Photothermal Properties of Size-Tunable Gold Nanotriangles with Matching near Infrared Plasmon Resonance Wavelengths

Metallic nanoparticles are among the preferred materials for nanoscale conversion of light into heat because of their localized plasmon resonances, which provide exceptionally high absorption cross sections. These materials are widely used in various fields such as biomedical applications, water desalinization, or solar energy harvesting. However, the absorption of light by plasmonic nanoparticles and their associated heat generation depends on multiple parameters such as composition, shape, size, wavelength, and concentration. This complexity makes their controlled design and optimization challenging and constitutes one of the bottlenecks in the field. Among the many available plasmonic nanoparticles, Au nanotriangles are particularly appealing due to their high photothermal stability and tunable resonances in the biological window. In this work, we study the influence of the dimensions on the light-to-heat conversion efficiency of Au nanotriangles. Isolating the role of geometry and size in the photothermal efficiency is challenging, as plasmon resonances are strongly size dependent. Here, we carefully synthesized two sets of Au nanotriangles with similar resonances but different dimensions. By evaluating and comparing multiple theoretical and experimental photothermal metrics, we provide insights on how nanoparticle size influences their efficiency at varying concentrations. It was found that smaller nanotriangles generate more heat per unit of Au mass if used at low concentrations, but these differences disappear at larger concentrations. On the other hand, larger nanotriangles generate more heat per nanoparticle, at all concentrations. These findings offer guidelines for designing and optimizing plasmonic nanoheaters according to their desired application.