Magnetic Nanoparticles in Rotating Magnetic Fields
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Beschreibung
In this work, the rotational dynamics of magnetic nanoparticles (MNPs) in a size range from 12nm to more than 100nm was investigated with respect to its application in rotating magnetic field-based homogeneous bioassays. This concept enables the direct quantitative detection of proteins in solution, which is a promising technique owing to the increasing need for patient-side laboratory diagnostics.
A
uxgate-based measurement system was developed, which detects the stray fieldof the MNP sample magnetization induced by a rotating magnetic field(RMF). The gradiometric arrangement of two
uxgate magnetometers facilitates even outside a magnetically shielded environment a robust magnetic detection of various MNP types. The performance of the measurement system was characterized with different reference samples. For instance, iron oxide nanoparticle samples with iron concentrations below 0:005 g=L could be detected. For the analysis of the rotational dynamics, the phase lag between the rotating magnetic fieldand the MNP sample magnetization was calculated. This physical quantity enables in the investigated concentration range a particle concentration-independent characterization of the dissolved MNPs, for example the determination of their hydrodynamic size. An accurate description of the measurement results for all fieldfrequencies and amplitudes was given by a numerical solution of the Fokker-Planck equation, which is the basic equation for the description of the magnetization dynamics of a MNP ensemble in magnetic fieldsincluding thermal agitation. An empirical model derived from these results was discussed and applied for the evaluation of the RMF bioassay concept, which relies on the change of the phase lag caused by proteins specifically bound to the particle surface.
Measurements on various spherical and rod-shaped MNPs with single- and multi-cores matched perfectly with simulations based on the presented theory and were supported by additional characterization techniques, for example photon correlation spectroscopy and static magnetization measurements. Experiments with spherical single-core iron oxide nanoparticles dominated by the Brownian relaxation and conjugated with protein G demonstrated the feasibility of the quantitative protein detection based on the RMF concept. For this single-core particle type a core diameter of 30nm was found to be optimal since its dynamics is significantly affected by small proteins bound to the surface but it is still clearly dominated by the Brownian relaxation. Multi-core particles with a larger hydrodynamic size and partly dominated by the Neel relaxation process were less suitable for the direct detection of proteins in solution when avoiding cross-linking effects. Finally, measurements on streptavidin functionalized single-core particles demonstrated the principle quantitative analysis of samples containing the biomedical relevant biomarker HER2.
Autor*in
Jan Henrik Dieckhoff
Themen in »Magnetic Nanoparticles in Rotating Magnetic Fields«
MNPs Nanoparticle RMF Rotating Magnetic Fields