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Garth J. Simpson

Garth J.  Simpson Profile Picture

Assisant Professor — Analytical Chemistry
Ph.D., 2000, University of Colorado, Boulder


Contact Info:

gsimpson@purdue.edu
765-496-3054


Training Group(s):
Membrane Biology


Current Research Interests:

The emphasis of the Simpson Group is on the development of novel techniques and their application in addressing important problems at biological interfaces. As biotechnology continues to be an area of rapid growth both academically and economically, so grows the need for new tools to interrogate biological systems.

Nonlinear Optics of Biological Interfaces

The growing availability of intense, pulsed laser sources has launched a new age in nonlinear optical spectroscopy. The simplest nonlinear optical phenomenon is the frequency doubling of light (second harmonic generation or SHG). SHG is forbidden in random media but can arise from surfaces, where symmetry breaking at the interface generates a localized surface-specific signal. Because of this surface specificity, SHG allows unique opportunities in studies of buried interfaces, where other measurements are often dominated by the bulk response. Furthermore, the basic measurements themselves are remarkably simple to perform and typically yield readily detectable signals from surface films less than a single molecular layer thick. A primary focus of our recent research has been the development of methods to mine the exquisite structural information contained within the polarization dependence of the nonlinear signals. Studies span the range from development of new fundamental theories regarding the nature of nonlinear optics to construction of state-of-the-art instrumentation to measurements of structure and function in biological membranes and protein films.

Nanoscale AC Electrokinetics  

Particles and cells behave strangely in alternating current (AC) electric fields. Particles can be attracted or repulsed from sharp electrode tips (dielectrophoresis), can be made to rotate (electrorotation), and can link together to form long chains (pearl-chaining). AC fields can induce nanoscopic pores in cell and vesicle membranes, allowing the introduction of macromolecules (electroporation). Additionally, cells and vesicles can be made to fuse together (electrofusion). We are developing a number of methods to allow extension of these remarkable phenomena to nanoscopic measurements and systems.



Selected Publications:

Simpson, G. J. "New Tools for Surface Second Harmonic Generation" Appl. Spec. 2001, 55, 16-32.

Simpson, G. J. "'Structural Origins of Circular Dichroism in Surface Second Harmonic Generation" J. Chem. Phys. 2002, 117, 3398-3410.

Simpson, G. J.; Wilson, C. F.; Gericke, K.-H.; Zare, R. N. "Coupled Electrorotation: Two Proximate Microspheres Spin in Registry with an AC Electric Field" ChemPhysChem 2002, 3, 416-423.

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