Spectrally resolved energy transfer using quantum dot donors: Ensemble and single-molecule photoluminescence studies

The photoluminescence spectrum of a quasimonodisperse semiconductor quantum dot (QD) population is composed of a continuum of extremely narrow single QD spectra. This is due to inhomogeneities in nanocrystal size within a population and the color-size dependency imposed by effects of carrier quantum confinements. We take advantage of this population heterogeneity to gain a unique insight into the fluorescence resonant energy transfer (FRET) process between a QD donor and proximal dye-labeled protein acceptors. Our steady-state, time-resolved ensemble and single-QD studies demonstrate that the spectral dependency of the energy transfer rate matches the acceptor absorption spectrum as predicted by Forster formalism. This allows ratiometric FRET measurements based on the QD donor emission.