Roa Simón, Kaihara Terunori, Pedano María Laura, Parsamyan Henrik, Vavassori Paolo
Instituto de Nanociencia y Nanotecnología (CNEA - CONICET), Nodo Bariloche, Av. Bustillo 9500, C.P. 8400, S.C. de Bariloche, Río Negro, Argentina.
Laboratorio de Fotónica y Optoelectrónica, Centro Atómico Bariloche, Av. Bustillo 9500, 8400 S. C. de Bariloche, Río Negro, Argentina.
Nanoscale. 2024 Aug 15;16(32):15280-15297. doi: 10.1039/d4nr00817k.
Nowadays, Au dimer-based nanostructures are exhaustively studied due to their outstanding potential as plasmonic nanoantennas for future applications in high-sensitivity molecular sensing by Surface-Enhanced Raman Spectroscopy (SERS). In this work, we analyze nano-gapped Au nanowires (NWs) or Au-NW dimers for designing efficient nanoantennas, reporting an exhaustive study about dimer length and laser polarization orientation effects on their SERS-based molecular sensing performance. Arrays of nanoantennas with gaps of about 22 ± 4 nm, nominal square cross-sections of 60 nm × 60 nm, and different segment lengths from 300 nm up to 1200 nm were fabricated by Au evaporation and subsequent e-beam lithography. The SERS performance was studied by confocal Raman microscopy using a linearly-polarized 633 nm laser. A critical impact of the polarization alignment on the spectral resolution of the studied Raman marker imprint was observed. The results show that the Raman signal is maximized by aligning the polarization orientation with the nanowire long axis, it is reduced by increasing the relative angle, and it is abruptly minimized when both are perpendicular. These observations were consistent with numerical simulations carried out by the FDTD method, which predicts a similar dependence between the orientation of linearly-polarized light and electric-near field amplification in the nano-gap zone. Our results provide an interesting paradigm and relevant insights in determining the role of laser polarization in the Raman signal enhancement in nano-gapped Au nanowires, showing the key role of this measurement condition on the SERS-based molecular sensing efficiency of this kind of nanostructure.
如今，基于金二聚体的纳米结构因其作为等离子体纳米天线在表面增强拉曼光谱（SERS）高灵敏度分子传感未来应用中的巨大潜力而得到了广泛研究。在这项工作中，我们分析了纳米间隙金纳米线（NWs）或金 - NW 二聚体以设计高效的纳米天线，报告了关于二聚体长度和激光偏振方向对其基于 SERS 的分子传感性能影响的详尽研究。通过金蒸发和随后的电子束光刻制备了间隙约为 22 ± 4 nm、标称方形横截面为 60 nm × 60 nm 且段长从 300 nm 到 1200 nm 不等的纳米天线阵列。使用线性偏振 633 nm 激光通过共焦拉曼显微镜研究了 SERS 性能。观察到偏振对准对所研究的拉曼标记印记的光谱分辨率有至关重要的影响。结果表明，通过将偏振方向与纳米线长轴对齐，拉曼信号最大化，随着相对角度增加信号降低，而当两者垂直时信号突然最小化。这些观察结果与通过时域有限差分（FDTD）方法进行的数值模拟一致，该模拟预测了线性偏振光的方向与纳米间隙区域中的电近场放大之间存在类似的依赖性。我们的结果为确定激光偏振在纳米间隙金纳米线拉曼信号增强中的作用提供了一个有趣的范例和相关见解，表明了这种测量条件对这类纳米结构基于 SERS 的分子传感效率的关键作用。
