Ultrafast energy transfer from 3-mercaptopropionic acid-capped CdSe/ZnS QDs to dye-labelled DNA

Femtosecond-resolved fluorescence upconversion and picosecond-resolved spectroscopic measurements have been employed to confirm a highly efficient ultrafast FRET from MPA-capped CdSe/ZnS QDs to dye molecules attached to dodecamer DNA. It appears that hydrogen bonding is the associative mechanism between the MPA-capped QDs and DNA. High FRET efficiency of 92% together with the estimated donor–acceptor distance suggests that the adsorptive interactions between DNA and MPA-capped QDs result in a conformation in which DNA lies along the surface of the QD. Circular dichroism studies have been performed which reveal some perturbation in the native B-form of DNA in the nanobioconjugate.