Interaction of flavonoids (baicalein and hesperetin) with CdTe QDs by optical and electrochemical methods and their analytical applications

3-mercaptopropionic acid (MPA) capped CdTe quantum dots (QDs) were synthesized with a diameter of about 3 nm in aqueous solution which were characterized by transmission electron microscopy (TEM) and fluorescence microscopy. The interaction between the two flavonoids (baicalein and hesperetin) and QDs was investigated by fluorescence, ultraviolet–visible (UV–vis) absorption spectroscopy, and electrochemical measurement. The fluorescence of QDs was quenched by baicalein and hesperetin via electron transfer progress. Additionally, the reason of different fluorescence quenching efficiency of QDs by baicalein and hesperetin was discussed, and it revealed that the fluorescence quenching efficiency of QDs is partly related to the antioxidant activity of flavonoids. Based on this, a simple and sensitive assay for determination of baicalein and hesperetin was proposed. Under the optimized conditions, the linear range of QDs fluorescence intensity versus the concentration of baicalein and hesperetin were 0.032–50 μg/mL and 0.082–120 μg/mL, with correlation coefficient (R) of 0.9977 and 0.9963, and limit of detections (3σ) of 9.736 ng/mL and 24.46 ng/mL, respectively. The presented method has been applied successfully for the determination of baicalein and hesperetin in urine samples.