Near-Infrared Ratiometric Fluorescent Probe for Detecting Endogenous Cu2+ in the Brain

Copper participates in a range of critical functions in the nervous system and human brain. Disturbances in brain copper content is strongly associated with neurological diseases. For example, changes in the level and distribution of copper are reported in neuroblastoma, Alzheimer's disease, and Lewy body disorders, such as Parkinson disease and dementia with Lewy bodies (DLB). There is a need for more sensitive techniques to measure intracellular copper levels to have a better understanding of the role of copper homeostasis in neuronal disorders. Here, we report a reaction-based near-infrared (NIR) ratiometric fluorescent probe CyCu1 for imaging Cu2+ in biological samples. High stability and selectivity of CyCu1 enabled the probe to be deployed as a sensor in a range of systems, including SH-SY5Y cells and neuroblastoma tumors. Furthermore, it can be used in plant cells, reporting on copper added to Arabidopsis roots. We also used CyCu1 to explore Cu2+ levels and distribution in post-mortem brain tissues from patients with DLB. We found significant decreases in Cu2+ content in the cytoplasm, neurons, and extraneuronal space in the degenerating substantia nigra in DLB compared with healthy age-matched control tissues. These findings enhance our understanding of Cu2+ dysregulation in Lewy body disorders. Our probe also shows promise as a photoacoustic imaging agent, with potential for applications in bimodal imaging.

A ratiometric fluorescent probe based on a novel fluorophore with high selectivity for imaging cysteine in living cells

As a biothiol, cysteine (Cys) is essential to both physiological and pathological processes and has been associated with many diseases, including neurological disorders, rheumatoid arthritis, and renal dysfunction. Therefore, the development of a high-performance probe for detecting Cys levels can help prevent and diagnose disease. In this study, a ratiometric fluorescent probe based on a novel fluorophore was developed for detecting Cys, and it showed high specificity and a rapid response time toward Cys. This probe demonstrates excellent biocompatibility and has been utilized effectively for the imaging of Cys in living cells.

Dual Fluorimetric Sensor for Tandem Detection of Cadmium and Cysteine: An Approach for Designing a Molecular Keypad Lock System

A fluorimetric sensor for dual and sensitive detection of Cd2+ ion and Cysteine (based on 2-picolylamine platform) was developed.The sensor was designed and synthesized by simple condensation method and characterized by using common spectroscopic methods. The observations made from the kinetics of absorption and emission profile shows that probe Pdac behaves as ''ON-OFF'' fluorescent quenching sensor for cadmium ions. The probe exhibit selectivity in fluorescence quenching behaviour over other competitive metal ions, and also the Pdac-Cd2+ ensemble behave as an efficient ''OFF-ON'' type sensor for an essential amino acid Cysteine. Moreover, this dual sensing nature of the sensor makes it successfully applied for the designing of a molecular keypad lock system.

Fluorescent probe for sensitive discrimination of GSH and Hcy/Cys with single-wavelength excitation in biological systems via different emission

Biothiols (GSH, Hcy, Cys) are important active sulfur substances in biological systems and widely participate in various physiological processes. The three kinds of biothiols have similar chemical structures, including the sulfhydryl group (-SH) and an amino group (-NH2), so distinguishing two or more of them simultaneously is an important challenge. Herein, a nopinone-based fluorescent probe 3-(3-((4-nitrobenzoxadiazole vinyl) nopinyl difluoride (NF-NBD) was designed to distinguish GSH and Hcy/Cys by generating different fluorescence channels with a single excitation wavelength. The nitrobenzodioxazole (NBD) was introduced in the fluorescent probe by ether bounds that can quench fluorescence and selectively discriminate GSH and Hcy/Cys. After reacting with GSH and Hcy/Cys, NF-NBD exhibited strong fluorescence (green for GSH and yellow for Hcy/Cys). NF-NBD displayed a wide linear range, low detection limit, a rapid response time, and superior selectivity for biothiols. Furthermore, NF-NBD was applied to image and distinguish different biothiols in living cells and zebrafish via different fluorescence signals at a single excitation wavelength.

A sensitive ratiometric fluorescence probe with a large spectral shift for sensing and imaging of palladium

Palladium (Pd) is an important heavy metal with excellent catalytic properties and widely used in organic chemistry and the pharmaceutical industry. Efficient and convenient analytical techniques for Pd are urgently needed due to the hazardous effects of Pd on the environment and human health. Herein, we have developed five new ratiometric probes for the selective detection of Pd0 based on the Pd-catalyzed Tsuji-Trost reaction. Among them, the F-substituted probe PF-Pd showed the largest spectral shift (148 nm) and the most sensitive response (detection limit 2.11 nM). PF-Pd was employed to determine Pd0 in tap water or lake water samples, which presented satisfactory accuracy and precision. In addition, profiting from its distinct colorimetric response, visual detection of Pd0 was performed on PF-Pd loaded test strips or in field soil samples. Furthermore, fluorescence imaging of living 4T1 cells demonstrated that PF-Pd is suitable for imaging of intracellular Pd0. The good analytical performance of PF-Pd may enable it to be widely used in the convenient, rapid, sensitive and selective detection of Pd0 in environmental or biological analysis.

Naphthalimide Fluorescent Skeleton for Facile and Accurate Quantification of Glutathione

Glutathione (GSH), the most prevalent nonprotein thiol in biological systems, acts as both an antioxidant to manipulate intracellular redox homeostasis and a nucleophile to detoxify xenobiotics. The fluctuation of GSH is closely related to the pathogenesis of diverse diseases. This work reports the construction of a nucleophilic aromatic substitution-type probe library based on the naphthalimide skeleton. After an initial evaluation, the compound R13 was identified as a highly efficient GSH fluorescent probe. Further studies demonstrate that R13 could readily quantify GSH in cells and tissues via a straightforward fluorometric assay with a comparable accuracy to the results from the HPLC. We then used R13 to quantify the content of GSH in mouse livers after X-ray irradiation, revealing that irradiation-induced oxidative stress leads to the increase of oxidized GSH (GSSG) and depletion of GSH. In addition, probe R13 was also applied to investigate the alteration of the GSH level in the Parkinson's mouse brains, showing a decrease of GSH and an increase of GSSG in Parkinson's mouse brains. The convenience of the probe in quantifying GSH in biological samples facilitates further understanding of the fluctuation of the GSH/GSSG ratio in diseases.

Light controlled reversible Michael addition of cysteine: a new tool for dynamic site-specific labeling of proteins

Cysteine-based Michael addition is a widely employed strategy for covalent conjugation of proteins, peptides, and drugs. The covalent reaction is irreversible in most cases, leading to a lack of control over the process. Utilizing spectroscopic analyses along with X-ray crystallographic studies, we demonstrate Michael addition of an engineered cysteine residue in human Cellular Retinol Binding Protein II (hCRBPII) with a coumarin analog that creates a non-fluorescent complex. UV-illumination reverses the conjugation, yielding a fluorescent species, presumably through a retro-Michael process. This series of events can be repeated between a bound and non-bound form of the cysteine reversibly, resulting in the ON-OFF control of fluorescence. The details of the mechanism of photoswitching was illuminated by recapitulation of the process in light irradiated single crystals, confirming the mechanism at atomic resolution.

Kinetics and Reaction Mechanism of Biothiols Involved in SNAr Reactions: An Experimental Study

Few kinetic parameters, or reaction rates, are known up to date in detail about 1-chloro and 1-fluoro-2,4-dinitrobenzene (ClDNB and FDNB, respectively) with a series of biothiols in aqueous media. These biological nucleophiles with thiol groups have been widely used as a reference in nucleophile reactivity assays due to their prevalence and cellular abundance. The main aim of this study was to elucidate the reaction mechanism based on Brönsted-type plots and reactivity patterns of the electrophile/nucleophile pairs. A complete kinetic study was performed in terms of the comparison of Brönsted-type slope parameters (β_nuc) for the reactions and was used for assigning the mechanism and the rate-determining step associated with the reaction route. A mass spectrometry analysis demonstrated that the nucleophilic center of the biothiols is the -SH group and there is only one kinetic product. The kinetic study suggests that the reaction mechanism might be the borderline between concerted and stepwise pathways. An amine–enol equilibrium for the most reactive nucleophiles appears to be the main determining factor controlling the nucleophilic attack in the nucleophilic aromatic substitution reactions investigated, highlighting the anionic form for these nucleophiles. This amine–enol equilibrium involves a hydrogen bond which stabilizes the intermediate species in the reaction pathway. Thus, intramolecular bonds are formed and enhance the nucleophilic strength through the contribution of the solvent surrounding the electrophile/nucleophile pairs. Finally, we highlight the importance of the formation of electrophile/nucleophile adducts that could modify structures and/or functions of biological systems with potential toxic effects. Therefore, it is essential to know all these kinetic and reactivity patterns and their incidence on other studies.

A Ratiometric, Fast-Responsive and Single-Wavelength Excited Fluorescent Probe for the Discrimination of Cys and Hcy

The ratiometric detection of cysteine (Cys) and homocysteine (Hcy) is very challenging because of their highly similar chemical structures and properties. By introducing the phenylethynyl group into a coumarin dye as the sensing group, the ratiometric fluorescent probe CP was developed to selectively and rapidly discriminate between Cys and Hcy. With a single-wavelength excitation, the presence of Cys or Hcy induced the probe to produce distinct ratiometric fluorescence changes: from red (λ_max^em = 608 nm) to blue (λ_max^em = 485 nm) toward Cys and from red to mixed red/blue toward Hcy. Moreover, the probe was capable of visualizing and discriminating between intracellular Cys and Hcy in HeLa cells and zebrafish by exhibiting different ratiometric fluorescence signals.

Design and synthesis of a novel "turn-on" long range measuring fluorescent probe for monitoring endogenous cysteine in living cells and Caenorhabditis elegans

Cysteine (Cys) is an indispensable small organic molecule containing sulfhydryl groups, which has essential regulatory effects on the physiological process of human body. In this work, a red emission fluorescent probe TCFQ-Cys was designed and exploited based on 2-(3-cyano-4,5,5-trimethylfuran-2(5H)-ylidene) malononitrile-derivatives. The probe could effectively monitor Cys through the typical acrylate cleavage. The detecting system showed a red emission at 633 nm and the fluorescence was stable within the pH range of 6-9. The detection could be completed in 30 min. TCFQ-Cys presented high sensitivity with a detection limit of 0.133 μM and high selectivity towards Cys from other biological mercaptans. The most important feature was that the system had a wide linear range of 0-300 μM, which covered the physiological requirements of Cys detection. Subsequently, we conducted the biological imaging of Cys in MCF-7 cells and Caenorhabditis elegans (C. elegans). Therefore, TCFQ-Cys had a practical application prospect for further investigating the physiological function of Cys.

Determination of thallium(iii) ions by oxidative hydrolysis of rhodamine–hydroxamate

A colorimetric and turn-on type fluorescence Tl³⁺ signaling probe for the early screening of elevated urinary thallium levels in acute poisoning cases using a readily available smartphone was developed.

Introducing ortho-methoxyl group as a fluorescence-enhancing and bathochromic-shift bi-functional strategy for typical cysteine sensors

A practical strategy of introducing ortho-methoxyl group was explored to achieve the fluorescence-enhancing and bathochromic-shift bi-functional optimization. It was tested in the Cys sensing ISOPH-X series, thus the successful case, ISOPH-2, was obtained. It realized the optimization in a simple and compatible way. The corresponding strategy was basically established during the confirmation of checkpoints including applicable steadiness (over 24 h), wide pH range (7.0-9.0), rapid response (20 min), good biocompatibility, high sensitivity (LOD = 0.072 nm), high selectivity and biological monitoring of Cys in living cells as well as C. elegans. In this work, the o-methoxyl introduction strategy led to a 15 nm red shift and a near 4-fold fluorescence enhancement. This strategy could be combined with the double bond-introducing approach. Compared with reported strategies, by breaking the dilemma between red shift and strong fluorescent intensity, this strategy might offer beneficial information for exploiting better sensors with more fluorophores and mechanisms for their targets.

Highly Selective and Sensitive Detection of Biogenic Defense Phytohormone Salicylic Acid in Living Cells and Plants Using a Novel and Viable Rhodamine-Functionalized Fluorescent Probe

Detecting plant-derived signal molecules using fluorescent probes is a key topic and a huge challenge for scientists. Salicylic acid (SA), a vital plant-derived defense hormone, can activate global transcriptional reprogramming to systemically express a network of prominent pathogenesis-related proteins against invasive microorganisms. This strategy is called systemic acquired resistance (SAR). Therefore, monitoring the dynamic fluctuations of SA in subcellular microenvironments can advance our understanding of different physiological and pathological functions during the SA-induced SAR mechanism, thus benefiting the discovery and development of novel immune activators that contribute to crop protection. Here, detection of signaling molecule SA in plant callus tissues was first reported and conducted by a simple non-fluorescent rhodamine-tagged architecture bearing a flexible 2-amino-N,N-dimethylacetamide pattern. This study can markedly advance and promote the usage of fluorescent SA probes for distinguishing SA in the plant kingdom.

Precise Synthesis of GSH-Specific Fluorescent Probe for Hepatotoxicity Assessment Guided by Theoretical Calculation

Drug-induced hepatotoxicity is the main cause of acute liver injury, and its early diagnosis is indispensable in pharmacological and pathological studies. As a hepatotoxicity indicator, the GSH distribution in the liver could reflect the damage degree in situ. In this work, we have provided a theoretical design strategy to determine the generation of photo-induced electron transfer mechanism and achieve high selectivity for the target. After that, we precisely synthesized a novel near-infrared fluorescent probe BSR1 to specifically monitor endogenous GSH and hepatotoxicity in biosystem with a moderate fluorescent quantum yield (Φ = 0.394) and low detection limit (83 nM) under this strategy. Moreover, this mapping method for imaging GSH depletion in vivo to assay hepatotoxicity may provide a powerful molecular tool for early diagnosis of some diseases and contribute to assay hepatotoxicity for the development of new drugs. Importantly, this theoretical calculation-guided design strategy may provide an effective way for the precise synthesis of the target-specific fluorescent probe and change this research area from "trial-and-error" to concrete molecular engineering.

Michael Addition/S,N-Intramolecular Rearrangement Sequence Enables Selective Fluorescence Detection of Cysteine and Homocysteine

Acrylate has been widely used as the recognition unit for Cys fluorescent probes. Despite this widespread use, a potential drawback of this probe type is that the ester linkage between the fluorophore and acryloyl recognition unit is liable to be hydrolyzed by abundant esterase in the cytosol, thus affording a high background signal. To solve this problem, we herein put forward a new strategy to construct a selective fluorescent probe for cysteine (Cys)/homocysteine (Hcy) with propynamide as the recognition moiety. The free probe CPA displays weakly fluorescent emission in aqueous media because of the donor-excited photoinduced electron transfer (d-PET) process within the molecule. The Michael addition of Cys (or Hcy) thiols to the conjugated alkyne of CPA gives the expected β-sulfido-α,β-unsaturated amides (1a/1b), which subsequently undergo an intramolecular S,N rearrangement, yielding β-amino-α,β-unsaturated amides (2a/2b) as the final products. The above cascade reaction results in the blockage of d-PET within CPA, thus affording a dramatic fluorescence enhancement at 495 nm. The involvement of the sulfhydryl and the adjacent amino groups in the sensing process renders CPA high selectivity for Cys/Hcy over glutathione as well as other amino acids. The probe has been successfully applied to image Cys in different cell lines. Further, CPA shows two-photon fluorescence properties, and its ability to monitor Cys in deep tissues has been demonstrated by using two-photon microscopy.

Simultaneous single-molecule discrimination of cysteine and homocysteine with a protein nanopore

Discrimination between cysteine and homocysteine at the single-molecule level is achieved within a K238Q mutant aerolysin nanopore, which provides a confined space for high spatial resolution to identify the amino acid difference with a 5'-benzaldehyde poly(dA)₄ probe. Our strategy allows potential detection and characterization of various amino acids and their modifications, and provides a crucial step towards developing nanopore protein sequencing devices.

An enhanced fluorescence sensor for specific detection Cys over Hcy/GSH and its bioimaging in living cells

Cysteine (Cys) is not only the central matter of sulfur metabolism in cells but also the only amino acid with reduced thiol group in 20 kinds of natural amino acids. In animal cells, Cys is taking part in many important and essential biological functions including protein synthesis, detoxification and metabolism. The development and application of fluorescent probes for the detection of Cys have attracted more and more attention and interest. Herein, we report a new fluorescent probe NFA that utilized naphthyl carboxy fluorescein as fluorophore and acryloyl group as reaction site for Cys specific detection. The probe essentially has weak fluorescence. Cys addition to NFA containing system induced distinct enhanced fluorescence emission which was attributed to the nucleophilic reaction of cysteine and acryloyl to release the fluorophore. The signal fluorescent response detection system allows NFA to be a reliable tool for Cys detection with low detection limit (0.58 μM). And NFA has been successfully applied for Cys imaging specifically in live Hela cells, which promotes the probe as a potential tool to understand the pathology of Cys related diseases.

A ratiometric fluorescent BODIPY-based probe for rapid and highly sensitive detection of cysteine in human plasma

Biological thiols, especially low molecular weight thiols, including cysteine (Cys), homocysteine (Hcy) and glutathione (GSH), play a pivotal role in physiological and pathological systems. Thus, the detection of biothiols is highly important for early diagnosis of diseases and evaluation of disease progression. Herein, we developed a highly selective and sensitive ratiometric fluorescent 8-Cl BODIPY-based probe with high fluorescence quantum yields. The probe displayed a sensitive response to Cys and Hcy over other biothiols, which can be visualized colorimetrically and/or fluorescently. The probe was successfully applied to detect Cys in human plasma, demonstrating its great value for practical application in biological sample analysis.

Fluorescein propiolate: a propiolate-decorated fluorescent probe with remarkable selectivity towards cysteine

A fluorescent probe decorated with an alkynyl ester unit (e.g. propiolate) displayed a selective turn-on type fluorescent response towards cysteine.

A novel fluorescent turn-on probe for imaging biothiols based on SNAr substitution-skeletal rearrangement strategy

2is a novel fluorescent turn-on probe for imaging biothiols based on S_NAr substitution-skeletal rearrangement strategy with dramatic fluorescence enhancement and high sensitivity.

Rational design of a ratiometric two-photon fluorescent probe for real-time visualization of apoptosis

A dialdehyde-functionalized ratiometric two-photon fluorescent probe (Mito-DCHO) based on a symmetric carbazole-containing two-dimensional ICT system was rationally designed for cysteine-specific detection in mitochondria, which was utilized for real-time assessing and dual-channel visualization of the early stage of apoptosis by monitoring mitochondrial oxidative stress levels.

A highly selective fluorescent and chromogenic probe for CN- detection and its applications in bioimaging

In this study, 3-ethyl-2-methylbenzothiazolium iodide and nitrophenyl-2-furancarboxaldehyde were used to synthesize a new fluorescent and chromogenic dual channel signal cyanide ion probe M, which showed high selectivity towards CN^- analysis and strong antijamming capability towards other anions. When CN^- is present in the solution, probe M indicates an obvious blue shift in UV-vis absorbance spectra, which can be observed clearly by unaided eyes. The limits of detection (LODs) of CN^- based on fluorescence and UV-vis absorbance were 0.11 μM and 0.16 μM, respectively. The mechanism of fluorescent and chromogenic cyanide ion detection refers to the nucleophilic addition of cyanide ion to carbon atom of -C˭N- in the benzothiazole. The π-conjugation and ICT transition between furfural and benzothiazole were broken due to this non-reversible reaction, resulting in the color change and fluorescent characterizations. In addition, probe M also showed the excellent optical properties and high biocompatibility, which enables the practical application of CN^- tracing in biomedical systems.

Bifunctional Fluorescent Probe for Sequential Sensing of Thiols and Primary Aliphatic Amines in Distinct Fluorescence Channels

Thiols and primary aliphatic amines (PAA) are ubiquitous and extremely important species in biological systems. They perform significant interplaying roles in complex biological events. A single fluorescent probe differentiating both thiols and PAA can contribute to understanding the intrinsic inter-relationship of thiols and PAA in biological processes. Herein, we rationally constructed the first fluorescent probe that can respond to thiols and PAA in different fluorescence channels. The probe exhibited a high selectivity and sensitivity to thiols and PAA. In addition, it displayed sequential sensing ability when the thiols and PAA coexisted. The application experiments indicated that the probe can be used for sensing thiols and PAA in human blood serum. Moreover, the fluorescence imaging of endogenous thiols and PAA as well as antihypertensive drugs captopril and amlodipine in living cells were successfully conducted.

Sensitive and Selective Fluorescent Probe for Selenol in Living Cells Designed via a p Ka Shift Strategy

Selenocysteine (Sec) is a primary kind of reactive selenium species in cells, and its vital roles in physiological processes have been featured. Thus, the development of highly sensitive and selective methods for the sensing of Sec is of great significance. This work reports a turn-on fluorescent probe for selenol based on the unique fluorescence OFF-ON switching between the Schiff base (SB) and its complementary protonated Schiff base (PSB) form of merocyanine dyes. The probe consists of a merocyanine Schiff base fluorophore and a 2,4-dinitrobenzenesulfonamide moiety that reacts especially with selenol. The fluorescence turn-on response of MC-Sec is realized via the selective removal of the strongly electron withdrawing 2,4-dinitrobenzenesulfonyl group by Sec, leading to a shift in the p K_a of the imine nitrogen of the probe from 6.40 to 9.04 and thus significantly increasing the population of the fluorescent PSB form of the dye at physiological pH. MC-Sec shows good selectivity and sensitivity for Sec and has been applied in the imaging of exogenous and endogenous selenol in living cells by confocal fluorescence microscopy. The proposed mechanism should be useful for developing future probes directed to other target molecules by employing this simple but effective p K_a shift strategy.

Recent Progress in Chemosensors Using Aldehyde-bearing Fluorophores for the Detection of Specific Analytes and their Bioimaging

In recent years, aldehyde-appended fluorescence probes have attracted increasing attention. Fluorescent biological imaging includes many modern applications for cell and tissue imaging in biomedical research. Meanwhile, the nucleophilic mechanism is a very simple and convenient procedure for the preparation of aldehyde-sensing probes. This tutorial review focuses on aldehyde-bearing chemosensors based on nucleophilic addition mechanism with biological applications.

A novel dual-emission fluorescent nanohybrid containing silica nanoparticles and gold nanoclusters for ratiometric determination of cysteine based on turn-on fluorescence strategy

A novel fluorescence sensor SiO₂NPs/AuNCs nanohybrid has been used developed for ratiometric visual detection of Cys.

A NIR facile, cell-compatible fluorescent sensor for glutathione based on Michael addition induced cascade spirolactam opening and its application in hepatocellular carcinoma

A NIR fluorescence probe with NIR emission wavelength at 746 nm and high quantum yield of 0.36 was designed and synthesized to selectively detect GSH over Hcy and Cys in living systems.

Carbon dots with red emission as a fluorescent and colorimeteric dual-readout probe for the detection of chromium(vi) and cysteine and its logic gate operation

A schematic illustration for assaying Cr(vi) and Cys activity by CDs with both fluorescent and colorimetric readouts.

A dual-selective fluorescent probe for GSH and Cys detection: Emission and pH dependent selectivity

A novel fluorescent probe 1 based on acridine orange was developed for the selective detection and bioimaging of biothiols. The probe exhibits higher selectivity and turn-on fluorescence response to cysteine (Cys), homocysteine (Hcy), and glutathione (GSH) than to other amino acids. Importantly, the probe responds to GSH and Cys/Hcy with distinct fluorescence emissions in PBS buffer at pH of 7.4. The Cys/Hcy-triggered tandem S_NAr-rearrangement reaction and GSH-induced S_NAr reaction with the probe led to the corresponding amino-acridinium and thio-acridinium dyes, respectively, which can discriminate GSH from Cys/Hcy through different emission channels. Interestingly, Cys finishes the tandem reaction with the probe and subsequently forms amino-acridinium and Hcy/GSH induces S_NAr reaction with the probe to form thio-acridiniums at weakly acidic conditions (pH 6.0), enabling Cys to be discriminated from Hcy/GSH at different emissions. Finally, we demonstrated that probe 1 can selectively probe GSH over Cys and Hcy or Cys over GSH and Hcy in HeLa cells through multicolor imaging.

Simultaneous quantification of multiple endogenous biothiols in single living cells by plasmonic Raman probes

Three endogenous biothiols in single cells were simultaneously quantified by plasmonic Raman probes and quantitative principal component analysis (qPCA).

Intracellular biothiols mediate many important physiological and pathological processes. Due to their low content and competing thiol-reactivity, it is still an unmet challenge to quantify them within a complicated intracellular environment. Herein, we demonstrated a strategy to discriminate three biothiols, i.e. cysteine (Cys), homo-cysteine (Hcy) and glutathione (GSH), and quantify their concentrations within single living cells, using one platform of Raman probe. By monitoring the reaction kinetics of biothiols with Raman probes and discriminating their products with a quantitative principal component analysis (qPCA) method, these three biothiols could be simultaneously quantified in both cell lysis and single living cells. The concentrations of Cys, Hcy and GSH in single Hela cells were 158 ± 19 μM, 546 ± 67 μM and 5.07 ± 0.62 mM, respectively, which gives the precise concentrations of these three biothiols at a single cell level for the first time. This method provides a general strategy for discriminating each component from a mixed system and has potential for quantifying any biomolecules within an in vitro or in vivo biological environment.

A Reversible Fluorescent Probe for Real-Time Quantitative Monitoring of Cellular Glutathione

The ability to monitor and quantify glutathione (GSH) in live cells is essential in order to gain a detailed understanding of GSH-related pathological events. However, owing to their irreversible response mechanisms, most existing fluorescent GSH probes are not suitable for this purpose. We have developed a ratiometric fluorescent probe (QG-1) for quantitatively monitoring cellular GSH. The probe responds specifically and reversibility to GSH with an ideal dissociation constant (K_d ) of 2.59 mm and a fast response time (t_1/2 =5.82 s). We also demonstrate that QG-1 detection of GSH is feasible in a model protein system. QG-1 was found to have extremely low cytotoxicity and was applied to determine the GSH concentration in live HeLa cells (5.40±0.87 mm).