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We designed and synthesized a water-soluble near-infrared (NIR) fluorescent probe with the recognition unit of the cyanine-like structure and acrylate group. Through an aromatic ring nucleophilic substitution reaction based on sulfhydryl moiety, an off-on fluorescence response toward cysteine (Cys) was realized. The probe exhibited excellent spectral performance with an emission wavelength of 720nm and a detection limit of 0.20μM. The spectral properties, selectivity and anti-interference performance of the probe were systematically investigated. Density functional theory (DFT) calculations were conducted to clarify the luminescence mechanism of the probe. Furthermore, the probe was successfully applied to the detection of free Cys in human serum and the NIR imaging of endogenous Cys in living cells. Thus, the probe has a promising application prospect in clinical diagnosis and fluorescence imaging., (Copyright © 2019 Elsevier B.V. All rights reserved.)

• 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]

Herein we propose a fluorescence turn-on strategy for the sensitive and selective detection of trypsin based on fluorescence resonance energy transfer (FRET) between gold nanoparticles (AuNPs) and amino-functionalized carbon dots (C-dots). In this assay, C-dots were treated as fluorometric reporter, while AuNPs were treated as fluorescence quencher. A specially designed negatively charged short peptide chain with one functioned cysteine group as the substrate for trypsin. The sensor works as follows: the negatively charged part of the peptide can be hydrolyzed by trypsin, resulting in the releasing of shorter and positively charged peptides. These shorter peptides then induces AuNPs aggregation due to the strong electrostatic interaction between positively charged peptides and the negatively charged AuNPs, thus leading to the restoration of the FRET-quenched fluorescence emission of C-dots. Measuring the changes in the fluorescence of C-dots, the concentrations of trypsin can be determined. Under the optimized conditions, we achieved quantitative evaluation of trypsin in a range of 2.5–80 ng mL −1 with the detection limit of 0.84 ng mL −1 . Meanwhile, this sensing system also exhibited excellent selectivity and sensitivity for trypsin, and we successfully applied it for the detection of trypsin in human serum samples. Based on the above findings, we conclude that this new FRET based sensor might be significant in disease diagnosis in the future. [ABSTRACT FROM AUTHOR]