A novel assembly of Au NPs–β-CDs–FL for the fluorescent probing of cholesterol and its application in blood serum‡§

A novel assembly of Au NPs–β-CDs–FL for the fluorescent probing of cholesterol (Cho) is provided. Gold nanoparticles (Au NPs) possessing a high extinction coefficient function can be used as excellent fluorescent quenchers in Au NP–fluorophore composites. Inclusion of fluorescein (FL) into β-cyclodextrin (β-CD) makes fluorescence resonance energy transfer (FRET) occur through the donor and quencher nearby. FRET switches off because of the cholesterol-induced release of FL from β-CD cavity, which results in the fluorescence recovery of the quenched dye. Spectral analysis supported the idea that the signal enhancement was attributed to the formation of an inclusion complex of the cholesterol moiety in β-CD, resulting in separation of FL from the Au NPs. This phenomenon is explained by the guest-induced location change of the FL from inside to outside the cavity, suggesting that the assembly of Au NPs–β-CDs–FL is effective as a fluorescent probe for cholesterol recognition. The fluorescence increase is proportional to the concentration of cholesterol in the range of approx. 30 nM to 15 μM. A concentration of cholesterol as low as 9 nM would be readily detected. The precision of the method applied to the determination of quantities of cholesterol present in human blood serum were satisfactory.