Development of new AFM based methodologies for the quantitative magnetic characterization of nanoparticles for biomedical applications

Authors: Angeloni, Livia
Advisor: Mantovani, D.; Rossi, Marco
Abstract: The objective of the PhD project is the development of a innovative measurement procedure and a data post-processing method to obtain quantitative information about the magnetic parameters of single magnetic nanoparticles through the use of the Magnetic Force Microscopy (MFM) technique. Magnetic nanoparticles (MNPs), thanks to their particular magnetic properties (single domains, superparamagnetism, etc.) and their nanometric size, are thought to be suitable for several biomedical applications, such as drug delivery systems, magnetic hyperthermia treatments, cell labelling, contrast agents for Magnetic Resonance Imaging (MRI). The design of these techniques requires a detailed knowledge on the magnetic properties of the adopted nanomaterials, like the saturation magnetization Ms, the saturation magnetic field Hs, the coercivity Hc. Standard techniques, like Superconducting Quantum Interference Devices (SQUID) or Vibrating Sample Magnetometer (VSM), to allow the detection of global magnetic properties of nanoparticles populations. Nevertheless, the detection of magnetic properties of single particles is not possible and the evaluation of the particle size dependence is not explicit. Thanks to its nanometric lateral resolution and its capability to detect weak magnetic fields, MFM is a potential powerful tool for the characterization of single nanoparticles dimensions, together with their magnetic properties. However, a methodology to extract quantitative information about the magnetic characteristics of single nanoparticles through MFM has not been individuated, mainly because of the complexity of tip-sample interactions affecting MFM measurements, which produces also non magnetic phenomena (e.g. electrostatic interactions), and the lack of a theoretical model describing the magnetic tip-NP interactions consistently with the detected experimental data. In order to exploit all the potential capabilities of MFM as a magnetic nanometrology tool, the strategy proposed and followed in this project is organized in the following four phases: 1) the theoretical and experimental verification and rationalization of the open issues and the problems limiting the applicability of MFM to the quantitative magnetic characterization of single NPs; in this phase the presence of electrostatic artifacts has been individuated as the main limitation responsible for the inconsistency between experimental data and theoretical models describing the tip-NP interactions. 2) the development of an instrumental apparatus and a measurement procedure to evaluate and eliminate the non-magnetic (electrostatic) contributions quantitatively affecting the MFM data; 3) the individuation of a theoretical model describing the magnetic tip-NP magnetic interaction, coherent with the experimental data, and able to establish a precise relationship between the measured data and the physical parameters desired to be determined (magnetization in the specific case); 4) the development of a procedure to quantitatively measure the magnetic properties, and eventually other parameters, of single nanoparticles by MFM. The results obtained with the procedures and methodologies presented in this thesis demonstrated the possibility of performing quantitative magnetic measurements on single magnetic NPs by MFM technology platform.
Document Type: Thèse de doctorat
Issue Date: 2017
Open Access Date: 24 April 2018
Grantor: Université Laval
Collection:Thèses et mémoires

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