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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]

The novel V-shaped donor-π-acceptor-π-donor compounds bearing an aldehyde group (1Pip , 2EtO , and 3TEG) were designed, synthesized, and evaluated as the two-photon excited fluorescence probes for the selective detection of cysteine (Cys). Their structures were fully characterized by 1H NMR, 13C NMR, FT-IR, and HRMS. The optical properties of the target compounds in various solvents were studied in details and the time-dependent density functional theory calculations were performed to shed light on their electronic structures. It is found that all of them exhibit large Stokes shifts (6331-10047 cm−1). 1Pip and 3TEG are capable of detecting Cys with high selectivity, good anti-interference ability, and favorable two-photon absorption performance. The limits of detection were determined to be equal to 0.15 μM for 1Pip and 0.73 μM for 3TEG. The possible recognition mechanism was also validated by 1H NMR and HRMS. One- and two-photon fluorescence imaging experiments indicate that 3TEG shows more satisfactory cellular membrane permeability than 1Pip , and it can successfully visualize the endogenous and exogenous Cys in living cells. These results imply that 3TEG has potential as a two-photon fluorescence probe for detecting Cys in biological samples. [Display omitted] • Three novel D-π-A-π-D type two-photon absorption compounds were developed to detect Cys. • 3TEG shows high selectivity to Cys, favorable two-photon absorption property, large Stokes shifts, and good biocompatibility. • 3TEG has been successfully utilized to image endogenous and exogenous Cys 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]

Abstract: A turn-on fluorescent probe DNBS-CSA is reported here with selective detection of thiols over other amino acids. Probe DNBS-CSA possesses the widely-used thiol-selective 2,4-dinitrobenzenesulfonyl (DNBS) group to react with thiols and release the fluorescent salicylaldehyde azine with aggregation-induced emission (AIE) characteristics. The use of AIE dye prevented the sensor from aggregation-induced fluorescence quenching which is challenging for other thiols sensors. Upon the addition of cysteine (Cys) to DNBS-CSA in aqueous solution (10 mM PBS buffer at pH 7.4 containing 30% DMSO), an intense fluorescence enhancement was observed at 558 nm with a large stokes shift of ∼170 nm. Under the optimal condition, the fluorescence intensity linearly increased with the concentration of Cys in the range of 8–18 μM with a correlation coefficient of R 2 = 0.991. The fluorescence enhancement of DNBS-CSA upon addition of Cys on test paper was also observed, enabling DNBS-CSA function as solid materials (such as test papers) for thiols detection. The detection of thiols in serum samples was successfully performed. With good cell permeability, the probe was applied to the imaging of thiols in HEK 293T cells. [Copyright &y& Elsevier]

Here, a coumarin-based probe 4-chloro-3-formyl-2-oxo-2H-chromen-7-yl acrylate (named CFCA), which performed high efficient and specific recognition for cysteine (Cys), was successfully synthesized and characterized by NMR and MS. The CFCA probe showed colorimetric and "turn-on" fluorescent signals to Cys, and its color changes could be recognized by naked eyes. CFCA responded to Cys with the characteristics of rapid response time (less than 40 s), high selectivity, and excellent anti-interference. Among all kinds of samples, only Cys could significantly enhance the fluorescence intensity of the solution, which was not affected by the presence of other interferences. At the same time, within a certain concentration range, there was a good linear relationship between relative intensity of fluorescence and Cys concentration. The detection limit has been calculated to be as low as 0.33 μM. And the sensing mechanism of CFCA with Cys has been well confirmed by 1H NMR and HR-MS spectra. Moreover, the fluorescence probe CFCA was successfully used for imaging Cys in living cells and processed into test strips for on-site analysis and testing. • A coumarin-based probe CFCA was successfully prepared, synthesized, and applied for Cys detection. • CFCA can perform high efficiency and specificity colorimetric and fluorescent double signal recognition for Cys. • CFCA has been used for imaging Cys in living cells and processed into test strips for on-site analysis and testing. [ABSTRACT FROM AUTHOR]

Based on the 7-nitro-1,2,3-benzoxadiazole (NBD) unit, many fluorescent probes have been developed for the differential detection of biothiols. Among them, however, the use of fluorescent probes for rapid simultaneous identification of biothiols in vivo has been rarely reported. In this work, a simple fluorescent probe (NC-NBD) is rationally designed and developed according to the different reactivity of biothiols, which can simultaneously distinguish homocysteine (Hcy), cysteine (Cys), and glutathione (GSH) by adjusting two different fluorescence signals (green and yellow). The probe NC-NBD can discriminatively detect biothiols using two fluorescence channels with fast response (120–360 s), which is suitable for real-time monitoring of biothiols in biological systems. As expected, the probe NC-NBD with excellent performance is able to determine the levels of Cys/Hcy and GSH in human serum samples, and therefore has potential applications in biological specimens. The robust probe shows low toxicity and high sensitivity when applied to living cells, and successfully achieves rapid sequence distinguishing of biothiols and intracellular imaging by using two different fluorescence signals. The probe can provide an effective tool for the real-time monitoring of intracellular biothiols. Image 1 • A fluorescent (FL) probe based on 7-nitro-1,2,3-benzoxadiazole (NBD) was developed. • The simple probe was used for rapid and sensitive sequence detection of biothiols in vitro. • The probe can determine the levels of Cys/Hcy and GSH in human serum samples. • The probe senses biothiols by two FL signals and images them in living cells. [ABSTRACT FROM AUTHOR]

As an important sulfur-containing amino acid, aberrant levels of cysteine are closely related with an array of dieases. Although many Cys-specific fluorescent probes have been designed, most of them wouldn't be able to detect Cys in buffer solution, which limits the application of the probe in biological system. In this work, a novel near-infrared fluorescent probe Cys-WR with a large Stokes shift (about 110 nm) was developed for the detection of Cys by conjugating the fluorophore WR-4 with crotonate moiety. The probe exhibited off-on response to Cys with wide linear range of 0–100 μM, as well as the color of the probe solution changes from deep pink to brown observed by naked eyes. Moreover, the probe showed little cytotoxicity. Imaging of Cys using this probe in living A549 cells and zebrafish had also been well demonstrated. Image 1 • A novel near-infrared fluorescent probe Cys-WR with a large Stokes shift was constructed for detection of Cys. • The probe Cys-WR showed NIR off-on response to Cys with high sensitivity and selectivity. • The probe Cys-WR can be employed to monitor exogenous and endogenous Cys fluctuation in living cells and zebrafish. [ABSTRACT FROM AUTHOR]