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[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]

A new fluorescent probe ( ABPA ) based on 1,8-naphthalimide, which designed on the “ receptor 1 -fluorophore-spacer-receptor 2 ” model and employed conjugated addition/cyclization sequence mechanism for Cys detection was reported. The probe shows high selectivity and sensitivity for cysteine (Cys) over other amino acids including the similar structured homocysteine (Hcy) and glutathione (GSH). It displays a highly sensitive fluorescence emission to Cys with a detection limit of 0.12 μM (S/N = 3), which is far below the normal level of Cys (30–200 μM) in living cells. Furthermore, ABPA was successfully applied to bioimage intracellular Cys in living cells with low cytotoxicity. [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 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]

Biological thiols are crucial in biological processes. Therefore, a probe capable of targeting and imaging biothiols in living cells, as well as rapidly labelling the thiols in proteins, is desirable and imperative. Herein, we designed and synthesized FRB-T containing α , β -unsaturated ketones to recognize thiols for detecting biothiols and selectively labelling the sulfhydryl-containing proteins. The probe initially exhibited weak fluorescence and then performed 1, 4-Michael addition reaction between its α , β -unsaturated ketone and thiols, along with the spiro ring-opening, leading to remarkable fluorescence enhancement and colour changes. The specificity of FRB-T towards thiols was high, and its detection limits were 70 nM for cysteine (Cys) and 1.51 μg/mL for ovalbumin (OVA). Furthermore, FRB-T has also been successfully applied to biothiols imaging in Hela cells, and rapid labelling of the sulfhydryl-containing proteins without washing step. [Display omitted] • A biothiol-specific probe with strong fluorescence enhancement and colorimetric response. • The probe owns low LOD of 70 nM and 1.51 μg/mL for Cys and OVA respectively. • A new type of reagent for labelling sulfhydryl-containing proteins without washing. [ABSTRACT FROM AUTHOR]

• A novel turn-on probe (ABTT-MA) based on "AIE + ESIPT" effect was developed. • The maleimide-appended probe presents high selectivity to Cys over structure-like Hcy and GSH. • New insight into the high selectivity of maleimide-appended probe: Michael addition/S,N-intramolecular rearrangement cascade reaction. • ABTT-MA was allowed in aqueous media with the lowest detection limit (9.4 nM). • ABTT-MA was successfully applied to imaging exogenous and endogenous Cys in living cells. Biothiols, including cysteine (Cys), homocysteine (Hcy) and glutathione (GSH), play pivotal roles in numerous physiological events, however, due to the similar structures and reactivities, differentiation of these biothiols remains a challenging task. Herein, we reported a maleimide-appended fluorescent probe ABTT-MA capable of specific sensing of Cys over other structure-alike biothiols with an ultralow detection limit (9.4 nM). Via a series of investigations into the mechanism, the high selectivity toward Cys is ascribed to a Michael addition/S,N-intramolecular rearrangement cascade reaction, in which the involvement of the mercapto and the adjacent amino groups is necessary to proceed the sensing process. Given this presupposition, Cys could be kinetically discriminated from Hcy and GSH. Upon the addition of Cys, a strong fluorescence appeared and the intensity at 503 nm was correlated with Cys concentration linearly over a wide range (0–10 μM). Thanks to the aggregation-induced emission (AIE) and excited-state intramolecular proton transfer (ESIPT) activity, the selective detection of Cys was realized not only in aqueous media but in the paper-based point-of-care test (POCT). Significantly, the practicability of ABTT-MA in exogenous and endogenous Cys imaging in living cells was elucidated as well. [ABSTRACT FROM AUTHOR]

In this study, a mitochondria-specific fluorescent probe for efficient ratiometric detection of Cys was designed and investigated. Probe 1 is composed of a xanthylene skeleton and a benzyl group containing an acryloyl moiety. The probe showed excellent water solubility, good selectivity and sensitivity toward Cys over other analytes, and afforded an extremely low detection limit of 33.7 nM. The possible detection mechanism was ascertained by HRMS analysis. Moreover, probe 1 had excellent mitochondrial-targeting ability (the Pearson's correlation coefficient was 0.96), and was capable of monitoring endogenous Cys in living HeLa cells by dual channel ratiometric bioimaging, demonstrating its significant potential in biological applications. Image 1 • A novel ratiometric and mitochondria-targetability fluorescent probe 1 with a xanthylene skeleton for Cys was developed. • Probe 1 showed excellent water solubility, high selectivity and sensitivity (detection limit of 33.7 nM) towards Cys. • Probe 1 could be successfully used for imaging cellular exogenous and endogenous Cys. [ABSTRACT FROM AUTHOR]