Ag@Cu2O-MXene core–shell nanostructures: plasmonic coupling and charge transfer for ultra-sensitive SERS detection

Abstract

The two-dimensional (2D) layered structure of MXene provides a large specific surface area, making it an ideal platform for optimizing geometric configurations in surface-enhanced Raman scattering (SERS) applications. In this study, we developed a novel ternary core–shell nanostructure, Ag@Cu₂O-MXene, in which Ag@Cu₂O core–shell nanoparticles (NPs) are uniformly anchored onto 2D Ti₃C₂T_x MXene nanosheets. The Ag NPs exhibit strong localized surface plasmon resonance, while the narrow bandgap and high electron mobility of the Cu₂O shell promote efficient charge transfer. Importantly, plasmonic coupling between the Ag core and the MXene substrate further enhances plasmon absorption, resulting in a substantial increase in SERS activity and enabling highly sensitive molecular detection. Using this composite, we achieved an ultra-low detection limit of 10⁻⁹ M for methylene blue. The MXene substrate further facilitates rapid electron transfer from the Ag core to the the Cu₂O shell, while its surface defects contribute additional charge carriers to Cu₂O, enhancing the utilization of photogenerated electrons. Notably, the SERS enhancement was positively correlated with the thickness of the Cu₂O shell, highlighting the tunable nature of the Ag@Cu₂O-MXene core–shell nanostructure.