Manganese(II)-doped zinc/germanium oxide nanoparticles as a viable fluorescent probe for visual and time-resolved fluorometric determination of ascorbic acid and its oxidase

A method is described for the determination of ascorbic acid (AA) in complex biological fluids. It based on maganese(II)-doped zinc/germanium oxide nanoparticles (Mn@ZnGe NPs) with appealing time-resolved phosphorescence (TRP). TRP can provide a background-free reporter signalin analytical methods. The absorption of AA overlaps the excitation band of Mn@ZnGe NPs at 254nm. This reduces the intensity of fluorescence via an inner filter effect (IFE) with increasing concentration of AA. Typical experimental conditions include an emission peak at 536nm, a delay time of 50s and a counting time of 2ms. This method can detect AA in a range of 5-500M with a 0.13M limit of detection. If AA is oxidized by the enzymeAA oxidase (AAOx), dehydroascorbic acid will be formed which doesn't absorb at 254nm. Hence, the IFE cannot occur and fluorescence is not reduced. The strategy can be used to quantify AAOx in the activity range of 1-4UmL(-1). By using a handheld UV lamp and a smart phone with a color-scanning feature, the feasibility for visual detection and real-time/onsite quantitative scanometric monitoring of AA and AAOx is demonstrated.