Cordula Grüttner

A novel and rapid method for quantification of magnetic nanoparticle?cell interactions using a desktop susceptometer

Activated endothelial cells (EC) are attractive prime targets for specific drug delivery using drug-carrying magnetic nanoparticles. In order to accomplish EC targeting, the interaction between magnetic particles and resting as well as activated endothelial cells must be characterized and quantified, because it will influence particle biodistribution, circulation half-time, and targeting efficacy. Here, we have quantified in vitro the interaction (adhesion/phagocytosis) between human endothelial cells and magnetite (Fe3O4) particles carrying different surface coatings with varying degrees of hydrophilicity and surface charge. Almost no adhesion was observed (about 1% or less) for three out of five particle types carrying plain dextran, carboxyl-substituted poly(ethylene glycol) and silica C18 coatings. In contrast, carboxyl-functionalized dextran and poly(ethylene glycol)-coated particles adhered or were phagocytosed to a considerable degree (58 and 26%, respectively). These clear and accurate results were obtained by measuring the magnetic response, i.e. magnetic susceptibility, from different fractions of the cell cultures as a means of determining the concentration of magnetic particles. Visible light and electron microscopy confirmed the magnetic quantification. To meet the need for a rapid yet sensitive instrument, we have developed a desktop magnetic susceptometer especially adapted for liquid samples or particles in a suspension. Despite its very high sensitivity, it is easy to operate and requires but a few seconds for a measurement. We also describe the construction and operation of this instrument.

Preparation and Characterization of Magnetic Nanospheres for in Vivo Application

New biodegradable magnetic nanospheres were synthesized for the application in the magnetic field assisted radionuclide therapy. For this purpose, superparamagnetic iron oxide cores were coated with several hydrophilic polymers, such as dextran, starch, chitosan, ficoll, polyethylene imine and polyvinylpyrrolidone. The different surface properties of these magnetic polymer nanospheres were demonstrated by a significant variation of the electrophoretic mobility of the particles in dependence on the pH-value.

Iron Oxide Nanoparticles - Tracer for Magnetic Particle Imaging

Magnetic Particle Imaging (MPI) is a tomographic imaging technique, which relies on the nonlinearity of the magnetization curves of magnetic particles such as iron oxide nanoparticles and the fact that the particle magnetization saturates at some magnetic field strength (1). Sensitivity of MPI highly depends on the magnetic characteristics of used tracer. We have developed colloidal stable iron oxide nanoparticles with different sizes and coatings and optimized their magnetic properties using a variety of fractionation techniques to improve tracer sensitivity. MPI spectra were obtained on the various iron oxide nanoparticles to select the most sensitive tracer for plaque imaging in homozygous mice for the Apoetm1Unc mutation. We conclude that iron oxide nanoparticles with appropriate magnetic properties are useful tracers for MPI.

Techniques for Electro- and Magnetokinetic Particle Characterization

The applicability of magnetic particles is strongly dependent on the electric surface charge and the magnetic susceptibility of the individual particles. Particle electrophoresis is a common method to control the production process and to assess the final colloidal solution. Particles within a wide size range are used and different measuring principles must therefore be applied. Laser based techniques using the Doppler or image transduction effect are very useful for the estimation of the mean electrophoretic mobility of particles within the size range below 500 nm. Automated techniques with image analysis are preferred for the analysis of mixtures of particles with sizes larger than 500 nm and with a broad variation of the surface charge. Electrophoretic fingerprints representing the mean electrophoretic mobility of a given particle suspension versus pH and ionic strength of the media are a helpful method for the assessment of the production and modification procedure of particles.