Date on Master's Thesis/Doctoral Dissertation

12-2012

Document Type

Master's Thesis

Degree Name

M. Eng.

Department

Bioengineering

Committee Chair

Gobin, Andre Mathura

Subject

Gold; Nanoparticles; Nanochemistry

Abstract

Gold nanoparticles (AuNPs) have attracted enormous attention in the field of nanotechnology for applications such as, immunoassay, drug delivery, contrast enhancement and tumor therapy. The typical range of gold nanoparticles varies from 1– 150 nm; there are many different subtypes of AuNPs mainly based on size, shape, and optical properties including: gold nanospheres, nanorods, nanocages, and nanoshells. The main advantage of using gold nanoparticles is the large surface-to-volume ratio; this will allow the particles to be functionalized with drugs and/or targeting agents to create many novel applications. Many AuNPs have another advantage as well, they can be fabricated to either absorb or scatter light in the visible to near-infrared (nIR) region of the spectrum. Current research, using gold nanoparticles, mainly focuses on taking advantage of the nIR window. In biomedical research the nIR window is very important; nIR light has minimal interference with tissue and only affects samples which absorb nIR light, which enables minimally invasive imaging and treatment. Specifically, gold/gold sulfide nanoparticles (GGS) have been introduced for many applications compared to silica-gold nanoshells due to the smaller size of particles. This project is focused on a novel purification/high yield process of GGS nanoparticles using chloroauric acid (HAuCl4) and sodium thiosulfate (Na2S2O3), with desired nIR peak that can be used for therapeutic applications. By combining the traditional published methods for 1-step self-assembly of GGS nanoparticles and dialysis techniques simultaneously, a new method for production of gold / gold-sulfide nanoparticles has been established in this research project which we call DiaSynth. In this process the equilibrium of the reaction is shifted to favor the formation of nIR absorbing particles. This technique minimizes production of gold nanoparticles with 530 nm resonance (colloidal gold), resulting in populations of nanoparticles that require minimum further processing for use as a therapeutic agent. The colloidal gold is considered a contaminant, formed during the self-assembly process, which are traditionally removed via multi-step centrifugation. We define a ratio of the absorbance of peaks, RnIR/Au ; this is based on the peak absorbance in of the nIR region (700 – 900 nm) relative to the colloidal gold peak (~530 nm) as a relative measure of the quality of nIR particles. The current method for producing nIR GGS, based on a single step procedure, results in a poor ratio, RnIR/Au = 0.7 – 1.0. The DiaSynth method utilizes a shift in kinetics via removal of smaller ions and other products during the reduction of gold and sulfur. This method has allowed us to increase the yield of as made product to have an RnIR/Au = 1.7 – 2.0. In comparison, purification by centrifugation results in great loss of particles during each step to achieve similar ratios. At a ratio of 1.7 – 2.36, no centrifugation is needed to separate out colloidal gold, resulting in reduced production costs and higher quality product.

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