Colloidal quantum dots (QDs) are now commercially available in a biofunctionalized
form, and Förster resonance energy transfer (FRET) between bioconjugated dots and
fluorophores within the visible range has been observed. We are particularly interested
in the far-red region, as from a biological perspective there are benefits in pushing
to ∼700 nm to minimize optical absorption (ABS) within tissue and to avoid cell autofluorescence.
We report on FRET between streptavidin- (STV-) conjugated CdTe quantum dots, Qdot705-STV,
with biotinylated DY731-Bio fluorophores in a donor-acceptor assay. We also highlight
the changes in DY731-Bio absorptivity during the streptavidin-biotin binding process
which can be attributed to the structural reorientation. For fluorescence beyond 700
nm, different alloy compositions are required for the QD core and these changes directly
affect the fluorescence decay dynamics producing a marked biexponential decay with
a long-lifetime component in excess of 100 nanoseconds. We compare the influence of
the two QD relaxation routes upon FRET dynamics in the presence of DY731-Bio.