Nanoparticelle di MgFe2O4 drogate con Ag: effetto della sintesi sull'attività antibatterica

This work is devoted to the synthesis and characterization of magnesium ferrite (MgFe2O4) nanoparticles and their application in biomedicine. The focus of this study is the analysis of the antibacterial activities of these nanoparticles when they are doped with silver. Magnesium ferrite are very interesting materials thanks to their physical and chemical properties, in particular the magnetic ones. These NPs are superparamagnetic and thanks to their properties, they are used for different applications such as the medical one, for example in drug- delivery processes, Magnetic Resonance Imaging (MRI) and Magnetic fluid hyperthermia. Magnesium ferrites have a cubic spinel crystal structure (space group "Fd" "3" ̅"m" ). They are composed by tetrahedral and octahedral sites in general occupied by M (II) ions and Fe (III) respectively. The magnesium ferrites NPs are instead partially inverted, which means that Fe (III) occupies both tetrahedral and octahedral sites and M (II) ions occupy only the octahedral sites. To obtain NPs with no impurities (such as Fe2O3, Fe3O4 and MgO) that can compromise the magnetic properties, several synthesis have been proved. In particular, solid State synthesis with Ball-Milling (in order to obtain a product that can be used as an example of a perfect cubic crystalline structure), microwave synthesis, reflux synthesis, co-precipitation and Sol-Gel method. Thanks to the XRD patterns (refined with the Rietveld method) we could determine that the best syntheses for this kind of NPs are the microwave and the Sol-Gel ones. So, the samples from these two syntheses were used for the following steps: doping with Ag+ and coating with PEG-4000 or SiO2. The results of the XRD analysis are also confirmed by other techniques such as Raman Spectroscopy, Infrared Spectroscopy (FT-IR) and Scanning Electron Microscopy (SEM). In order to prevent the possible aggregation of the nanoparticles, which can be an issue for the biomedical use, and to obtain a more biocompatible material, the selected samples were submitted to two different coating processes: the first one is with a polymeric material, PEG-4000 and the second one is with SiO2. These coated samples have been characterized with the previously described techniques. The most important technique used for the characterization of the coated NPs is the Transmission Electron Microscope (TEM). Thanks to the selected TEM images it was possible to understand if the coating was effective. The TEM images show that the best material for the coating process of the magnesium ferrite NPs is PEG-4000, which can also be functionalized. Furthermore, in order to study the antibacterial properties, the magnesium ferrite NPs were doped with a different amount of Ag+. In addition, these samples were submitted to a thermal treatment, in order to obtain NPs with a bigger grain sizes and improved crystallinity. These treatments allowed us to evaluate the effects of doping with silver and thermal treatments on the antibacterial activities. The study of the possible antibacterial activities. Was performed with two different pathogenic bacteria: S. aureus and E.coli. The antibacterial activity can be evidenced by the diffusion of each sample on the agar plates. It turns out that the sample with the higher antibacterial activity is SG-Ag 0.3 thermically treated, followed by SG-Ag 0.3, SG-Ag 0.1 and SG-Ag 0.1 thermically treated. The MW samples have low antibacterial activity (only MW-Ag 0.1 and MW-Ag 0.3, both thermically treated have showed some activity). However, the antibacterial activity was more pronounced towards S. aureus. In conclusion, this study demonstrated that the best synthesis for the magnesium ferrite nanoparticles are the microwave and the Sol-Gel method, both rapid and green.