Optical analysis of lactate dehydrogenase and glucose by CdTe quantum dots and their dual simultaneous detection

Biomolecules detection by size-controlled quantum dots (QDs) was promising in developing clinic diagnostic techniques. In this work, a novel bioanalytical platform was developed to detect the activity of nicotinamide adenine dinucleotide (NAD) dependent enzyme, lactate dehydrogenase (LDH), and the concentration of glucose by the changes of fluorescence intensities of the QDs based on the electron transfer between QDs and sensitive biomolecules. The fluorescence intensities of the QDs was firstly quenched by NAD and then intensified with increasing amounts of the LDH because of the consumption of the NAD by the biocatalyzed reaction. Also the glucose led to the decline of fluorescence due to the formation of hydrogen peroxide (H₂O₂) which was the product of the glucose reacting with the glucose oxidase (GOD). The linear calibration plots of the activity of LDH and glucose were obtained from 250 to 6000U/L and 1.67 to 6.67mM, respectively. The detection system was also successfully applied to detect LDH and glucose in human serum samples. This analysis process was very convenient and simple because the QDs need not to be modified by any organic or biological molecules before they were used into the system. Moreover, the established method had great potential in detection of the physiological level of some biomolecules in clinical diagnostics of various diseases.