Quantification of specific bindings of biomolecules by magnetorelaxometry

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

Quantitative reconstruction of a magnetic nanoparticle distribution using a non-negativity constraint

Magnetorelaxometry (MRX) is a non-invasive method for the specific quantification of magnetic nanoparticles (MNP). Here, we investigate experimentally the reconstruction of the MNP concentration in an extended volume. A phantom with varying but known MNP distribution was subsequently magnetized by 48 planar coils at different locations. The MRX signal was measured using the PTB 304 SQUID-magnetometer system. The inverse problem was solved by means of a non-negative least squares (NNLS) algorithm and compared to a minimum norm estimation (TSVD-MNE). The reconstruction by NNLS shows a deviation of the total MNP amount of less than 3 % (10% by TSVD-MNE). Hence, adapted non-invasive MRX methods can reliable reconstruct the MNP content in extended volumes

Cross-Correlation of Motor Activity Signals from dc-Magnetoencephalography, Near-Infrared Spectroscopy, and Electromyography

Neuronal and vascular responses due to finger movements were synchronously measured using dc-magnetoencephalography (dcMEG) and time-resolved near-infrared spectroscopy (trNIRS). The finger movements were monitored with electromyography (EMG). Cortical responses related to the finger movement sequence were extracted by independent component analysis from both the dcMEG and the trNIRS data. The temporal relations between EMG rate, dcMEG, and trNIRS responses were assessed pairwise using the cross-correlation function (CCF), which does not require epoch averaging. A positive lag on a scale of seconds was found for the maximum of the CCF between dcMEG and trNIRS. A zero lag is observed for the CCF between dcMEG and EMG. Additionally this CCF exhibits oscillations at the frequency of individual finger movements. These findings show that the dcMEG with a bandwidth up to 8 Hz records both slow and faster neuronal responses, whereas the vascular response is confirmed to change on a scale of seconds

Imaging of magnetic nanoparticles based on magnetorelaxometry with sequential activation of inhomogeneous magnetization fields

Magnetrelaxometrie (MRX) ist eine spezifische Messmethode zur Detektion des Zerfalls der Magnetisierung eines Ensembles von Nanopartikeln, nachdem ein Magnetisierungsfeld abgeschaltet wurde. Als Sensoren für MRX können hochempfindliche supraleitende Quanteninterferometer (SQUIDs) verwendet werden. Wir präsentieren ein Konzept, wie quantitative dreidimensionale Bilder der Verteilung magnetischer Nanopartikel in biologischem Gewebe durch die Kombination der SQUID-Messtechnik mit multiplen räumlich inhomogenen Magnetisierungsfeldern erzielt werden können. Das inverse Problem der Bildrekonstruktion wird durch die Kombination der unterschiedlichen Magnetisierungsfelder stabilisiert. Als Beispiel wurde ein Shepp-Logan-Phantom mit 4096 Voxeln und 10x10x10 cm3 Volumen bei einem Signal-zu-Rausch-Verhältnis von 250 numerisch rekonstruiert