Recent Developments in Magnetic Molecular Sensing and Low-Field MRI

Shoujun Xu, University of Houston, sxu7@uh.edu

Magnetic molecular sensing is widely used in biomedical research via labeling molecules with magnetic nanoparticles and microparticles. Several techniques and methods have been developed for achieving high sensitivity, spatial resolution, and molecular specificity. For sensitivity, atomic magnetometers are used for detection, which are the most sensitive devices for measuring magnetic signal. The spatial resolution is obtained by a scanning magnetic imaging technique. The quantity and spatial information of the magnetically labeled molecules can be obtained with prior knowledge on either parameter. In general, magnetic sensing does not contain a spectroscopic parameter for resolving magnetic signal into a group of individual signals for different molecules. To solve this problem, a force-induced remnant magnetization spectroscopy (FIRMS) technique is developed. It measures the magnetization of the magnetic particles as a function of the binding force between the magnetically-labeled ligand molecules and the receptor molecules on the target surface. Molecular specificity is obtained from the spectrum of magnetization vs. binding force. Various applications of these techniques in molecular and cellular recognition will be presented.

We also demonstrate the technique of using atomic magnetometry in magnetic resonance imaging (MRI): laser-detected MRI. Contrary to conventional MRI, which is performed in a strong magnetic field, we conduct spatial encoding in the Earth’s magnetic field. Spatial resolution in millimetre has been achieved. One unique feature of laser-detected MRI is that the low Larmor frequency can penetrate metallic materials. Other advantages include low cost, portability, and low power consumption. Future applications and technical difficulties will be discussed.