Construction of a turn off-on fluorescent nanosensor for cholesterol based on fluorescence resonance energy transfer and competitive host-guest recognition

Using chloroauric acid as precursor and beta-cyclodextrin (beta-CD) as reducing agent and stabilizer, beta-CD@AuNPs with negative charge were synthesized by one-step colloidal synthesis method. The positive charged carbon quantum dots (CQDs) were synthesized by one-step of sonication of cetylpyridinium chloride. Under the role of static electricity, the fluorescence resonance energy transfer (FRET) occurred between CQDs and beta-CD@AuNPs. CQDs and beta-CD@AuNPs served as the fluorescence energy donors and receptors, respectively, i.e., the fluorescence of CQDs was turned off by beta-CD@AuNPs. Based on the specific host-guest recognition between the inner cavity of beta-CD and cholesterol, CQDs was replaced by cholesterol, the FRET could be interrupted, and then the fluorescence of CQDs was turned on. A good linear relationship between cholesterol concentration (10-210 mu mol L-1) and fluorescence intensity was obtained and the LOD was 343.48 nmol L-1. Because of excellent fluorescence quenching ability of FRET, the analytical performance (including LOD and linear scope) of such a turn off-on fluorescent nanosensor (e.g., CQDs/beta-CD@AuNPs) was better than nanosensor only via competitive host-guest recognition (e.g., beta-CD functionalized CQDs). The synergistic effect of competitive host-guest recognition and FRET was proved. Because of selective recognition, ultrasensitive, wide linear range, and strong anti-interference ability, CQDs/beta-CD@AuNPs as a turn off-on fluorescent nanosensor was developed to determine cholesterol in porcine serum.