Comparative efficiency of energy transfer from CdSe-ZnS quantum dots or nanorods to organic dye molecules

Fluorescence resonance energy transfer (FRET) in conjugates of CdSe-ZnS semiconductor nanocrystals of different shapes (FRET donors) and an Alexa Fluor organic dye (FRET acceptors) is examined. The dye molecules are chemically conjugated with quantum dots (QDs) or nanorods (NRs) in dimethyl sulfoxide colloidal solutions, and FRET efficiency in the purified conjugates is measured. The FRET from NR to a single dye molecule is less efficient than that of the QD-dye conjugates and this effect is explained in terms of distance-limited energy-transfer rate in the case of a point-like acceptor and extended donor dipoles. However, the larger surface area of NRs allows for many more dye acceptors to be bound, and the total FRET efficiency in NR-dye conjugates approaches those of QD-dye conjugates.