Enzyme biosensor based on NAD-sensitive quantum dots

A novel quantum dots (QDs) based biosensor has been developed to detect the activity of lactate dehydrogenase (LDH) by the change of fluorescence intensities of the QDs. In this system, the fluorescence intensities of the QDs are quenched by nicotinamide adenine dinucleotide (NAD, the coenzyme of LDH) first and then intensified with increasing amounts of the LDH because of the consumption of the NAD in the biocatalyzed reaction. A linear calibration plot of the activity of LDH is obtained in the wide amounts range from 150 to 1500 U/L and the detection limit is 75 U/L. Furthermore, the effect of several possible interfering substances, such as uric acid (UA), lactose, and glucose on the QDs-based biosensor is also investigated. This enzyme biosensor is of considerable interest due to its promise for simple procedure and the established method has great potential in detection of the physiological level of some biomolecules in clinical diagnostics of various diseases.