Date of Graduation

5-2015

Document Type

Thesis

Degree Name

Master of Science in Microelectronics-Photonics (MS)

Degree Level

Graduate

Department

Microelectronics-Photonics

Advisor/Mentor

Jin-Woo Kim

Committee Member

Steve Tung

Second Committee Member

Joshua Sakon

Third Committee Member

Matthew Patitz

Fourth Committee Member

Rick Wise

Keywords

Pure sciences, Applied sciences, Near-infrared, Physical chemistry, Plasmonics

Abstract

Near-infrared (NIR) responsive nanoparticles (NPs) like gold nanorods (GNRs) are important in biomedical fields because of their transparency for biological tissues. Although GNRs are sought after as contrast agents for theranostics in cancer studies, capping ligands like cetyltrimethylammonium bromide (CTAB) for the GNR synthesis are toxic for biological tissues. The need for an alternative to toxic GNRs is of interest to alleviate the problem.

This work aimed to optimize the synthesis of NIR responsive nanosphere composites (NSCs) by inertial force (g-force) using colloidal gold NPs as model, elucidate the mechanism for the NSC formation, and study their detailed physicochemical characteristics. The inertial force-driven synthesis of NSCs resulted in NP composites of two NPs combined together with little or no gaps between them. The synthesis process was simple and cost-effective, and did not require the use of a toxic chemical like CTAB. The formed NSCs showed rod-like characteristics, which are typified by the evolution of absorption spectra from the transverse to longitudinal mode.

Factors, such as NP sizes, g-force, capping ligand, and electrostatic force, were found to influence NSC formation. Variations of g-forces showed that there was a critical g-force to form NSCs at fixed centrifugation duration and those critical g-force values were inversely proportional to centrifugation duration. This implied that both g-forces and the duration of NPs' exposure to g-forces should be considered to investigate optimal reaction conditions for maximal NSC yields and detailed mechanisms of their formation. When three combinations of gold NPs with different sizes were used, NSCs with NPs of two different sizes (hetero-dimers) were formed and their NIR plasmonic responses shifted further to the right compared to those of homo-dimers, demonstrating high promise of tuning NIR plasmonic responses of NSCs. Evaluating capping ligands of NPs with different charge characteristics, only absorbance spectra of NPs with charged ligands evolved from the transverse to longitudinal mode, confirming that NP surface charge characteristics played important roles in the NSC formation. Although more works remain and challenges ahead, these new nanomaterials by the inertial force-driven technique showed high potential to be an effective alternative to many existing nanoparticles, particularly GNRs.

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