An Investigation On The Use Of Au@SiO2@Au Nanomatryoshkas As Gap Enhanced Raman Tags Dataset

Gap-enhanced Raman tags are a new type of optical probe that have wide applications in sensing and detection. A gap-enhanced Raman tag is prepared by embedding Raman molecules inside a gap between two plasmonic metals such as an Au core and Au shell. Even though placing Raman tags beneath an Au shell seems counter-intuitive, it has been shown that such systems produce a stronger surface-enhanced Raman scattering response due to the strong electric field inside the gap. While the theoretical support of the stronger electric field inside the gap was provided in the literature, a comprehensive understanding of how the electric field inside the gap compares with that of the outer surface of the particle was not readily available. We investigated Au@SiO$_2$@Au nanoparticles with diameters ranging from 35 nm to 70 nm with varying shell (2.5--10 nm) and gap (2.5--15 nm) thicknesses and obtained both far-field and near-field spectra. The extinction spectra from these particles always have two peaks. The low-energy peak redshifts with the decreasing shell thickness. However, when the gap thickness decreases, the low-energy peaks first blueshift and then redshift, producing a C-shape in the peak position. For every system we investigated, the near-field enhancement spectra were stronger inside the gap than on the outer surface of the nanoparticle. We find that a thin shell combined with a thin gap will produce the greatest near-field enhancement inside the gap. Our work fills the knowledge gap between the exciting potential applications of gap-enhanced Raman tags and the fundamental knowledge of enhancement provided by the gap.

间隙增强拉曼标签（Gap-enhanced Raman tags）是一类新型光学探针，在传感与检测领域拥有广泛应用。其制备方式为将拉曼分子嵌入两种等离子体金属（plasmonic metals）之间的间隙中，例如金核-金壳结构。尽管将拉曼标签置于金壳下方看似有悖直觉，但已有研究表明，此类体系借助间隙内的强电场可产生更强的表面增强拉曼散射（surface-enhanced Raman scattering）响应。虽然已有文献为间隙内强电场提供了理论支撑，但目前尚缺乏对间隙内电场与颗粒外表面电场的系统性对比认知。本研究针对直径介于35 nm至70 nm之间的金@二氧化硅@金（Au@SiO₂@Au）纳米颗粒，调控其壳层厚度（2.5~10 nm）与间隙厚度（2.5~15 nm），并获取了其远场与近场光谱。该类颗粒的消光光谱始终存在两个特征峰：低能峰随壳层厚度减小发生红移；而当间隙厚度减小时，低能峰先发生蓝移后转为红移，峰位变化呈现C形曲线。在所研究的所有体系中，间隙内的近场增强光谱强度均高于纳米颗粒外表面。本研究发现，薄壳层搭配薄间隙可使间隙内的近场增强效果达到最优。本研究填补了间隙增强拉曼标签极具应用潜力的场景与间隙所提供的增强效应基础认知之间的知识空白。