Control of the Magnetic Properties of a Magnetic Field Guidable Biocompatible Nanovehicle

Abstract

Within this work a biocompatible magnetic nanovehicle which is movable in aqueous solutions by a magnetic field is presented. The nanovehicle consists of a porous silicon template and encapsulated iron oxide nanostructures. Both materials employed, porous silicon (PSi) as well as iron oxide are known to be biocompatible (1, 2). Mainly the synthesis of the nanocomposite as well as the magnetic properties of the systems will be discussed. Two routes are employed to produce various iron oxide phases of the embedded nanostructures within PSi. On the one hand, readily synthesized magnetite nanoparticles (NPs) which are superparamagnetic (SPM) due to their size, are infiltrated into the pores. On the other hand chemical deposition of iron oxide inside the PSi templates is used. The loading process of the templates depends not only on the pore-diameter/particle-size ratio but also on the particle-template interactions due to different surface treatments (e.g. as etched or oxidized PSi). Considering the chemically grown iron oxide, it does not form monodisperse particles but mainly clusters of particles. An increase of the temperature during the deposition resulted in a decrease of the coercivity which can be due to an iron oxide phase modification or due to a modification of the shape of the deposits. An adjustability of the magnetic properties of the system is achieved by a variation of the iron oxide loading within the PSi. An investigation of the iron oxide deposition dependent on the template and on the chemical parameters as well as of the magnetic properties in dependence on the particle size and on the template morphology of the nanocomposite will be presented. Temperature dependent magnetization measurements give information about the nature of the particle filling (packing density, spatial distribution), from field dependent magnetization measurements characteristics such as saturation magnetization, coercivity and remanence can be evaluated. For a sample containing a moderate filling with 8 nm Fe3O4 NPs the saturation magnetization has been estimated in using the measured hysteresis curves and considering the 1/H approach to be in the order of 6×10-3 emu/cm2. The amount of iron oxide particles inside the pores of the PSi matrices has been estimated in taking the magnetic moment of an individual iron oxide NP which is about 1.49 × 10-18 emu. In this case this leads to a number of about 1.3 × 1019 particles/cm3. The coercivity HC of the nanocomposite systems below TBdecreases with decreasing particle size which is due to SPM relaxation effects. The fabricated magnetic nanovehicles can be tuned in its magnetic behavior (e.g. coercivity, TB) due to the morphology of the template, the particle size and the filling conditions. The resulting magnetic moment of the samples is high enough to be moved within aqueous surroundings by a magnetic field of 0.1 T. (1) D. Ling, T. Hyeon, Small 9, 2013. (2) L.T. Canham, Adv. Mater. 7, 1033, 1995.