Development of magnetic temperature sensors for hyperthermia and cryogeny applications

• Autor(a) principal: Perfeito, Francisca Gonçalves
• Data de Publicação: 2021
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/31221
• topic: Magnetic nanoparticles; Mn-Zn ferrites; Nanothermometers; Wireless sensors; Hyperthermia; Cryopreservation

Magnetic iron oxide nanoparticles have gathered increasing attention from the scientific community over the years due to their promising features such as their in vivo biocompatibility, versatile surface modifications, and facile synthesis. With this in mind, temperature sensing comprises one of the most delicate areas of thermometry when applied to processes such as magnetic hyperthermia and cryopreservation, which strongly depend on minute temperature changes. In fact, gaining insight into the small temperature variations occurring at cellular scale is currently addressed using nanothermometers based on the well-defined temperature dependence of a given property. However, current approaches are mainly based on optical properties, being limited by several drawbacks, such as the inefficient penetration of light in many tissues, for example. In view to overcome this great challenge, magnetic nanoparticles have a huge potential, since they combine adequate size for cellular internalization and magnetic fields can easily penetrate tissues, enabling remote temperature monitorization. In this context, the objective of this thesis is to develop stable Mn-Zn ferrite nanoparticles dispersed in aqueous medium to act as remote distance temperature sensors for bioapplications, in particular for hyperthermia and cryogenic applications. MnxZn1-xFe2O4 NPs were successfully produced using two distinct methodologies, namely thermal decomposition, and a molten salt-assisted thermal decomposition approach. The prepared NPs were then analyzed by scanning Electron Microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared (FT-IR) spectroscopy, dynamic light scattering (DLS), zeta potential, and magnetic properties. X-ray powder diffraction (XRD) successfully verified the presence of a cubic crystal structure with a predominant phase in the Fd3" m space group of the Mn-Zn ferrites produced by both methodologies. FT-IR spectroscopy was used to assess presence of several compounds on the NPs surface, such as the functionalization of the particles with citric acid and EDTA. Moreover, Rietveld refinement was useful to discriminate the NPs sizes, which overall constituted diameters ranging from 5.9 to 15 nm by thermal decomposition methodology and 1.3 to 4.2 nm by molten salts methodology. Magnetization measurements were made to evaluate the potential of the NPs as magnetic nanothermometers, in which the 6.9 nm-sized Mn0.30Zn0.47Fe2O4 (sample TD9) nanoparticles exhibited magnetic reversibility between 100 to 375 K with a maximum sensibility of 2.9 %.K-1 at 225 K. In addition, the 8.0 nm-sized Mn0.11Zn0.78Fe2O4 (sample TD4) nanoparticles also revealed potential sensor applications between 300 and 400 K, with a maximum sensibility of 2.1 %.K-1 at 300 K. According to these findings, the produced NPs are deemed suitable for both hyperthermia and cryopreservation applications. Lastly, the encapsulation of these ferrofluids was carried out with gelatin, in order to simulate a 3-D phantom tissue to be subjected to temperature changes to assess the effectiveness of the behavior of the nanoparticles as wireless sensors. In sum, all the results highlight great potential in the hereby produced MnxZn1-xFe2O4 NPs for nanothermometry.