Phonon-assisted radiofrequency absorption by gold nanoparticles resulting in hyperthermia

TL;DR

This paper proposes a physical mechanism involving phonon-assisted electron absorption explaining RF hyperthermia in gold nanoparticles, accounting for size dependence and impurity effects, with implications for optimizing nanoparticle design.

Contribution

It introduces a phonon-assisted absorption model for RF heating in gold nanoparticles, highlighting size and impurity effects, and suggests specific nanoparticle compositions for enhanced hyperthermia.

Findings

Maximum heating rates occur in 5-7 nm GNPs.

Impurities like Ta and Fe can enhance heating.

Size dependence explains experimental observations.

Abstract

It is suggested that in gold nanoparticles (GNPs) of about 5 nm sizes used in the radiofrequency (RF) hyperthermia, an absorption of the RF photon by the Fermi electron occurs with involvement of the longitudinal acoustic vibrational mode (LAVM), the dominating one in the distribution of vibrational density of states (VDOS). This physical mechanism helps to explain two observed phenomena: the size dependence of the heating rate (HR) in GNPs and reduced heat production in aggregated GNPs. The argumentation proceeds within the one-electron approximation, taking into account the discretenesses of energies and momenta of both electrons and LAVMs. The heating of GNPs is thought to consist of two consecutive processes: first, the Fermi electron absorbs simultaneously the RF photon and the LAVM available in the GNP; hereafter the excited electron gets relaxed within the GNP's boundary, exciting a LAVM with the energy higher than that of the previously absorbed LAVM. GNPs containing the Ta and/or Fe impurities are proposed for the RF hyperthermia as promising heaters with enhanced HRs, and GNPs with rare-earth impurity atoms are also brought into consideration. It is shown why the maximum HR values should be expected in GNPs with about 5-7 nm size.