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 ex/em 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 ex = 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. Graphical Abstract