Magnetorelaxometry Assisting Biomedical Applications of Magnetic Nanoparticles

Due to their biocompatibility and small size, iron oxide magnetic nanoparticles (MNP) can be guided to virtually every biological environment. MNP are susceptible to external magnetic fields and can thus be used for transport of drugs and genes, for heat generation in magnetic hyperthermia or for contrast enhancement in magnetic resonance imaging of biological tissue. At the same time, their magnetic properties allow one to develop sensitive and specific measurement methods to non-invasively detect MNP, to quantify MNP distribution in tissue and to determine their binding state. In this article, we review the application of magnetorelaxometry (MRX) for MNP detection. The underlying physical properties of MNP responsible for the generation of the MRX signal with its characteristic parameters of relaxation amplitude and relaxation time are described. Existing single and multi-channel MRX devices are reviewed. Finally, we thoroughly describe some applications of MRX to cellular MNP quantification, MNP organ distribution and MNP-based binding assays. Providing specific MNP signals, a detection limit down to a few nanogram MNP, in-vivo capability in conscious animals and measurement times of a few seconds, MRX is a valuable tool to improve the application of MNP for diagnostic and therapeutic purposes

Standardisation of magnetic nanoparticles in liquid suspension

Suspensions of magnetic nanoparticles offer diverse opportunities for technology innovation, spanning a large number of industry sectors from imaging and actuation based applications in biomedicine and biotechnology, through large-scale environmental remediation uses such as water purification, to engineering-based applications such as position-controlled lubricants and soaps. Continuous advances in their manufacture have produced an ever-growing range of products, each with their own unique properties. At the same time, the characterisation of magnetic nanoparticles is often complex, and expert knowledge is needed to correctly interpret the measurement data. In many cases, the stringent requirements of the end-user technologies dictate that magnetic nanoparticle products should be clearly defined, well characterised, consistent and safe; or to put it another way—standardised. The aims of this document are to outline the concepts and terminology necessary for discussion of magnetic nanoparticles, to examine the current state-of-the-art in characterisation methods necessary for the most prominent applications of magnetic nanoparticle suspensions, to suggest a possible structure for the future development of standardisation within the field, and to identify areas and topics which deserve to be the focus of future work items. We discuss potential roadmaps for the future standardisation of this developing industry, and the likely challenges to be encountered along the way

Glass like magnetic alternating field susceptibility behavior of structurally frozen ferrofluids

Four ferrofluids, distinct in size distribution and aggregate structure, were investigated. The relaxation time tm(T), related to the temperature of susceptibility maximum, was fitted to a Vogel-Fulcher law. A mean ordering temperature, T0, was calculated using magnetic particle parameters derived from the structure. It is assumed that at T0 the particle moments of particle clusters correlate, leading to a spin glass-like transition. Hence, then dynamic slows down considerably, as indicated by a strong broadening of relaxation-time distribution. T0 roughly agrees with the energy of competing interaction between particle moments, as calculated from the structure of particle aggregates. Differences between particle arrangements clearly influence the dispersion and absorption, particularly within the cluster phase

Blocking of magnetic moments of magnetosomes measured by magneto relaxometry and direct observation by magnetic force microscopy

Large magnetosomes of 40 nm diameter were characterised by altogether four different methods, i.e. DC-magnetometry and magnetorelaxometry as integral tools, and atomic and magnetic force microscopy as microscopic tools. The results suggest that the integral hysteretic behaviour of magnetosomes can be understood as a superposition of their microscopic behaviour, ignoring interaction between the particle moments

In vitro Simulation von Magnetischem Drug Targeting mit einem Arterienmodell

Ein Hauptproblem bei der Tumorbehandlung mit Chemotherapeutika stellt das häufige Missverhältnis zwischen erzielter Wirkung und unerwünschten Nebenwirkungen dar. Beim Magnetischen Drug Targeting (MDT) werden Wirkstoffe mit magnetischen Nanopartikeln gezielt an den gewünschten Wirkort transportiert. Dieses System ermöglicht eine deutliche Erhöhung der Wirkstoffkonzentration in der Zielregion gegenüber der regulären Chemotherapie. Der zielgerichtete Transport der Nanopartikel ist von unterschiedlichen Parametern abhängig, wie z.B. dem Magnetfeldgradienten, der physiologischen Umgebung, der Partikelgröße oder der Partikeloberfläche. In einem "in vitro-Gefäßmodell" sollen die Auswirkungen dieser Parameter unter unterschiedlichen Bedingungen untersucht werden. In diesem Gefäßmodell wurden isolierte Rinderarterien mit Albumin substituiertem Puffer durchspült und in unmittelbarer Nähe des Magnetfeldes platziert. Während der Magnetfeldeinwirkung wurden die Nanopartikel in das Flussmedium injiziert und danach die Arterien histologisch und magnetrelaxometrisch untersucht. Die Attrahierbarkeit der Partikel zur Polschuhspitze des Magneten konnte in diesem Arterienmodell visualisiert werden. Auch die unterschiedliche Partikelanreicherung in verschiedenen Gefäßabschnitten ließ sich histologisch nachweisen und mit der Magnetrelaxometrie quantifizieren. Es erfolgte eine Aufnahme der Partikel in die Endothelzellen der Gefäßwand. Partikelmessungen mit dynamischer Lichtstreuung zeigten eine Größenzunahme der Partikel nach der Magnetfeldanwendung. Mit dieser Umlaufapparatur können die Magnetfeldstärke und die Partikelgröße unter konstanten Bedingungen im Vorfeld von Tierversuchen getestet werden, die wichtige Parameter für das MDT sind. Unterstützt durch: DFG, Wilhelm-Sander-Stiftung, Münche