Student Project Abstracts 2005 - Pluto - University of Washington

Synthesis and Analysis of Thiol-Stabilized NanoparticlesEddie HowellNorfolk State UniversityJoe Perry and Wojtek HaskePerry Lab, School of Chemistry and BiochemistryGeorgia Institute of TechnologyDr. Carl BonnerCenter for Materials ResearchNorfolk State UniversityINTRODUCTIONMetal nanoparticles have gained much interest in the scientificcommunity in recent years due to the unique optical andelectronic properties that these particles possess. Potential applicationsfor metal nanoparticles include biological imaging, threedimensionalmicrofabrication, and optical data storage. 1The primary obstacle scientists are currently trying to overcomeis identifying ways to manipulate the size, shape, and distributionsof these nanoparticles. A characteristic of all metalnanoparticles is that delocalized electrons exhibit collective oscillationsin an electric field. These collective oscillations are commonlyreferred to as plasmons. The particles can absorb energyfrom electromagnetic waves when the frequency is in resonancewith the plasmons. Large local electric fields are present near thenanoparticle surface. This effect is called near-field enhancementof the electric field. It has been shown in some cases that this nearfield enhancement can enhance the nonlinear optical properties ofmolecules near the surface of the nanoparticle.The first four weeks of this research project were spent atNorfolk State University working with Dr. Carl Bonner to findsuitable methods and reagents for synthesizing the silver nanoparticles.During the following five weeks in Dr. Perry’s research labat Georgia Tech the research project has involved the synthesisof silver nanoparticles with different thiol ligands on their surface.Polymer nanocomposite films were prepared using thesenanoparticles and their optical properties were investigatedMETHODSSynthesis of Silver NanoparticlesA single-phase method was used for synthesizing the silvernanoparticles which involves reducing silver ions with sodiumborohydride in the presence of thiol ligands (see Fig. 1 for the ligandsused). The process begins with making a solution of silvernitrate dissolved in ethanol. The desired amounts of thiol ligandswere then added to the solution. The ratio or type of ligands foreach batch was varied, but the silver to total thiol ratio was heldconstant at 3:1 for all batches. The solution was then placed in anice bath and stirred for 15 minutes. A solution of sodium borohydridedissolved in ethanol was then added dropwise to the silvernitrate solution and allowed to reflux for another 15 minutes. Theresulting solution was then placed in a freezer and allowed tosit overnight, causing the thiol-coated nanoparticles to precipitateout of the suspension and settle to the bottom of the flask. Thenanoparticles were then filtered and washed sequentially withethanol, distilled water, and acetone to remove any excess sodiumborohydride. The particles were dried in a vacuum oven at roomtemperature overnight.Figure 1. Thiol ligands used to coat the silver nanoparticles.CMDITR Review of Undergraduate Research Vol. 2 No. 1 Summer 2005 57