Membrane Structure Analysis by Enhanced Raman Scattering

在化学系化学测量和成像项目的支持下，莱斯大学的Hafner教授开发了一种测量细胞周围膜中生物分子结构的新方法。在生物学中，生物分子的结构决定其功能，因此测量结构是在分子尺度上理解生命的重要一步。构成膜的分子是不溶于水的，因此研究它们的结构是一项具有挑战性的任务。哈夫纳和他的团队将这些分子附着在金纳米粒子上，并分析从它们散射出来的光。纳米粒子将光聚焦到分子尺度。通过监测光散射的方式，可以确定分子结构。这种新方法将应用于理解生物学中膜功能的开放性问题，以及帮助理解化学和生物学研究中广泛使用的分子探针和药物的作用。Hafner教授还致力于开发这项研究背后的三个基本科学概念的课程材料：光波，光散射和分子振动。开发的材料将用于莱斯大学提供的高中教师专业发展计划，其中大多数教师来自休斯顿独立学区（HISD）。研究小组最近开发了一种新的生物膜分子结构分析方法，并进行了概念验证。具体而言，将脂质膜应用于溶液中的金纳米棒表面，记录了其表面增强拉曼散射（SERS）。利用有限元法（FEM）和时间依赖密度泛函理论（TDDFT）分别计算了金纳米棒（负责增强）的电磁近场和目标分子的拉曼散射张量。在没有金纳米棒的情况下，也记录了未增强的拉曼光谱。由于近场增强的对准和快速衰减，这些实验和理论结果然后通过比率分析相结合，以产生负责特定振动的分子成分的位置和方向。研究人员最近通过测量二油酰磷脂酰胆碱脂膜中色氨酸的位置和取向证明了这一点。具体研究目标包括：(1)建立振动标记物，进一步分析脂质膜结构以及可包含的脂质种类；(2)评价纳米棒曲率对脂膜结构的影响；(3)根据Stokes和反Stokes拉曼散射的比值计算激光激发膜的光热加热；(4)研究色氨酸残基在α螺旋模型中的位置、肽链及其对膜结构的影响；(5)确定多不饱和脂肪酸和荧光膜探针的膜位置和取向，以及它们对膜结构的影响。

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.