Plasmonic Coupling and Thermal Effects on Photothermal Response of Randomly Distributed Nanoparticles

Abstract

Plasmonic coupling has attracted considerable attention in research due to its promising applications in thermoplasmonics, which is increasingly utilized across various nanotechnologies, particularly in the fields of biology and medicine. Applications include photothermal cancer therapy, drug delivery, nanosurgery, and photothermal imaging, thanks to their capability to significantly enhance electromagnetic fields. Localized Surface Plasmon Resonances (LSPR) in metal nanostructures enable substantial electromagnetic field enhancement and precise localization at the nanoscale. The characteristics of LSPR, including the resonance wavelengths, can be adjusted by altering the geometry of the nanostructures and are highly sensitive to changes in the surrounding refractive index. The interaction of localized plasmon resonances can lead to the formation of new hybrid modes that individual nanostructures cannot support, surmounting some limitations of standalone LSPR and facilitating novel applications and the active manipulation of plasmon resonances. In this thesis work, we explore how plasmonic coupling influences the photothermal behavior of randomly distributed silver nanoparticles. We used the discrete dipole approximation method and thermal Green’s function to compute the spatial temperature profiles of illuminated nanoparticles. Our findings suggest that plasmonic coupling among nanoparticles in a random assembly, along with thermal accumulation, induces a photothermal response that differs from that observed in isolated nanoparticles. We qualitatively analyzed the individual effects of plasmonic coupling and thermal accumulation on temperature increases in nanoparticle assemblies. Our results indicate that at wavelengths far from a single nanoparticle’s plasmonic resonance, plasmonic coupling among clustered nanoparticles can lead to significant temperature increases, an effect not anticipated in the absence of plasmonic coupling. Conversely, at the resonance wavelength of a single nanoparticle, plasmonic coupling results in a lesser temperature rise compared to a group of non-coupled nanoparticles. These insights enhance our understanding of the photothermal dynamics in random nanoparticle systems, with significant implications for their use in biological applications