Radiofrequency heating of gold nanoparticles for medical applications
Time: Fri 2025-01-17 09.30
Location: H1, Teknikringen 33, Stockholm
Video link: https://zoom.us/j/64235189553
Language: English
Subject area: Electrical Engineering
Doctoral student: Brage B. Svendsen , Elektromagnetism och fusionsfysik
Opponent: Associate Professor Francesca Apollonio, Sapienza University of Rome,
Supervisor: Mariana Dalarsson, Elektromagnetism och fusionsfysik; Martin Norgren, Elektromagnetism och fusionsfysik
Abstract
In this thesis, the electromagnetic radiofrequency (RF) heating of gold nanoparticles (AuNPs) is investigated by means of analytical and numerical methods. The aim is to establish methods to identify model parameters for AuNP-mediated RF heating of biological tissue. These investigations can ultimately be used to assess the feasibility of a non-invasive and targeted method of cancer therapy by hyperthermia.
As a first step, an analytical model is developed, as a tool to study the absorption in a thin AuNP-treated cell substrate inserted in a waveguide. The interior of the waveguide is modeled as a continuous material composite with graded transition between the AuNP-treated layer and its surroundings. Exact analytical solutions for the fields, and the transmission and absorption parameters are obtained. The introduction of a scaling factor allows the calculation of the absorption within the AuNP-treated layer only, thus excluding losses in the surrounding material. Dispersive dielectric models describing the electromagnetic properties of relevant tissues are discussed and applied in numerical examples. The waveguide structure is numerically simulated in COMSOL Multiphysics, confirming the validity of analytical results.
The physical mechanisms that enable the heating of AuNPs by RF irradiation are not entirely understood. This thesis studies two proposed mechanisms and evaluates under what conditions they can amount to the required heating of the targeted tissue: electrophoretic oscillation and Joule heating. These effects are studied using electrostatic scattering theory.
RF Joule heating is found to be negligible in spherical AuNPs, but deemed possible in long nanowires. It is of particular interest to study how the presence of a thin dielectric shell affects the heating capacity in ellipsoidal AuNPs. In the context of the medical application, AuNPs are coated with functionalized ligands for tumor targeting. The Joule heating of coated AuNPs submerged in tissue is thus studied with respect to coating properties for AuNPs of all nanoscale-sized spheroidal shapes. The coating is found to strongly affect the overall AuNP heat absorption, and the effect is heavily dependent on the electromagnetic and spatial properties of the coating. The type of ligands to be used in practical applications should therefore be evaluated based on these properties, in addition to its targeting efficacy and biocompatibility.
Finally, the electrophoretic heating of AuNP suspensions is investigated. In the literature, this mechanism has been evaluated only for spherical AuNPs and mostly when they are submerged in aqueous solutions. Here, the electrophoretic heating is studied for any spheroidal shape in all nanoscale sizes. Heating is found to be strongest for spherical AuNPs a few nanometers in size dispersed in water, but significant heating is also observed in nanorods up to 40 nm in length and nanodisks with diameters up to 10 nm. However, the potency of the effect is strongly affected by the solvent. Due to the high viscosity in tissues, and in particular cancerous tissues, the study suggests that electrophoretic heating of AuNPs is negligible in these media.