Combinatorial Strategy to Identify Fluorescent Probes for Biothiol and Thiophenol Based on Diversified Pyrimidine Moieties and Their Biological Applications

A ratiometric upconversion nanoprobe enables super-resolution imaging sensing of biothiols in living cells

We have developed an upconversion luminescent ratiometric nanoprobe, specifically designed for detection of biothiols with high sensitivity (∼25 nM) at the single-particle level. Using a single-particle localization and rendering method, this nanoprobe enables super-resolution imaging sensing of biothiols within a confined 22 nm space in living cells.

Activatable Dual-Optical Molecular Probe for Bioimaging Superoxide Anion in Epilepsy

Superoxide anion (O2•-) plays a pivotal role in the generation of other reactive oxygen species within the body and is closely linked to epilepsy. Despite this connection, achieving precise imaging of O2•- during epilepsy pathology remains a formidable challenge. Herein, we develop an activatable molecular probe, CL-SA, to track the fluctuation of the level of O2•- in epilepsy through simultaneous fluorescence imaging and chemiluminescence sensing. The developed probe CL-SA demonstrated its efficacy in imaging of O2•- in neuronal cells, showcasing its dual optical imaging capability for O2•- in vitro. Furthermore, CL-SA was successfully used to observe aberrantly expressed O2•- in a mouse model of epilepsy. Overall, CL-SA provides us with a valuable tool for chemical and biomedical studies of O2•-, promoting the investigation of O2•- fluctuations in epilepsy, as well as providing a reliable means to explore the diagnosis and therapy of epilepsy.

Green-emitting carbon dots as a "turn on" fluorescence bio-probe for highly sensitive and selective detection of lipase in human serum

Enzyme activity assays play a crucial role in numerous fields, including biotechnology, the food industry, and clinical diagnostics. Lipases are particularly important enzymes due to their widespread use in lipid metabolism and esterification reactions. Here, we present a pioneering method for the sensitive and selective determination of lipase activity using green carbon dots (G-CDs) for first time. G-CDs are a fascinating class of carbon nanomaterials with unique optical properties and biocompatibility, making them ideal candidates for enzyme activity assays. This approach eliminates the need for traditional fluorophores or chromogenic substrates, reducing costs, fast response time (1 min), and environmental impact with a quantum yield (QY) of 7.42%. As designed, the G-CDs fluorescent probe turn-on demonstrated a reliable linear detection range from 0 to 9 mg/mL under ideal conditions, with detection limit of 0.01 mg/mL and limit of quantification (LOQ) of 0.045 mg/mL, respectively. Furthermore, the G-CDs system was thoroughly evaluated in human serum samples, showing recoveries ranging from 100.0 to 105.0%. These findings highlight the promising applicability of the G-CDs probe for lipase detection, yielding highly favorable results.

ESIPT-based fluorescent enhanced probes prompted by methylated β-cyclodextrin for the detection of thiophenols

Thiophenol and its derivatives are compounds with high toxicity to organisms and environmental pollution, so it is necessary to detect the level of thiophenols in the environment and biological samples. The probes 1a-b were obtained by introducing the 2,4-dinitrophenyl ether group into diethylcoumarin-salicylaldehyde based compounds. And they can form host-guest compounds with methylated β-cyclodextrin (M-β-CD), the association constants of inclusion complexes are 49.2 M-1, 125 M-1 respectively. The fluorescence intensities of probes 1a-b at 600 nm (1a) and 670 nm (1b) increased significantly in thiophenols detection. Meanwhile, with the addition of M-β-CD, the hydrophobic cavity of M-β-CD significantly increased the fluorescence intensity of probes 1a-b, thus the detection limits of probes 1a-b to thiophenols were reduced from 410 nM, 365 nM to 62 nM, 33 nM respectively. Whereas, the good selectivity and short response time of probes 1a-b towards thiophenols was not affected in the presence of M-β-CD. Moreover, probes 1a-b were used for further water sample detection and HeLa cell imaging experiments due to their good response to thiophenols and the results suggested that probes 1a-b had the potential to detect the content of thiophenols in water samples and living cells.

A Simple but Effective Fluorescent Probe for the Detection of 4-Methylthiophenol

In this paper, a fluorescent probe (QFR) for the detective work of 4-methylthiophenol was successfully synthesized with a simple but highly effective probe structure. In the buffer solution (V(ACN): V(PBS) = 3:7), by observing the response of the probe after the fluorescence was turned on, we concluded that the probe had good characteristics such as high selectivity, low detection limit (116 nM), and fast response speed (20 min). In addition, the probe was a rare fluorescent probe that detected 4-methylthiophenol but did not respond to thiophenol. Fluorescence intensity was linearly related to 4-methylthiophenol concentration in the range of 0 to 2 equivalents (0-10 μM). The probe demonstrated good results in the determination of the recovery rate (92.28% to 110.1%) of actual water samples, and has great potential in environmental monitoring.

Fluorescent probes and functional materials for biomedical applications

Due to their simplicity in preparation, sensitivity and selectivity, fluorescent probes have become the analytical tool of choice in a wide range of research and industrial fields, facilitating the rapid detection of chemical substances of interest as well as the study of important physiological and pathological processes at the cellular level. In addition, many long-wavelength fluorescent probes developed have also proven applicable for in vivo biomedical applications including fluorescence-guided disease diagnosis and theranostics (e.g., fluorogenic prodrugs). Impressive progresses have been made in the development of sensing agents and materials for the detection of ions, organic small molecules, and biomacromolecules including enzymes, DNAs/RNAs, lipids, and carbohydrates that play crucial roles in biological and disease-relevant events. Here, we highlight examples of fluorescent probes and functional materials for biological applications selected from the special issues “Fluorescent Probes” and “Molecular Sensors and Logic Gates” recently published in this journal, offering insights into the future development of powerful fluorescence-based chemical tools for basic biological studies and clinical translation.

A novel dibenzo[a,c]phenazine-based fluorescent probe for fast and selective detection of thiophenols in environmental water

A new dibenzo[a,c]phenazine-based fluorescent probe exhibits high selectivity and sensitivity towards thiophenols in environmental water.

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.

An ICT-based fluorescent probe guided by theoretical calculation for selectively mapping endogenous GSH in living cells

Glutathione (GSH) is one of the most essential bio-thiols to maintain the redox balance of organisms which is strongly associated with many physiological processes. Detecting the concentration and mapping the distribution of GSH in the living system is significant to study many related diseases. In this work, we have successfully constructed an ICT-based model to guide the design and synthesis of GSH specific fluorescent probe CF1. A serials spectroscopy test demonstrated that the response of CF1 towards GSH owned large stokes shift (~167 nm) and an excellent linear relationship (0-120 μM, R² = 0.9961). Furthermore, CF1 was successfully applied to image endogenous GSH in different cell lines with high sensitivity. This work is instructive for the oriented synthesis of ICT-based functional fluorescent probe and the further visualization of intracellular targets in the living system.

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 3,5-dinitropyridin-2yl substituted naphthalimide-based fluorescent probe for the selective detection of biothiols and its application in cell-imaging

A highly selective OFF–ON fluorescent probe has been developed for the sensing of biothiols with a satisfactory response time and low detection limit. Also, the probe can be successfully applied for the sensing of biothiols in living cells.

On the Route to Quantitative Detection and Real-Time Monitoring of Glutathione in Living Cells by Reversible Fluorescent Probes

In the last few decades, growing numbers of fluorescent probes have been developed to detect intracellular GSH. However, the majority of probes for GSH were irreversible without monitoring the changes of intracellular GSH concentration. Therefore, recently, fluorescent probes for monitoring concentrations of GSH in real-time in living cells have come into being to address this challenge. This Perspective aimed at the development of reversible probes for GSH was organized by structural features, chemical reactions, and physicochemical properties. The reversible probes designed by a coumarin skeleton as a read-out fluorophore and the Michael addition reaction as a response mechanism accounted for most of the reported reversible probes. The performances of reversible fluorescent probes based on Michael addition could be roughly predicted by fundamental laws of kinetics and thermodynamics in physical chemistry. Essentially, the design principles included a highly reactive site for GSH, a small thermodynamic driving force, a desirable K_d of 1-10 mM, and excellent cell membrane permeability. Prospectively, the development of various mechanisms and fluorophores will be effective measures to enrich the types of reversible probes for GSH.

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 dicyanoisophorone-based highly sensitive and selective near-infrared fluorescent probe for sensing thiophenol in water samples and living cells

Thiophenol (PhSH) is an important sulfhydryl compound in organic synthesis, but it is also a volatile environmental pollutant with high toxicity to organisms. Herein, we reported a novel near-infrared (NIR) probe (1) for turn-on fluorescence detection of PhSH. The probe was prepared by coupling 2,4-dinitrophenyl (DNP) to a dicyanoisophorone-based fluorophore (2). PhSH can specifically perform a nucleophilic aromatic substitution on probe 1 and result in the release of fluorophore 2, thus achieving a turn-on fluorescence response (λ_em = 693 nm). A dramatic color change from red (λ_abs = 525 nm) to blue (λ_abs = 668 nm) was also observed. This fluorescent assay displayed a large Stokes shift (∼133 nm) and a high sensitivity for PhSH, as well as a low detection limit (34 nM). Moreover, probe 1 was successfully applied to monitor PhSH in real water samples and image PhSH in living cells.

Rational design of an ESIPT-based fluorescent probe for selectively monitoring glutathione in live cells and zebrafish

Glutathione (GSH), an extremely important antioxidant, is a major participant in maintaining redox homeostasis and tightly associated with various clinical diseases. Thus, accurate and rapid detection of intracellular GSH is imperative to elucidate its role in physiological and pathological processes. Herein, by modifying 2-(2'-hydroxyphenyl) benzothiazole (HBT) scaffold, we developed an excited-state intramolecular proton transfer (ESIPT)-based fluorescent probe BTFMD for tracking GSH, which exhibited good selectivity, excellent water solubility, a large Stokes shift (181 nm) and fast response rate (within 10 min). Furthermore, the probe was successfully applied for imaging of endogenous GSH in live cells and zebrafish, and probing into the role of GSH in the development of cancer and Parkinson's disease.

A ratiometric fluorescent probe for visualization of thiophenol and its applications

Thiophenol has a broad application in agriculture and industry. However, thiophenol can harm to the environment and health for its high toxicity. Developing an effective method for detection of thiophenol in the field of environmental and biology is valuable. In this work, we construct a reaction-based ratiometric fluorescent probe (E)-4-(2-(7-(diethylamino)-2-oxo-2H-chromen-3-yl)vinyl)-1-(4-(2,4-dinitrophenoxy)benzyl)pyridin-1-ium bromide (DCVP-DNP) for probing thiophenol in environment and cells by employing (E)-7-(diethylamino)-3-(2-(pyridin-4-yl)vinyl)-2H-chromen-2-one (DCVP) as the fluorophore and 2,4-dinitrophenyl (DNP) ether as the recognition group for the first time. The probe has high selectivity for thiophenol though thiophenol-triggered nucleophilic substitution reaction. In addition, the ratio of emission intensities of the probe has linearly with thiophenol concentration in the range of 0-65 μM and the detection limit of thiophenol is as low as 4.8 × 10^-8 M. Moreover, the probe can not only be applied for detection of thiophenol in water samples, but also image thiophenol in living cells, suggesting its potential application in environment and biological system.

A water-soluble fluorescent probe for the detection of thiophenols in water samples and in cells imaging

Water pollution is the main cause of death of aquatic organisms such as fish et al. Content of thiophenols in water samples is an important indicator for assessing the degree of water pollution. The development of fluorescent probes with high selectivity and high sensitivity to detect thiophenols in water samples is extremely important in both environmental and life sciences. Although several fluorescent probes for thiophenols detection have been reported in recent years, most of them required the assistance of organic solvents to remedy the restriction caused by the poor water solubility of the probe, which did not fully reflect the actual situation of thiophenols in actual water samples. To fully overcome this shortage, we modified the 1,8-naphthylimide moiety with carboxyl to obtain a water-soluble fluorescent probe which could react with thiophenols specifically through nucleophilic aromatic substitution reaction (S_NAr) reaction with turn-on fluorescent responses. The corresponding detection limit was 71 nM. Supported by the spectroscopic changes, test strips based on the probe could detect thiophenols quantificationally and conveniently. At the same time, the probe could detect thiophenols in water sample with quantitative recovery. Besides, cell imaging experiments demonstrated the possibility of the probe to detect thiophenols in living cells.

A novel pyridinium-based fluorescent probe for ratiometric detection of peroxynitrite in mitochondria

Peroxynitrite (ONOO^-) is a primary kind of reactive oxygen species. Excessive ONOO^- can induce oxidative damage to biomolecules and further results in various diseases. So, quantitative monitoring ONOO^- with excellent selectivity and sensitivity is imperative for elucidating its role in biological processes. In this study, a novel pyridinium fluorescent ONOO^- probe (CPC) has been constructed base on ICT-modulated by combining coumarin fluorophore and diphenylphosphinate recognition group. The fluorescence response of CPC for ONOO^- is realized via the removal of diphenylphosphinate group. The probe CPC shows prominent features for detection of ONOO^- including fast response rate (within 3 min), excellent selectivity and sensitivity, distinct colorimetric (red to green), and a large emission wavelength shift (105 nm). The emission intensity ration (I₅₃₈/I₆₄₃) exhibits 153-fold enhancement along with the increasing ONOO^- and the detection limit is as low as 1.60 × 10^-8 M. These good response properties make CPC possible to quantitative detection of ONOO^- concentration. By using the strategy, the ratiometric CPC has been employed to detection of mitochondrial ONOO^- in live cell successfully.

Thiol-Chromene "Click" Reaction Triggered Self-Immolative for NIR Visualization of Thiol Flux in Physiology and Pathology of Living Cells and Mice

Understanding the pathological process of biological systems can greatly improve the prevention and treatment of diseases. The study of pathological processes has now reached the molecular level, and molecular fluorescent probes have become a powerful tool. Chromene, also known as benzo-pyran molecule, is a structural element of natural products with good biological compatibility and was developed as a fluorescent probe. The thiol-chromene "click" nucleophilic pyran ring-opening reaction allows the quick detection of thiol. In this work, the chromene alcohol can function as an efficient self-immolative spacer, which covalently links NIR fluorophore via a carbonyl ester. Due to its favorable characteristics and superior applicability, the self-immolative amplifier NIR-HMPC achieves the specific, rapid, sensitive, NIR fluorescent detection of thiols. Furthermore, the indoles iodized salt in the system can specifically target thiols in mitochondria. Thus, this probe was used to visualize the fluctuations of thiols during oxidative stress and cell apoptosis, cerebral ischemia reperfusion, demonstrating that it is valuable for elucidating pathophysiology process in living organism. This discovery provides an effective means for studying the pathological process of thiol related diseases.

A novel near-infrared xanthene-based fluorescent probe for detection of thiophenol in vitro and in vivo

A novel near-infrared xanthene-based fluorescent probe for detection of thiophenol in living cells and mice.

A highly sensitive Ru(ii) complex-based phosphorescent probe for thiophenol detection with aggregation-induced emission characteristics

A novel AIEE-active Ru(ii) based phosphorescent probe was designed for the detection of thiophenol in aqueous solution and on test paper.

BODIPY based realtime, reversible and targeted fluorescent probes for biothiol imaging in living cells

Real-time live cell imaging and quantification of biothiol dynamics are important for understanding pathophysiological processes.

Thiophenol detection using an AIE fluorescent probe through self-assembly with TPE-based glycoclusters

We describe a novel green-emitting tetraphenylethylene-dicyanomethylene-4H-pyran (TPE-DCM) based fluorescent probe (TD-1). Conjugating TPE and DCM moieties allowed TD-1 to display high selectivity for thiophenol with excellent AIE properties in aqueous solution. Nevertheless, the poor water solubility of the hydrophobic structure resulted in a weak and unstable emission intensity. The non-covalent self-assembly of TD-1 with a TPE glycocluster (TPE2S) led to a largely improved water solubility producing a reliable and stable sensing system. The corresponding glyco-probe could sensitively detect exogenous thiophenol concentrations in PBS buffer or environmental water samples.

Recent Progress in the Development of Fluorescent Probes for Thiophenol

Thiophenol (PhSH) belongs to a class of highly reactive and toxic aromatic thiols with widespread applications in the chemical industry for preparing pesticides, polymers, and pharmaceuticals. In this review, we comprehensively summarize recent progress in the development of fluorescent probes for detecting and imaging PhSH. These probes are classified according to recognition moieties and are detailed on the basis of their structures and sensing performances. In addition, prospects for future research are also discussed.

A fast responsive chromogenic and near-infrared fluorescence lighting-up probe for visual detection of toxic thiophenol in environmental water and living cells

Thiophenols as high toxic environmental pollutants are poisonous for animals and aquatic organisms. Therefore, it is indispensable to monitor thiophenols in the environment. Herein, a novel near-infrared fluorescent probe was developed for the detection of thiophenols, which was easily prepared by one-step coupling of 2,4-dinitrobenzenesulfonyl chloride with Nile blue. The probe showed a significant near infrared (∼675 nm) fluorescence "turn-on" response to thiophenols with some good features including chromogenic reaction, high sensitivity and selectivity, fast response, near-infrared emission along with low detection limit (1.8 nM). The probe was employed to rapidly and visually determine thiophenols in several industrial wastewaters with good recoveries (90-110%). Moreover, this probe has been demonstrated good capability for imaging thiophenol in HeLa cells.

A pyrazolopyrimidine based fluorescent probe for the detection of Cu2+ and Ni2+ and its application in living cells

A fluorescent sensor L based on a pyrazolopyrimidine core simultaneously detects Cu²⁺ and Ni²⁺ ions by photoluminescence quenching, even in the presence of other metal cations. Sensor L possesses high association constants of 5.24 × 10³ M^-1 and 2.85 × 10⁴ M^-1 and low detection limits of 0.043 μM and 0.038 μM for Cu²⁺ and Ni²⁺, respectively. The binding stoichiometry ratios of L to Cu²⁺ or Ni²⁺ is 1:1 as determined by Benesi-Hildebrand and Job's plots, and by crystal structures. DFT calculations on L-Cu²⁺ indicated reduced electron donation from the coordinated pyrazolopyridine to the fused pyrimidine and pendant phenyl group which, together with a smaller HOMO-LUMO orbital gap could favour non-radiative decay and explain the observed fluorescence quenching. Sensor L possessed low cytotoxicity and good imaging characteristics for Cu²⁺ and Ni²⁺ in living cells, suggesting potential applications for detecting Cu²⁺ and Ni²⁺in vivo.

A water-soluble and highly specific fluorescent probe for imaging thiophenols in living cells and zebrafish

A water-soluble and highly specific fluorescent probe was developed to track thiophenols in living cells and zebrafish.

The construction of an effective far-red fluorescent and colorimetric platform containing a merocyanine core for the specific and visual detection of thiophenol in both aqueous medium and living cells

Thiophenol is toxic to the environment and biological systems although it is an indispensable material for chemical products.

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 two-photon fluorescent probe for ratiometric visualization of hypochlorous acid in live cells and animals based on a selenide oxidation/elimination tandem reaction

Utilizing the oxidation/elimination tandem reaction of the α-phenylseleno carbonyl moiety, a two-photon fluorescent probe for ratiometric visualization of hypochlorous acid was developed. Its superior sensing performance and practical applications were well demonstrated.

Challenges and Opportunities for Small-Molecule Fluorescent Probes in Redox Biology Applications

SIGNIFICANCE

The concentrations of reactive oxygen/nitrogen species (ROS/RNS) are critical to various biochemical processes. Small-molecule fluorescent probes have been widely used to detect and/or quantify ROS/RNS in many redox biology studies and serve as an important complementary to protein-based sensors with unique applications. Recent Advances: New sensing reactions have emerged in probe development, allowing more selective and quantitative detection of ROS/RNS, especially in live cells. Improvements have been made in sensing reactions, fluorophores, and bioavailability of probe molecules.

CRITICAL ISSUES

In this review, we will not only summarize redox-related small-molecule fluorescent probes but also lay out the challenges of designing probes to help redox biologists independently evaluate the quality of reported small-molecule fluorescent probes, especially in the chemistry literature. We specifically highlight the advantages of reversibility in sensing reactions and its applications in ratiometric probe design for quantitative measurements in living cells. In addition, we compare the advantages and disadvantages of small-molecule probes and protein-based probes.

FUTURE DIRECTIONS

The low physiological relevant concentrations of most ROS/RNS call for new sensing reactions with better selectivity, kinetics, and reversibility; fluorophores with high quantum yield, wide wavelength coverage, and Stokes shifts; and structural design with good aqueous solubility, membrane permeability, low protein interference, and organelle specificity. Antioxid. Redox Signal. 29, 518-540.

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.

Evaluating Drug-Induced Liver Injury and Its Remission via Discrimination and Imaging of HClO and H2S with a Two-Photon Fluorescent Probe

Drug-induced liver injury (DILI) has aroused wide concern. Finding new markers or indicators as well as detoxification molecules for DILI is of great significance and good application prospect, which can help develop effective preclinical screening methodology and corresponding treatment protocols. Herein, in this article, DILI caused by antidepressant drugs of duloxetine and fluoxetine and its remission were evaluated by a two-photon fluorescent probe, RPC-1, through discriminating and imaging HClO and H₂S simultaneously. By being applied both in vitro and in vivo, RPC-1 revealed slight up-regulation of HClO and negligible liver damage after administration of either of the two drugs. In contrast, an apparent up-regulation of HClO and obvious liver damage was observed after combined administration of the drugs. Meanwhile, the pretreatment of N-acetyl cysteine (NAC) resulted in the increasing of endogenous H₂S level, which contributed to the remission of DILI. The histological analysis and serological test both gave good consistency with the imaging results. These findings demonstrate that HClO may be an appropriate indicator of DILI, and H₂S plays an important role in the antidotal effect of NAC. We envision that RPC-1 can be used as a powerful tool to predict clinical DILI and study the effect of antidote, as well as explore the molecular mechanisms involved.

A ratiometric nanoprobe based on silver nanoclusters and carbon dots for the fluorescent detection of biothiols

Ratiometric fluorescent probes could eliminate the influence from experimental factors and improve the detection accuracy. In this article, a ratiometric nanoprobe was constructed based on silver nanoclusters (AgNCs) with nitrogen-doped carbon dots (NCDs) and used for the detection of biothiols. The fluorescence peak of AgNCs was observed at 650nm with excitation wavelength at 370nm. In order to construct the ratiometric fluorescent probe, NCDs with the excitation and emission wavelengths at 370nm and 450nm were selected. After adding AgNCs, the fluorescence of NCDs was quenched. The mechanism of the fluorescence quenching was studied by fluorescence, UV-Vis absorption and the fluorescence lifetime spectra. The results indicated that the quenching could be ascribed to the inner filter effect (IFE). With the addition of biothiols, the fluorescence of AgNCs at 650nm decreased due to the breakdown of AgNCs, and the fluorescence of NCDs at 450nm recovered accordingly. Thus, the relationship between the ratio of the fluorescence intensities (I₄₅₀/I₆₅₀) and biothiol concentration was used to establish the determination method for biothiols. Cysteine (Cys) was taken as the model of biothiols, and the working curve for Cys was I₄₅₀/I₆₅₀=0.60C_Cys-1.86 (C_Cys: μmol/L) with the detection limit of 0.14μmol/L (S/N=3). Then, the method was used for the detection of Cys in human urine and serum samples with satisfactory accuracy and recovery ratios. Furthermore, the probe could be applied for the visual semi-quantitative determination of Cys by naked eyes.

Two-photon imaging of formaldehyde in live cells and animals utilizing a lysosome-targetable and acidic pH-activatable fluorescent probe

Lyso-TPFP presents lysosomal targetability and an acidic pH-activatable response toward formaldehyde. Thus, it exclusively visualizes lysosomal formaldehyde and is immune against it in neutral cytosol and other organelles. In addition, two-photon fluorescence imaging endows Lyso-TPFP with the capability of in situ tracking formaldehyde in live cells and animals.

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.

A rhodamine-based fluorescent probe for colorimetric and fluorescence lighting-up determination of toxic thiophenols in environmental water and living cells

Thiophenols are a class of highly toxic environmental pollutant, hence it is very necessary to monitor thiophenols in environment and living cells with an efficient and reliable method. Herein, a novel fluorescent probe for thiophenols has been developed, which exhibited a colorimetric and fluorescence turn-on dual response towards thiophenols with good selectivity and fast response. The sensing mechanism for thiophenols was attributed to nucleophilic substitution reaction, which was confirmed by HPLC. The probe exhibited good recovery (from 90% to 107%) and low limit of detection for thiophenols (37nM) in industrial wastewater. Moreover, the probe has been successfully employed to visualize thiophenol in living cells. Therefore, the fluorescent probe has good capability for monitoring thiophenols in environmental samples and biological systems.

Dual-site lysosome-targeted fluorescent probe for separate detection of endogenous biothiols and SO2 in living cells

A novel lysosome-targeted fluorescent probe was developed for the separate detection of endogenous biothiols and SO₂ in living cells.