Abstracts

Between the technological interests of plasmonic nanoparticles is their ability to transform light into heat. This fact can be used in biomedical applications (photothermia), promotion of chemical reactions at the nanoscale or water remediation. All those applications, though, take place in aqueous environments, which is not totally transparent to the excitation beam (typically in the visible or near-infrared ranges). In the biomedical case, besides water, the environment may also have additional components, such as melanin, haemoglobin, lipids, etc. which may also absorb or scatter the light beam. This composition of the environment implies that there is not a good accuracy on the illumination that really reaches the plasmonic nanoparticles, thus uncontrolled heating doses are delivered. This fact calls for the development of in situ temperature measurements.Our approach to this problem starts developing and optimizing a specific luminescent nanomaterial: CaF₂:Nd³⁺, Yb³⁺. It has been precisely designed to work (both regarding excitation and emission) in the wavelength ranges in which typical biological media attenuates light the least. Following a thorough spectroscopy study, required due to the complex optical-sites characteristics of the material, we have designed the best thermometry approach it allows.Afterwards, we have tested its performance in the biological environment, triggering heat optically through plasmonic nanoparticles. We have developed measurement strategies to guarantee the accuracy of the measurements. Given the heterogeneous and optically dense nature of biological tissues, this second part is a challenge, as the interaction of the emitted light with the tissue may involve a deformation of the luminescent spectrum, and thus create inaccurate thermal readings.