Date

2014

Document Type

Dissertation

Degree

Doctor of Philosophy

Department

Physics

First Adviser

Rotkin, Slava V.

Other advisers/committee members

Dierolf, Volkmar R.; Biaggio, Ivan; Stavola, Michael J.; Jagota, Anand

Abstract

The studies of Single Wall Nanotube (SWNT) complexes may be important for development of bio-compatible materials as well as future generations of electronic and optical devices. For bio-marker applications the complexes of SWNTs with Rare Earth ions (REIs) are of large interest. Signicant acceleration of the REI photoluminescence (PL) decay rate was observed in water solutions of complexes of rare earth ions, Tb and Eu, with SWNTs. We propose that the time-resolved PL spectroscopy data are explained by a fluorescence resonance energy transfer (FRET) between the REIs and SWNTs. Similar FRET was also studied between two REIs (in the absence of nanotubes). In these experiments FRET was directly confirmed by detecting the induced PL of the energy acceptor, Eu ion, under the PL excitation of the donor ion, Tb. FRET efficiency reached 7% in the most saturated solution, where the distance between the unlike REIs is the shortest. Using this as a calibration experiment, a comparable FRET was measured in the mixed solution of REIs with SWNTs wrapped with DNA. From the FRET efficiency of 10% and 7% for Tb and Eu, respectively, the characteristic distance between the REI and SWNT/DNA was obtained as 15.9 A independent of concentration of species. Such a short distance suggests that the complexes are formed. Coulomb attraction between the REI and the ionized phosphate groups of the DNA is proposed as the mechanism of the complex formation. SWNT samples often made with the help of surfactants other then DNA. For example, DOC was successfully used to disperse SWNTs in water solutions. Here the interactions of REIs with DOC were studied. Formation of stable complexes of REIs and DOC and their evolution in a crowded environment of silica hydrogels are described. By comparing the behaviour of REI complexes in bulk solution and small compartments inside the hydrogel the nature of the 5x-longer lifetime of REIs was understood. The effect is due to binding of REI to surfactant molecules followed by formation of a closed shell micelle, completely or partially screening REI from the water molecules. Formation of DOC micelles is accompanied by diffusion of REI between/through the micelles. The process is shown to be slowed down in the crowded environment of a hydrogel.Multi-wavelength excitation was applied to study the interaction of SWNT with the DNA, excited by UV light. An additional non-radiative recombination channel, created by the photo-ionized DNA was found. In two-color excitation scheme, by combining a standard visible excitation with an additional UV pump, Gvis + GUV , which can be tuned to the resonant excitation of ssDNA, unexpected quenching of SWNT PL was observed for all SWNT species presented in solution.

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