Fluorescence detection of cholesterol using a nitrogen-doped graphene quantum dot/chromium picolinate complex-based sensor

Nitrogen-doped graphene quantum dots (N-GQDs), with superior biocompatibility, strong resistance to photobleaching and convenient surface grafting, have sparked a surge of related-bio applications. In this study, combined with chromium picolinate (CrPic), N-GQDs synthesized by a facile hydrothermal approach are used to construct an environmentally-friendly sensor for the detection of cholesterol by exploiting the fluorescence enhancement of N-GQDs/CrPic. Herein, CrPic is grafted on N-GQDs via the linker of cysteamine (Cys), and the fluorescence of the N-GQDs is quenched by photoinduced electron transfer (PET), wherein CrPic functions as an electron donating group and the N-GQDs serves as an electron accepting group. Besides, cholesterol is stimulated to form a favourable complex with N-GQDs/CrPic because CrPic also acts as a potential receptor for cholesterol by strong affinity and π-π interaction, and the fluorescence of N-GQDs/CrPic is enhanced indicating that cholesterol could impede electron transfer from CrPic to the N-GQDs. This N-GQDs/CrPic-based sensor has been successfully applied to selectively determine the concentration of cholesterol with a linear range of 0-520 μM and a limit of detection (LOD) of 0.4 μM. Meanwhile, this present sensing strategy in human serum has acceptable practicability, reproducibility and precision.