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[Display omitted] • Two spirobifluene-based turn-on fluorescent probes for Cysteine were synthesized. • The probes shows highly selectivity for Cysteine. • The probes had been applied to imaging Cysteine under two-photon excitation. • One probe displayed excellent detection limit for Cysteine. Two spirobifluene-based fluorescent probes SPF1 and SPF2 , were designed and synthesized. The probes displayed "turn-on" fluorescence response for Cysteine. One of the challenges in developing a Cysteine probe is to secure high selectivity. SPF1/SPF2 can discriminate Cysteine from GSH as well as Hcy, and showed high substrate selectivity. The detection limit of SPF1 is 36 nM, which is excellent comparing with other optical sensors for Cysteine. The sensing mechanism of SPF1/SPF2 was verified by experimental data and theoretical calculations. There was a good linear relationship between the fluorescence intensity of SPF1/SPF2 and the concentration of Cysteine. The MTT tests indicated that SPF1/SPF2 had low cytotoxicity and good biocompatibility. Theoretical calculations demonstrated that SPF1 , SPF2 , and their related reaction products with Cysteine exhibited good two-photon absorption properties. Finally, SPF1/SPF2 had been successfully applied to the imaging of Cysteine in living cells under two-photon excitation. [ABSTRACT FROM AUTHOR]

[Display omitted] • A mitochondria-targetable fluorescent probe for cysteine has been reported. • The probe displays high sensitivity and high selectivity for cysteine. • The probe can be utilized for determination of cysteine within the mitochondria of living cells. Cysteine (Cys) is of great significance in biological systems and in the process of mitochondrial function. Highly selective and specificity recognizable probes for mitochondrial Cys are still in demand. In this work, a new fluorescent probe for detecting mitochondrial Cys was developed based on a rhodamine derivative. In this probe, acrylate unit was selected as group of Cys recognition and quaternized pyridinium moiety was utilized as mitochondrial targeting group. The probe showed colorless in daylight and extremely weak fluorescence in 365 nm due to its spirolactone structure when Cys did not exist. In the presence of Cys, the probe exhibited orange in daylight and produced intensely green fluorescence in 365 nm owing to the formation of the conjugated xanthene structure. The probe exhibited specific recognition for Cys. There was an excellent linear relationship between fluorescence intensity at 540 nm of the probe and the Cys concentration from 4.0 × 10-8 to 1.0 × 10-5 mol⋅L-1. And the detection limit was estimated to be 1.57 × 10-8 mol/L. Moreover, the probe was almost non-cytotoxic, possessed targeting-mitochondria ability and could sense Cys at the cellular level. The good bioimaging ability makes the probe a potential tool for studying mitochondrial Cys in biological samples. [ABSTRACT FROM AUTHOR]

[Display omitted] • The probe 3-STF is first designed based on 3-thiolflavone. • The probe 3-STF exhibited a specific "turn-on" fluorescence response towards biothiols (Cys, Hcy, and GSH) with a large stokes shift of 140.6 nm. • The detection of biothiols did not suffer from the interference of other amino acids. • The detection mechanism was discussed in detail. • The probe 3-STF can be successfully applied to monitor endogenous and exogenous biothiols in HepG-2 cells. Abnormal levels of intracellular biothiol species, including glutathione (GSH), homocysteine (Hcy), and cysteine (Cys), are closely relevant to a variety of diseases. In this study, we first report the design and synthesis of a 3-thiolflavone-based probe 3-STF with an S–S linkage both as the fluorescence quenching agent and the recognition site. Upon treatment with biothiols, the S–S linkage was cleaved by nucleophilic attack of RS-, and 3 -STF exhibited a specific "turn-on" fluorescence response at 543.8 nm upon 390 nm excitation. Meanwhile, 3 -STF was proved to be highly sensitive and selective for the detection of biothiols over other nucleophiles such as amino acids and H 2 S. The sensing mechanism was further verified by 1H NMR and ESI-MS analysis. In addition, 3-STF with low cytotoxicity can be successfully applied to detect endogenous and exogenous biothiols in HepG-2 cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • A fluorescent probe NBPI, utilizing cyanine phenothiazine and 7-nitro-1,2,3-benzoxadiazole (NBD), was developed for selective detection of Cys-SO 2 components. • The phenothiazine structure increased the bond energy of sulfonamide, thus the probe NBPI achieved a selective response to Cys. • The probe NBPI was successfully employed for the imaging of endogenous and exogenous Cys and SO 2 in HepG2 cells. A fluorescent probe has been designed using cyanine phenothiazine and 7-nitro-1,2,3-benzoxadiazole (NBD) for selective detection of Cys-SO 2 components. The probe utilizes the NBD structure to achieve specificity towards Cys and employs a reaction mechanism between the double bond of cyanine and phenothiazine with SO 3 2− to achieve selectivity towards SO 2. Importantly, the NBPI phenothiazine structure incorporates a large C-O bond energy attached to NBD, effectively eliminating interference from Hcy and ensuring highly selective response to Cys. The optimized design of the probe enables excellent linearity and extremely low detection limits for Cys-SO 2 components in vitro experiments. The probe NBPI allows separate detection of Cys-SO 2 in the presence of both components. Furthermore, the probe NBPI demonstrated successful imaging of endogenous and exogenous Cys and SO 2 in cell studies. [ABSTRACT FROM AUTHOR]

[Display omitted] • An "off–on" long-wavelength fluorescent probe is synthesized for Cys detection. • The probe has a large Stokes shift (211 nm) and reacted with Cys specifically. • The probe can monitor Cys fluctuations caused by redox imbalance in HepG2 cells. • The probe can be used for fluorescence imaging in cells and mice. In this research, an "off–on" long-wavelength fluorescent probe (DCMN-Cl) based on (E)-2-(3-(2-(6-hydroxynaphthalen-2-yl)vinyl)-5,5-dimethylcyclohex-2-en-1-ylidene) malononitrile (DCMN) is designed and synthesized for cysteine (Cys) detection. DCMN-Cl exhibits a large Stokes shift (211 nm) and shows rapid response and high specificity to Cys. The fluorescence initensity at 635 nm reveals a good linear relationship with Cys concentration in the 0 to 50 μM range, and the detection limit is as low as 159 nM. The probe is also used for fluorescence imaging of Cys in cells and mice. Moreover, the probe provided visual evidence of Cu2+ and curcumin-induced intracellular Cys fluctuations. [ABSTRACT FROM AUTHOR]

The abnormality of Cys concentration in organism could lead to a series of diseases, so its effective detection is of great importance in disease diagnosis. Here we developed a novel ESIPT fluorescent probe HBT-IDAc based on the classic ESIPT fluorophore 2-(2′-hydroxyphenyl)benzothiazole (HBT) and indanone, which could selectively and sensitively detect Cys with a large Stokes shift up to 210 nm and the detection limit to 0.89 μM. In addition, the probe exhibited good anti-interference and low cytotoxicity, and has been successfully applied to monitor Cys in cells. • A novel ESIPT fluorescent probe for selective and sensitive detection of Cys was developed. • The probe has the large stokes shift (210 nm) and good LOD (0.89 μM) in aqueous environment. • The probe exhibits low cytotoxicity and has been applied for imaging Cys in cells. [ABSTRACT FROM AUTHOR]

A smart fluorescent probe DPAS-Cys has been rationally designed based on a typical AIEgen DPAS and an acrylate moiety. The probe DPAS-Cys not only can be used for the detection of cysteine (Cys) selectively with large Stokes shift (200 nm) and relatively low detection limit (2.4 μM), but also shows lipid droplets (LDs) targeting property. The response mechanism for Cys was carefully verified. Importantly, due to the aggregation-induced emission characteristic, the introduction of considerable percentage of traditional organic solvent is avoidable, which makes it suitable for bioimaging in physiological systems. In addition, the confocal fluorescence imaging demonstrates that DPAS-Cys is able to detect Cys in LDs of different cell lines with universality. Our study opens a new avenue to understand the importance of LDs in biosystem, for which the gap between the essential biothiol Cys and the energy storage organelle LDs was bridged for the first time. Image 1 • A smart fluorescent probe DPAS-Cys is developed for selective detection of cysteine. • DPAS-Cys shows aggregation-induced emission characteristic and large Stokes shift. • DPAS-Cys exhibits lipid droplets targeting property with universality. [ABSTRACT FROM AUTHOR]

Cysteine/cystine redox couple plays a vital role in maintaining the cellular redox state of living bio-systems. However, the dynamic changes of the intracellular cysteine/cystine pool mediated by cysteine/glutamate transporter (System X C −) in various cellular processes have remained incompletely understood. Here we established a series of strategies around fluorescent probe CP2 for effectively monitoring the intracellular cysteine level in living cells and in vivo zebrafish model, therefore for tracking dynamic changes of system X C −-mediated cysteine/cystine pool under ferroptosis. Living cell imaging and in vivo visualization both revealed that intracellular cysteine levels could be significantly reduced upon blocking system X C − activity and inducing ferroptotic cell death. This kind of blocking was potent against cisplatin-resistant A549R cancer cells, which might bring new potential for treating drug-resistant carcinoma through regulating system X C − and processes of ferroptosis. With further improvements in monitoring tools, understanding of system X C −-mediated cystine/cysteine pool and ferroptosis could certainly offer crucial information in more physiological or pathological processes. In this work, we established a series of strategies around fluorescent probe CP2 for effectively monitoring the intracellular cysteine level in living cells and zebrafish model, therefore for tracking dynamic changes of system X C −-mediated cysteine/cystine pool under ferroptosis. Living cell imaging and in vivo visualization both revealed that intracellular cysteine level could be significantly reduced upon treatment with system X C − inhibition and ferroptosis induction. This kind of blocking was potent against cisplatin-resistant A549R cancer cells, which might bring new potential for treating drug-resistant carcinoma through regulating system X C − and processes of ferroptosis. With monitoring tools further improved, further understanding of system X C −-mediated cystine/cysteine pool and ferroptosis could certainly offer crucial information in more physiological or pathological processes. Image 1 • New strategy for monitoring endogenous cysteine in cancer and dynamic changes of Cys/cystine pool in external stimulation. • Effectively monitoring intracellular cysteine in living cells and zebrafish thus tracking Cys/cystine changing. • The first report for imaging Cys/cystine pool dynamics during ferroptosis. • Revealing physiological or pathological role of the system XC--mediated Cys/cystine pool in ferroptosis> Providing possibility to circumvent drug resistance of cisplatin and identify inhibitors for ferroptosis-mediated therapy. [ABSTRACT FROM AUTHOR]

We report on the synthesis of manganese oxide doped CDs (MnO x -CDs) by a hydrothermal strategy using manganese (III) acetylacetonate (Mn(III) (C 5 H 7 O 2) 3) as the only raw materials. The MnO x -CDs exhibit water solubility, favorable biocompatibility, low cytotoxicity, and show blue fluorescence with excitation/emission maxima at 326/442 nm with a quantum yield of 11.3%, allowing efficient cellular imaging. The MnO x -CDs have a reversible temperature-sensitive fluorescent property in vitro within 10–60 °C, which can also be used as a sensitive thermometer in living cells. By a scratch assay, the MnO x -CDs can restrain the migration of HepG2 cancer cells, which make the MnO x -CDs be attractive candidates for liver cancer adjuvant treatment. Besides, the fluorescence of the MnO x -CDs is quenched in the presence of Fe3+ due to the formation of a nonfluorescent MnO x -CDs-Fe3+ complex between oxygen-containing groups on the surface of MnO x -CDs and Fe3+, and the quenched fluorescence of MnO x -CDs can be turn-on by dissociation of MnO x -CDs-Fe3+ complexes by biothiols including L -cysteine, homocysteine and glutathione. Therefore, the Fe3+ and biothiols can be sequentially detected with high reliability and accuracy via exploiting the on-off-on nanosensor at room temperature, respectively. Further application to detection biothiols in human serum indicated that the probe was practicality and feasibility in medical field. Image 1 • First synthesis of manganese oxide doped CDs (MnO x -CDs) using manganese (III) acetylacetonate as the single precursor. • The MnO x -CDs have reversible temperature-sensitive fluorescent behaviors in vitro and can be used as a thermometer in vivo. • The MnO x -CDs can restrain the migration of HepG2 cancer cells, which facilitate liver cancer adjuvant treatment. • Fe3+ and biothiols can be sequentially detected with high reliability and accuracy based on the MnO x -CDs. [ABSTRACT FROM AUTHOR]

The nitrogen and sulfur co-doped carbon dots (NSCDs) were synthesized using cysteine as precursor by hydrothermal approach, which showed good aqueous solubility, high fluorescent quantum yield (QY = 38.7%) and good photostability. The experiments with cells demonstrated that NSCDs possessed excellent biocompatibility and their cytotoxicity was low (cell viability ≥90%) in both normal and cancer cell lines. Furthermore, NSCDs as fluorescent probes could be used for the imaging of cells, which showed a good membrane permeability and strong resistance to photobleaching. In addition, the cellular uptake of NSCDs presented a time-dependent saturation. The imaging applicability of NSCDs in different cancer cells (MCF-7, A375, Hela and U251 cells) has also been demonstrated. Therefore, NSCDs are considered as promising candidates for the design of low cytotoxicity bioimaging agents and a cellular location system based on fluorescence measurements. Unlabelled Image • NSCDs show well-dispersed, high QY of 38.7% and good photostability. • NSCDs possess excellent biocompatibility in normal and cancer cell lines. • NSCDs are as fluorescent probes for cancer cell imaging and locating • The cellular uptake of NSCDs presents a time-dependent saturation. . [ABSTRACT FROM AUTHOR]

Cys is one of the important biothiols and its abnormal concentration may pose a threat to human health. Therefore, the monitoring of Cys in organisms is of great significance. GSH and Hcy, as the other two biothiols, have similar chemical structures and active sites to Cys. Consequently, developing fluorescent probes to independently detect Cys has become a challenging problem. Keeping this in mind, α-β unsaturated ketone as a recognition group was integrated into the coumarin group skeleton to synthesize a fluorescent probe SC. After the nucleophilic addition reaction of Cys with SC , the conjugated system of SC was blocked and the fluorescent enhanced obviously. SC was able to detect Cys specifically under the same excitation with a low detection limit (11.1 nM). SC showed a rapid respond to Cys (120 s) and good fluorescent stability over a wide pH range. In addition, it achieved extracorporeal circulation in the presence of H 2 O 2 or NEM. In the end, SC could be applied to detecting endogenous and exogenous Cys under biological condition due to its slight cytotoxicity and good biocompatibility. This provided a powerful tool for studying the physiological function of Cys exclusively. Image 1 • The probe SC possessed a high specificity of Cys over Hcy and GSH under the same excitation and test system. • SC had satisfactory reversibility in the presence of NEM or H 2 O 2. • SC displayed a fast response to Cys (120 s). • Cytotoxicity test indicated that probe SC had very low cytotoxicity even at the concentration of 100 µM. • The probe SC could be used to monitor endogenous and exogenous Cys in living cells. [ABSTRACT FROM AUTHOR]

Abnormal levels of Cys, Hcy and GSH are associated with various diseases, thus monitoring biothiols is of great significance. In this work, a dual-emission responsive near-infrared fluorescent probe NIR-NBD for detecting Hcy and Cys/GSH was developed based on the conjugation of a dicyanoisophorone based fluorophore (NIR-OH) and 7-nitrobenzofurazan (NBD). To our surprise, the addition of Hcy induced significant fluorescence enhancement at both 549 and 697 nm; while Cys/GSH resulted in major fluorescence emission at 697 nm. The detection limit was determined to be 33.2 nM for Cys, 33.5 nM for Hcy, and 34.4 nM for GSH. Therefore, the probe can be used for discriminative detection of Hcy and Cys/GSH. Moreover, fluorescence imaging of HeLa cells indicated that the probe was cell membrane permeable and could be used for visualizing Hcy and Cys/GSH in living cells. Image 1 • A novel NIR fluorescent probe for discriminative sensing of Hcy and Cys/GSH in dual channel was developed. • The probe can measure Hcy level in serum samples. • The probe could sense intracellular Hcy and Cys/GSH in living HeLa cells. [ABSTRACT FROM AUTHOR]

• The synthetic route of the probe is very simple. • The probe has good reversibility in physiological environment. • The probe Cu-1 shows excellent selectivity toward Cys. • This assay has high sensitivity and exhibits short response time. • This probe is AIE-active leading to high luminous efficiency in cell imaging. In this work, an effective and simple aggregation-induced emission (AIE) active fluorescent probe based on ESIPT luminescence principle, 2-hydroxy-1-naphthal-4-aminoantipyrine (1), was synthesized via a simple chemical reaction. It displayed strong fluorescence enhancement in water. The AIE mechanism of 1 was explored by electron microscopy and computational analysis. We demonstrate the combination effect of intramolecular hydrogen bonds and π-π stacking to endow 1 with such a property. Importantly, the ensemble of 1 with copper ions (Cu-1) as a fluorescent probe enables highly selective and sensitive turn-on fluorescence detection of cysteine (Cys) over other interfering substances. Under optimal detection conditions, this probe has a good linear relationship in the concentration range of Cys between 0 and 8 μM, and the detection limit of Cys was estimated as 84 nM. Furthermore, this assay exhibits good reversibility of 1 to Cu2+ and Cys. Due to its good biocompatibility evaluated by CCK-assay, the probe Cu-1 was finally applied in imaging of Cys within Min6 cells successfully. [ABSTRACT FROM AUTHOR]

Abstract The detection of cysteine (Cys) is of great significance ascribed to its important role in physiological and psychological process. This paper reported a new fluorescent probe CBFA with red emission signal, which can be prepared through a simple method and exhibited potential application value. Solution experiments demonstrated that the probe revealed high selectivity towards Cys in spite of the interference of its two analogues, homocysteine (Hcy) and glutathione (GSH). And the sensitivity indicated that the probe was suitable for Cys detection in living cells. Furthermore, the recognition mechanism was confirmed to be a concerted reaction including Michael addition and intramolecular cyclization by high resolution mass spectrometer (HRMS) and high-performance liquid chromatography (HPLC). Besides, CBFA showed favorable pH adaptability in biological conditions and low cytotoxicity. Finally, CBFA was successfully applied to selectively imaging Cys in living MCF-7 cells with good cell permeability. We hope this probe will bring some help to the diagnosis of Cys-related diseases. Graphical abstract Image 1 Highlights • A new fluorescent probe for cysteine detection with red emission signal. • Preparing process of the probe was rather simple. • Sensitivity of the probe was satisfactory for Cys detection in living cells. • Endogenous Cys imaging in living cells with high selectivity and sensitivity. [ABSTRACT FROM AUTHOR]

Abstract Cysteine (Cys) plays a vital role in many physiological processes, and also is closely related to various diseases, thus the development of novel high selectivity and sensitivity fluorescent probes for in situ monitoring of biothiol (Cys) is crucial. Herein, we present a fluorogenic method to detect Cys in vitro and live cells based on fluorescent protein chromophores, which have been modulated by chemical reaction. Probe (RFP) is a fluorescence turn on probe with red emission wavelength and large Stokes shift (127 nm). This Michael-addition reaction-based probe exhibits low detection limit (18.7 μM), fast response time, and low cytotoxicity. RFP can differentiate the Cys and Hcy, using the difference of reaction time between probe and Cys or Hcy. Together, this probe exhibited excellent cell permeability, and can be successfully applied to detect the endogenous Cys in living cells. Highlights • Provide a fluorogenic method to detect Cys based on fluorescent protein chromophores. • Realize the red emission and large Stokes shift using chemical modulation method. • Differentiate the Cys and Hcy using the difference of reaction time. • Detection endogenous or exogenous Cys in living cells and served as bioimaging reagent. [ABSTRACT FROM AUTHOR]

• Development of a novel red-emitting fluorescent probe (HSA) for the detection of Cys. • The probe can high sensitivity detect Cys with a low LOD. • Successfully verified the experimental results by the theoretical calculation study. • The probe can be used for exogenous Cys monitoring and endogenous Cys cell imaging experiments. Herein, we synthesized a red-emitting fluorescence turn-on probe (HSA) for specific detection of cysteine (Cys) over other biothiols (glutathione (GSH) and homocysteine (Hcy)). The acrylate group was chosen as the recognition site for specific discrimination of Cys. Absorption and emission spectra display a high selectivity towards Cys over GSH/Hcy, organic small-molecule interfering substances and anions, with a high sensitivity towards Cys (0.12 μM) in 1% ethanol-containing PBS buffer solution (25 mM, pH = 7.4). Density functional theory (DFT) and time-dependent DFT (TDDFT) calculations were conducted to clarify the luminescence mechanism of the probe. Furthermore, the probe was successfully applied to the determination of free Cys in human serum and the fluorescence imaging of endogenous Cys in living cells. [ABSTRACT FROM AUTHOR]

Abstract In pure water system, the specific and rapid detection of cysteine (Cys) is very important and challenging. Herein, a new optical probe was developed for the purpose based on the complex of cupric ion (Cu2+) with a water-soluble conjugated polymer, poly[3-(3- N,N -diacetateaminopropoxy)-4-methyl thiophene disodium salts] (PTCO 2). The fluorescence of PTCO 2 in 100% aqueous solution can almost completely extinguished by Cu2+ ions due to its intrinsic paramagnetic properties. Among various amino acids, only Cys causes immediately the efficient recovery of the Cu2+-quenched fluorescence of PTCO 2 with ~31-folds fluorescence enhancement because of the stronger affinity of Cys to Cu2+ leading to the formation of Cu2+-Cys complex through Cu-S bond and separation of Cu2+ from weak-fluorescent PTCO 2 - Cu(II) ensemble and thereby restoring the free PTCO 2 fluorescence. In tris-HCl buffer solution (2 mM, pH 7.4), the intensity of the restored fluorescence is linear with the concentration of Cys, ranging from 0 to 120 μM and the estimated detection limit of Cys is 3.3 × 10−7 M with the correlation coefficient R = 0.9981. In addition, the PTCO 2 -Cu(II) ensemble probe exhibits low cytotoxicity and good membrane penetration, and its application in living cell imaging of Cys has also been explored. Graphical abstract Specific and fast detection of cysteine (Cys) in pure water was achieved based on a new fluorescent probe PTCO 2 -Cu(II) through replacement strategy. The probe also shows good pH-stability, membrane penetration and biocompatibility, and can be applied to cell imaging of Cys. fx1 Highlights • A specific probe for fast detection of Cys in 100% water was developed. • The probe showed good biocompatibility, and was suitable for cell imaging of Cys. • The sensing mechanism was demonstrated by DFT simulations and XPS study. [ABSTRACT FROM AUTHOR]

Highlights • A novel thiol-response fluorescent probe, SCD , was developed for detection of proteins with free cysteine residue. • Using HSA as an example, SCD realized its quantitative determination in urine and serum media. • SCD could also be applied in the cell imaging for HSA. Abstract A microenvironment-sensitive probe SCD is developed with a thiol-activated functional group, which could identify specific proteins containing free cysteine residues, such as human serum albumin (HSA), bovine serum albumin (BSA), and β-lactoglobulin. The probe displays good selectivity and sensitivity toward thiol-containing proteins over other proteins, ions, and amino acids under physiological conditions. Due to the twisted intramolecular charge transfer property, SCD exhibits a fluorescence "turn-on" which is utilized for the quantitative detection of trace HSA contents in urine and serum media for the assessment of kidney function and diagnosis of renal diseases. Furthermore, SCD realizes HSA imaging in human breast cancer cells. [ABSTRACT FROM AUTHOR]

Abstract In this work, we have designed and synthesized a dinitrobenzene-sulfonate tetrahydro[5]helicene (H-DNP) as an effective fluorescent probe for detection of hydrogen sulfide (H 2 S). Upon the addition of H 2 S, a significant fluorescence enhancement (75-fold) at 495 nm can be observed with a distinct color change from colorless to yellow. Additionally, H-DNP shows low background spectroscopic signal, large Stokes Shift up to ~140 nm, good sensitivity, rapid response time less than 2 min, low detection limit (48 nM) and high selectivity toward common bio-thiols (Cysteine, Homocysteine and Glutathione). Compared with the previous dinitrophenoxy tetrahydro[5]helicene, this probe has shorter response time and lower detection limit. Most importantly, this probe H-DNP has low toxicity to cells and excellent cell permeability, which can be applied to visualize H 2 S in living cells. Graphical abstract Unlabelled Image Highlights • A tetrahydro[5]helicene based fluorescence probe displayed a rapid, sensitive and selective in response to H 2 S. • The probe has very low detection limit and fast response time. • The response mechanism is confirmed to be thiolysis reaction induced by H 2 S. • The detection of intracellular H 2 S was successfully demonstrated in living cells. [ABSTRACT FROM AUTHOR]

Abstract A novel dansyl-tetrapeptide fluorescent probe (L) for the continuous fluorescent "off-on-off" response detection of Cd2+ ions and Cysteine (Cys) has been designed and synthesized. In our approach, L exhibited very high selectivity to Cd2+ ions over other common metal ions in buffer aqueous solution at natural pH. The resulting L -Cd binding motif system could continuously detect Cys among Glutathione (GSH), Homocysteine (HCy) and 20 natural amino acids. The excellent reversibility and cyclicity of L were also confirmed during the detection of Cd2+ ions and Cys. The detection limit of Cd2+ ions and Cys were obtained to be 93 nM and 35 nM, and lower than EPA and WHO guidelines. What's more, L showed low cytotoxicity and exciting cell infiltration toward living cells, which successfully fluorescent "off-on-off" biological imaged Cd2+ ions and Cys effectively in HeLa cells and renal tubule epithelium (HK2) cells by confocal fluorescence imaging. This study will promote the development of novel multifunctional peptide-based fluorescent probe for Cd2+ ions and Cys in environmental and biological systems. Graphical abstract Unlabelled Image Highlights • A novel peptide fluorescent probe L was synthesized. • L displayed high sensitivity for Cd(II) with a low detection limit of 93 nM. • L -Cd binding motif system could continuously detected Cys with detection limits of 35 nM, and cycle effect were very good. • As a potential probe, L could continuously detected Cd2+ ions and Cys in living HeLa cells. [ABSTRACT FROM AUTHOR]

Abstract 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. Graphical abstract 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. fx1 Highlights • A new long-wavelength-emitting fluorescent turn-on probe NR-CY for simultaneous determination of biothiols was developed. • This probe is easily prepared from readily available inexpensive reagents. • Probe shows rapid response (90 s for Cys, 30 s for H 2 S) to these thiols. • The first PET and ICT-based fluorescent probe is suitable for biological imaging applications. [ABSTRACT FROM AUTHOR]

Abstract A new simple and facile fluorescent ratiometric probe (probe 1) has been designed for the detection of cysteine (Cys). Probe 1 as the fluorophore contains a typical excited-state intramolecular proton transfer (ESIPT) dye. In probe 1 to restore the ESIPT process, the group of acrylate which acts as the recognition unit can block the ESIPT process and can be selectively achieved by Cys, which makes the probe as the ratiometric fluorescent detection for Cys in aqueous solution. This probe shows highly selectivity towards Cys over other biothiols including glutathione (GSH) and homocysteine (Hcy) because of specific cyclization between Cys and acrylate group, and having a detection limit of 42.3 nM. In addition, the experiment of cell imaging shows that probe 1 possesses low cytotoxicity and excellent cell permeability towards the living cells, and has been successfully applied to the ratiometric imaging not only for the endogenous but also for the exogenous cysteine in the living cells effectively. Graphical abstract A new simple and facile ratiometric fluorescent probe (probe 1) has been designed for detecting cysteine (Cys). Probe 1 can be synthesized by 2-(5-bromothiophen-2-yl)-3-hydroxy-chromen-4-one (compound 2) and acryloyl chloride. Probe 1 shows high selectively towards Cys due to the acrylate moiety as the recognized unit can distinguish Cys from Hcy and GSH by different reaction kinetics during the conjugate addition–cyclization reaction. The ratiometric fluorescent measurement can be achieved based on ESIPT process. To demonstrate the application of the probe 1 , in this manuscript, the probe 1 has been successfully applied to the ratiometric imaging for the intracellular and exogenous cysteine in living Hela cells. fx1 Highlights • Probe 1 synthesized by excited-state intramolecular proton transfer (ESIPT) dye. • Probe 1 shows remarkable properties including the ratio of dual emission, high selectivety and sensitivity for cys. • Probe 1 can be used not only detecting and imaging exogenous Cys but also endogenous Cys. [ABSTRACT FROM AUTHOR]

Abstract A new imidazo [1,5- a ]pyridine-based fluorescent probe, named MZC-AC, is developed for the detection of cysteine (Cys) based on an excited state intramolecular proton transfer (ESIPT) mechanism. The probe MZC-AC uses an acrylate moiety as the ESIPT blocking group as well as the recognition site. Upon the treatment with Cys, MZC-AC exhibits a dramatic fluorescence enhancement (85-fold) and a large Stokes shift (166 nm). The limit of detection obtained from fluorescent titration was as low as 0.07 μM. MZC-AC displays highly sensitive and selective response to Cys over homocysteine (Hcy) and glutathione (GSH). Significantly, MZC-AC could be used to detect Cys in living cells. Graphical abstract Image 1 Highlights • An imidazo [1,5- a ]pyridine-based fluorescent probe MZC-AC was developed. • MZC-AC can detect cysteine with high sensitivity and selectivity. • MZC-AC shows a large Stokes shift. • The limit of detection was as low as 0.07 μM. • MZC-AC can be applied in imaging intracellular cysteine in living cells. [ABSTRACT FROM AUTHOR]

A hydroxyphenylquinazolinone-based fluorescent probe DAP-1 with a large Stokes shift (162 nm) was firstly developed for detection of cysteine. The probe DAP-1 with two acrylate as highly Cys-selective sites was designed based on the combination of excited state intramolecular proton transfer (ESIPT) and aggregation-induced emission (AIE) mechanism. Upon the treatment with cysteine, DAP-1 displayed a strong fluorescence enhancement (65-fold). The limit of detection obtained from fluorescent titration was as low as 0.03 μM. DAP-1 could detect cysteine with high selectivity and sensitivity. Significantly, DAP-1 could be used to detect cysteine in living cells. [ABSTRACT FROM AUTHOR]

A novel 4′-hydroxybiphenyl-4-carbonitrile-based fluorescent probe, 1 , for selective detection of cystein (Cys) over homocystein (Hcy) and glutathione (GSH) was developed. This probe had simple structure and could be easily synthesized with good yield from commercially available materials. Moreover, probe 1 showed a remarkable large Stokes shift (180 nm) and displayed a rapid (5 min) and highly sensitive response (the detection limit was 0.15 μM) for Cys with fluorescence turn-on signal changes (142-fold fluorescence enhancement). Importantly, probe 1 could be used to detect and image both exogenous and endogenous Cys in living A549 cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • Organic small molecule fluorescent probes for the specific recognition of Cys were designed and synthesised on the basis of nitrile biphenyls. • The detection of Cys by probe ZHJ-X was studied systematically. • Probe ZHJ-X can be used for specific recognition of Cys with more rapid and efficient detection ability, the corresponding detection limit could be as low as 3.8 × 10-6 M. • The probe has also been successfully applied to detection of target ions in MCF-7 cells、HL60 cells and zebrafish. Cys play an important physiological role in the human body. Abnormal Cys concentration can cause many diseases. Therefore, it is of great significance to detect Cys with high selectivity and sensitivity in vivo. Because homocysteine (Hcy) and glutathione (GSH) have similar reactivity and structure to cysteine, few fluorescent probes have been reported to be specific and efficient for cysteine. In this study, we designed and synthesized an organic small molecule fluorescent probe ZHJ-X based on cyanobiphenyl, which can be used to specifically recognize cysteine. The probe ZHJ-X exhibits specific selectivity for cysteine, high sensitivity, short reaction response time, good anti-interference ability, and has a low detection limit of 3.8 × 10-6 M. The probe ZHJ-X was successfully applied to the visualization of Cys in living cells and had great application prospects in cell imaging and detection. [ABSTRACT FROM AUTHOR]

In this work, a dicyanoisophorone-based turn-on fluorescent probe, DCIP , for highly selective and sensitive detection of cysteine was designed based on nucleophilic substitution mechanism. Moreover, compared with typical cysteine probes, DCIP showed great selectivity and sensitivity for cysteine over other amino acids including the similar structured homocysteine (Hcy) and glutathione (GSH). Further, the detection limit toward cysteine was calculated to be as low as 0.70 μM. In addition, the utility of DCIP as a bioanalytical molecular tool was demonstrated by fluorescence imaging of biothiols in living cells. [ABSTRACT FROM AUTHOR]

Carbazole-based fluorescent probes have a significant edge on structure and optical properties, but stokes shift of them were mostly less than 100 nm. In this work, a novel carbazole-based fluorescent probe, which featured with a large stokes shift (128 nm), was used to effectively detect homocysteine (Hcy) and cysteine (Cys). This probe revealed obvious color variation and a “turn-on” alteration of fluoresence toward Hcy and Cys. Furthermore, the probe works under physiological conditions and can image thiol in living cells as well as zebrafish because of its wonderful cell permeability. Notably, it provides a possibility to detect endogenous bio-thiols quantitatively in living cells. [ABSTRACT FROM AUTHOR]

Biothiols such as cysteine (Cys), homocysteine (Hcy), and glutathione (GSH) play vital roles in various physiological and pathological processes. In this work, a BODIPY-based fluorescent probe XCN was synthesized from multi-step reactions. We first synthesized a BODIPY derivative with a cyano and a bromine moiety attached to the 8-diphenylaminophenyl substituent of BODIPY, followed by the reaction with p -aminothiophenol under basic condition. Interestingly, compound XCN was successfully obtained with the p -aminophenylthio moiety introduced into one of the α-positions of the pyrrolic units. This reaction may compose an efficient approach for synthesizing novel BODIPY derivatives with substituents attached to the pyrrolic unit without previously brominating it. XCN can be used as a fluorescence turn-on probe to selectively detect Cys and Hcy using the cyano group as the recognition site, with the p -aminophenylthio moiety left unreacted. XCN was found to be nearly nonfluorescent, and it exhibits only slight fluorescence enhancement when treated with GSH. However, upon interaction with Cys or Hcy, the fluorescence was enhanced by 1081 and 1126 folds, respectively. In addition, XCN exhibits good selectivity and sensitivity towards Cys and Hcy over GSH and other amino acids in a wide pH range from 2 to 10 in aqueous buffers. Furthermore, XCN was successfully used for imaging biothiols in living A549 lung cancer cells. [ABSTRACT FROM AUTHOR]

A new fluorescent probe ( TRDM-F ) based on a molecular chain of open-loop maleic anhydride, rhodamine B and fluorescein was designed, synthesized and evaluated to develop a chemosensor. Photochemical studies show that fluorescence properties of TRDM-F are dominated by fluorescein group in the pH range of 2–10. UV–vis absorption and fluorescence spectroscopic studies further display a high selectivity towards Cys over GSH/Hcy and other amino acids and a high sensitivity towards Cys (0.088–270 μM) with 95-fold fluorescence enhancement in a HEPES buffer solution (10 mM, pH = 7.4) containing 20% MeCN at room temperature. We further demonstrated that the proposed method was satisfactorily applied to the discrimination of Cys in living Hela cells with low cell toxicity. [ABSTRACT FROM AUTHOR]

[Display omitted] • A lysosome-targetable fluorescent probe for cysteine has been reported. • The probe displays high sensitivity and high selectivity for cysteine. • The probe can be utilized for determination of cysteine within the lysosomes of living cells. An essential sulfhydryl amino acid in the human body is cysteine (Cys). Its abnormal level is related to coronary heart disease, hypertension, growth retardation, sleepiness, liver injury and AIDS. At present, although many cysteine fluorescent probes have been synthesized, there are relatively few fluorescent probes for sensing cysteine in lysosomes. Therefore, based on a rhodamine derivative, we constructed a fluorescent probe with high selectivity for detecting cysteine in lysosome. The probe chose acrylate as the recognition group and morpholine as the positioning group. The probe was in spirolactone state and displayed very weak fluorescence when cysteine was absent. After adding cysteine, the conjugated xanthene structure was formed through the conversion of the closed spirolactone structure and strong green fluorescence appeared. Compared with glutathione (GSH) and homocysteine (Hcy), the probe had better selectivity to Cys. When the Cys concentration was altered from 1.0 × 10−7 to 6.0 × 10−6 mol·L−1, there was a good linear relationship between fluorescence intensity of the probe and Cys concentration. The detection limit had been evaluated to be 7.5 × 10−9 mol·L−1 for Cys. The probe can work under a wide pH range, including pH under physiological conditions. The probe also has a good effect in non-cytotoxic confocal imaging of endogenous and exogenous cysteine in A549 cells. These findings showed that the fluorescent probe synthesized in this study could be a useful tool for the detection of endogenic and exogenic cysteine. [ABSTRACT FROM AUTHOR]

Cysteine is an organic small molecule that plays an important role in human physiological processes. It is meaningful to detect it easily with high selectivity and sensitivity. In this work, a fluorescent probe Lyso-CDC based on chalcone fluorescent dyes for the effective detection of Cys in lysosomes was designed and synthesized. After adding Cys, the fluorescence of the probe Lyso-CDC at 568 nm was significantly enhanced, displaying a large Stokes shift (168 nm) and a color change from light yellow to bright yellow that was visible to naked eyes. The selectivity and sensitivity of the probe Lyso-CDC for Cys were much higher than other amino acids, and the detection limit for Cys was calculated to be 1.44 × 10−8 M. Furthermore, the probe Lyso-CDC possessed low cytotoxicity, excellent biocompatibility and outstanding lysosome targeting ability. The probe was successfully applied to detect Cys in lysosomes of living cells. [Display omitted] • Lyso-CDC was easy to synthesize. • Lyso-CDC specifically recognized Cys with a large Stokes shift of 168 nm. • Lyso-CDC had a low detection limit of 1.44 × 10−8 M for Cys. • Lyso-CDC has been successfully used to detect and image Cys in living cells. • Lyso-CDC was lysosome-targeting. [ABSTRACT FROM AUTHOR]

[Display omitted] • Synthesized a fluorescent probe based on the structure of GFP for detection of cysteine in vitro. • The probe is characterized by outstanding sensitivity, selectivity and anti-interference. • Probe successfully used for imaging in MCF-7 cells and applied to cysteine detection in mouse serum with high accuracy. Cysteine (Cys) is a vital amino acid in the body, and its abnormal expression level is associated with many diseases. In this study, a novel fluorescent probe ACHB was synthesized, showing high selectivity, anti-interference ability and achieving accurate detection of cysteine. Different from most previous off–on probes, ACHB showed an on–off fluorescence response to Cys. Acrylic ester was used as a recognizer while green fluorescence protein (GFP) chromophore derivative 4-hydroxybenzylidene-imidazolinone (HBI) was used as the fluorophore. The addition of Cys leads to the hydrolysis of the red-emitting probe (613 nm), releasing a precursor with a lower fluorescent signal and showing an on–off spectral signal, which was ideal for obtaining sensitive detection with high specificity. Furthermore, the probe was successfully applied for simultaneous determination of cysteine (Cys) in living cells and biological sample (mouse serum). In conclusion, probe ACHB is a promising tool to display the intracellular cysteine concentration level, providing a good visualization method for clinical diagnosis and scientific basic research. [ABSTRACT FROM AUTHOR]

A fluorescent probe ( 1 ) for distinguishing amongst biothiols, including cysteine (Cys), homocysteine (Hcy) and glutathione (GSH), is developed based on different cascade reactions. The key design feature of fluorescent probe 1 is the integration of two potential reaction groups for the thiol and amino groups of biothiols in one molecule. By reacting with the halogen atom and α, β-unsaturated malonitrile in probe 1 , Cys, Hcy and GSH can generate a total of three main products with distinct photophysical properties. Probe 1 shows a strong fluorescence turn-on response to Cys with blue–green emission by using an excitation wavelength of 390 nm. At an excitation wavelength of 500 nm, probe 1 responds to GSH over Cys and Hcy and emits strong orange fluorescence. The discrimination of biothiols can be demonstrated by cell imaging experiments, indicating that probe 1 can be a useful tool for the selective imaging of Cys and GSH in living cells. [ABSTRACT FROM AUTHOR]

Biological thiols including cysteine (Cys), homocysteine (Hcy), and glutathione (GSH) possess the similar structures, but they play different important biological roles. So the detection and discrimination of these biological thiols are of great importance. To date, a number of fluorescent probes have been developed for detection of biothiols. Unfortunately, it is difficult for the probes in discrimination of Cys from Hcy. In this paper, the borondipyrrolemethene -based fluorescent probe named 1 is successfully synthesized. The probe itself exhibits weak fluorescence because the fluorophore is quenched by the acrylate group through a photoinduced electron-transfer (PET) process. Upon reaction of the probe with cysteine, large fluorescence enhancement is produced. The probe could be applied to the quantification of Cys with a linear range covering from 0.2 to 30 μM and the detection limit is 0.05 μM. Furthermore, the fluorescence enhancement shows high sensitivity towards Cys owing that there is more fast reaction rate between the probe and Cys than that of Hcy. Moreover, the response behavior of 1 towards Cys is pH independent in the neutral range from 6.0 to 8.0 and the response of 1 toward Cys was fast. Finally, the probe has low cytotoxicity and is applied for detection of Cys in living cells with encouraging results. [ABSTRACT FROM AUTHOR]

Herein, we report a novel fluorescent probe based on coumarin to detect cysteine (Cys). The probe can react rapidly and selectively with Cys but not with the other amino acids. When the Cys was added to the solution of the probe, we could observe obvious color change from pale green to bright green. The detection limit of this probe for Cys was found to be 0.06 μM. Additionally, bioimaging of intracellular Cys by this probe was successfully applied in living cells, which indicating that this probe holds great potential for biological applications. [ABSTRACT FROM AUTHOR]

A combination of aggregation-induced emission and intramolecular charge transfer was achieved by using a triphenylamine analogue and a dicyanovinyl moiety as the electron donating and accepting units, respectively. Hence, we designed and synthesized a probe with a D-π-A framework as a near-infrared fluorescence turn-on probe for biothiols (cysteine and homocysteine). Owing to the remarkable intramolecular charge transfer effect as well as intramolecular rotations associated with the donor moiety, the probe exhibits extremely weak fluorescence, which becomes a good starting point for developing fluorescence “turn-on” probes. Upon reaction with cysteine or homocysteine utilizing the dicyanovinyl moiety, the intramolecular charge transfer character was weakened, and the reacting products were observed to aggregate in aqueous solutions, resulting in the aggregation-induced emission effect with red fluorescence at 651 and 656 nm, respectively. Hence, the probe could be used as a fluorescence “turn-on” sensor for cysteine and homocysteine, with the sensing time of less than 4 min and the detection limits of 8.4 μM and 5.7 μM towards cysteine and homocysteine, respectively. The probe could distinguish cysteine and homocysteine from glutathione. The sensing mechanism was systematically investigated by employing high resolution mass spectrometry, 1 H NMR and density functional theory calculations as well as checking the solvent viscosity dependent fluorescence, and thus the nucleophilic addition products, the intramolecular charge transfer character, and the aggregation-induced emission behaviour were clearly elucidated. It is noteworthy that the low cytotoxicity, the intrinsic aggregation-induced emission nature and near-infrared emissions enable the application of the probe in living cell imaging. [ABSTRACT FROM AUTHOR]

Development of an excited-state intramolecular proton transfer (ESIPT)-based fluorescent probe ( BIHM ) for selective recognition to homocysteine (Hcy) over glutathione (GSH), cysteine (Cys) and other amino acids is described. The distinctive fluorescence response of BIHM to Hcy over Cys is interpreted by density functional theory calculations. Bioimaging experiments of intracellular Hcy detection manifest the great potential utility of the probe. [ABSTRACT FROM AUTHOR]

A novel fluorescent probe, viz . PI-Cys, was developed on the basis of the excited state intramolecular proton transfer (ESIPT) mechanism for the detection of cysteine (Cys). It consists of an new ESIPT dye as the fluorophore, linked via a hydroxyl moiety to an acrylate group. The acrylate group acts as an ESIPT blocking agent as well as a functional recognition moiety. In the presence of Cys, the reaction of Cys with PI-Cys results in cleavage of the acrylate moiety from PI-Cys, thereby unleashing the ESIPT process and leading to about 20-fold enhancement of fluorescence. The probe exhibits high sensitivity and selectivity toward Cys over homocysteine and glutathione. Finally, the probe was successfully applied for fluorescence bioimaging of Cys in living cancer cells. [ABSTRACT FROM AUTHOR]

A new coumarin-based fluorescent probe CAA containing an acrylamide group has been designed and synthesized for the detection of biothiols. The probe CAA shows high selectivity and sensitivity for cysteine (Cys), homocysteine (Hcy), and glutathione (GSH) over other amino acids. A fluorescence turn-on response is induced by a Michael-type reaction. It shows a highly sensitive fluorescence emission to Cys, Hcy, and GSH, with detection limits of 192 nM for Cys, 158 nM for Hcy, and 155 nM for GSH (S/N = 3). Furthermore, confocal fluorescence microscopy imaging using RAW264.7 macrophages demonstrates that CAA can be an effective fluorescent probe for thiols in living cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • An easily prepared and novel flavone-based fluorescent probe LFA was synthesized for detecting Cys in lysosome. • Experimental results indicated that LFA exhibited rapid response, high sensitivity and selectivity toward Cys. • Living cell imaging of LFA toward Cys was successfully performed for lysosomal imaging in CHL cells with low cytotoxicity. Cysteine (Cys) is one of the most important biothiols that plays a crucial role in many physiological and pathological processes, and therefore it is of great importance to detect and analyze Cys in subcellular environments, such as in lysosomes. However, only a few fluorescent probes were reported to be capable of detecting Cys in lysosomes selectively. In this wok, we designed and developed a simple, accessible flavone-based fluorescent probe LFA for detecting Cys in lysosomes. Morpholine was employed as the targeting unit for lysosome, and acrylate group was chosen as the Cys-response unit. The probe was easily prepared by a two-step procedure and displayed large Stokes shift, high sensitivity, turn-on response toward Cys over homocysteine (Hcy), glutathione (GSH), and other amino acids. With low cytotoxicity and good cell permeability, the probe could be successfully applied for fluorescence imaging of Cys in living cells. Furthermore, colocalization experiment revealed that lysosomal-targetable ability of LFA was significant. These results indicated that such simple fluorescent probe could provide a promising tool for detection of lysosomal Cys in living biological systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel indanone-based fluorescent probe for detection Cys/Hcy was developed. • The stronger acceptor makes the probe with longer emission and higher activity. • The detection mechanism should be from ICT change of the probe after with Cys/Hcy. • The probe has low cytotoxicity and been applied for imaging the biothiols in cells. Effective detection of Cys and Hcy plays an important role in the diagnosis of diseases. In this work, a novel indanone-based fluorescent probe INIAc-CN for sensitively and effectively detecting Cys and Hcy was developed. The probe exhibited weak fluorescence, but obvious fluorescent enhancement after reacted with Cys/Hcy. Moreover, the good anti-interference and low cytotoxicity of the probe made it successfully applied for monitoring Cys and Hcy of in living cells. [ABSTRACT FROM AUTHOR]

We constructed a novel cysteine fluorescent probe with large stokes shift for imaging in the living cells, zebrafish, and living mice. [Display omitted] • The new probe Ty-Cys1 had a very large Stokes shift. • The robust probe Ty-Cys1 showed a good selectivity, sensitivity to Cysteine. • The novel probe Ty-Cys1 was successfully applied to measure Cys in living cells, zebra fishes, and living mice. The small molecule biological thiols, such as Cysteine (Cys), homocysteine (Hcy), and glutathione (GSH), play crucial roles in maintaining various cellular vital activities. In the organism, abnormal levels of small-molecule biological thiols have been associated with a variety of diseases. Therefore, quantitative determination of biological thiols, especially Cys, is significant for understanding their functions in various biological processes. Thus, in this work we designed a new fluorescent probe Ty-Cys1 with a large Stokes shift of 207 nm to monitor Cysteine. The maximum absorption wavelength of Ty-Cys1 was 418 nm, and the maximum emission wavelength was 625 nm. Significantly, the novel probe Ty-Cys1 was effectively in detecting of Cys changes in living cells, zebrafishes, and living mice. [ABSTRACT FROM AUTHOR]

Very recently, the development of fluorescent probes which are capable of specific imaging of Cys/Hcy/GSH in living cells has attracted great attention. The aim of this review is to highlight the representative examples of the specific thiol fluorescent probes reported from 2013 to 2014. However, in this review, we will restrict the discussion to specific thiol fluorescent probes developed based on organic fluorophores for bioimaging applications. [ABSTRACT FROM AUTHOR]

In this study, Cu(II)-mediated differential alteration of cysteine (Cys) reactivity is reported by using a Cys-specific fluorescent probe. The probe could react with Cys to give out strong fluorescence. When Cys was preincubated with Cu(II), the fluorescence of the probe was decreased due to the inhibition of Cys's reactivity by Cu(II). Remarkably, experimental results reveal that the probe could detect Cu(II) at subnanomolar concentrations. In contrast, Cu(II) could only partially inhibit the reaction between Cys and Ellman's reagent (DTNB). Furthermore, selectivity experiments show that Cu(II) is a much more potent inhibitor for Cys compared to other metal ions. Cell imaging experiments also confirm the inhibitory effects of Cu(II) on Cys's reactivity in living cells. We envision that the probe could add a useful tool for sensitive and selective detection of Cu(II) for biomedical research. [ABSTRACT FROM AUTHOR]

A new colorimetric and ratiometric fluorescent probe 1 based on a chlorinated coumarinyl aldehyde was developed for selective detection and cellular imaging of glutathione (GSH) over cysteine (Cys) and homocysteine (Hcy). Probe 1 exhibits a dramatic colorimetric and ratiometric fluorescence responses toward biothiols Cys, Hcy and GSH with high selectivity over other amino acids. Cys (or Hcy) induces a tandem S N Ar-rearrangement reaction to form the corresponding amino-coumarins ( 2a or 2b ), which result in about 75 nm and 35 nm blue-shifts in absorption and emission, respectively. By comparison, the thio-coumarin ( 3′ ) derived from the S N Ar reaction with GSH, which does not occur rearrangement because of steric hindrance, undergoes an intramolecular aldimine condensation lead to a cyclic iminium cation ( 3 ) with 47 nm and 39 nm red-shifts in absorption and emission, respectively. The significantly difference of photophysical properties enable excellent selectivity towards GSH over Cys and Hcy. Further application to cellular imaging indicates that the probe has appreciable cell permeability and is highly responsive to the changes of GSH level. As a result, it is applicable to monitor GSH level in living cells. [ABSTRACT FROM AUTHOR]

Detection and imaging of Cysteine (Cys) and Homocysteine (Hcy) in living systems have drawn extensive attention over the years due to their significant biological role. However, few fluorescence probes have been reported to distinguish Cys and Hcy in near-infrared (NIR) range. In this paper, an original NIR Cys and Hcy fluorescent probe, namely DTRN , was synthesized. DTRN was constructed by using an acryloyl ester group as a trigger and dicyanoisophorone-derived as the fluorophore unit, it was found to emit NIR fluorescence with a 718 nm emission and have large stokes shift (∼176 nm). DTRN hold excellent performances such as ultrasensitivity (LOD = 0.09 μM), high specificity and fast response (<2 min) for Cys. Distinctly, after Hcy was introduced, the emission intensity of DTRN at 718 nm must take 20 min to reach a plateau and the LOD was found to be 0.12 μM. The sensing mechanism for Cys and Hcy in C 2 H 5 OH/PBS (4/6, v/v, pH = 7.4) was studied by 1H NMR spectroscopy and HRMS. Most importantly, the ability of DTRN to detect Cys in HeLa cells had also been achieved. A NIR fluorescent probe (DTRN) was synthesized by using acryloyl ester group as a trigger and dicyanoisophorone-derived as the fluorophore unit, it can detect Cys and Hcy emit NIR fluorescence at 718 nm and have large stokes shift (∼176 nm). [Display omitted] • A NIR fluorescent probe (DTRN) with large stokes shift (∼176 nm) was synthesized. • DTRN could distinguish Cys and Hcy by time-dependent fluorescence signals. • The LOD for Cys and Hcy was calculated to be 0.09 μM and 0.12 μM. • DTRN was successfully exploited for detecting Cys in HeLa cells. [ABSTRACT FROM AUTHOR]

Biothiols such as cysteine (Cys), homocysteine (Hcy) and glutathione (GSH) play important roles in regulating the redox balance of life process and are closely associated with human health and diseases. In order to better understand their roles in physiological process and the early diagnosis of related diseases, it is crucial for the selective detection of biothiols in biological systems. In this paper, we developed a 4-phenylselenium coumarin-nitroolefin conjugate as the fluorescent probe for the detection of biothiols. By introducing the 4-phenyselenium as the active site, probe CouSeNO 2 is capable of detecting Cys/Hcy and GSH in dual fluorescence channels. For the biothiols, the first-step sensing reaction is proved to be nucleophilic substitution of 4-phenylselenium by the thiol group. Furthermore, through two-channel fluorescence imaging, probe CouSeNO 2 has been successfully applied to sense the exogenous and endogenous biothiols in living cells. A dual-active-site fluorescent probe can distinguish Cys/Hcy and GSH rapidly. [Display omitted] • A rapid-response fluorescent probe was developed through introducing 4-phenylselenium as the active site. • The proposed probes realizes distinguishing detections of Cys/Hcy and GSH via two reaction sites. • Cys/Hcy and GSH in living cells were detected successfully by fluorescence cell imaging. [ABSTRACT FROM AUTHOR]

A series of fluorescent dyes based on 2-(2′-hydroxyphenyl)benzothiazole derivatives were designed and synthesized. Because of their structural characteristics of "AIE + ESIPT", they have long-wavelength emission and a larger Stokes shift. The fluorescent probe HBTN-Y was prepared based on the fluorescent dye HBTN. Probe HBTN-Y can recognize cysteine (Cys) with a high selectivity, "OFF-ON" fluorescence response, a large Stokes shift (263 nm) and long-wavelength emission (637 nm) in MeCN/H 2 O (1:1, v/v, PBS 20 mM, pH = 8.4) solution. The probe exhibits good anti-interference ability, a low detection limit of 6.51 × 10−6 M, and is suitable for application at near neutral and weak alkaline pH (7–9) conditions. Moreover, HBTN-Y is applicable to image Cys in living MCF-7 cells. A new fluorescence "AIE + ESIPT" characteristics probe HBTN-Y for the detection of cysteine has been developed. [Display omitted] • A series of fluorescent dyes with "AIE + ESIPT" features were synthesized. • A cascade reaction-based fluorescence "turn on" probe (HBTN-Y) has been developed. • HBTN-Y displays highly selective recognition for Cys in an aqueous solution. • HBTN-Y can detect Cys with a long wavelength emission and a large Stokes shift. • HBTN-Y is capable of imaging Cys in living MCF-7 cells. [ABSTRACT FROM AUTHOR]

The optical monitoring of thiols such as glutathione (GSH), cysteine (Cys) and homocysteine (Hcy) is of significant interest due to their crucial roles in maintaining the biological redox homeostasis through the equilibrium of free thiols and oxidized disulfides in biological systems. In this work, a molecular chemodosimeter DPP-DNBS with a highly photostable diketopyrrolopyrrole (DPP) fluorophore connected to a 2,4-dinitrobenzenesulfonyl (DNBS) electron-withdrawing group for selective detection of biothiols was effectively synthesized. The specific reaction between biological thiols and DPP-DNBS gives rise to an obvious fluorescence intensity enhancement at 615 nm which is induced by the cleavage of O S bond liberates DPP fluorophore. High sensitivity and selectivity for pathless over other amino acids were also obtained. Moreover, via turn-on signal toward cysteine in Hela cells, DPP-DNBS was also employed in cellular detection of cysteine and realized discrimination of cysteine from homocysteine and glutathione in Hela cells. [ABSTRACT FROM AUTHOR]