电磁与化学增强协同作用实现单分子拉曼光谱的明确观测
Unambiguous Observation of Single-Molecule Raman Spectroscopy Enabled by Synergic Electromagnetic and Chemical Enhancement
AI总结：
本研究通过二维材料-等离激元纳米间隙复合体系中电磁与化学增强的协同作用，实现了罗丹明B分子单分子拉曼光谱的明确观测，增强因子达16个数量级，为单分子科学研究开辟了新路径。
摘要：
拉曼光谱是一种用于检测、分析和识别分子的强大工具。将拉曼光谱的检测极限推进到基础的单分子（SM）水平是一项有着悠久历史的研究追求。由于分子本征拉曼散射的截面极小，必须引入某些光与物质相互作用的增强机制，将拉曼散射强度提升约14-15个数量级，使其达到与分子荧光强度相当的水平。\n在本研究中，我们报道了通过电磁增强与化学增强的协同作用，对吸附在等离激元纳米间隙内的罗丹明B（RhB）分子实现了单分子拉曼光谱的明确观测；该纳米间隙由位于二维（2D）单层WS₂上的金纳米颗粒与镀有2 nm SiO₂的金薄膜共同构成。即使在10⁻¹⁸ mol/L的极低浓度下，拉曼光谱仍清晰可见，与检测限为10⁻² mol/L的硅片参考检测样品相比，统计增强因子可达16个数量级。其中，电磁增强源自纳米间隙处激发的局域表面等离激元共振，增强幅度可达~10-11个数量级；化学增强则来自单层WS₂二维材料，增强幅度可达4-5个数量级。\n这两种经典的拉曼散射增强机制在这种特殊设计的二维材料-等离激元纳米间隙复合纳米体系中的协同实现与作用，使得RhB分子的单分子拉曼光谱得以被明确实验观测到。这种拉曼增强器件的研究路线有望开辟单分子科学的新前沿，实现对单分子及其在各种内外刺激下的时空演化的检测、识别与监测。
英文摘要：
Raman spectroscopy is a powerful tool to detect, analyze and identify molecules. It has been a long-history pursuit to push the detection limit of Raman spectroscopy down to the fundamental single-molecule (SM) level. Due to the tiny cross section of intrinsic Raman scattering of molecule, some enhancement mechanisms of light-matter interaction must be implemented to levitate the Raman scattering intensity by a huge number of ~14-15 orders of magnitude, to the level comparable with the molecule fluorescence intensity. In this work we report unambiguous observation of single-molecule Raman spectroscopy via synergic action of electromagnetic and chemical enhancement for rhodamine B (RhB) molecule absorbed within the plasmonic nanogap formed by gold nanoparticle sitting on the two-dimensional (2D) monolayer WS2 and 2 nm SiO2 coated gold thin film. Raman spectroscopy down to an extremely dilute value of 10-18 mol/L can still be clearly visible, and the statistical enhancement factor could reach 16 orders of magnitude compared with the reference detection sample of silicon plate with a detection limit of 10-2 mol/L. The electromagnetic enhancement comes from local surface plasmon resonance induced at the nanogap, which could reach ~10-11 orders of magnitude, while the chemical enhancement comes from monolayer WS2 2D material, which could reach 4-5 orders of magnitudes. The synergic implementation and action of these two prestigious Raman scattering enhancement mechanisms in this specially designed 2D material-plasmon nanogap composite nanoscale system enables unambiguous experimental observation of single-molecule Raman spectroscopy of RhB molecule. This route of Raman enhancement devices could open up a new frontier of single molecule science, allowing detection, identification, and monitor of single molecules and their spatial-temporal evolution under various internal and external stimuli.
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