Throughout the history of science, comparison among calculated parameters and experimental observables has been considered as obvious to accomplish and reciprocate a fundamental hypothesis. The exploitation of sharp edges toward a plethora of paraphernalia has been continued from the prehistoric evidence to modern nanotechnology. To validate the hypotheses of the sharp edges, gold nanostars that exhibit their localized surface plasmon resonances in the visible−near-infrared region and contain multiple sharp tips have been considered as the model structures. Efficient control on the length and sharpness of the spikes has been achieved by judicious manipulation of the respective synthetic protocol. The electromagnetic simulation considering the topological parameters demonstrates an exotic interplay between the depolarization factor (P z ) and aspect ratio (α) to express the strength of the electric field generated at the tip heads as a function of their sharpness. Subsequent profiling of photothermal response caused by resistive heat exhibits an outstanding proof-of-concept resemblance between the local thermal manipulation and replicated in vitro laboratory experiment. Thus, the present work investigates an interdisciplinary analytical landscape enumerating the role of sharpness on the enhanced field and the temperature distribution localized at the tip head in the realm of plasmonic photothermal therapy.

Physicochemical aspects of anisotropic gold nanostructures have been of considerable interest due to intrinsic shape-dependent phenomena that open up newer perspectives from nanoscale electromagnetism to basic thermodynamics since gold has a highly symmetric facecentered cubic (fcc) structure and usually tends to afford a spherical geometry to reduce surface free energy. The emergence of novel properties of these anisotropic structures could be attributed to the lack of symmetry at the interface or to the confinement of electrons that does not scale linearly with size. Based on these concepts, anisotropic gold nanospike has been chosen as a typical nanostructural system that possesses different surface energy around the nanostructure in comparison to isotropic gold nanosphere to quantify the precise surface energy at the tips of these intricate nanostructures. Cetyltrimethylammonium bromide-stabilized gold nanospheres and nanospikes have been synthesized in aqueous medium under ambient conditions. Since fluorescence spectroscopy is a very sensitive technique, fluorescent dye, alizarin red, has been employed as a local probe to elucidate the detailed spectral characteristics of the metal−probe hybrid assemblies. The influence of morphological anisotropy of these nanostructures has been, further, emphasized by following the temporal changes in the emission characteristics during the photoinduced conversion of gold nanospikes to nanospheres under NIR laser irradiation. Experimental realization of excess surface energy at the tips of the nanospikes has been calculated from theoretical perspectives.

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Confinement of the electromagnetic field in gold nanoparticle dimers and trimers with variations in the interparticle distances and angles has been calculated.

Plasmonic sensitivity of noble metals has often been attributed to the morphology of the nanostructures and dielectric effects of both the materials and the surrounding medium. The measurable plasmonic shift with respect to the change in local dielectric as a function of analyte concentrations within nanoscale volume forms the basis of plasmonic sensing. However, the situation of the surrounding medium in the presence of multicomponent systems and, moreover, inhomogeneous adsorption around the anisotropic nanostructures become seemingly complicated as the precise description of several individual components becomes nearly impossible. Therefore, we have designed a retrospective formalism through a critical condensation of the electromagnetic scattering theories, macroscopic mixing rules, and micromechanics at the metal−analyte interface that can be adopted as generalized model irrespective of morphology of the nanostructures and the nature of analytes to account for the response of all the individual (microscopic) components to the observed (macroscopic) plasmonic sensing.