Significant increase in dipole moments of functional groups using cation bonding for excellent SERS sensing as a universal approach

Abstract The recently developed dipole-based surface-enhanced Raman scattering (SERS) technique has opened a new opportunity to fabricate high-performance sensing platforms with advantages including molecular identification abilities, decreased costs, and high sensitivity. Although extensive efforts have been devoted to increasing the area density of molecular dipoles on graphene to improve sensing sensitivity, limited dipole moments hinder them from further enhancement and applications. Here, we propose a versatile approach to significantly increase the dipole moments of oxygen-containing functional groups (OFGs) on graphene using cation bonding. Taking Cu2+ as a model, dozens of enhancements in dipole moments are demonstrated using theoretical calculations as confirmed by SERS measurements, and a comparison is made with general OFGs and graphene oxide-based SERS platforms. The outstanding contribution of Cu OFG bonds to SERS is proven using IR, XPS, and EFM, where electromagnetic and typical chemical mechanisms are excluded by the TEM and UPS results. The as-prepared Cu-OFG SERS platforms not only show a high sensitivity to Rhodamine 6 G (10-10 M), but also demonstrate their further applications in detecting trace nitrate (10-10 M), a harmful substance in drinking water, and thiabendazole (0.01 ppm), a parasiticide for fruits. The cation bonding strategy applies to various cations to fabricate excellent versatile SERS platforms for use in various fields, such as trace poison detection and biomedical sensing.