The Use of Silica Microparticles to Improve the Efficiency of Optical Hyperthermia (OH)

Abstract

Although optical hyperthermia could be a promising anticancer therapy, the need for high concentrations of light-absorbing metal nanoparticles and high-intensity lasers, or large exposure times, could discourage its use due to the toxicity that they could imply. In this article, we explore a possible role of silica microparticles that have high biocompatibility and that scatter light, when used in combination with conventional nanoparticles, to reduce those high concentrations of particles and/or those intense laser beams, in order to improve the biocompatibility of the overall procedure. Our underlying hypothesis is that the scattering of light caused by the microparticles would increase the optical density of the irradiated volume due to the production of multiple reflections of the incident light: the nanoparticles present in the same volume would absorb more energy from the laser than without the presence of silica particles, resulting either in higher heat production or in the need for less laser power or absorbing particles for the same required temperature rise. Testing this new optical hyperthermia procedure, based on the use of a mixture of silica and metallic particles, we have measured cell mortality in vitro experiments with murine glioma (CT-2A) and mouse osteoblastic (MC3T3-E1) cell lines. We have used gold nanorods (GNRs) that absorb light with a wavelength of 808 nm, which are conventional in optical hyperthermia, and silica microparticles spheres (hereinafter referred to as SMSs) with a diameter size to scatter the light of this wavelength. The obtained results confirm our initial hypothesis, because a high mortality rate is achieved with reduced concentrations of GNR. We found a difference in mortality between CT2A cancer cells and cells considered non-cancer MC3T3, maintaining the same conditions, which gives indications that this technique possibly improves the efficiency in the cell survival. This might be related with differences in the proliferation rate. Since the experiments were carried out in the 2D dimensions of the Petri dishes, due to sedimentation of the silica particles at the bottom, whilst light scattering is a 3D phenomenon, a large amount of the energy provided by the laser escapes outside the medium. Therefore, better results might be expected when applying this methodology in tissues, which are 3D structures, where the multiple reflections of light we believe will produce higher optical density in comparison to the conventional case of no using scattering particles. Accordingly, further studies deserve to be carried out in this line of work in order to improve the optical hyperthermia technique.

Optoplasmonic Effects in Highly Curved Surfaces for Catalysis, Photothermal Heating, and SERS

“…The dramatic difference in the photothermal properties of the Au NPs-coated microspheres and the bare glass microspheres is the result of the strong scattering properties of the glass microspheres. Given that the temperature probe is placed directly into the solution, it is likely that photons scattered by the glass microspheres can interact with the temperature probe, leading to an observed increase in temperature, also observed elsewhere . If the probe is placed directly into the path of the beam, the temperature increase is both sharper and higher than what is shown in Figure S8.…”

“…Given that the temperature probe is placed directly into the solution, it is likely that photons scattered by the glass microspheres can interact with the temperature probe, leading to an observed increase in temperature, also observed elsewhere. 60 If the probe is placed directly into the path of the beam, the temperature increase is both sharper and higher than what is shown in Figure S8. The additional heating caused by adding the Au NPs onto the glass microspheres is likely the result of cooperative optical effects.…”

Effectiveness of Gold Nanorods of Different Sizes in Photothermal Therapy to Eliminate Melanoma and Glioblastoma Cells

“…The coating of GNRs with PEG not only prevents direct contact with CTAB but also modifies the surface charge. The cytotoxicity of GNRs has been extensively studied in various human tumor cell lines, including Hep-2 [37] and A549 [38], as well as in rodent cell lines like CT2A [39] and B16F10 [40]. These studies provided valuable insights into the cytotoxic effects of GNRs on different cell lines.…”