University at Albany, State University of New York, 1400 Washington Avenue, Albany, New York 12222, USA.
Analyst. 2013 Mar 21;138(6):1665-73. doi: 10.1039/c2an36478f.
Surface- and tip-enhanced Raman spectroscopy (SERS and TERS) are modern spectroscopic techniques, which are becoming widely used and show a great potential for the structural characterisation of biological systems. Strong enhancement of the Raman signal through localised surface plasmon resonance enables chemical detection at the single-molecule scale. Enhanced Raman spectra collected from biological specimens, such as peptides, proteins or microorganisms, were often observed to lack the amide I band, which is commonly used as a marker for the interpretation of the secondary protein structure. The cause of this phenomenon was unclear for many decades. In this work, we investigated this phenomenon for native insulin and insulin fibrils using both TERS and SERS and compared these spectra to the spectra of well-defined homo peptides. The results indicate that the appearance of the amide I Raman band does not correlate with the protein aggregation state, but is instead determined by the size of the amino acid side chain. For short model peptides, the absence of the amide I band in TERS and SERS spectra correlates with the presence of a bulky side chain. Homo-glycine and -alanine, which are peptides with small side chain groups (H and CH(3), respectively), exhibited an intense amide I band in almost 100% of the acquired spectra. Peptides with bulky side chains, such as tyrosine and tryptophan, exhibited the amide I band in 70% and 31% of the acquired spectra, respectively.
表面增强拉曼光谱（SERS）和针尖增强拉曼光谱（TERS）是现代光谱技术，它们正变得越来越普及，并且在生物系统的结构表征方面展现出巨大的潜力。通过局域表面等离子体共振实现拉曼信号的强烈增强，使得在单分子尺度上进行化学检测成为可能。从生物标本（如肽、蛋白质或微生物）中收集到的增强拉曼光谱通常缺乏酰胺 I 带，酰胺 I 带通常被用作解释蛋白质二级结构的标记。几十年来，这种现象的原因一直不清楚。在这项工作中，我们使用 TERS 和 SERS 研究了天然胰岛素和胰岛素原纤维的这种现象，并将这些光谱与明确定义的同肽的光谱进行了比较。结果表明，酰胺 I 拉曼带的出现与蛋白质聚集状态无关，而是由氨基酸侧链的大小决定的。对于短模型肽，TERS 和 SERS 光谱中酰胺 I 带的缺失与大侧链的存在相关。具有小侧链基团（H 和 CH(3)，分别）的同型甘氨酸和丙氨酸，在几乎 100%的采集光谱中表现出强烈的酰胺 I 带。具有大侧链的肽，如酪氨酸和色氨酸，在 70%和 31%的采集光谱中分别表现出酰胺 I 带。
