Fabrication of a Dopamine Sensor Based on Carboxyl Quantum Dots.

A quantum dot (QD)-based optical biosensor was developed to detect the activity of dopamine (DA) via the quenching of QD fluorescence intensity. In this study, we examined the fluorescence quenching of DA-conjugated quantum dots (DA@QDs) at various solution pH values. The fluorescence intensity of the QDs is quenched by electronic energy transfer from the QDs to the o-quinone group of dopamine oxide. The degree of fluorescence quenching was dependent on DA concentration. The influence of the external environment pH factor on fluorescence quenching was investigated. The results showed that the degree of fluorescence quenching of DA@QDs was highest in a slightly alkaline solution--pH of approximately 9. Fluorescence enhancement with increased pH appears to be due to electronic energy transfer, which is related to an increased degree of dopamine-o-quinone oxidation. The fluorescence quenching of QDs by DA is of considerable interest due to its potential for the direct detection of the DA in vivo via a simple procedure with a very low limit of detection.