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The plasmonic spectra of solution phase ensembles of triangular silver nanoplates have been analysed in order to examine the fundamental properties underlying their size-dependent enhanced refractive index sensitivities. Linewidth studies highlight variations in the response of these solution phase nanostructures to those previously reported for single immobilized triangular nanostructures. The observation of insignificant broadening of the resonance linewidth for larger edge length nanoplates highlights minimal contribution of radiative damping processes at these dimensions. Comparative single nanoplate studies using discrete dipole approximations were performed to analyse the dephasing processes contributing to these reduced linewidths and to determine the key parameters defining the underlying plasmonic response. These single nanoplate approximations highlight the dominance of absorption processes over radiative processes and demonstrate that this dominance can be attributed to the platelet nature/geometry of the nanoplates. These calculations indicate that the higher aspect ratio allows for the maintenance of coherent plasmon oscillations as the edge length of the triangular platelet increases within the sols. Thickness studies verify that this reduction in radiation damping is due to high aspect ratio and can act to confine electromagnetic fields at the nanoplate surface, thereby increasing near-field enhancement and hence the resultant plasmonic refractive index sensitivity.

A rapid and readily reproducible seed-based method for the production of high quality silver nanoprisms in high yield is presented. The edge-length and the position of the main plasmon resonance of the nanoprisms can be readily controlled through adjustment of reaction conditions. From UV-vis spectra of solutions of the nanoprisms, the inhomogeneously broadened line width of the in-plane dipole plasmon resonance is measured and trends in the extent of plasmon damping as a function of plasmon resonance energy and nanoprism size have been elucidated. In addition, an in-depth analysis of the lamellar defect structure of silver nanoprisms is provided that confirms that the defects can lead to a transformation of the crystal structure in the vicinity of the defects. These defects can combine give rise to lamellar regions, thicker than 1 nm, that extend across the crystal, where the silver atoms are arranged in a continuous hexagonal-close-packed (hcp) structure. This hcp structure has a periodicity of 2.50 A, thus explaining the 2.50 A lattice fringes that are commonly observed in 〈111〉 oriented flat-lying nanoprisms. A new understanding of the mechanisms behind anisotropic growth in silver nanoprisms is presented.

Recent advancements in solution-based methods have enabled a wide range of remarkable morphologies and sizes of silver nanoparticles to be produced. In this chapter, some of the different approaches that have been taken to prepare Ag nanomaterials are discussed. Both, aqueous-based and organic-based procedures for the preparation of spherical particles are described. The controlled synthesis of shaped Ag nanoparticles is particularly highlighted, and theories regarding the growth of anisotropic silver particles are reviewed. The seed structure and growth-directing abilities of different organic stabilizers are especially important. Keywords: silver; nanoparticles; spherical; anisotropic; seeds; multiply twinned particles; shape; synthetic methods

Solution phase triangular silver nanoplates (TSNP) with versatile tunability throughout the visible-NIR wavelengths are presented as highly sensitive localized surface plasmon refractive index sensors. A range of 20 TSNP solutions with edge lengths ranging from 11 to 200 nm and aspect ratios from 2 to 13 have been studied comprehensively using AFM, TEM, and UV-vis-NIR spectroscopy. Studies of the localized surface plasmon resonance (LSPR) peak's sensitivity to refractive index changes are performed using a simple sucrose concentration method whereby the surrounding refractive index can solely be changed without variation in any other parameter. The dependence of the TSNP localized surface plasmon resonance (LSPR) peak wavelength lambda(max) and its bulk refractive index sensitivity on the nanoplate's structure is determined. LSPR sensitivities are observed to increase linearly with lambda(max) up to 800 nm, with the values lying within the upper limit theoretically predicted for optimal sensitivity, notwithstanding any diminution due to ensemble averaging. A nonlinear increase in sensitivity is apparent at wavelengths within the NIR region with values reaching 1096 nm.RIU(-1) at lambda(max) 1093 nm. Theoretical studies performed using a simple aspect ratio dependent approximation method and discrete dipole approximation methods confirm the dependence of the LSPR bulk refractive index sensitivity upon the TSNP aspect ratio measured experimentally. These studies highlight the importance of this key parameter in acquiring such high sensitivities and promote these TSNP sols for sensing applications at appropriate wavelengths for biological samples.

Within this work we present a new class of shaped silver nanoparticle ensembles which have demonstrated high sensitivities to variations in the refractive index of their surrounding environment. The ensembles' collective response has proven to exceed that of other sensitivities quoted in literature by various other nanoparticle structures, with sensitivity values of up to 376.6 nm/RIU recorded. A quick, simple sucrose sensitivity test has been developed in which any corresponding shift in the nanoparticles' spectrum can be associated solely to a change in the surrounding refractive index. AFM, TEM and dynamic light scattering characterisation of the mean diameter and height distributions of the nanoparticle ensembles provides information on the relationship between the structural properties of the nanoparticles and their sensitivity.