Simulating the optical properties of isolated and dimer nanoshells for photothermal therapy

Photothermal therapy, the process of converting light from a laser into heat strong enough to destroy cancer cells, has risen as a promising, safe and minimally invasive means for cancer therapy. The ongoing progress in nanotechnology and material fabrication has revealed a novel class of metal nanoparticles whose free electrons resonate with incident light, exhibiting enhanced local electric field properties, an effect known as surface plasmon resonance. Designing nanoparticles that can efficiently absorb light is of critical importance for photothermal therapy while their ability to scatter light is useful for imaging. The presence of a simple, accurate and flexible method to investigate the optical response of different nanoparticle designs would be a huge step towards such goal. This work presents the use of the finite elements method to calculate the spectra of absorption and scattering efficiencies of gold nanoshells of different geometries. The size dependent dielectric function was used to model the gold shells. The results were compared to those of a previous study that uses Mie theory. The optical response of nanoshell dimers at different separations was also calculated and the results were compared with studies that use Wigner Eckart theorem, boundary elements method and experiments. Our model results were consistently found to be in very good agreement with those of the other studies. The finite elements method has proven its reliability to model the optical responses of nanoparticles and can be used to investigate more advanced nanoparticle designs that would be too complicated to model analytically.