• Theoretical Condensed-Matter Physics
• Theoretical Elementary Particle Physics
• Astrophysics and General Relativity
• Experimental Elementary Particle Physics
• Accelerator Physics
• Experimental Condensed-Matter Physics
• Biological Physics
• Multidisciplinary Research
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B.S., 1985, Physics, Nanjing University. Ph.D. student, 1985-86, Institute of Physics, Chinese Academy of Sciences. M.S, 1988, Physics, University of Southern Mississippi. Ph.D., 1993, Biophysics, University of Michigan at Ann Arbor. Postdoctoral Fellow, Biophysics, Princeton University, 1994-97. Assistant Professor, Physics, Cornell University, 1998-2004. Associate Professor, Physics, Cornell University, 2004-2009. Professor, Physics, Cornell University, 2009. Outstanding Student Award, Nanjing University, 1985. University of Michigan Biophysics Fellowship, 1988-89. National Cancer Institute Fellowship, 1994. Damon Runyon-Walter Winchell Foundation Postdoctoral Fellowship, 1995-97. Damon Runyon Scholar Award, 1999-00. Dale F. and Betty Ann Frey Scholar of the Damon Runyon-Walter Winchell Foundation, 1999. Alfred P. Sloan Research Fellow, 1999-01. Beckman Young Investigator Award, 1999-02. Keck Foundation Distinguished Young Scholar in Medical Research Award, 2000-07. Provost's Award for Distinguished Scholarship, 2008. Howard Hughes Medical Institute Investigator, 2008-present. Member, American Physical Society. Member, American Biophysical Society. Member, American Society for Cell Biology.

Research Areas
Single molecule mechanical manipulations of biological molecules; high-resolution optical trapping and detection; single molecule fluorescence imaging and detection; nanofabrication; molecular motor mechanisms; biopolymer kinetics and dynamics; protein-DNA interactions (especially those involved in gene expression); genomics; modeling of diffusion, kinetics, and dynamics of biomolecules

Current Research

We are a single molecule biophysics lab. We develop state-of-the-art optical trapping techniques to probe the motions and dynamics of molecular motors that translocate along DNA, as well as the regulation of these motions by the presence of other proteins that interact with the same DNA substrate. We also develop theoretical models to elucidate the mechanism of the molecular motors based on thermodynamics and statistical mechanics. Here we'll highlight a couple of novel experimental approaches that we have recently developed.

We have developed the unzipping technique as a versatile and powerful single-molecule method to explore protein-DNA interactions. A single DNA double helix is unzipped in the presence of DNA-binding proteins using a feedback-enhanced optical trap. When the unzipping fork in a DNA reaches a bound protein molecule, we observe a dramatic increase in the tension in the DNA, followed by a sudden tension reduction. Analysis of the unzipping force throughout an unbinding event reveals information about the precise spatial location and dynamic nature of the protein-DNA complex.

 Conventional optical traps are only capable of applying a force on a trapped particle. Our angular optical trap is also capable of applying a torque on the particle. This opens up new possibilities for experiments on biological molecules, many of which are known to generate rotational motions and work against topological obstacles. As an example, shown below is a DNA molecule that is torsionally constrained at one end to a nanofabricated quartz cylinder, and at the other end to a microscope coverglass surface. As the cylinder is rotated via rotation of the input laser polarization, turns are added to the end of the DNA molecule, resulting in a supercoiled DNA with the formation of plectonemes. The rapid dynamics of supercoiling is monitored by simultaneous detection of four signals: force, position, torque, and angular orientation of the cylinder.

Spotlight

Jalina Keeling is an undergraduate student with the Itai Cohen Group on Complex Matter Physics (who is at Cornell as part of the NSF's Research Experiences for Undergraduates program). She is conducting experiments similar to the epitaxial growth of crystals, but using polymer beads. She uses a confocal microscope to scan a sample of these beads from bottom to top. Her research seeks to answer the questions "What structures form? How do we tune the concentration of polymers to change ...
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