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Cysteine (Cys), homocysteine (Hcy) and glutathione (GSH) play many crucial physiological roles in organisms. Their abnormal levels can cause and indicate various diseases. In the present study, a small-molecule fluorescent probe 2-(imidazo[1,2-a]pyridin-2-yl)phenyl acrylate (IPPA) was designed, synthesized and characterized by NMR, FT-IR and HRMS. IPPA can selectively detect Cys over other analytes because of an approximately 76 times enhancement in fluorescence intensity. The limit of detection of IPPA for Cys was 0.33 μM. The pseudo-first-order rate constant of the reaction between IPPA and Cys was approximately 10 times that of the reaction between IPPA and Hcy (K Cys 3.18 × 10 -3  S -1 vs K Hcy 4.92 × 10 -4  S -1 ), indicating that Cys can be distinguished from Hcy. In addition, IPPA exhibits strong anti-interference ability, small molecular weight, high efficiency, low toxicity and good cell permeability. It was successfully used in imaging HepG2 cells and zebrafish. The fluorescence response of IPPA for calf serum are powerful proofs for practical application. Therefore, IPPA has high potential for bioassay applications., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Biothiols such as cysteine (Cys) and homocysteine (Hcy) are essential biomolecules participating in molecular and physiological processes in an organism. However, their selective detection remains challenging. In this study, ethyl 2-(3-formyl-4-hydroxyphenyl)-4-methylthiazole-5-carboxylate (NL) was synthesized as a ratiometric fluorescent probe for the rapid and selective detection of Cys and Hcy over glutathione (GSH) and other amino acids. The fluorescence intensity of the probe in the presence of Cys/Hcy increased about 3-fold at a concentration of 20 equiv. of the probe, compared with that in the absence of these chemicals in aqueous media. The limits of detection of the fluorescent assay were 0.911 μM and 0.828 μM of Cys and Hcy, respectively. ¹H-NMR and MS analyses indicated that an excited-state intramolecular proton transfer is the mechanism of fluorescence sensing. This ratiometric probe is structurally simple and highly selective. The results suggest that it has useful applications in analytical chemistry and diagnostics.

Cysteine (Cys), homocysteine (Hcy) and glutathione (GSH) play many crucial physiological roles in organisms. Their abnormal levels can cause and indicate various diseases. In the present study, a small-molecule fluorescent probe 2-(imidazo[1,2-a]pyridin-2-yl)phenyl acrylate (IPPA) was designed, synthesized and characterized by NMR, FT-IR and HRMS. IPPA can selectively detect Cys over other analytes because of an approximately 76 times enhancement in fluorescence intensity. The limit of detection of IPPA for Cys was 0.33 μM. The pseudo-first-order rate constant of the reaction between IPPA and Cys was approximately 10 times that of the reaction between IPPA and Hcy (KCys 3.18 × 10-3 S-1vs KHcy 4.92 × 10-4 S-1), indicating that Cys can be distinguished from Hcy. In addition, IPPA exhibits strong anti-interference ability, small molecular weight, high efficiency, low toxicity and good cell permeability. It was successfully used in imaging HepG2 cells and zebrafish. The fluorescence response of IPPA for calf serum are powerful proofs for practical application. Therefore, IPPA has high potential for bioassay applications.

Cysteine (Cys) plays a key role in all life forms. In the present study, a novel and effective fluorescent probe, 2-(benzo[d]thiazol-2-yl)-1,4-phenylene diacrylate (BT-AC), was developed for selectively sensing Cys over other analytes. BT-AC alone essentially emits no fluorescence, whereas it achieves a 4725-fold enhancement with a large Stokes shift (135 nm) in the presence of Cys. Moreover, the limit of detection of the fluorescent assay was as low as 32.6 nM Cys. The fluorescence response of BT-AC to calf serum provided strong evidence of the practical applicability of this probe. This probe was successfully used for imaging Cys in HepG2 cells and zebrafish. [ABSTRACT FROM AUTHOR]

As a biothiol in human body, cysteine (Cys) is related to many diseases. To specifically monitor the level of Cys, a ratiometric fluorescent probe (DDEA) with a large Stokes shift (186 nm) was developed. Due to the excellent spectral performance and stable absorption of dicyanoisophorone, the DDEA probe was designed on the basis of intramolecular charge transfer (ICT) mechanism. DDEA can emit intense orange-red fluorescence in the presence of Cys and realize accurate quantitative analysis of Cys. The detection limit of DDEA for Cys is as low as 91 nM. In addition, the results of test strips and calf serum provided strong evidence of the practical applicability of DDEA. Benefitting from the advantages of good cell permeability and low cytotoxicity, DDEA has been successfully utilized to image endogenous Cys in HeLa cells and zebrafish. Image 1 • A ratiometric Cys fluorescent probe DDEA was successfully synthesized. • The reaction mechanism was confirmed by DFT calculation, HRMS and NMR. • DDEA exhibits low toxicity, high sensitivity and large Stoke shift (186 nm). • DDEA was also successfully utilized to image of Cys in HeLa cells and zebrafish. [ABSTRACT FROM AUTHOR]

Aminothiol levels are indicative of cellular and physiological statuses. A colorimetric and ratiometric dual-site fluorescent probe, NL-S , has been designed and synthesized. NL-S contains both a 2,4-dinitrobenzenesulfonyl group and an aldehyde group as recognition units for aminothiols. NL-S exhibited highly selective and sensitive detection of aminothiols, with a 27–44-fold enhancement of the fluorescent signal observed within 30 min of the addition of up to 20 equiv. of cysteine (Cys), homocysteine (Hcy) or glutathione (GSH) in aqueous media. The probe undergoes a turn-on excited-state intramolecular proton transfer process derived from cleavage and condensation reactions. The limits of detection for Cys, Hcy and GSH were 0.114, 0.146 and 0.202 μM, respectively. NL-S with negligible cytotoxicity was successfully employed to fluorescent imaging of aminothiols in living cells and zebrafish, suggesting good potential of NL-S in biological applications. [ABSTRACT FROM AUTHOR]