Synthesis, Properties, and Applications of Colloidal Gold NanoprismsPublic Deposited
Au nanoprisms are a new type of inorganic nanoparticle that is particularly interesting because these particles can be made in high yield, are composed of a metal with well known surface chemistry, exhibit strong, architecture and environment-sensitive optical features, and have well-defined crystallographic facets. All of these features make Au nanoprisms an excellent testbed for understanding, characterizing, and using the effects of particle shape at the nanoscale. In Chapter 2, a seed-mediated growth process is presented for the production of colloidal Au nanoprisms with relatively homogeneous size distributions. The purity of nanostructures produced in this synthesis allowed the first observation of a weak quadrupole surface plasmon resonance in addition to a strong dipole resonance associated with the Au nanoprisms. The experimental optical spectra are shown to agree with discrete dipole approximation calculations modeled from the dimensions of Au nanoprisms produced in the synthesis. Chapter 3 builds on this work by describing a method for controlling Au nanoprism edge length using seeding methodology. In this manner, the edge length of Au nanoprisms can be tailored over a range of 100 - 300 nm without appreciable changes in either nanoprism thickness or crystallinity. This work provided new insight into anisotropic gold nanoparticle growth and reactivity, and expanded the library of prism structures with optical features ranging from 1000 - 1800 nm. Based on this work and existing silver halide crystal growth theories, a preliminary nanoprism formation mechanism is proposed. In Chapter 4, the site-selective chemical reactivity of the Au nanoprisms described in Chapter 3 is used to investigate the functionalization of the nanoprism and elucidate its surface chemistry. It is shown that face-selective, DNA-ligand adsorption onto the nanoprism is time dependent, and can be exploited to selectively immobilize DNA on the edges of the particle. Chapter 5 builds on the methods and techniques developed in Chapter 4 to make and use a variety of DNA-functionalized anisotropic nanostructures. This chapter describes the use of such conjugates in both diagnostic and therapeutic applications. For detections, DNA-conjugated nanodisk arrays are used as barcodes to readout the presence of biological target moieties. Additionally, gene delivery applications of Au nanoprisms are described by presenting a method for the preparation and cellular uptake of DNA-nanoprism conjugates. Chapter 6 describes the most recent work completed on the shape-directing factors in the synthesis of Au nanoprisms. In this chapter, it is shown that CTAB, depending upon supplier, has an iodide contaminant (at a significant but varying level), which acts as a key shape directing element, because it can strongly and selectively bind to the gold (111) faces and favor the formation of anisotropic structures. Furthermore, by starting with pure CTAB and deliberately adjusting iodide concentration, it is shown that one can reproducibly drive the reaction to predominantly produce nanorods, nanoprisms, or nanospheres.