Research efforts are underway to probe biological molecules with Raman spectroscopy in three states-crystal, semi-solid, and solution-to illuminate the structural transformations that occur across phases. The optical characterization of biological molecules using vibrational spectroscopy supplies critical, detailed structural information unavailable through fluorescent measurements and unhampered by water absorption. To observe Raman-active vibrational modes, physiological concentrations, enhancement of the Raman scattering cross-section is often necessary. Enhancement factors of orders of magnitude are achievable through resonance Raman (i.e., matched laser excitation with electronic transition, or surface enhanced Raman), where anisotropic, metallic nanoparticles of silver or gold are placed in close proximity to the molecule, either in solution or on a surface. Two Raman spectrometers are available for this effort, including a microscope and multiple laser lines. Also exciting is a combination of Raman microscopy and microfluidic technology to monitor the vibrational spectra of biomolecules while rapidly changing the buffer environment to induce conformational changes. Raman spectroscopy can be used to query the structure of membrane proteins immobilized in supported, synthetic lipid bilayers both on a surface and in suspended liposomes. Furthermore, Raman microscopy can be used to view protein concentration gradients throughout a cell.

Another angle of our research effort focuses on the low-frequency torsional modes (<200 cm^-1) of proteins and polynucleotides. This region of the spectrum is rich with dynamical and structural information. A triple-grating monochromator provides the rejection capabilities necessary for observing these low-frequency vibrations. A companion molecular modeling effort is absolutely critical due to the complexity and nascency of this spectroscopic region, and is implemented with the aid of a 6-node UNIX cluster and computational software. The combination of this effort, with both its experimental and theoretical sections, with the complementary CW Terahertz Spectroscopy effort described elsewhere, greatly increases our ability to assign torsional vibrational modes to the flexibility of the biological molecule and provide the force field information needed to delineate the driving forces responsible for protein structure, folding, and function.

 

key words

Biophysics; Magnetic field; Modeling; Nanoparticles; Protein; Raman imaging; Resonance Raman; Surface-enhanced Raman spectroscopy (SERS);

Citizenship:  Open to U.S. citizens

Level:  Open to Postdoctoral applicants