Abstract
In this paper, we review the preparation technology, integration in measurement systems and tests of high-Tc superconducting quantum interference devices (SQUIDs) intended for biomagnetic applications. A focus is on developments specific to Forschungszentrum Jülich GmbH, Chalmers University of Technology, MedTech West, and the University of Gothenburg, while placing these results in the perspective of those achieved elsewhere. Sensor fabrication, including the deposition and structuring of epitaxial oxide heterostructures, materials for substrates, epitaxial bilayer buffers, bicrystal and step-edge Josephson junctions, and multilayer flux transformers are detailed. The properties of the epitaxial multilayer high-Tc direct current SQUID sensors, including their integration in measurement systems with special electronics and liquid nitrogen cryostats, are presented in the context of biomagnetic recording. Applications that include magnetic nanoparticle based molecular diagnostics, magnetocardiography, and magnetoencephalography are presented as showcases of high-Tc biomagnetic systems. We conclude by outlining future challenges.
Highlights
The field of biomagnetism encompasses the detection of extremely weak magnetic fields generated by biological systems, e.g., by ion currents in nerve cells and heart tissue or by magnetic nanoparticles (MNPs) of magnetite (Fe3O4) that occur naturally in living organisms due to biomineralization or are used as a contrast agent for protein assays
At an optimal bias current, the superconducting quantum interference devices (SQUIDs) voltage V is periodic as a function of magnetic flux Φ through the loop of a direct current (DC) SQUID, with a period given by the flux quantum Φ0
The primary advantage of the modulation scheme is an increase in the readout voltage signal that is available to the field effect transistor in the first amplification stage of the SQUID readout electronics
Summary
The field of biomagnetism encompasses the detection of extremely weak magnetic fields generated by biological systems, e.g., by ion currents in nerve cells and heart tissue or by magnetic nanoparticles (MNPs) of magnetite (Fe3O4) that occur naturally in living organisms due to biomineralization or are used as a contrast agent for protein assays. Sufficient sensitivity and frequency bandwidth for biomagnetic measurements in the presence of relatively large background magnetic fields of >100 nT can currently only be achieved by using special sensors (‘biomagnetometers’) that are based on superconducting quantum interference devices (SQUIDs) Another promising technique for neuromagnetic recording utilizes atomic magnetometers ( referred to as opticallypumped or spin exchange relaxation-free magnetometers). State-of-the-art noise levels in high-Tc technology (
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