Semester

Spring

Date of Graduation

2012

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Nianqiang Wu.

Abstract

Gold nanoparticles (GNPs) exhibit unique optical properties, depending on the particle size, geometrical shape, and medium refractive index and interparticle interactions, etc. Among these optical properties, localized surface plasmon resonance (LSPR) has significant effects on the electromagnetic field around the GNPs. The LSPR-induced electromagnetic field enhancement is beneficial to the surface-enhanced Raman scattering (SERS) and energy transfer processes. This dissertation deals with the effects of LSPR on SERS and energy transfer between CdSe/ZnS quantum dots and GNPs. Specifically, the research aims to gain better understanding of (i) the electromagnetic enhancement induced by charge transfer from GNP to molecules, (ii) the SERS in various shaped gold nanostructures, (iii) the energy transfer from quantum dots (QDs) to GNPs, and (iv) SERS- and energy transfer-based sensing platforms for detection of chemical species and biomolecules.;The SERS of two different types of molecules on GNPs has been investigated. It has been found that the aromatic molecules such as p-mercaptobenzenoic acid (MBA) exhibit stronger SERS activity than the linear-chain molecules such as 3-mercaptopropionic acid (MPA) and L-cysteine (Cys). The difference in the SERS activity is attributed to the distinct electronic structures among these molecules. The electron transfer from GNPs to MBA can occur under laser excitation. The transferred electron can effectively strengthen the electromagnetic field around GNPs, leading to electromagnetic enhancement of SERS.;Furthermore, the SERS in different shaped gold nanostructures (gold nanospheres (GSPs), nanorods (GRDs) and nanostars (GSTs)) has been investigated. GSTs show the highest SERS enhancement. Three-dimensional finite-difference time domain (FDTD) method has been used to simulate the electric field distribution. It is demonstrated that the electric field can be concentrated around two ends of GRDs and these tips of GSTs, and the GSTs show the highest maximum electric field intensity under both excitations of 532 nm and 785 nm. It is suggested that the shape of gold nanostructures governs the SERS difference among GSPs, GRDs and GSTs. In addition, gold malachite green isothiocyanate(MGITC) SiO 2 sandwiched nanostructures have been prepared. SiO2 encapsulation not only improves the colloidal and LSPR stability but also endows excellent reproducibility of SERS signal due to the prevention of MGITC leaking. It is demonstrated that the GST MGITC SiO2 can be used for monitoring of DNA hybridization and for detection of adenosine triphosphate (ATP) with high sensitivity.;Energy transfer between the CdSe/ZnS QDs and GNPs was investigated. The 3 nm GNPs without observable LSPR absorption quench the fluorescence emission of the QDs following a nanometal surface energy transfer (NSET) while the large sized GNPs quench the fluorescence emission via the Forster resonance energy transfer (FRET) with a 1/d6 distance dependence. The quenching efficiency of fluorescence emission increases with the increase of particle size. It is suggested that the involvement of LSPR and the increasing spectral overlap between the LSPR band and the fluorescence emission spectra are responsible for the enhanced energy transfer from CdSe/ZnS quantum dots to GNPs.;An ultra-sensitive fluorescent sensor based on the quantum dot-DNA-gold nanoparticle ensemble has been developed for detection of Hg(II). When Hg(II) ions are present in the aqueous solution containing the DNA-conjugated quantum dots (QDs) and GNPs, the QDs and the GNPs are brought into the close proximity, which enables the nanometal surface energy transfer (NSET), quenching the fluorescence emission of the QDs. This nanosensor exhibits a limit of detection of 0.4 ppb and 1.2 ppb toward Hg(II) in the buffer solution and in the river water, respectively.

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