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

The accurate quantification of hydrogen peroxide (H₂O₂) and glucose is essential significance in clinical diagnosis. Herein a selective and sensitive ratiometric fluorescent nanosensor was developed for the determination of H₂O₂ 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 H₂O₂ 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 H₂O₂ while the fluorescence signal of GSH-AuNCs at 600 nm remained unchangeable. Based upon on these facts, a ratiometric fluorescent nanosensor was fabricated for H₂O₂ assay with TAOH as response unit and GSH-AuNCs as reference, respectively. By converting glucose into H₂O₂ 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 H₂O₂ and 20 nmol/L glucose were acquired. The relative standard deviations were less than 5% for both H₂O₂ 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 H₂O₂ produced or consumed.