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Biomagnetic Research and Technology (1)
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Steinhoff, Uwe (3)
Eberbeck, Dietmar (2)
Trahms, Lutz (2)
Wiekhorst, Frank (2)
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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.
magnetic binding assay; magnetic drug targeting; magnetic nanoparticles; magnetofection; nanoparticle biodistribution
Quantification of specific bindings of biomolecules by magnetorelaxometry
Journal of Nanobiotechnology
The binding reaction of the biomolecules streptavidin and anti-biotin antibody, both labelled by magnetic nanoparticles (MNP), to biotin coated on agarose beads, was quantified by magnetorelaxometry (MRX). Highly sensitive SQUID-based MRX revealed the immobilization of the MNP caused by the biotin-streptavidin coupling. We found that about 85% of streptavidin-functionalised MNP bound specifically to biotin-agarose beads. On the other hand only 20% of antibiotin-antibody functionalised MNP were specifically bound. Variation of the suspension medium revealed in comparison to phosphate buffer with 0.1% bovine serum albumin a slight change of the binding behaviour in human serum, probably due to the presence of functioning (non heated) serum proteins. Furthermore, in human serum an additional non-specific binding occurs, being independent from the serum protein functionality.
The presented homogeneous bead based assay is applicable in simple, uncoated vials and it enables the assessment of the binding kinetics in a volume without liquid flow. The estimated association rate constant for the MNP-labelled streptavidin is by about two orders of magnitude smaller than the value reported for free streptavidin. This is probably due to the relatively large size of the magnetic markers which reduces the diffusion of streptavidin. Furthermore, long time non-exponential kinetics were observed and interpreted as agglutination of the agarose beads.
Pseudo current density maps of electrophysiological heart, nerve or brain function and their physical basis
Biomagnetic Research and Technology
In recent years the visualization of biomagnetic measurement data by so-called pseudo current density maps or Hosaka-Cohen (HC) transformations became popular.
The physical basis of these intuitive maps is clarified by means of analytically solvable problems.
Examples in magnetocardiography, magnetoencephalography and magnetoneurography demonstrate the usefulness of this method.
Hardware realizations of the HC-transformation and some similar transformations are discussed which could advantageously support cross-platform comparability of biomagnetic measurements.
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