Nanoparticle-mediated photothermal therapy of tumors : a comparative study of heating efficiencies for different particle types

Cancer is one of the most notorious diseases affecting the human population today with very few effective treatments. Due to the disparate nature of cancers, it is difficult to obtain a treatment that can cure cancer. Thus, there is a large influx of research towards cancer therapies, leading to one of the discovery that cancer cells (tumors) have a low thermotolerance in comparison to normal cells. If the temperature of the cancer cells is increased into the hyperthermia range (~45°C) thermal damage occurs, causing cell death by protein denaturation and membrane disruption. A recent development in this field has been in the photothermal treatment of tumors, which is starting to utilize plasmonic particles to enhance the specificity of the treatment. The plasmonic nanoparticles, specifically gold, can reach the tumor site using passive targeting and when irradiated with a tuned laser will emit heat localized to a small region around the nanoparticle killing the surrounding cancer cells. This process has been shown to reduce tumor size in vivo with gold nanoshells and gold nanorods.
However, it has not been shown which particle is better at delivering the heat to the tumor site. Therefore in this study, it will be shown which particle generates the most heat. Solutions of tissue simulating phantom and different concentrations of nanoparticles were irradiated with a laser to measure the increase in temperature. Additionally, simulations were performed using Mie Theory for nanoshells and the Discrete Dipole Approximation for nanorods. Based on the physical parameters of the nanoshells and nanorods used in this experiment, the adjusted absorption cross-section was determined. It was found that nanoshells generated the most amount of heat on a per particle basis, and that it was necessary to have a nanorod concentration of 5.5 times the concentration of nanoshells to generate the same amount of heat as nanoshells. These results were confirmed using Monte Carlo and Finite Difference Modeling of the nanoparticle heating experiments. However, the choice of nanoparticle still depends on the application and the targeting efficiency in vivo.