Magnetic nanoparticles (MNPs) have superparamagnetic properties that can be detected by high sensitivity magnetometers which record the decay of the magnetic field they produce following their magnetization by an externally applied magnetic field pulse. The relaxation time of the MNPs’ magnetization has a strong dependence on the MNPs’ surrounding. The use of functionalized MNPs that preferentially attach to defined biological entities (magnetic tagging), such as cancer cells or specific organs thus allows the specific mapping of those entities.
After magnetizing the particles by exposing them to a strong external magnetic field, the relaxation of the sample's magnetization is measured by recording the time-dependence of the magnetic field that they generate by one (or an array of) magnetometers. The technique is known as magneto-relaxometry (MRX). The state of the art in MRX measurements is currently defined by SQUID magnetometers that have to be operated at cryogenic temperatures. The use of room-temperature atomic magnetometers promises several advantages that will increase the flexibility of an MRX apparatus and will thus significantly simplify the wider spreading of this technique.
In the past two years we have developed a technique for detecting magneto-relaxation signals from magnetic nanoparticles (MNP) by means of atomic magnetometers in a second-order gradiometer configuration. The three partners of our interdisciplinary collaboration have joined their complementary expertise (magnetometry by partner FRAP, sample preparation by partner AMI at Adolph-Merkle Institute, and source localization by solving the inverse problem by partner 3 (BMZ, now at Paul Scherrer Institute, PSI) to achieve first encouraging results: we have shown that atomic magnetometers have the sensitivity required to detect MRX signals from dilute samples of matrix-embedded nanoparticles, thereby breaking the monopoly position held so far by SQUID detectors for MRX measurements.
In the granted one-year extension of the project, we want to consolidate and further develop the methods, techniques and algorithms. Partner FRAP will record the spatial magnetic field distribution of structured distributions of in vitro MNPs (prepared by partner AMI) embedded in bulk matrices or on surfaces by deploying arrays of atomic magnetometers for large samples. We will modify the geometry, sensor spacing and detection method of our current set-up. Partner BMZ will collaborate with partner FRAP in the design of the new system and will be responsible for solving the inverse problem of relating the measured magnetic field maps to source distributions. In parallel to the large scale system, we will optimize our original “magnetic field mapping camera” for the imaging of small (cm-size) samples backed by numerical simulations.
The project is coordinated by Prof. Antoine Weis (University of Fribourg, partner FRAP), whose laboratories hosts the experimental installations for the MRX measurements. Partner AMI (Prof. A. Fink) will focus on the synthesis and characterization of monodisperse single superparamagnetic iron oxide nanoparti-cles (SPIONs) as well as magnetic beads whose iron oxide content, and with that the magnetic response, can be tuned during the synthesis. Derivatization to enhance colloidal stability, increased circulation time and target cell surfaces will be key issues. Dr. Bison's team (partner BMZ) will work on various aspects of multi-sensor magnetometry and source reconstruction.