Department of Materials Science and Engineering, University of California, Los Angeles, CA, 90095, United States.
School of Nano-Science and Nano-Engineering, Suzhou & Collaborative Innovation Center of Suzhou Nano Science and Technology, Xi'an Jiaotong University, Xi'an, 710049, China.
Anal Biochem. 2020 Jun 15;599:113709. doi: 10.1016/j.ab.2020.113709. Epub 2020 Apr 13.
The orientation dependence of the Raman spectral features of individual protein/biomolecules is studied using surface-enhanced Raman spectroscopy (SERS). Large variation in spectral features mainly in term of peak intensity is observed from small proteins/peptides. We aim to address the question of whether the spectral features of SERS are uniquely determined by the type of protein/molecules or are influenced prominently by factors more than the identity of the molecules such as orientation of molecules relative to the substrate surface. The standard deviation in the intensity of individual Raman peaks diminishes for protein size larger than 13 amino acids. Secondary structure of protein (such as protein-protein interaction) remains unchanged regardless of protein orientation. Numerical simulation studies corroborate the experimental observation in that the SERS spectral features of biomedically relevant protein (of larger than 13 amino acids in size, which represent all human protein types) are not affected by the orientation of amino acids randomly dispersed on SERS-active surfaces. These findings are instrumental to understanding the exceedingly high (label-free) specificity when SERS is used in identifying proteins/peptides as can be found in numerous publications from different research groups in both in vivo and in vitro analyses. It was noted that the spectral position of all Raman peaks assignable to the various amino acids are independent of molecule orientation even though their intensities do vary.
使用表面增强拉曼光谱（SERS）研究了单个蛋白质/生物分子的拉曼光谱特征的各向异性。从小蛋白质/肽中观察到光谱特征（主要是峰强度）的很大变化。我们旨在解决 SERS 的光谱特征是否仅由蛋白质/分子的类型决定，还是受分子的身份以外的因素（如分子相对于基底表面的取向）的显著影响的问题。对于大于 13 个氨基酸的蛋白质，单个拉曼峰强度的标准偏差减小。无论蛋白质取向如何，蛋白质的二级结构（如蛋白质-蛋白质相互作用）都保持不变。数值模拟研究证实了实验观察结果，即生物医学相关蛋白质（大于 13 个氨基酸大小，代表所有人类蛋白质类型）的 SERS 光谱特征不受随机分散在 SERS 活性表面上的氨基酸取向的影响。这些发现对于理解 SERS 在识别蛋白质/肽时具有极高的（无标记）特异性非常重要，这在来自不同研究小组的体内和体外分析的众多出版物中都有报道。值得注意的是，即使强度有所变化，所有可归因于各种氨基酸的拉曼峰的光谱位置都与分子取向无关。
