CdTe quantum dots as probes for near-infrared fluorescence biosensing using biocatalytic growth of Au nanoparticles

A near-infrared (NIR) fluorescence sensing strategy for glucose and xanthine has been developed based on the interaction between CdTe quantum dots (QDs) and biocatalytic generated Au nanoparticles. The fluorescence of CdTe QDs is modulated by changing concentration of AuCl4- and Au nanoparticles during the growth process of Au nanoparticles. Two cases were considered. In the first case, the glucose oxidase (GOx) catalyzes the oxidation of glucose to generate H2O2. Under the catalysis of Au nanoparticles seeds, the AuCl4- is reduced by the H2O2 to form the Au nanoparticles. In the second case, the xanthine oxidase acts as the reducing reagents to reduce AuCl4- forming Au nanoparticles. The interaction between CdTe quantum dots (QDs), AuCl4-, and Au nanoparticles resulted in the fluorescence changes of CdTe QDs, allowing the detection of glucose and xanthine. The effects of Au nanoparticles and AuCl4- on the fluorescence of CdTe QDs were discussed. A model was developed to explain the mechanism of the CdTe QDs fluorescence changes by biocatalytic growth of Au nanoparticles. The difference in the Stern-Volmer quenching constant between AuCl4- and Au nanoparticles is the dominant factor for the CdTe QDs fluorescence changes. The developed method provides low limits of detection, wide linear ranges, and detection wavelengths in the NIR region and can be easily extended to other substrate/oxidase systems.