Nanoparticles for Biomedical Applications

Particles with diameters in the range of 2 to 100 nm, so-called nanocrystalline materials, have become a major interdisciplinary area of research during recent decades. In fact, since the seventeenth century, noble metallic nanomaterials, though not understood, have been obtained and used to give rise to a brilliant rose color throughout Europe in stained glass windows of cathedrals and by the Chinese in coloring vases and other ornaments [1, 2]. The scientific preparation of nanoparticles dates back to the nineteenth century, with Faraday reporting the preparation of colloids of relatively monodispersed gold nanoparticles. The scientists who major in nanoscience and nanotechnology should appreciate the inventors who designed transmission electron microscopy (TEM). The high-resolution TEM (HRTEM) and low-resolution (LRTEM) allow one to observe a substance at a nanometer scale directly. The magic machines make it possible to investigate the nanomaterials with respect to size, size distribution, shape evolution, and shape uniformity and even the structure. The past couple of decades have witnessed an exponential growth of activities in this field worldwide, driven both by the excitement of understanding new science and by the potential hope for applications and economic impacts. Indeed, many efforts have been devoted to investigation into the synthesis, characterization, and application of nanomaterials. In general, nanomaterials can be classified into three groups: zero-dimensional materials, so-called nanoparticles, with variations in shape and diameter, one-dimensional materials, including nanorod and nanowire, and two-dimensional materials, including nanobelts, nanodisks, films, and nanosheets. Herein we focus on the nanoparticles (NPs), especially the metallic ones. The intense interest in the metallic NPs derives from their unique chemical and electronic properties arising from the small volume to big surface area ratio and the separation in the electronic energy level. The change in the properties at this length scale from their bulk counterparts is not a result of only scaling factors. It results from different causes as far as different materials are concerned. In semiconductors, it results from the further confinement of the electronic motion to a length scale that is comparable to or smaller than the length scale characterizing the electronic motion in bulk semiconducting material (called the electron Bohr radius, which is