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Experimental investigation of fluorescence resonance energy transfer using quantum dots

Quantum dots (QDs) are light emitting nanoscale semiconductor crystals with novel optical properties that are markedly different from the conventional organic dyes. Their size tunable emission, broad absorption and resistance to photo- and chemical degradation have afforded a new route to biomolecular studies, especially in long term live cell imaging that is hardly feasible with the utility of organic dyes. With the advent of highly luminescent core-shell QDs with quantum yields over 0.5, sensitive and robust optical sensing assays can be realised in which organic dyes rarely have much success. In this research, I incorporated these core-shell QDs of variable core compositions that are tailored to emit in the visible and the far-red spectral regimes into the development of multiplexed QD-dye assays via a ligand-receptor binding scheme. The close proximity of QDs to energetically resonant dyes is commensurate to Forster/fluorescence resonance energy transfer (FRET) from which course we set to evaluate the potential of QDs as energy donors through the use of the steady state and the time-resolved spectroscopic techniques. Both approaches not only complement each other but also can provide substantive evidence in verifying the suitability of QDs in the design of FRET based assays where the efficiency of energy transfer is generally governed by the donor-acceptor separation and in turn, the size of QDs. Henceforth from that notion, the relevance of FRET efficiency to the proximity relationships in QD-dye self-assemblies are examined theoretically as a function of acceptor-to-donor ratio. Besides the experimental studies of QDs in proximity-induced energy coupling, I take the initiative to develop a theoretical treatment of the multilayer structure of QDs based on the parabolic band approximation to offer a simple analytical route to investigate the size dependency of energy gap and the localisation of carriers which in essence underpin the QD optical behaviour. The analyses are further extended to the type-II QDs with a slight different band profile in which the conduction and the valence band extrema centre on different regions of the heterostructure leading to the separation of carriers and thus, contributing to the distinctive optical characteristics that strongly depart from typical type-I QDs.

Identiferoai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:584055
Date January 2007
CreatorsChong, Ee Zhuan
PublisherCardiff University
Source SetsEthos UK
Detected LanguageEnglish
TypeElectronic Thesis or Dissertation
Sourcehttp://orca.cf.ac.uk/54612/

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