Emerging non-traditional Forster resonance energy transfer configurations with semiconductor quantum dots: Investigations and applications

Forster resonance energy transfer (FRET) configurations incorporating colloidal semiconductor quantum dots (QDs) have proven to be a valuable tool for bioanalysis and bioimaging. Mirroring well established techniques with only fluorescent dyes, traditional FRET configurations with QDs have involved single-step energy transfer to organic dye acceptors mediated by biomolecular interactions. Here, we review recent progress in characterizing non-traditional FRET configurations incorporating QDs and their application to challenges in biosensing, energy conversion, and fabrication of optoelectronic devices. Such non-traditional FRET configurations with QDs include substitution of organic dyes with lanthanide complexes, polypyridyl transition metal complexes, azamacrocyclic metal complexes, graphene (oxide), carbon nanotubes, gold nanoparticles, and dyes exhibiting photochromism. Other non-traditional configurations of interest include FRET relays (with or without organic dyes) that feature multiple sequential energy transfer steps, and thin films of QDs where discrete FRET pairs cannot be defined, including those where QDs are layered in a size-sequential or rainbow structure. The calculation of FRET efficiencies and donor-acceptor distances in the above configurations are reviewed, as are distance scaling relationships for non-zero dimensional acceptors, and the related dipolar energy transfer mechanism, nanosurface energy transfer (NSET). To illustrate the utility of non-traditional QD-FRET configurations, we highlight examples of optically switchable probes, photonic wires, time-gated and multiplexed probes for biosensing, enhanced light harvesting in QD and dye sensitized solar cells (DSSC), and colour conversion in light emitting diodes (LEDs). We close by providing a perspective on how the combined utility of these non-traditional QD-FRET configurations may be useful for engineering complex nanoscale devices in the future. (C) 2013 Elsevier B.V. All rights reserved.