The Gold Nanoparticle. Nanoparticles have been used extensively for modern biotechnological applications due to their dispersibility, surface area and ability to be utilized with various devices.1 However, there is an extensive history of the use of metallic nanoparticles to produce art.2,3 The Lycurgus cup, circa 4th century Rome, is an example of how gold and silver nanoparticles were used to create a dichromic effect, in which the glass reflects one color and transmits the light of another. The glass of Lycurgus’s cup is green when viewing the glass from the outside but red when viewed with a light source on the inside. The dichromic effect is due to the varying sizes of the nanoparticles since metallic nanoparticles demonstrate different optical properties depending on their sizes.3 The use of AuNPs has diversified to include biotechnological advancements. During the 20th century, AuNPs started to be used for more scientific applications, including conjugation to attached enzymes for biocatalysts4, biosensing5, biofuels6, disease diagnosis7, and drug delivery7. Advancements in functionalization of AuNPs have led to an expansion of their potential in biomedical application, which has led to many in vitro and in vivo studies using AuNPs. Biodistribution in vivo studies in mice determined clearances and toxicities of various bioconjugates of AuNPs used for therapeutics and diagnostics. These AuNP conjugates tend to be deposited in the liver, spleen and other organs.7 Furthermore, it was found that AuNPs with larger diameters tend to have a slower clearance rate in vivo,7 making it imperative to study how varying sizes of AuNP effects the characteristics of bioconjugates in vitro and in vivo. The same study also tested conjugated to necrotic receptor proteins that would target cancer cells within mice. The conjugation of enzyme to the gold nanoparticles was important because it allowed for the tumor to be located on X-rays. However, these diagnostic techniques never reached clinical trials due to the slow clearance rates of AuNPs.7 Another unique characteristic of AuNPs is their surface plasmon resonance (SPR). SPR is an optical technique used to detect molecular reactions by measuring the resonant oscillations of conduction electrons at the interface of both negatively and positively charged material that is stimulated by incident light.8,9 The SPR absorption of AuNPs varies depending on the size and shape of the AuNP and changes depending on the dielectric constants of the con...
