Force-Induced Remnant Magnetization Spectroscopy (FIRMS)
Our FIRMS technique implements a spectroscopic character into magnetic sensing for the first time: it distinguishes molecules based on the binding force of the noncovalent bonds between the target receptor molecules and their corresponding ligand molecules labeled with magnetic particles. FIRMS uses an atomic magnetometer to measure the magnetization of ligand-conjugated magnetic particles as a function of an external force. By gradually increasing the force amplitude, different noncovalent bonds will undergo dissociation at different forces determined by their respective binding force. The dissociation is indicated by a decrease in magnetization, because the dissociated magnetic particles undergo Brownian motion that leads to randomization of their magnetic dipoles (Scheme A). A FIRM spectrum will be obtained by taking the derivative of the magnetization with regard to force amplitude, in which peak positions indicate the binding forces of the interactions and peak amplitudes represent the abundance of the corresponding interactions (Scheme B).
Applications of FIRMS have been demonstrated with antibody-antigen dissociation and cellular recognition through ligand-receptor interactions. Ongoing research projects include DNA-protein binding and cellular analysis.
Scanning Magnetic Imaging (SMI)
Revealing the location of magnetic dipoles from measuring the magnetic field is a classic inverse problem. Without prior knowledge on the amplitude or the spatial information of the magnetic source, the two parameters cannot be uniquely determined by a single measurement of magnetic field. We introduce a scanning detection scheme (Scheme A) in which the sample of an ensemble of magnetic particles is scanned along the x-axis, which is perpendicular to the detection axis (d-axis) of a vector atomic magnetometer. By fitting the magnetic field profiles, the quantity and the location of the magnetic particles can be simultaneously obtained without any prior knowledge of either parameter (Scheme B). The spatial resolution for well separated magnetic samples has reached nearly 20 microns along the d-axis and at a detection distance of about 1 cm.
Applications of SMI have been demonstrated for two-dimensional localization of two separated samples containing magnetically labeled molecules. Ongoing research activities include improving spatial resolution and resolving more complicated magnetic samples.
Details coming soon!
Laser-Detected Magnetic Resonance Imaging (LD MRI)
LD MRI refers to MRI detected by an optical atomic magnetometer, which was first introduced by the Pines group and the Budker group (Xu et al., PNAS 103:12668, 2006). The spatial encoding can be performed in the Earth’s magnetic field (~0.04 mT) (Scheme). The apparatus is much cheaper than conventional MRI and does not require cryogenics. The unique features of performing LD MRI in such a low magnetic field are enhanced contrast based on spin-lattice relaxation and improved penetration in metal, which are our research aims.
Applications of this technique have been demonstrated by quantitative enhanced contrast and imaging of flow in porous metallic materials. We are currently designing new detection schemes to improve the detection efficiency and implementing new pulse sequences to improve the spatial resolution.
Atomic Magnetometry (AM)
Atomic magnetometry is arguably the most sensitive device for measuring magnetic field, due to the recent progresses in this field. This technique is based on magneto-optical interactions between coherent alkali atoms and polarized laser beams. The scheme here shows the principle of atomic magnetometers that are based on nonlinear magneto-optical resonance.
We use Cs atoms for the atomic sensor, the main component of an atomic magnetometer, because Cs has lowest boiling point among the alkali metals. The operating temperature is typically 37 ˚C, significantly lower than that of most other atomic sensors of comparable sizes. The sensitivity is approximately 150 fT for dc magnetic signal with 1 s signal averaging. We are researching on improving its sensitivity and applying it for the abovementioned techniques.