Bifunctional gold nanoclusters enable ratiometric fluorescence nanosensing of hydrogen peroxide and glucose.

The accurate quantification of hydrogen peroxide (HO) and glucose is essential significance in clinical diagnosis. Herein a selective and sensitive ratiometric fluorescent nanosensor was developed for the determination of HO and glucose by integrating peroxidase-like catalytic and fluorescent bifunctional properties of glutathione protected gold nanoclusters (GSH-AuNCs). The GSH-AuNCs exhibit inherent peroxidase-like activity and accelerate the decomposition of HO into hydroxyl radicals. The produced hydroxyl radicals oxidize terephthalic acid (TA), a typical non-fluorescent substrate of peroxidase, to a highly fluorescent product hydroxyterephthalate (TAOH). Upon excitation with single-wavelength at 315 nm, dual-emission fluorescence peaks were recorded at 430 and 600 nm simultaneously. The fluorescence signal of TAOH at 430 nm continuously increased with increasing the concentration of HO while the fluorescence signal of GSH-AuNCs at 600 nm remained unchangeable. Based upon on these facts, a ratiometric fluorescent nanosensor was fabricated for HO assay with TAOH as response unit and GSH-AuNCs as reference, respectively. By converting glucose into HO with catalytic oxidation of glucose oxidase (GOx), this nanosensor was further exploited for glucose assay. Under the optimum conditions, the detection limits of 10 nmol/L HO and 20 nmol/L glucose were acquired. The relative standard deviations were less than 5% for both HO and glucose (5.0 μmol/L solution, n = 11). The practicability of the nanosensor was verified by the determination of glucose in human serum samples. This nanosensor can be easily expanded as a general platform for the detection of other substances involving HO produced or consumed.