Small fluorescent molecules are widely used as probes of biomembranes. Different probes optically indicate membrane properties such as the lipid phase, thickness, viscosity, and electrical potential. The detailed molecular mechanisms behind probe signals are not well understood, in part due to the lack of tools to determine probe position and orientation in the membrane. Optical measurements on aligned biomembranes and lipid bilayers provide some degree of orientational information based on anisotropy in absorption, fluorescence, or nonlinear optical properties. These methods typically find the polar tilt angle between the membrane normal and the long axis of the molecule. Here we show that solution-phase surface enhanced Raman scattering (SERS) spectra of lipid membranes on gold nanorods can be used to determine molecular orientation of molecules within the membrane. The voltage sensitive dye 4-(2-(6-(dibutylamino)-2-naphthalenyl)ethenyl)-1-(3-sulfopropyl)-hydroxide, known as di-4-ANEPPS, is studied. Through the analysis of several peaks in the SERS spectrum, the polar angle from the membrane normal is found to be 66°, and the roll angle around the long axis of the molecule to be 305° from the original orientation. This structural analysis method could help elucidate the meaning of fluorescent membrane probe signals, and how they are affected by different lipid compositions.

中文翻译：

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通过增强拉曼散射的结构分析，确定膜探针的方向。

小荧光分子被广泛用作生物膜的探针。不同的探针从光学上指示膜的性质，例如脂质相，厚度，粘度和电势。探针信号背后的详细分子机制尚未得到很好的理解，部分原因是缺少确定膜中探针位置和方向的工具。对准的生物膜和脂质双层的光学测量可基于吸收，荧光或非线性光学性质的各向异性提供一定程度的取向信息。这些方法通常在膜法线和分子的长轴之间找到极性倾斜角。在这里我们显示金纳米棒上脂膜的溶液相表面增强拉曼散射（SERS）光谱可用于确定膜内分子的分子取向。研究了电压敏感染料4-（2-（6-（二（丁基丁氨基）-2-萘基）乙烯基）-1-（3-磺丙基）氢氧化物，称为di-4-ANEPPS。通过分析SERS光谱中的几个峰，发现与膜法线的极角为66°，围绕分子长轴的侧倾角为原始方向的305°。这种结构分析方法可以帮助阐明荧光膜探针信号的含义，以及它们如何受到不同脂质成分的影响。研究了称为di-4-ANEPPS的物质。通过分析SERS光谱中的几个峰，发现与膜法线的极角为66°，围绕分子长轴的侧倾角为原始方向的305°。这种结构分析方法可以帮助阐明荧光膜探针信号的含义，以及它们如何受到不同脂质成分的影响。研究了称为di-4-ANEPPS的物质。通过分析SERS光谱中的几个峰，发现与膜法线的极角为66°，围绕分子长轴的侧倾角为原始方向的305°。这种结构分析方法可以帮助阐明荧光膜探针信号的含义，以及它们如何受到不同脂质成分的影响。