Research Article Seed-Mediated Growth of Gold Nanorods: Limits of Length to Diameter Ratio Control Christopher J. Ward, Robert Tronndorf, Alicia S. Eustes, Maria L. Auad, and Edward W. Davis Department of Polymer and Fiber Engineering, Auburn University, Auburn, AL 36849, USA Correspondence should be addressed to Edward W. Davis; ewd0001@auburn.edu Received 11 February 2014; Revised 16 March 2014; Accepted 16 March 2014; Published 14 April 2014 Academic Editor: William W. Yu Copyright © 2014 Christopher J. Ward et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Te efects of the seed reaction conditions on the two-step seed-mediated growth of gold nanorods and the efect of gold and reducing agent content in the growth solution were evaluated. Results indicate that the reaction conditions used to produce the seeds have a signifcant impact on the aspect ratio of the gold nanorods produced. Increasing the concentration of gold or the reaction temperature in the seed production step results in lower length to diameter (aspect ratio) gold rods. In addition, the amount of prepared seed added to the growth solution impacts the rod aspect ratio, with increasing amounts of seed reducing the aspect ratio. Te efects of reducing agent, ascorbic acid (AA), and gold content of the growth solution on the aspect ratio of the produced rods are strongly interrelated. Tere exists a minimum ascorbic acid to gold concentration below which rods will not form; however, increasing the ratio above this minimum results in shorter rods being formed. Characterization of nanorod growth is performed by UV-vis-NIR spectrophotometry and transmission electron microscopy (TEM). 1. Introduction In metallic nanoparticles, the mean free path of electrons under standard conditions is generally about 10 to 100 nm. As a result, metal nanoparticles display signifcantly diferent properties than either individual atoms or bulk materials [1]. One of the frst applications for metallic nanoparticles was as a nanocatalyst [2]. Since then, other industries and processes potentially impacted by nanotechnology have been identifed. Tese industries and processes include petroleum cracking, controlled release, mechanical enhancement, fre- proofng, and control of gas permeation rates [3–8]. Gold nanoparticles, in particular, have been shown to be simple to functionalize and stable under oxidative environments, making them particularly attractive for biomedical applica- tions such as biomedical sensing and cancer treatment and as carriers for bioactive compounds [9–13]. Gold nanoparticles are relatively easy to synthesize in the spherical form [13, 14]; nanorods are signifcantly more difcult to produce. However, changing the shape of gold nanoparticles alters their interaction with resonant electro- magnetic radiation, leading to potential advances in the feld of sensors, contrast agents for optical detection, drug delivery, and cancer cell diagnostics [9]. In particular, the peak absorption can be varied across a wide range of frequencies by changing the length to diameter ratio. Both Kityk et al. and Ozga et al. have demonstrated nonlinear optical properties of Au doped thin flms [15, 16]. In these studies the surface plas- mon resonance of the gold particles was shown to increase local charge transfer and determine the second order optical efects. In the last 20 years, several synthesis routes have been developed for the production of gold nanorods, including multiple template methods, variations of electrochemical methods, and photochemical methods [2, 12, 14]. However, these routes sufer from low yield of the nanorods, damage to the nanorods during production, and many times, low quality products due to a lack of substantial control over the growth. One of the simplest methods for production of gold nanorods Hindawi Publishing Corporation Journal of Nanomaterials Volume 2014, Article ID 765618, 7 pages http://dx.doi.org/10.1155/2014/765618