Fluxgate-Magnetrelaxometrie magnetischer Nanopartikel in der Bioanalytik

Magnetic nanoparticles find wide application in medicine and biotechnology. Established applications include the use of magnetic nanoparticles as contrast agents for magnetic resonance imaging and for the separation and purification of biomolecules. The nanoparticles have to be tailored for a given application which, for example, requires a defined size and size distribution or functionalization to specifically bind to targets. In bioanalytics, the magnetic properties of superparamagnetic nanoparticles can be used to detect biomolecules. The magnetic moments of superparamagnetic nanoparticles are aligned by a magnetic field and after abruptly switching off the field the moments relax into random directions. The temporary decay depends on the mobility of the nanoparticles. The mobility of the nanoparticles changes by binding to targets and offers the possibility to quantify the amount of targets. A measurement system was developed and characterized that measures the magnetic relaxation with highly sensitive magnetic field sensors at room temperature without the need of costly cooling and magnetic shielding. Coils are built in a measurement unit which magnetizes the sample. In addition, two fluxgate magnetometers were integrated which measure the stray field of the sample. A differential arrangement of the fluxgate magnetometers suppresses interfering signals and increases the signal-to-noise ratio. Coil electronics were developed which switch the coil current in fractions of the coil time constant. To control the measurement cycle and to analyze the magnetorelaxation data, software applications were developed. The measurement uncertainty and the detection limits of the system were determined with respect to measuring small amounts of magnetic nanoparticles and biomolecules. With this measurement system, binding experiments with superparamagnetic nanoparticles and targets of different sizes were performed. Furthermore, binding kinetics were investigated. Within the scope of the Sonderforschungsbereich 578 “from gene to product”, the method of magnetorelaxation measurement was used to characterize the kinetics of polymerization and load capacities of hydrogels. After the measurement unit had been tested successfully, a laboratory instrument was developed which integrates the measurement coil system and electronics together with a personal computer in a single 19“ instrument. With this instrument, the characterization of magnetic nanoparticles in terms of size distribution and agglomeration as well as magnetic properties can be investigated. Such a laboratory instrument allows the cost-effective quality control of magnetic nanoparticles and their application in research and industry.