Ratiometric CdSe/ZnS quantum dot protein sensor.

We have created a platform for the ratiometric fluorescent sensing of targeted proteins by conjugating conjoined protein binding agent/organic dye ligands to water-soluble, emissive semiconductor quantum dots (QDs). The QD emission is tuned such that it may serve as an energy transfer donor to the dye acceptor. Upon exposure to the target proteins, these analytes bind to the surfaces of the QDs and change the microenvironments of the QD-bound dyes such that the emissive properties of the dyes are perturbed. The resulting alteration in the QD and dye fluorescence spectra creates a readout that is fully quantitative. The advantage of our methodology is that the detection of proteins is very fast as the platform is fully homogeneous, whereas the heterogeneous ELISA assay involves multiple steps with blocking agents and secondary reporters that ultimately complicate the process. The calculated detection limits for the two QD protein-sensing examples reported here are also competitive with the ubiquitous ELISA assay.