Label-free and non-contact optical biosensing of glucose with quantum dots

We present a label-free, optical sensor for biomedical applications based on changes in the visible photoluminescence (PL) of quantum dots in a thin polymer film. Using glucose as the target molecule, the screening of UV excitation due to pre-absorption by the product of an enzymatic assay leads to quenching of the PL of quantum dots (QDs) in a non-contact scheme. The irradiance changes in QD PL indicate quantitatively the level of glucose present. The non-contact nature of the assay prevents surface degradation of the QDs, which yields an efficient, waste-free, cost-effective, portable, and sustainable biosensor with attractive market features. The limit of detection of the demonstrated biosensor is ~3.5 µm, which is competitive with existing contact-based bioassays. In addition, the biosensor operates over the entire clinically relevant range of glucose concentrations of biological fluids including urine and whole blood. The comparable results achieved across a range of cost-affordable detectors, including a spectrophotometer, portable spectrometer, and iPhone camera, suggest that label-free and visible quantification of glucose with QD films can be applied to low-cost, point-of-care biomedical sensing as well as scientific applications in the laboratory for characterizing glucose or other analytes.