With support from the Chemical Measurement and Imaging Program in the Division of Chemistry, Professor Hafner at Rice develops a new way to measure the structure of biomolecules in the membranes that surround cells. In biology, a biomolecule's structure drives its function, so measuring structures is an important step in understanding life at the molecular scale. Molecules that are components of membranes are not soluble in water so it is a challenging task to solve their structures. Hafner and his group attach these molecules to gold nanoparticles and analyze light that is scattered from them. The nanoparticles focus light to the molecular scale. By monitoring how light scattered, a molecular structure can be determined. This new methodology will be applied to open questions in understanding the function of membranes in biology, as well as helping to understand the effects of molecular probes and drugs widely used in chemical and biological research. Professor Hafner also works on developing course materials on three fundamental scientific concepts behind this research: light waves, light scattering, and molecular vibrations. The developed materials are to be used in the high school teacher professional development programs offered by Rice University where most teachers are coming from Houston Independent School District (HISD).
The researcher team develops a new method for biomembrane molecular structure analysis that they have recently concept-proofed. Specifically, lipid membranes is applied to the surface of gold nanorods in solution, and their surface enhanced Raman scattering (SERS) is recorded. The electromagnetic near field of the gold nanorods (responsible for enhancement) and the Raman scattering tensors of the molecules of interest are calculated by the finite element method (FEM) and time dependent density functional theory (TDDFT), respectively. Unenhanced Raman spectra in the absence of gold nanorods are also recorded. Due to the alignment and rapid decay of the near field enhancement, these experimental and theoretical results are then combined through a ratiometric analysis to yield the position and orientation of molecular constituents responsible for specific vibrations. The researchers have recently demonstrated this by measuring the position and orientation of tryptophan in dioleoylphosphatidylcholine lipid membranes. The specific research objectives include: (1) Vibrational markers will be established to further analyze lipid membrane structure as well as the variety of lipids that can be included; (2) The effect of nanorod curvature on the lipid membrane structure will be evaluated; (3) Photothermal heating of the membrane due to laser excitation will be calculated based on the ratio of Stokes and anti-Stokes Raman scattering; (4) The position of tryptophan residues in a model alpha helix will be studied, as well as the peptide chain and the effect on membrane structure; and (5) The membrane position and orientation of polyunsaturated fatty acids and fluorescent membrane probes, and their impact on membrane structure, will be determined.
