Design of Highly Sensitive Plasmonic Nanocavities and the Application in Trace Detection of Chromium (VI) Ion

The development of plasmonic nanocavities with high structural complexity is essential for various applications, particularly for SERS sensing, where their powerful electromagnetic field confinement capabilities enable efficient optical signal conversion and enhancement. In this study, six morphologies of Au–Ag core–shell nanocuboids (NCs) were prepared using the seed growth method and electrolytic reduction reaction, and assembled on the surface of an Au film to form a plasma nanocavity SERS substrate. The SERS performance of different structural plasmonic nanocavities was investigated using the 4-MBA probe molecule. The results showed that the most prominent SERS performance appeared in Au film/Au–Ag Rough nanocuboids (Au film/Au–Ag RNCs), with an enhancement factor as high as 2.17 × 10 9 . Since the Au–Ag nanoparticles (NPs) on the surface of Au film/Au–Ag RNCs not only increase the specific surface area and provide more adsorption sites but act as a metal isolation layer, forming abundant plasmonic nanocavities between the NPs and the Au film as well as between the NPs themselves. Finally, with the help of machine learning algorithms, this highly sensitive plasmonic nanocavities SERS substrate was used for the quantitative detection of Cr 6+, with a coefficient of determination between the predicted concentration and the actual concentration as high as 0.990, strongly indicating its advantages as a highly sensitive SERS nanoprobe.