CdSe−ZnS Quantum Dots as Resonance Energy Transfer Donors in a Model Protein−Protein Binding Assay

Specific binding of biotinilated bovine serum albumin (bBSA) and tetramethylrhodamine-labeled streptavidin (SAv−TMR) was observed by conjugating bBSA to CdSe−ZnS core−shell quantum dots (QDs) and observing enhanced TMR fluorescence caused by fluorescence resonance energy transfer (FRET) from the QD donors to the TMR acceptors. Because of the broad absorption spectrum of the QDs, efficient donor excitation could occur at a wavelength that was well resolved from the absorption spectrum of the acceptor, thereby minimizing direct acceptor excitation. Appreciable overlap of the donor emission and acceptor absorption spectra was achieved by size-tuning the QD emission spectrum into resonance with the acceptor absorption spectrum, and cross-talk between the donor and acceptor emission was minimized because of the narrow, symmetrically shaped QD emission spectrum. Evidence for an additional, nonspecific QD−TMR energy transfer mechanism that caused quenching of the QD emission without a corresponding TMR fluorescence enhancement was also observed.