various types of RSS and RSeS in vivo is to detect them at the molecular level, and one of the most effective methods for this is to use fluorescent probes. Nucleophilic aromatic substitution (SNAr) reactions are commonly exploited as a detection mechanism for RSS and RSeS in fluorescent probes. In this review, we cover recent progress in fluorescent probes for RSS and RSeS based on SNAr reactions, and discuss their response mechanisms, properties, and applications. Benzenesulfonate, phenyl-O ether, phenyl-S ether, phenyl-Se ether, 7-nitro-2,1,3-benzoxadiazole (NBD), benzoate, and selenium-nitrogen bonds are all good detection groups. Moreover, based on an integration of different reports, we propose the design and synthesis of RSS- and RSeS-selective probes based on SNAr reactions, current challenges, and future research directions, considering the selection of active sites, the effect of substituents on the benzene ring, and the introduction of other functional groups.

A dual-functional fluorescent probe for sequential determination of Cu2+/S2- and its applications in biological systems

A new acylhydrazine-derived Schiff base fluorescence probe DMI based on "ON-OFF-ON" fluorescence strategy was presented in this paper. Probe DMI could detect Cu²⁺ selectively and sensitively with dramatic fluorescence quenching in CH₃OH-PBS (v/v = 3:7) mixed solution. Once the complex DMI-Cu²⁺ interacted with S^2-, 10.67-folds fluorescence increase was induced via a displacement mechanism under the same experimental conditions. The corresponding detection limits for Cu²⁺ and S^2- were calculated to be 1.52 × 10^-8 M and 1.79 × 10^-8 M, respectively. The structures of DMI and DMI-Cu²⁺ were systematically characterized by Job's plot analysis, ESI-MS, IR, X-ray diffraction and density functional theory calculations. Furthermore, fluorescence imaging in MCF-7 cells and zebrafish demonstrated the probe DMI could act as a useful tool to monitor and track intracellular Cu²⁺ and S^2-, which was encouraged by remarkable fluorescence performance and low cytotoxicity. Importantly, the complex DMI-Cu²⁺ could be applied to detect corrupt blood samples, which could estimate the time of death.

Nucleophilicity of cysteine and related biothiols and the development of fluorogenic probes and other applications

Biothiols such as l-cysteine, l-homocysteine, and glutathione play essential roles in many biological processes, and are directly associated with several health conditions. Therefore, the development of fast, selective, sensitive, and inexpensive methods for quantitatively analyzing biothiols in aqueous solution, but especially in biological samples, is a very attractive research field. In this feature review, we have approached the relevance of biothiols' nucleophilicity to develop selective fluorogenic probes. Since biothiols have considerable structural similarity, relevant strategies are in full development, including several fluorescent molecular platforms, specific receptor sites, reaction conditions, and optical responses. All of these features are properly presented and discussed. Biothiol sensing protocols are based on traditional organic chemistry reactions such as (hetero)aromatic nucleophilic substitution, addition, and substitution at carbonyl carbon, conjugate addition, and nucleophilic substitution at saturated carbon, amongst others including combined processes; furthermore, mechanistic aspects are detailed herein, including some interesting historical contexts. The feasibility of related fluorogenic probes is illustrated by analysis in complex matrices such as serum, cells, tissues, and animal models. Applications of these reactions in more complex systems such as sulfhydryl-based peptides and proteins are also presented, aiming at functionalizing and detecting these nucleophiles. Most literature cited in this review is recent; however, some other prominent works are also detailed. It is believed that this review may be accessible for many academic levels and may efficiently contribute not only to popularizing science but also to the rational development of fluorogenic probes for biothiol sensing.

Sensing and Bioimaging of the Gaseous Signaling Molecule Hydrogen Sulfide by Near-Infrared Fluorescent Probes

A fluorescent probe for the monitoring of H₂S levels in living cells and organisms is highly desirable. In this regard, near-infrared (NIR) fluorescent probes have emerged as a promising tool. NIR-I and NIR-II probes have many significant advantages; for instance, NIR light penetrates deeper into tissue than light at visible wavelengths, and it causes less photodamage during biosample analysis and less autofluorescence, enabling higher signal-to-background ratios. Therefore, it is expected that fluorescent probes having emission in the NIR region are more suitable for in vivo imaging. Consequently, a considerable increase in reports of new H₂S-responsive NIR fluorescent probes appeared in the literature. This review highlights the advances made in developing new NIR fluorescent probes aimed at the sensitive and selective detection of H₂S in biological samples. Their applications in real-time monitoring of H₂S in cells and in vivo for bioimaging of living cells/animals are emphasized. The selection of suitable dyes for designing NIR fluorescent probes, along with the principles and mechanisms involved for the sensing of H₂S in the NIR region, are described. The discussions are focused on small-molecule and nanomaterials-based NIR probes.

A fluorescent probe for specific detection of cysteine in lysosomes via dual-color mode imaging

Biothiols, as part of the reactive sulfur species (RSS), are a class of bioactive molecules that play important physiological roles in human body. However, due to the similarity in structure and reaction sites of biothiols, it is difficult to differentiated detection them at the same time. In this work, a fluorescent probe CM-NBD combined coumarin derivative and 7-nitrobenzofurazan has been developed, which can effectively detect biothiols through simple ether cleavage. Because of a specific location group, CM-NBD can well localize in lysosomes with a high co-localization coefficient. Interesting, due to the weakly acidic environment of lysosomes, Cys can be distinguished from Hcy/GSH and H₂S via dual-color mode. The probe is able not only to image exogenous biothiols but also to discriminate Cys from Hcy/GSH and H₂S in cells and zebrafish model.

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 photostable fluorescent probe based on PET off for the detection of hydrogen sulfide and its application in bioimaging

As an important small gas signal molecule, H₂S has become an important research hotspot for both chemists and biologists.

NBD-based fluorescent probes for separate detection of cysteine and biothiols via different reactivities

A NBD-based fluorescent probe is developed to seperately detect Cys and all biothiols via different reactivity.

One-step microchip for DNA fluorescent labeling

In this study, we propose a microchip that is sequentially capable of fluorescently staining and washing DNAs. The main advantage of this microchip is that it allows for one-step preparation of small amounts of solution without degrading microscopic bio-objects such as the DNAs, cells, and biomolecules to be stained. The microchip consists of two inlets, the main channel, staining zone, washing zone, and one outlet, and was processed using a femtosecond laser system. High molecular transport of rhodamine B to deionized water was observed in the performance test of the microchip. Results revealed that the one-step procedure of on-chip DNA staining and washing was excellent compared to the conventional staining method. The one-step preparation of stained and washed DNAs through the microchip will be useful for preparing small volumes of experimental samples.

Nitrobenzoxadiazole Ether-Based Near-Infrared Fluorescent Probe with Unexpected High Selectivity for H2S Imaging in Living Cells and Mice

H₂S is an important endogenous gasotransmitter, and its detection in living systems is of great significance. Especially, selective and sensitive near-infrared (NIR) fluorescent H₂S probes with rapid response and large Stokes shift are highly desirable because of their superiority for in vivo detection. Probes with nitrobenzoxadiazole (NBD) ether as reaction sites have been well-explored recently to detect biothiols or H₂S/biothiols simultaneously, rather than to detect H₂S selectively. In this work, a new NBD ether-based NIR fluorescent probe was developed, which was unexpectedly found to show high selectivity for H₂S over various other analytes including biothiols, making it practical for specific detection of H₂S both in vitro and in vivo. Upon response to H₂S, this probe showed rapid and significant turn-on NIR emission changes centered at 744 nm within 3 min, together with a remarkable large Stokes shift (166 nm) and high sensitivity (LOD: 26 nM). Moreover, imaging exogenous and endogenous H₂S in living cells and rapid imaging of H₂S in living mice with this probe was successfully applied with excellent performance.

A two-separated-emission fluorescent probe for simultaneous discrimination of Cys/Hcy and GSH upon excitation of two different wavelengths

It is challenging to simultaneously discriminate two or three biothiols from each other due to their structural similarities as well as reactions sites. The development of multiple-signal fluorescent probes would be a promising way to overcome this issue. Herein, a two-separated-emission fluorescent probe for biothiols was developed based on the combination of nitrobenzofurazan (NBD) and phenanthroimidazole fluorophores linked by a facile ether bond. In the presence of Cys and Hcy, the probe in DMF-H₂O demonstrates two separate fluorescence emissions at 480 and 550 nm upon excitation of two independent wavelengths. However, addition of GSH to the probe only leads to blue fluorescence at 480 nm. This difference can be reasonably ascribed to the fact that the NBD-GSH intermediate, unlike NBD-Cys/Hcy, cannot undergo an intramolecular cyclization-rearrangement reaction. The probe exhibits a rapid response with low limits of detection (14.7 nM for Cys, 14.4 nM for Hcy, and 13.4 nM for GSH) with large concentration ranges of 0-100 μM for Cys/Hcy and 0-200 μM for GSH. Furthermore, the probe is successfully applied to simultaneously distinguish endogenous Cys, Hcy, and GSH in living HeLa cells and zebrafish models.

A novel NBD-based fluorescent turn-on probe for the detection of cysteine and homocysteine in living cells

Biothiols, such as cysteine (Cys), homocysteine (Hcy) and glutathione (GSH), are involved in a number of biological processes and play crucial roles in biological systems. Thus, the detection of biothiols is highly important for early diagnosis of diseases and evaluation of disease progression. Herein, we developed a new turn-on fluorescent probe 1 based on 7-nitro-2,1,3-benzoxadiazole (NBD) with high selectivity and sensitivity for Cys/Hcy on account of nucleophilic substitution and Smiles rearrangement reaction. The probe could sense Cys/Hcy rapidly, the intensity of fluorescence increased immediately within 1min. Furthermore, the probe is low toxic and has been successfully applied to detect intracellular Cys/Hcy by cell fluorescence imaging in living normal and cancer cells.

Highly Sensitive Ratiometric Self-Assembled Micellar Nanoprobe for Nitroxyl and Its Application In Vivo

Nitroxyl (HNO) is a derivative of nitric oxide (NO) that plays an essential role in various biological and pharmacological events. Until now, the in situ trapping and specific detection of HNO in living samples is still challenging. In this project, we fabricated a novel BODIPY-based micellar nanoprobe for monitoring nitroxyl in vitro and in vivo in ratiometric mode in aqueous solution. The probe (P-BODIPY-N) contains an asymmetrical BODIPY dye for fluorescent signaling and a diphenylphosphinobenzoyl as the trigger moiety; then we encapsulated P-BODIPY-N into the hydrophobic interior of an amphiphilic copolymer (mPEG-DSPE) and prepared a novel BODIPY-based micellar nanoprobe: NP-BODIPY-N. As far as we know, this probe is the first reported ratiometric fluorescent nanoprobe for HNO, which exhibits ultrasensitivity, high selectivity, and good biocompatibility. Above all, this nanoprobe shows favorable cellular uptaken and was successfully used to detect intracellular HNO released by Angeli's salt in living cells and zebrafish larvae. These results indicate that our newly designed nanoprobe will provide a promising tool for the studies of HNO in living system.

A NBD-S-rhodamine dyad for dual-color discriminative imaging of biothiols and Cys/Hcy

A fluorescent probe based on fast thiolysis of NBD thioether is developed for dual-color discriminative imaging of Cys and GSH.

A novel 3-hydroxychromone fluorescent probe for hydrogen sulfide based on an excited-state intramolecular proton transfer mechanism

A novel fluorescent probe based on an excited-state intramolecular proton transfer mechanism can detect H₂S with high sensitivity and high selectivity.

A multi-signal fluorescent probe for simultaneously distinguishing and sequentially sensing cysteine/homocysteine, glutathione, and hydrogen sulfide in living cells

A multi-signal fluorescent probe was engineered for simultaneously distinguishing and sequentially sensing cysteine/homocysteine, glutathione, and hydrogen sulfide in living cells.

Biothiols, which have a close network of generation and metabolic pathways among them, are essential reactive sulfur species (RSS) in the cells and play vital roles in human physiology. However, biothiols possess highly similar chemical structures and properties, resulting in it being an enormous challenge to simultaneously discriminate them from each other. Herein, we develop a unique fluorescent probe (HMN) for not only simultaneously distinguishing Cys/Hcy, GSH, and H₂S from each other, but also sequentially sensing Cys/Hcy/GSH and H₂S using a multi-channel fluorescence mode for the first time. When responding to the respective biothiols, the robust probe exhibits multiple sets of fluorescence signals at three distinct emission bands (blue-green-red). The new probe can also sense H₂S at different concentration levels with changes of fluorescence at the blue and red emission bands. In addition, the novel probe HMN is able to discriminate and sequentially sense biothiols in biological environments via three-color fluorescence imaging. We expect that the development of the robust probe HMN will provide a powerful strategy to design fluorescent probes for the discrimination and sequential detection of biothiols, and offer a promising tool for exploring the interrelated roles of biothiols in various physiological and pathological conditions.

Cascade Reaction-Based, Near-Infrared Multiphoton Fluorescent Probe for the Selective Detection of Cysteine

The ability to detect and visualize cellular events and their associated target biological analytes through use of cell-permeable profluorogenic probes is dependent on the availability of activatable probes that respond rapidly and selectively to target analytes by production of fluorescent reporting molecules whose excitation and emission energies span a broad range. Herein is described a new probe, DCM-Cys, that preferentially reacts with cysteine to form a dicyanomethylene-4H-pyran (DCM) reporter whose red-energy fluorescence can be stimulated by two-photon, near-infrared excitation so as to provide visualization of cysteine presence inside living human cells with a high signal-to-background ratio. These aforementioned characteristics and the ability of DCM-Cys to provide selective, nanomolar-level in vitro cysteine detection, as demonstrated by its lack of significant response to other thiols and potential interfering agents from biological environments, are attributed to the molecular designs of the DCM-Cys probe and DCM reporter. Attachment of an acryl moiety to the DCM reporter via a self-eliminating, electron-withdrawing benzyl alcohol-carbamate linker offers a probe having selective, sensitive reaction with cysteine to rapidly produce a reporter whose energies of excitation and emission (λ_abs^report = 480 nm, λ_emis^report = 640 nm) are red-shifted from those of the DCM-Cys probe (λ_abs^probe = 440 nm, λ_emis^probe = 550 nm), thereby leading to low background signal from abundant probe and a large signal from the resulting reporter of cysteine presence.

A multifunctional logic gate by means of a triple-chromophore fluorescent biothiol probe with diverse fluorescence signal patterns

Multiple logic gates such as OR, TRANSFER, INH, NOT, and YES operations were achieved on a single triple-chromophore fluorescent probe by using biothiols and fluorescence signal patterns as the multiple inputs and outputs.

Thiolysis of NBD-based dyes for colorimetric and fluorescence detection of H2S and biothiols: design and biological applications

H₂S-specific fluorescent/colorimetric probes based on the thiolysis of NBD dyes are summarized.

Investigation of thiolysis of NBD amines for the development of H2S probes and evaluating the stability of NBD dyes

Colorimetric and fluorescent turn-on probes based on thiolysis of NBD ether were explored for selective detection of H₂S.

An aryl-thioether substituted nitrobenzothiadiazole probe for the selective detection of cysteine and homocysteine

An aryl-thioether substituted nitrobenzothiadiazole probe was synthesized and employed to detect cysteine and homocysteine selectively in living cells. Interestingly, both cysteine (Cys) and homocysteine (Hcy) promote an enhancement of the fluorescence intensity of the probe at pH 7.4 while only Cys gives rise to this enhancement under weakly acidic conditions (pH 6.0).

Chemiluminescent detection of enzymatically produced H2S

Hydrogen sulfide (H2S) has emerged as an important biological signaling molecule. To better understand the multifaceted biological roles of H2S, the development of selective and sensitive biocompatible assays for H2S is becoming increasingly important. Motivated by these challenges, our laboratory is developing new methods to further detect and monitor biological H2S. Here, we describe in detail our recent advances in the development and the use of chemiluminescence-based H2S sensors to assist other investigators with use of these chemical tools. We highlight the use of these tools use by displaying their selectivity and high sensitivity toward H2S and provide examples of assays we have developed to detect enzymatically produced H2S.

Facile synthesis of a class of aminochromene–aniliniumion conjugated far-red to near-infrared fluorescent dyes for bioimaging

An innovative class of aminochromene–aniliniumion conjugated far-red to near-infrared dyes, namely ACA, was developed.

A two-photon fluorescent turn-on probe for nitroxyl (HNO) and its bioimaging application in living tissues

The first two-photon fluorescent probe for specific detection of nitroxyl is designed and synthesized, and we have further demonstrated that the new two-photon fluorescent probe could be employed to image nitroxyl in living cells and tissues.

Highly sensitive and selective detection of biothiols by a new low dose colorimetric and fluorescent probe

A low dose colorimetric and fluorescent turn-on probe for highly selective and sensitive detection of biothiols was reported.

Colorimetric and fluorescent detection of GSH with the assistance of CTAB micelles

Two fluorescent probes STP1–2 for GSH and mercapto-containing proteins were designed. Both probes have potential application in fluorescence imaging of GSH within living cells.