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GWU Experimental Biophysics Group

Research Projects

The experimental biophysics group at GW is led by faculty (Mark Reeves and Xiangyun Qiu) with expertise in scanning probe-based near-field microscopy and nanofabrication. These techniques are being applied to the study of electronic materials, biomaterials, and to problems in cellular biological physics. Our projects allow our students to study structural linkages in proteins and crystalline systems, and to study biological and electronic functionality through sub-wavelength length-scale probes of the electromagnetic response of materials. Collaborations with federal laboratories (Naval Research Laboratory/NRL, Oak Ridge National Laboratory/ORNL, National Institute of Health/NIH) and with faculty in chemistry, biology, and in the medical school allow us to address a wide array of research questions and expose our students to interdisciplinary research. In the Physics Department, new approaches to investigating protein functionality are being developed, based on the electronic and optical response of self assembled nanoparticle systems. Below are some example projects which come from our current research.

Protein microarray fabrication

The determination of protein structures is a complicated and important issue for determining protein function and for drug design. Solid state NMR provides a new approach for determining protein structure in systems previously inaccessible to other methods of structure determination. We are also developing NMR techniques to probe cellular functions such as nitrogen uptake and DNA replication.

Electromagnetic response of new, thin-film dielectrics

Dielectric thin films promise to provide new approaches to microwave technology and as alternative gate dielectric in the semiconductor industry. In collaboration with materials scientists at Oak Ridge and the University of Florida, we are studying new materials and novel geometries such as potassium tantalum niobate. Our approach is to place a 1.6 GHz electromagnetic source on a scanning probe microscope platform to form a microwave microscope, capable of imaging the dielectric response of small volumes, 1 mm x 1 mm x 1 mm. Our flexibility in shaping the electromagnetic fields shape allows for the fundamental exploration of physical phenomena such as multilayer coupling and the effect of the anisotropic dielectric tensor.

Fluorescent NSOM

An extension of the near field approach from microwave to optical wavelengths (near-field scanning optical microscopy - NSOM) allows 500 nm wavelength light to illuminate regions as small as 50 nm in diameter. To extend this approach, tool, we are developing new approaches to create tips that will pass large amounts of light while still maintaining high spatial resolution to investigate the dynamics of proteins on the surfaces of cells.

Sub-micron proteomics

In collaboration with faculty in the chemistry department, we are developing a new kind of microscopy that produces spatial maps of protein distributions across the surfaces of cells. Proteins are sampled from the cell by ablating its surface with infrared light focused through a near-field tip. The proteins are captured into a mass spectrometer and then identified by their mass fingerprint. In this way, images of proteins expressed by lie cells can be produced in approximately one second time frames and with spatial resolutions less than one micron. Such unprecedented spatial and temporal resolution of protein function will bring new understanding to our knowledge of the physics of living systems.

Chip based proteomics

A number of recent advances have enabled the optical detection of proteins and DNA in solution. By combining chemical selectivity of ligands bound to nanoparticles with attachment-mediated shifts in light scattering from those particles, scientists have devised sensitive assays of biological activity. Our approach is to measure the electrical resistivity of self-assembled nanoparticle wires to which chemically selective linkers are bound. Such chip-based approaches to proteomics logically extend optical and scanning probe approaches and will provide the large-scale data sets needed to develop new physical models or complex biological systems.

Fundamentals of nanoparticle composites

We are developing new approaches to the bench-top synthesis of nanoparticles, into wire-like and planar geometries. Such materials can be the basis of a new generation of biological sensing elements if we can capitalize on the unique physical properties of the nanoparticles sensed by conventional electronics. As a first developmental step, we are measuring fundamental phenomena such as quantum, size-limited effects, as they are translated to the properties of macroscopically assembled devices.

Laboratory Facilities

Scanning microwave microscope
2 T electromagnet
Agilent vector network analyzer
closed cycle refrigerator
high-pressure diamond anvil cell
zeta potential apparatus for minidialyzers
Nanonics Multiview 4000 NSOM
Optical Tweezers
Fluorescence Microscopy (GW Medical School)
Flow Cytometry Facility (GW Medical School)
Kratos Axima MALDI-TOF Mass Spectrometer (GW Medical School)
Affymetrix GeneChip Microarray facility (GW Medical School)
Transmission electron microscope (GW Medical School)
Differential Scanning Calorimetry (GW-Inst. for Material Science)
Thermogravimetric Analysis (GW-Inst. for Material Science)
Differential Thermal Analysis (GW-Inst. for Material Science)
JEOL Scanning Electron Microscope with EDX (GW-Inst. for Material Science)
Quantum Design SQUID Magnetometer (GW-Inst. for Material Science)
Atomic force microscope (GW-Inst. for Material Science)
X-ray diffractometer (GW-Inst. for Material Science)
UV-VIS and FT-IR spectroscopies (GW-Inst. for Material Science)
Flourescence Spectroscopy (GW-Inst. for Material Science)
X-ray Flourescence (GW-Inst. for Material Science)
14 T vertical, cold-bore magnet (NRL)
6 T horizontal, rotating, room-temperature-bore magnet (NRL)
Atomic force microscopes (NRL)
UV near-field optical microscope (NRL)
Class 100 clean room (NRL)