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

A Near-Infrared Fluorescent Probe with Large Stokes Shift for Sensitive Detection of Hydrogen Sulfide in Environmental Water, Food Spoilage, and Biological Systems

Hydrogen sulfide (H2S) is an important endogenous gas transmitter that plays a critical role in various physiological and pathological processes and can also cause a negative impact on foodstuffs. In this study, we designed and synthesized a simple, easily available, high-yield, and low-cost near-infrared (λem = 710 nm) fluorescent probe, DEM-H2S, with a substantial Stokes shift (205 nm) for the detection of H2S. DEM-H2S features high selectivity and sensitivity (LOD = 80 nM) toward H2S, accompanied by a noticeable color change. Upon interaction with H2S, DEM-H2S exhibits a restored ICT (Intramolecular Charge Transfer) process, thereby manifesting near-infrared fluorescence. DEM-H2S has been successfully utilized to detect H2S in actual water samples and to monitor the spoilage of food items, such as pork, shrimp, and eggs. Furthermore, DEM-H2S enables the imaging of endogenous and exogenous H2S in living MCF-7 cells and zebrafish. Hence, DEM-H2S provides an attractive method for the detection of H2S in environmental, food, and biological systems, holding potential value in physiological and pathological research.

GSH-specific fluorescent probe for sensing, bioimaging, rapid screening of natural inhibitor Celastrol and ccRCC theranostics

High level of intracellular glutathione (GSH) has been identified as a major barrier for cancer therapy. Therefore, effective regulation of GSH can be regarded as a novel approach for cancer therapy. In this study, an off-on fluorescent probe (NBD-P) is developed for selective and sensitive sensing GSH. NBD-P has a good cell membrane permeability that can be applied in bioimaging endogenous GSH in living cells. Moreover, the NBD-P probe is used to visualize GSH in animal models. In addition, a rapid drug screening method is successfully established using the fluorescent probe NBD-P. A potent natural inhibitor of GSH is identified as Celastrol from Tripterygium wilfordii Hook F, which effectively triggers mitochondrial apoptosis in clear cell renal cell carcinoma (ccRCC). More importantly, NBD-P can selectively respond to GSH fluctuations to distinguish cancer tissues from normal tissues. Thus, the present study provides insights into fluorescence probes for the screening GSH inhibitors and cancer diagnosis, as well as in-depth exploration of the anti-cancer effects of Traditional Chinese Medicine (TCM).

All-Nontoxic Fluorescent Probe for Biothiols and Its Clinical Applications for Real-Time Glioblastoma Visualization

Fluorescence-guided surgery (FSG) is a surgical method to selectively visualize the tumor site using fluorescent materials with instrumental setups in the operation rooms. It has been widely used in the surgery of brain tumors, such as glioblastoma (GBM), which is difficult to distinguish from normal tissue. Although FSG is crucial for GBM surgery, the commercially available fluorescent materials for FSG have shown serious adverse effects. To satisfy the clinical demand, we recently reported reaction-based fluorescent probes based on a 4-chloro-7-nitrobenzofurazan (NBD) fluorophore that can detect cysteine (Cys) and homocysteine (Hcy), a biomarker of GBM, and their applications for the GBM diagnosis and FSG. However, our probes have cellular toxicity issues arising from the leaving group (LG) that is generated after the reaction of the fluorescent probe and the analytes. In this study, we disclosed a nontoxic fluorescent probe for sensing biothiols and their clinical applications for real-time human glioblastoma visualization. Systematic toxicity analysis of several LGs was conducted on several cell lines. Among the LGs, 2-hydroxy-pyridine showed negligible toxicity, and its fluorescent probe derivative (named NPO-o-Pyr) showed high specificity and sensitivity (LOD: 0.071 ppm for Cys; 0.189 ppm for Hcy), a fast response time (<5 min) to Cys and Hcy, and high biocompatibility. In addition, NPO-o-Pyr can significantly detect the GBM site both in actual clinical samples as well as in the GBM-xenografted mouse model. We are confident that NPO-o-Pyr will become a new substitute in FSG due to its capability to overcome the limitations of the current fluorescent probes.

Enlightening the Path to Protein Engineering: Chemoselective Turn-On Probes for High-Throughput Screening of Enzymatic Activity

Many successful stories in enzyme engineering are based on the creation of randomized diversity in large mutant libraries, containing millions to billions of enzyme variants. Methods that enabled their evaluation with high throughput are dominated by spectroscopic techniques due to their high speed and sensitivity. A large proportion of studies relies on fluorogenic substrates that mimic the chemical properties of the target or coupled enzymatic assays with an optical read-out that assesses the desired catalytic efficiency indirectly. The most reliable hits, however, are achieved by screening for conversions of the starting material to the desired product. For this purpose, functional group assays offer a general approach to achieve a fast, optical read-out. They use the chemoselectivity, differences in electronic and steric properties of various functional groups, to reduce the number of false-positive results and the analytical noise stemming from enzymatic background activities. This review summarizes the developments and use of functional group probes for chemoselective derivatizations, with a clear focus on screening for enzymatic activity in protein engineering.

STAT Protein Thermal Shift Assays to Monitor Protein-Inhibitor Interactions

STAT3 protein is a sought-after drug target as it plays a key role in the progression of cancer. Many STAT3 inhibitors (STAT3i) have been reported, but accumulating evidence suggests many of these act as off-target/indirect inhibitors of STAT signaling. Herein, we describe the STAT protein thermal shift assay (PTSA) as a novel target engagement tool, which we used to test the binding of known STAT3i to STAT3 and STAT1. This revealed STATTIC, BP-1-102, and Cpd188 destabilized both STATs and produced unique migratory patterns on SDS-PAGE gels, suggesting covalent protein modifications. Mass spectrometry experiments confirmed these compounds are nonspecifically alkylating STATs, as well as an unrelated protein, NUDT5. These experiments have highlighted the benefits of PTSA to investigate interactions with STAT proteins and helped reveal novel reactivity of Cpd188. The described PTSA represents a promising chemical biology tool that could be applied to an array of other protein targets.

Red and Near-Infrared Fluorescent Probe for Distinguishing Cysteine and Homocysteine through Single-Wavelength Excitation with Distinctly Dual Emissions

Small-molecule biothiols, including cysteine (Cys), homocysteine (Hcy), and glutathione (GSH), participate in various pathological and physiological processes. It is still a challenge to simultaneously distinguish Cys and Hcy because of their similar structures and reactivities, as well as the interference from the high intramolecular concentration of GSH. Herein, a novel fluorescent probe, CySI, based on cyanine and thioester was developed to differentiate Cys and Hcy through a single-wavelength excitation and two distinctly separated emission channels. The probe exhibited a turn-on fluorescence response to Cys at both 625 nm (the red channel) and 740 nm (the near-infrared channel) but only showed fluorescence turn-on to Hcy at 740 nm (the near-infrared channel) and no fluorescent response to GSH. With the aid of built-in self-calibration of single excitation and dual emissions, simultaneous discriminative determinations of Cys and Hcy were realized through red and near-infrared channels. CySI exhibited excellent selectivity toward Cys and Hcy with a fast response. This probe was further exploited to visualize exogenous Cys and Hcy in cells through dual emission channels under one excitation. Moreover, it could efficiently target mitochondria and was applied to monitor the endogenous Cys fluctuations independently in mitochondria through the red emission channel.

Specific two-photon fluorescent probe for cysteine detection in vivo

Cysteine (Cys), an essential amino acid, plays several crucial functions in numerous biological processes. Notably, the detection of Cys is critical to disease diagnosis. Fluorescent probes that can quickly detect Cys will help to study the mechanism of certain diseases. Herein, a new fluorescent probe, ANP, which is based on 6-acetyl-N-methyl-2-naphthyl amine, has been developed for Cys detection over Hcy and GSH in vivo. The addition of thiol on α,β-unsaturated ketone promotes 87-fold fluorescence turn-on response with a 65 nM limit of detection. The high two-photon efficiency of the probe ANP (cross-section = 22.3) makes it a suitable probe for evaluating Cys in living cells without background fluorescence interference. Its application was extended to monitor the Cys distribution in live cells and tissues.

Molecular Probes, Chemosensors, and Nanosensors for Optical Detection of Biorelevant Molecules and Ions in Aqueous Media and Biofluids

Synthetic molecular probes, chemosensors, and nanosensors used in combination with innovative assay protocols hold great potential for the development of robust, low-cost, and fast-responding sensors that are applicable in biofluids (urine, blood, and saliva). Particularly, the development of sensors for metabolites, neurotransmitters, drugs, and inorganic ions is highly desirable due to a lack of suitable biosensors. In addition, the monitoring and analysis of metabolic and signaling networks in cells and organisms by optical probes and chemosensors is becoming increasingly important in molecular biology and medicine. Thus, new perspectives for personalized diagnostics, theranostics, and biochemical/medical research will be unlocked when standing limitations of artificial binders and receptors are overcome. In this review, we survey synthetic sensing systems that have promising (future) application potential for the detection of small molecules, cations, and anions in aqueous media and biofluids. Special attention was given to sensing systems that provide a readily measurable optical signal through dynamic covalent chemistry, supramolecular host-guest interactions, or nanoparticles featuring plasmonic effects. This review shall also enable the reader to evaluate the current performance of molecular probes, chemosensors, and nanosensors in terms of sensitivity and selectivity with respect to practical requirement, and thereby inspiring new ideas for the development of further advanced systems.

One-step synthesis of PY-NBD to distinguish Cys/Hcy and GSH in aqueous solutions and living cells by dual channels

An easy-to-synthesize fluorescent probe PY-NBD was developed to distinguish Cys/Hcy and GSH by two channels in aqueous solutions and living cells.

Activatable NIR-II Fluorescence Probe for Highly Sensitive and Selective Visualization of Glutathione In Vivo

Visualization of glutathione (GSH) enables us to understand GSH-related pathophysiological processes in living subjects. Currently, in vivo visualization methods of GSH are based on visible or first near-infrared (NIR-I) window fluorescence (FL) probes, which possess limitations due to their low tissue penetration depth and strong tissue autofluorescence. Herein, we developed a GSH-activatable second near-infrared (NIR-II) window FL probe (denoted as LET-7) for highly sensitive and selective visualization of GSH in vivo. LET-7, composed of an anionic polymethylcyanide skeleton linked with a FL quenching group of 3,5-bis(trifluoromethyl)benzenethiol, can be specifically activated by GSH, thus triggering a significant NIR-II FL emission enhancement with excellent photostability, which enables us to efficiently distinguish GSH from closely related low-molecular-weight biothiols. The limit of detection of LET-7 for GSH was determined to be as low as 85 nM. Most intriguingly, the in vivo studies demonstrated that LET-7 showed high sensitivity and good selectivity toward GSH. Therefore, our study provides a solution to design activatable NIR-II FL probes for in vivo imaging of GSH and other disease-related biomarkers.

Dinitrobenzene ether reactive turn-on fluorescence probes for the selective detection of H2S

Two novel fluorescent probes, namely, 3-(2,4-dinitrophenoxy)-2-(4-(diphenylamino)phenyl)-4H-chromen-4-one (P1) and 3-(2,4-dinitrophenoxy)-2-(pyren-1-yl)-4H-chromen-4-one (P2), were designed and synthesized here. The probes (P1 and P2) were found to be highly selective and sensitive toward hydrogen sulfide (H₂S) in the presence of a wide range of anions. The new probes (P1 and P2) were fully characterized by analytical, NMR spectroscopy (¹H and ¹³C), and ESI mass spectrometry. The sensing capability of chemodosimeters (P1 and P2) toward H₂S was confirmed by fluorescence studies. The 'turn-on' fluorescence was used to calculate the detection limit of probes (LOD), which were found to be 2.4 and 1.2 μM for P1 and P2, respectively. Moreover, the probes were tested for their cytotoxicity against HeLa cells using the MTT assay and found to be non-cytotoxic in nature; hence, the probes P1 and P2 were successfully utilized to visualize H₂S in the living 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.

Fluorescent labeling of the root cap cells with the bioactive NBD-S chemical probe based on the cellulose biosynthesis inhibition herbicides

Development of the methods to examine the molecular targets of biologically active compounds is one of the most important subjects in experimental biology/biochemistry. To evaluate the usability of the (7-nitro-2,1,3-benzoxadiazole)-thioether (NBD-S) probe for this purpose, bioactive chemical probe (1) as the cellulose biosynthesis (CB) inhibitor was synthesized and tested. As a result, a variety of fluorescently-labeled particles and organelles were found in the columella root cap cells of radish plants. Of note, well-defined cellular organelles were clearly recognized in the detaching root cap cells (border-like cells). These results imply that the bioactive NBD-S chemical probe could be a valuable direct-labeling reagent. Analysis of these fluorescent substances would be helpful in providing new information on defined molecular targets and events.

•Nobel S-NBD type chemical probe for cellulose biosynthesis inhibitors was prepared.

•This S-NBD type probe was designed for triaziflam and indaziflam.

•This S-NBD type probe labeled columella and detaching root cap cells fluorescent.

•S-NBD probe would be practical as a target exploring tool compound.

Deciphering protein microenvironment by using a cysteine specific switch-ON fluorescent probe

Fluorescent probes provide an unparalleled opportunity to visualize and quantify dynamic events. Here, we employ a medium-size, cysteine specific coumarin based switch-ON fluorescent probe 'L' to track protein unfolding profiles and accessibility of cysteine residues in proteins. It was established that 'L' is highly selective and exhibits no artifact due to interaction with other bystander species. 'L' is able to gauge subtle changes in protein microenvironment and proved to be effective in delineating early unfolding events that are difficult to otherwise discern by classic techniques such as circular dichroism. By solving the X-ray structure of TadA and probing the temperature dependent fluorescence-ON response with native TadA and its cysteine mutants, it was revealed that unfolding occurs in a stage-wise manner and the regions that are functionally important form compact sub-domains and unfold at later stages. Our results assert that probe 'L' serves as an efficient tool to monitor subtle changes in protein structure and can be employed as a generic dye to study processes such as protein unfolding.

Fluorescent Probes for Live Cell Thiol Detection

Thiols play vital and irreplaceable roles in the biological system. Abnormality of thiol levels has been linked with various diseases and biological disorders. Thiols are known to distribute unevenly and change dynamically in the biological system. Methods that can determine thiols' concentration and distribution in live cells are in high demand. In the last two decades, fluorescent probes have emerged as a powerful tool for achieving that goal for the simplicity, high sensitivity, and capability of visualizing the analytes in live cells in a non-invasive way. They also enable the determination of intracellular distribution and dynamitic movement of thiols in the intact native environments. This review focuses on some of the major strategies/mechanisms being used for detecting GSH, Cys/Hcy, and other thiols in live cells via fluorescent probes, and how they are applied at the cellular and subcellular levels. The sensing mechanisms (for GSH and Cys/Hcy) and bio-applications of the probes are illustrated followed by a summary of probes for selectively detecting cellular and subcellular thiols.

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.

Investigation of thiolysis of 4-substituted SBD derivatives and rational design of a GSH-selective fluorescent probe

In order to evaluate 7-sulfonamide benzoxadiazole (SBD) derivatives for the development of fluorescent probes, herein we investigated the thiolysis reactivity and selectivity of a series of SBD compounds with different atoms (N/O/S/Se) at the 4-position. Both SBD-amine and SBD-ether are stable toward biothiols in buffer (pH 7.4), while SBD-selenoether can react efficiently with biothiols GSH/Hcy, Cys, and H2S to produce SBD-SG/S-Hcy, SBD-NH-Cys, and SBD-SH, respectively, with three different sets of spectral signals. Therefore, the SBD-selenoether compounds should be useful platforms for the differentiation of these biothiols. Though SBD-alkylthioether shows much lower reactivity than SBD-selenoether, SBD-arylthioether is a tunable motif and structural modifications at the aryl moiety enable the rate of thiol-mediated thiolysis to be modified. To this end, an ER-targeted GSH-selective fluorescent probe 7 was rationally designed via thiolysis of SBD-arylthioether. Compared with control probe SBD-Cl, probe 7 exhibits improved GSH selectivity and better biocompatibility. In total, this study highlights that the modification at the 4-position of SBD is an efficient strategy for the development of new fluorescent probes with tunable reactivity and selectivity.

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.

Luminescence Enhancement based Sensing of L-Cysteine by Doped Quantum Dots

The interaction of a presynthesized orange emitting Mn²⁺ -doped ZnS quantum dots (QDs) with L-Cysteine (L-Cys) led to enhance emission intensity (at 596 nm) and quantum yield (QY). Importantly, the Mn²⁺ -doped ZnS QDs exhibited high sensitivity towards L-Cys, with a limit of detection of 0.4±0.02 μM (in the linear range of 3.3-13.3 μM) and high selectivity in presence of interfering amino acids and metal ions. The association constant of L-Cys was determined to be 0.36×10⁵  M^-1 . The amplified passivation of the surface of Mn²⁺ -doped ZnS QDs following the incorporation and binding of L-Cys is accounted for the enhancement in their luminescence features. Moreover, the luminescence enhancement-based detection will bring newer dimension towards sensing application.

BODIPY-Based Fluorescent Probes for Biothiols

Fluorescent probes for biothiols have aroused increasing interest owing to their potential to enable better understanding of the diverse physiological and pathological processes related to the biothiol species. BODIPY fluorophores exhibit excellent optical properties, which can be readily tailored by introducing diverse functional units at various positions of the BODIPY core. In the present review, the development of fluorescent probes based on BODIPYs for the detection of biothiols are systematically summarized, with emphasis on the preferable detection of individual biothiols, as well as simultaneous discrimination among cysteine (Cys), homocysteine (Hcy), reduced glutathione (GSH). In addition, organelle-targeting probes for biothiols are also highlighted. The general design principles, various recognition mechanisms, and biological applications are elaboratively discussed, which could provide a useful reference to researchers worldwide interested in this area.

A novel fluorescent probe for rapidly detection cysteine in cystinuria urine, living cancer/normal cells and BALB/c nude mice

Cysteine (Cys), an important organic small molecule containing sulfhydryl groups, plays paramount functions in human pathologies and physiologies. The detection of Cys in living vivo is essential for studying its roles. Here, we designed and synthesized a novel red-emission fluorescent probe AXPI-Cys with highly sensitivity (LOD = 48.9 ± 0.23 nM), rapidly response (<7 min) and colorimetric for detection cysteine. More importantly, the AXPI-Cys was determined Cys in real cystinuria urine samples for the first time with the satisfactory results (92%-99.96%) and employed for specifically location of endogenous/exogenous Cys in living cancer/normal cells and almost non-toxic, that is very valuable for diagnosis of cystinuria and observation of the distribution of Cys in normal cells. Notably, the AXPI-Cys was applied to imaging Cys in BALB/c nude mice with good biocompatibility and desirable tissue-penetration depth. Owing to the superior capability of AXPI-Cys, it provided a desired method to detect Cys in urine samples and cells, and exhibited munificent potential usage in biosystems and imaging studies in vivo.

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.

A visible and near-infrared dual-fluorescent probe for discrimination between Cys/Hcy and GSH and its application in bioimaging

The probe Cy2 showed high sensitivity and excellent selectivity with a distinct fluorescence off-on response to GSH with NIR emission and Cys/Hcy with green emission, respectively.

Development of a new fluorescent probe for cysteine detection in processed food samples

Cysteine is a crucial amino acid, found in a huge amount in protein-rich foods. We focused our research to determine the amount of free cysteine consumed highly in foods such as pork, beef, poultry, eggs, dairy, red peppers, soybeans, broccoli, brussels sprouts, oats, and wheat germs. A newly designed carbazole-pyridine-based fluorescent probe (CPI) has been introduced for quantitative estimation of cysteine (Cys) with a "turn on" fluorescence in some popular processed food samples chosen from our daily diet. CPI shows both naked eye and UV-visible color changes upon interaction with cysteine. The binding approach between CPI and Cys at biological pH has been thoroughly explored by UV-visible and fluorescence spectroscopy. From Job's plot analysis, 1:1 stoichiometric reaction between CPI and Cys is observed with a detection limit of 3.8 μM. NMR, ESI mass spectrometry, and time-dependent density functional theory (TD-DFT) study enlightens the formation of more stable product CPI-Cys. The "turn on" response of the probe CPI occurs due to the interruption of intra-molecular charge transfer (ICT) process upon reacting with cysteine. Moreover, CPI is a very stable, cost-effective compound and exhibits excellent real-time selectivity towards Cys over all other comparative biorelevant analytes. Interestingly, our proposed method is much advantageous as it is able to estimate cysteine predominantly by screening out other comparative biocomponents found in different protein-rich foods.

A colorimetric and fluorescent chemosensor based on diarylethene for simultaneous detection and discrimination of biothiols

In this work, a novel probe D-HBT-NBD (1O) based on diarylethene to detect biothiols (including Cys, Hcy and GSH) was synthesized and the relative colorimetric and fluorescent properties were tested. The probe exhibited excellent photochromic properties and showed apparent colorimetric and fluorescent signals for Cys, Hcy and GSH. The probe can selectively detect Cys, Hcy and GSH by naked eyes for its open-ring isomer 1O and can discriminate Cys from Hcy/GSH by apparent color change from light orange to dark pink at the closed-ring state under the irradiation of UV light. At the excitation wavelength of 465 nm, the probe could be used to discriminate GSH from Cys/Hcy with no fluorescent emission at 570 nm. Taking advantage of the photochromic property of the diarylethene moiety and the different fluorescent properties of NBD derivatives of GSH and Cys/Hcy, 1O could be used as a novel probe to discriminate Cys, Hcy and GSH from each other simultaneously. Meanwhile, a logic gate was constructed based on the colorimetric and fluorescent properties of 1O.

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.

Powder carbonization to synthesize novel carbon dots derived from uric acid for the detection of Ag(I) and glutathione

This article first reported that a simple synthesis of carbon dots (UCDs) by pyrolysis of uric acid was proposed. The excitation wavelength was 350 nm and the emission wavelength was 402 nm for the synthesized UCDs. And the corresponding fluorescence quantum yield was 52.06%. The obtained UCDs could be served as a fluorescence probe to recognize Ag⁺ and glutathione (GSH), respectively. The fluorescence of UCDs was quenched after the addition of Ag⁺. The obtained UCDs had a linear relationship with Ag⁺ in the detection range of 0.1 μM to 2.0 μM, and the detection limit was 39 nM. The quenching fluorescence of this system could be restored after adding GSH. The fluorescence intensity increased linearly on increasing the concentration of glutathione in the range of 4 to 9 μM, and the detection limit was 66 nM. Based upon these phenomena, we proposed a novel fluorescence probe to detect Ag⁺ and detect GSH, respectively. In addition, the prepared UCDs were successfully applied to analyze Ag⁺ in mineral waters and GSH in blood serums.

A fast-response and highly specific Si-Rhodamine probe for endogenous peroxynitrite detection in living cells

Peroxynitrite (ONOO⁻) is involved in a variety of physiological and pathological processes.

A rhodol-hemicyanine based ratiometric fluorescent probe for real-time monitoring of glutathione dynamics in living cells

A new rhodol-hemicyanine based ratiometric and reversible fluorescent probe has been developed for real-time monitoring of glutathione dynamics in living cells.

A novel turn-on fluorescent probe for selective sensing and imaging of glutathione in live cells and organisms

A novel 1-oxo-1H-phenalene-2,3-dicarbonitrile (OPD)-based fluorescent probe was developed to sense and image GSH in HeLa cells, different imatinib-resistant K562 cells, D. magna and zebrafish embryos.

A long-wavelength-emitting fluorescent probe for simultaneous discrimination of H2S/Cys/GSH and its bio-imaging applications

A long-wavelength fluorescent probe NR-CY was developed for simultaneous identification of cysteine/glutathione and sulphide by combining the derivative of Nile red with 7-nitrobenzofurazan. The response of NR-CY to thiols is regulated by intramolecular charge transfer and photoinduced electron transfer mechanisms. For sulphide at 560 nm, cysteine at 475 nm and glutathione at 425 nm, different absorbance increases can be observed. NR-CY can detect cysteine at fluorescence emission 543 nm and distinguish sulphide from other analytes by kinetic experiments at 636 nm. The probe showed a rapid response to these thiols (cysteine was 90 s and sulphide was 30 s). In addition, NR-CY has been successfully applied to live MCF-7 cell imaging.

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 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 Ratiometric Two-Photon Fluorescent Cysteine Probe with Well-Resolved Dual Emissions Based on Intramolecular Charge Transfer-Mediated Two-Photon-FRET Integration Mechanism

The development of an efficient ratiometric two-photon fluorescence imaging probe is crucial for in situ monitoring of biothiol cysteine (Cys) in biosystems, but the current reported intramolecular charge transfer (ICT)-based one suffers from serious overlap between the shifted emission bands. To address this issue, we herein for the first time constructed an ICT-mediated two-photon excited fluorescence resonance energy transfer (TP-FRET) system consisting of a two-photon fluorogen benzo[ h]chromene and a Cys-responsive benzoxadiazole-analogue dye. Different from a previous mechanism that utilized single two-photon fluorogen to acquire a ratiometric signal, ICT was used to switch on the TP-FRET process of the energy transfer dyad by eliciting an absorption shift of benzoxadiazole with Cys to modulate the spectral overlap level between benzo[ h]chromene emission and benzoxadiazole absorption, resulting in two well-separated emission signal changes with large emission wavelength shift (120 nm), fixed two-photon excitation maximum (750 nm), and significant variation in fluorescence ratio (over 36-fold). Therefore, it can be successfully employed to ratiometrically visualize Cys in HeLa cells and liver tissues. Importantly, this new ICT-mediated TP-FRET integration mechanism would be convenient for designing ratiometric two-photon fluorescent probes with two well-resolved emission spectra suitable for high resolution two-photon fluorescence bioimaging.

Fluorescent Chemosensors for Various Analytes Including Reactive Oxygen Species, Biothiol, Metal Ions, and Toxic Gases

The development of fluorescent chemosensors for various analytes has been actively pursued by chemists. Since their inception, these efforts have led to many new sensors that have found wide applications in the fields of chemistry, biology, environmental science, and physiology. The search for fluorescent chemosensors was initiated by a few pioneering groups in the late 1970s and 1980s and blossomed during the last two decades to include more than hundreds of research groups around the world. The targets for these sensors vary from metal ions, anions, reactive oxygen/nitrogen species, biothiols, and toxic gases. Our group has made contributions to this area in last 18 years. In this perspective, we briefly introduce the history of chemosensors and review studies that we have carried out.