Rational design of a novel acryl-modified CQDs fluorescent probe for highly selective detection and imaging of cysteine in vitro and in vivo.

A novel fluorescent nanoprobe CQDs-O-Acryl has been designed and synthesized to directly and accurately identify Cys over other biothiols in PBS (10 mM, pH 7.4) buffer. The carbon quantum dots (CQDs-OH) (λ maxima = 495/525 nm) were fabricated by a solvothermal method using resorcinol as the carbon source. The CQDs-O-Acryl was achieved through covalently grafting the acryloyl group on the surface of carbon quantum dots by nuclear reaction based on static quenching. The structure and morphology of CQDs-OH and CQDs-O-Acryl have been characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and UV-vis absorption spectroscopy. Upon the addition of Cys, the ester bond of CQDs-O-Acryl has been broken, and the free CQDs were released by conjugated addition and cyclization reactions successively, emitting strong green fluorescence at 525 nm (λ = 495 nm). Under the optimized conditions, CQDs-O-Acryl exhibited good sensing of Cys within the range 0.095-16 μM (the LOD of 0.095 μM). Due to the high sensitivity, reliability, fast fluorescence response (10 min), and low toxicity of CQDs-O-Acryl, it was successfully applied to fluorescence imaging of Cys in A549 cells and zebrafish.