Plasmonic Nanocavities with Metallic Spacer Layers for Ultrasensitive Detection of Cr<sup>6+</sup> Ions
Xiaotian Wang, Wuliji Hasi, Shuang Lin, Siqingaowa Han, Guoqiang Fang, Xiang Lin
Abstract
Plasmonic nanocavities are ideally suited for optical sensing due to their unique ability to localize and focus light on the nanoscale. However, plasmonic nanocavities formed between metallic nanoparticles on a metal film are either hydrophobic or entirely filled with nonmetallic spacer layers, hindering molecular diffusion into the hotspot regions. In this study, we designed and fabricated a plasmonic structure of multitipped Au@Ag–Au particle in nanocuboids (PCs), integrated with a metal film to create open plasmonic nanocavities. By adjusting the pH of the growth solution to control the reduction rate and the etching rate of Au 3+, we precisely regulated the selective growth of metallic nanoparticles on the surface of Au@Ag core–shell nanocuboids. This plasmonic nanocavity is spaced by metal nanoparticles and forms 5 nm cavities open to the surroundings, which results in significantly enhanced Raman performance compared to traditional plasmonic nanocavities. Finally, functionalization of this plasmonic nanocavity enabled ultrasensitive detection of Cr 6+ Ions.