Functionalized N-doped graphene quantum dots for electrochemical determination of cholesterol through host-guest inclusion

Functionalized nitrogen-doped graphene quantum dots (N-GQD) with mean particle size of 8.5 ± 0.5 nm were covalently linked to β-cyclodextrin (β-CD) to form a β-CD@N-GQD nanoprobe. The probe is shown to enable voltammetric determination of cholesterol via selective host-guest recognition and by using ferrocene (FC) as the redox indicator. FC is first included in β-cyclodextrin. Cholesterol has a higher affinity for β-CD (in comparison to FC). It forms a strong inclusion complex with β-CD and can replace FC from its cavities. The quantity of released FC is proportional to the concentration of cholesterol. The differential pulse voltammetric signal for FC (with a peak at typically 0.22 V vs Ag/AgCl) increases linearly in the 0.5–100 μM cholesterol concentration range, with a limit of detection as low as 80 nM. The assay is found to be highly selective over 15 potentially interfering species. The method was successfully applied to the detection of cholesterol in spiked serum samples which gave recoveries between 96 and 101%. The probe can be stored for at least 28 days after which the activity still is 87%. .