K. Liu, X. Xue, E.P. Furlani
University at Buffalo,
Keywords: localized surface plasmon resonance (LSPR), plasmonic nanocages, photothermal energy conversion, LSPR-induced optical absorption, pulsed-laser photothermal heating, photothermal therapy, plasmonic nanobubble cancer treatment
Summary:In this presentation, we use 3D computational models to compare the optical and photothermal behavior of plasmonic nanostructures that are commonly used for near-infrared (NIR) applications. These include SiO2@Au core-shell, Au nanocage and Au nanorod nanostructures. While the LSPR wavelength all of these particles can be tuned to the NIR, we show that there are significant differences in behavior that can impact their selection of applications. The SiO2@Au and nanocage structures exhibit superior absorption at all spatial orientations due to their geometric symmetry. Thus, for colloidal applications they are more effective than Au nanorods, which have a strong orientation dependent absorption. The SiO2@Au and nanocage particles also have comparable photothermal conversion efficiencies even though in our study, the former has significantly less gold content than the latter. This is somewhat counterintuitive and is explained from our thermal analysis. Specifically, we show that the heating efficiency of the particles is a complex function of multiple factors, not only the amount of gold a particle contains as is sometimes cited in the literature, but importantly, how the gold is configured, i.e. the degree to which it can support LSPR-enhanced current to promote Joule heating. We show that the surface to volume ratio (i.e. effective surface area) is another important factor that governs the dissipation of energy to the surrounding environment. The analysis demonstrates the advantages of the core-shell and nanocage structures over the nanorod in terms of the absorption cross-section, insensitivity to a change of spatial orientation and local field enhancement. In this regard, the nanocage exhibits superior field enhancement throughout its interior, which holds potential for enhanced theranostics. The plasmonic tunability and enhanced photothermal transduction of these particles are attractive for several bioapplications such as photothermal hyperthermia, thermally-induced therapeutic nanobubble generation and drug delivery with controlled release. Lastly, the combined photonic and thermodynamic computational approach applied here provides insight into fundamental mechanisms that govern the plasmonic and thermal behavior of colloidal nanoparticles. It is useful for the rational design of plasmonic nanoparticles for a wide range of applications.