In Situ Enzymatically Generated Photoswitchable Oxidase Mimetics and Their Application for Colorimetric Detection of Glucose Oxidase

In this study, a simple and amplified colorimetric assay is developed for the detection of the enzymatic activity of glucose oxidase (GOx) based on in situ formation of a photoswitchable oxidase mimetic of PO43--capped CdS quantum dots (QDs). GOx catalyzes the oxidation of 1-thio--d-glucose to give 1-thio--d-gluconic acid which spontaneously hydrolyzes to -d-gluconic acid and H2S; the generated H2S instantly reacts with Cd2+ in the presence of Na3PO4 to give PO43--stabilized CdS QDs in situ. Under visible-light ( 400 nm) stimulation, the PO43--capped CdS QDs are a new style of oxidase mimic derived by producing some active species, such as h(+), (OH)-O-center dot, O-2(center dot-) and a little H2O2, which can oxidize the typical substrate (3,3,5,5-tetramethylbenzydine (TMB)) with a color change. Based on the GOx-triggered growth of the oxidase mimetics of PO43--capped CdS QDs in situ, we developed a simple and amplified colorimetric assay to probe the enzymatic activity of GOx. The proposed method allowed the detection of the enzymatic activity of GOx over the range from 25 g/L to 50 mg/L with a low detection limit of 6.6 g/L. We believe the PO43--capped CdS QDs generated in situ with photo-stimulated enzyme-mimicking activity may find wide potential applications in biosensors.