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Shoujun Xu


Shoujun Xu
Associate Professor
Postdoctoral: Lawrence Berkeley National Laboratory
Postdoctoral: California Institute of Technology
Ph.D., Physical Chemistry, Johns Hopkins University, 2002
B.S., Nanjing University, 1993

Department of Chemistry
University of Houston
Houston, Texas 77204-5003

Office: 1019 - SERC
Phone: 832.842.8828

We focus on developing various magnetic-based techniques for molecular and cellular imaging and magnetic resonance imaging. The following is a list of research themes we are currently pursuing. This list will be updated upon the invention of new technologies.

Force-Induced Remnant Magnetization spectroscopy (FIRMS)
Ligand-conjugated magnetic particles are widely used in molecular and cellular imaging. This technique implements a spectroscopic character into magnetic imaging for the first time: it uses the binding force to distinguish physisorption and specific binding between the receptor molecules and the ligands on the magnetic particles. By applying an external force with varying amplitude, the different interactions will undergo selective dissociation. For each force the magnetization of the bound magnetic particles is measured. 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 force of the interactions and peak amplitudes represent the abundance of the corresponding interactions. We are applying this new technique for magnetic molecular imaging.

Scanning Magnetic Imaging (SMI)
Revealing the location of a magnetic dipole from measuring its 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 in which the sample of an ensemble of magnetic particles is scanned across a magnetic sensor. By fitting the magnetic field profile, the quantity and the location of the magnetic particles can be simultaneously obtained without any prior knowledge on either parameter. The spatial resolution on the detection axis of the magnetic sensor is nearly 20 microns at a distance of about 1 cm. We are improving the resolution for practical applications.

Laser-Detected Magnetic Resonance Imaging (LD MRI)
Conventionally, MRI is carried out in a strong magnetic field (> 3 T). It offers excellent spatial resolution and involves no radiative isotopes. Among its few limitations, high cost and incapability of penetrating metal stand out. We develop a laser-based detection technique that uses optical atomic magnetometers. The spatial encoding is performed in the Earth’s magnetic field (~ 0.04 mT) or lower. The expensive superconducting magnet is thus eliminated, which substantially reduces the cost of MRI. Our current spatial resolution is just below 1 mm. Further improvement on spatial resolution is ongoing. This technique won a R&D 100 award in 2007.

Atomic Magnetometry (AM)
Atomic magnetometry is arguably the most sensitive device for measuring magnetic field, rivaling superconducting quantum interference device. This technique is based on magneto-optical properties of coherent alkali atoms interacting with polarized laser beams. We use cesium atoms for its lowest boiling point among the alkali metals. The operating temperature is ~37 Celsius which is significantly lower than other atomic magnetometers. The sensitivity is approximately 100 fT for 1 s measuring time of dc magnetic signal. We are improving its sensitivity and applying it for the abovementioned techniques.

Details about our research can be found on our group website or by contacting Dr. Shoujun Xu at Thank you for your interest.