Title

Semiconductor quantum dots: Surface chemistry, surface modification and applications

Date of Award

2005

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Chemistry

First Committee Member

Roger M. Leblanc, Committee Chair

Abstract

Semiconductor quantum dots (QDs) have captivated scientists and engineers over the past two decades due to their fascinating optical and electronic properties that are not available from either isolated molecules or bulk solids. Nanoscience, the study of materials with nanometer-scale dimensions, has revealed that their properties are strongly dependent on the particle size. Nanotechnology has recently aimed to utilize these unique properties to create useful nanoscale devices. Because the size-dependent properties of quantum dots are so pronounced in fluorescence, their use as biological probes has attracted considerable attention. Indeed, QDs are often used as a model system for nanoscience, and have become one of the first commercial applications of nanotechnology. Thus, the fundamental research on the surface properties of QDs is of great importance in the field of nanotechnology.The surface chemistry behavior of the (CdSe)ZnS/TOPO and CdSe/Thiol QDs at the air-water interface was carefully examined by various physical measurements. The surface pressure-area isotherms of the Langmuir films of both types of QDs gave the average diameter which matched the value determined by TEM measurements. Topographic study of the Langmuir films of both QDs revealed the 2D aggregation during the early stage of the compression process. The stability of the Langmuir film of the (CdSe)ZnS/TOPO QDs was tested by two different methods, the compression/decompression cycle and the kinetic measurements, both of which indicated that TOPO capped (CdSe)ZnS QDs can form stable Langmuir films at the air-water interface. Langmuir-Blodgett (LB) film of the (CdSe)ZnS/TOPO QDs were prepared on quartz slides at different surface pressures and characterized by photoluminescence (PL) spectroscopy. The linear increase of the PL intensity with the increase of the number of layers deposited onto the quartz slide implied a homogeneous deposition of the Langmuir film.The bioconjugate of (CdSe)ZnS QDs and organophosphorus hydrolase (OPH) is introduced and applied to detect the pesticide paraoxon. The OPH was coupled to (CdSe)ZnS core-shell QDs through electrostatic interaction. Detectable secondary structure changes were observed by CD spectroscopy when the OPH/QDs bioconjugate was exposed to paraoxon. A quenching of the photoluminescence (PL) of the bioconjugate was observed in the presence of paraoxon, the mechanism of which was discussed in term of enzymatic kinetics. (Abstract shortened by UMI.)

Keywords

Health Sciences, Toxicology; Chemistry, Biochemistry; Chemistry, Physical

Link to Full Text

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