Hossain Mohammad Kamal
Interdisciplinary Research Center for Sustainable Energy Systems (IRC-SES), Research Institute, King Fahd University of Petroleum & Minerals (KFUPM), 31261, Dhahran, Saudi Arabia.
K.A.CARE Energy Research & Innovation Center at Dhahran, King Fahd University of Petroleum & Minerals (KFUPM), 31261, Dhahran, Saudi Arabia.
Sci Rep. 2024 May 8;14(1):10559. doi: 10.1038/s41598-024-61503-7.
Hotspots are high-intensity electromagnetic zones that form, for example, at the interstitials of plasmonic nanoaggregates, resulting in a considerable rise in the enhancement factor. However, it is inevitable to achieve specific nanometric geometry as well as a suitable technique to capture the details of hotspots. We report near-field surface-enhanced Raman scattering (SERS) spectroscopy of a well-defined gold nanoaggregate of a few nanoparticles adsorbed with a small number of target analytes. A spectrally and spatially resolved SERS measurement setup using an aperture near-field scanning optical microscope (a-NSOM) facilitated the direct observation of localized electromagnetic (EM) fields at the interstitials through SERS. Correlated optical image and corresponding nanometric geometry were captured through the home-built a-NSOM setup. Near-field SERS spectra were recorded at different sites of interest. It was evident that the interstitial positioned at the center of the tetramer provided the most intense Raman scattering, implying the possibility of a SERS-active hotspot therein. SERS bands of the spectrum of the Raman-active dye Rhodamine 6G recorded at the same hotspot coincided well with those reported so far. It was noteworthy that most of the SERS bands in such scenery got enhanced. Such direct observation with high spatial resolution is indispensable to understanding the origin of localized EM fields at "hotspots" and the EM enhancement factor in the SERS process. A finite-difference time-domain (FDTD) analysis was carried out to validate the results.
热点是高强度电磁区域，例如在等离子体纳米聚集体的间隙处形成，导致增强因子显著提高。然而，实现特定的纳米几何形状以及采用合适的技术来捕捉热点的细节是不可避免的。我们报道了一种由少数几个吸附有少量目标分析物的纳米颗粒组成的明确的金纳米聚集体的近场表面增强拉曼散射（SERS）光谱。使用孔径近场扫描光学显微镜（a-NSOM）的光谱和空间分辨SERS测量装置通过SERS促进了对间隙处局部电磁场（EM）的直接观察。通过自制的a-NSOM装置捕获了相关的光学图像和相应的纳米几何形状。在不同的感兴趣位置记录了近场SERS光谱。很明显，位于四聚体中心的间隙提供了最强的拉曼散射，这意味着其中存在SERS活性热点的可能性。在同一热点记录的拉曼活性染料罗丹明6G光谱的SERS谱带与迄今为止报道的谱带非常吻合。值得注意的是，在这种情况下，大多数SERS谱带都得到了增强。这种具有高空间分辨率的直接观察对于理解“热点”处局部电磁场的起源以及SERS过程中的电磁增强因子是必不可少的。进行了时域有限差分（FDTD）分析以验证结果。
