Research Starter Grant: Three-Dimensional Polarization Second-Harmonic Generation Microscopy

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A grant is awarded to Dr. Toussaint of the University of Illinois at Urbana-Champaign to develop a three-dimensional polarization second harmonic generation microscope. This approach is an alternative approach to traditional fluorescence microscopy using nonlinear optical scattering to completely obviate any reliance on exogenous probes, and rather uses the chemical properties of the specimen under study as the contrast agent, thereby allowing for truly noninvasive imaging. The caveat here is that SHG microscopy works for a special, but extremely relevant, class of biological systems?those that exhibit an ordered spatial arrangement of molecules (noncentrosymmetry). In this case, such systems upon interacting with an intense laser pulse naturally produce light at twice the frequency of the original laser pulse. This SHG light is what is used to image specimens in much the same way as fluorescence is used in two-photon fluorescence microscopy. However, utilization of this technique has been limited to exploiting only two degrees-of-freedom of the electric field vector (polarization) of the original light generating the SHG. In this case, the polarization is used to yield information on the molecular symmetries of specimens. The proposed technique will utilize the full 3D state of polarization of the light in order to generate, for the first time, three-dimensional polarization SHG. Three-dimensional polarization SHG microscopy will be created by integrating vector beams with standard polarization optics. Specifically, a radially polarized vector beam produces an enhanced polarization at a microscope?s focus, while the transverse polarization components are obtained from manipulation of commercial polarization optics. This new instrument will allow for advances in biological discovery as well as provide unique training and educational opportunities to undergraduate and graduate students in the biological sciences as well as engineering. Through interdisciplinary research and development students across these disciplines will gain insights into the fundamentals of design and development as well as cell biology.