Low frequency heating of gold nanoparticle dispersions for non-invasive thermal therapies

Recently gold nanoparticles (GNPs) have been proposed in non-invasive thermal therapies for cancer treatment coupled with radiofrequency (RF) waves. In this work, the dissipation of RF energy by GNPs is systematically investigated both experimentally and theoretically under an EM frequency of 13.56 MHz. To elucidate the impurity effect, purified GNP dispersions are obtained through an ultrasonic-aided method. The result reveals a small bulk temperature increase, i.e., less than one centigrade for impurified samples, and even smaller for purified samples, which contrasts significantly to some earlier publications. The measured dielectric properties of GNP dispersions show a negligible change in the effective conductivities for purified samples, which indicates that the dielectric loss alone does not predict substantial temperature increase of GNPs. Further discussion shows that none of the established theories supports the idea that GNPs can dissipate RF energy significantly.