Photothermal properties of core-capped gold nanoparticles

Photothermal effects associated with noble metal nanostructures have shown wide potential applications in photo-thermal cancer therapy, photo-thermal imaging, nanomedicine, etc. These applications benefit from the localized surface plasmon resonance (LSPR) effect of the nanoparticles. Due to the LSPR effect, the nanoparticles exhibit unique optical properties such as strong scattering and absorption in the band ranging from visible to near-infrared region. The absorption enables the plasmonic nanoparticle to be a thermal source to increase the temperature of itself and the localized surrounding environment. Among these particels, the anisotropic core-capped nanostructures distinguish themselves by their strong polarization selectivity. The absorptions are different when the incident light is polarized in the directions vertical (90) and parallel (0) to its symmetry axis, respectively. At 90, a large red-shift can be achieved and the absorption cross section is greatly enhanced. Moreover, their absorption peaks can be flexibly manipulated by slightly adjusting one of the geometrical parameters. However, the photothermal responses to these parameters are left blank. In this paper, photothermal effects of SiO2@Au core-capped nanoparticles are studied based on the numerical finite elemental analysis method (COMSOL software). The thermal response to each of the paramenters, including shell thickness, core diameter, core-shell ratio, and metal surface coverage is achieved. The calculation shows that the temperature of these core-capped nanoparticles can be adjusted efficiently in the near infrared band by easily rotating the polarization, i.e. slightly adjusting the geometric parameters. Especially in a range between 30 and 70, the temperature varying with the polarization follows almost a linear relationship. The comparisons with other popular structures including solid sphere, core-shell and nanorod are also made. The results indicate that at a similar size, the core-capped structure can offer a higher temperature than solid spheres and core-shell structures. To obtain the same temperature variation, the core-capped one has a smaller size than a nanorod. The comparisons demonstrate that the core-capped structure can be an alternative to a high-efficient nano heat source in the photothemal applications.