Gold Nanoparticles

Nanoparticles have become important materials in modern technologies compared with their bulk analogues not only as a result of their excellent structural features but also as a result of their unusual functional attributes. Most of the bulk materials we use in everyday life such as steel or sand are composed of micrometer scale particles. The properties of a material are related to the bonding/interactions acting between and within its constituent units. Scientists are discovering new ways to reduce the size of constituent particles of every material to the nanometer length scale (to produce nanomaterials) as it gives them one way to modify the properties of materials. Besides reduction in size, controlling chemical composition at such smaller length scales also can result in new properties. Advances in nanofabrication and synthesis provided new ways to manipulate the size of materials. In gold, the changes in size of constituent particles to nanometer scale result in drastic modification of its properties. Such changes in dimension can be realized even with simple chemical manipulations, and such modified gold is extremely stable allowing diverse phenomena to be examined. Therefore, gold has been a material of choice for nanoscience enthusiasts. Importantly, these changes can be examined with the simplest of tools available in any laboratory that took GNP research to every nook and corner of the world. Gold has been an object fascinating to knowledge-seekers since prehistoric times, and applications of GNPs have grabbed the attention of researchers in the information age. Systematic efforts in the synthesis and evaluation of properties of GNPs have exposed new avenues to some very unique and exciting capabilities. Although this article provides an outline of the present understanding of GNPs, as a result of space constraints, it will only briefly touch on the historical aspects and theoretical understanding of the optical and spectroscopic properties. For more detailed information, we direct the readers to several books and review articles (1–14).