Tang Yuchen, Zhuang Yongpeng, Zhang Shaohua, Smith Zachary J, Li Yuee, Mu Xijiao, Li Mengna, He Caili, Zheng Xingxing, Pan Fangfang, Gao Tingjuan, Zhang Lizhi
China Key Laboratory of Pesticide and Chemical Biology of Ministry of Education, Wuhan 430079, China.
College of Chemistry, Central China Normal University, Wuhan 430079, China.
ACS Cent Sci. 2021 May 26;7(5):768-780. doi: 10.1021/acscentsci.1c00117. Epub 2021 Apr 27.
Raman scattering provides stable narrow-banded signals that potentially allow for multicolor microscopic imaging. The major obstacle for the applications of Raman spectroscopy and microscopy is the small cross section of Raman scattering that results in low sensitivity. Here, we report a new concept of azo-enhanced Raman scattering (AERS) by designing the intrinsic molecular structures using resonance Raman and concomitant fluorescence quenching strategies. Based on the selection of vibrational modes and the enhancing unit of azobenzenes, we obtained a library of AERS molecules with specific Raman signals in the fingerprint and silent frequency regions. The spectral characterization and molecular simulation revealed that the azobenzene unit conjugated to the vibrational modes significantly enhanced Raman signals due to the mechanism of extending the conjugation system, coupling the electronic-vibrational transitions, and improving the symmetry of vibrational modes. The nonradiative decay of azobenzene from the excited state quenched the commitment fluorescence, thus providing a clean background for identifying Raman scattering. The most sensitive AERS molecules produced Raman signals of more than 4 orders of magnitude compared to 5-ethynyl-2'-deoxyuridine (EdU). In addition, a frequency tunability of 10 distinct Raman bands was achieved by selecting different types of vibrational modes. This methodology of AERS allows for designing small-molecule Raman probes to visualize various entities in complex systems by multicolor spontaneous Raman imaging. It will open new prospects to explore innovative applications of AERS in interdisciplinary research fields.
拉曼散射提供了稳定的窄带信号，这有可能实现多色显微成像。拉曼光谱和显微镜应用的主要障碍是拉曼散射的截面小，导致灵敏度低。在此，我们通过使用共振拉曼和伴随荧光猝灭策略设计固有分子结构，报告了一种偶氮增强拉曼散射（AERS）的新概念。基于振动模式的选择和偶氮苯的增强单元，我们获得了一系列在指纹区和沉默频率区具有特定拉曼信号的AERS分子。光谱表征和分子模拟表明，由于扩展共轭体系、耦合电子-振动跃迁以及改善振动模式对称性的机制，与振动模式共轭的偶氮苯单元显著增强了拉曼信号。偶氮苯从激发态的非辐射衰变猝灭了荧光，从而为识别拉曼散射提供了干净的背景。与5-乙炔基-2'-脱氧尿苷（EdU）相比，最灵敏的AERS分子产生的拉曼信号增强了4个多数量级。此外，通过选择不同类型的振动模式，实现了10个不同拉曼带的频率可调性。这种AERS方法允许设计小分子拉曼探针，通过多色自发拉曼成像可视化复杂系统中的各种实体。它将为探索AERS在跨学科研究领域的创新应用开辟新的前景。
