Optimized electromagnetic enhancement and charge transfer in MXene/Au/Cu₂O hybrids for achieving efficient SERS

The rational optimization of the electromagnetic field enhancement and charge transfer in a Raman substrate is vital for achieving efficient surface-enhanced Raman scattering (SERS). Herein, a ternary plasmonic substrate, whose structure-adjustable Au nanotriangle/Cu₂O hybrids are combined with two-dimensional Ti₃C₂T MXene ultrathin nanosheets, is prepared and used for efficient SERS detection of molecules. By controlling the growth of Cu₂O on Au nanotriangles, Au/Cu₂O hybrids with three tips exposed are prepared, which show much better SERS performance than bare Au and core-shell Au@Cu₂O in detecting methylene blue (MB) under excitation at 785 nm due to the optimized electromagnetic field enhancement and charge transfer. Furthermore, the Au/Cu₂O hybrids are transferred to the plasmonic Ti₃C₂T nanosheet, generating a further enhanced electromagnetic field around their interfaces. As a result, the MXene/Au/Cu₂O hybrids present further improved SERS activity, and their analytical enhancement factor reaches 2.4 × 10⁹ and the detection limit is as low as 10^-12 M. The enhancement mechanism can be ascribed to the improved electric field enhancement around the Au tips and the interface between MXene and Au/Cu₂O. Meanwhile, the multiple charge-transfer processes between Au, Cu₂O, MXene, and MB also play an important role in improving the SERS signal.