Date of Graduation

8-2014

Document Type

Thesis

Degree Name

Master of Science in Biological Engineering (MSBE)

Degree Level

Graduate

Department

Biological and Agricultural Engineering

Advisor/Mentor

Kim, Jin-Woo

Committee Member

Zaharoff, David A.

Second Committee Member

Patitz, Matthew J.

Third Committee Member

Sakon, Joshua

Keywords

Gold nanosphere dimer; Nanoparticle synthesis; Nanotechnology; Plasmonic materials; Self-assembly; Surface plasmon resonance

Abstract

The morphology and composition of a nanoparticle (NP) play a critical role in determining the NP's properties and function. To date, researchers have created a myriad of NPs of different shapes, sizes, and compositions with interesting attributes and applications ushering a revolution in medicine, electronics, microscopy, and microfluidics.

In this study, gold (Au) nanosphere dimers (NSDs) have been synthesized through a novel self-assembly method. These particles were created from Au NPs mono-dispersed in aqueous solution via a process of centrifugation and capping agent replacement. Au NSDs consist of two Au NPs combined together with minimal gaps between them. Optical spectral analysis showed two wavelength bands: a wavelength band around 520 nm, which is attributed to the transverse surface plasmon resonance (SPR), and another wavelength in the near-infrared (NIR) region with a peak around 650 nm, which is attributed to the longitudinal SPR, as in the case of Au nanorods (GNRs). Synthesis of Au NSDs does not require toxic precursors, such as cetyltrimethylammonium bromide (CTAB) when making GNRs, suggesting that Au NSDs could be more clinically applicable nanotheranostic agents for molecular imaging and therapy as well as other applications such as drug delivery.

It is hypothesized that G-Force polarizes the NPs, which reduces the repulsive electrical double layer, allowing attractive van der Waal's forces to dominate and bring the surfaces in contact, causing surface reconstruction at the junction. The presence of capping agents, such as citrate, on the NP surface plays a key role in the electrostatic forces that bind the two spheres into a single, stabilized dimer by preventing further NP aggregation. Other popular NPs, including platinum (Pt) and silver (Ag) NPs were also investigated and showed significant shifts in SPR, suggesting that this method can be generalized across NPs of different compositions.

Although the detailed mechanisms and the applicability to other NPs with different shapes and/or compositions remain to be determined, considering its simplicity, controllability, and versatility, this G-Force driven technique could be implemented to assemble noble NP dimers with unique opto-electro-chemical properties for many applications, including optoelectronics, nanophotonics, biosensing, biosecurity, and nanomedicine.

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