Quantum dot-modified paper-based assay for glucose screening

The article describes a simple optical assay for glucose. It is based on the use of paper spots loaded with colloidal CdSe/ZnS quantum dots (Q-dots) and the enzyme glucose oxidase (GOx). Circular paper sheets were uniformly loaded with Q-dots and then displayed strong fluorescence under a UV lamp (365 nm exCitation). The action of GOx causes the production of H2O2 which, after a typical exposure time of 20 min, causes fluorescence intensity to be quenched. To obtain a reading, the paper sheets were photographed under 365 nm excitation using a digital camera. Several parameters, including the amount of Q-dots, sample pH, and amount of GOx were optimized to maximize the response to glucose. The paper-based assay showed a sigmoidal-shaped response with respect to the glucose concentration in the 5-200 mg center dot dL(-1) range (limit of detection of 5 mu g center dot dL(-1)), demonstrating their potential use for biomedical applications.