Metamaterial absorbers with Au nanoctahedrons hybrid Ag nanowires for highly efficient UV–Vis absorption and SERS sensing

Herein, a class of functional metamaterial absorbers (MAs) was developed: chemically synthesized Au nanoctahedrons randomly arranged on Ag nanowires (NWs) to form 3D-stacked hybrid structures that is capable of effective absorption of UV–Vis light, and exhibiting surface-enhanced Raman scattering (SERS) sensing performance. Interestingly, these MAs were constructed using a simple functional-group binding and droplet-evaporation self-assembly strategy. Experimental results show that well-designed MAs, with appropriate surface coverage (15–25 %) of Au nanoctahedrons on Ag NWs exhibit a measured average absorptance above 95 % across the 200 to 800 nm wavelength range. Additionally, the proposed MAs demonstrate a SERS enhancement factor of 1.5–2.2 × 109, which is much higher than that of individual Ag NWs or Au nanoctahedrons. The limit of detection for 4-mercaptopyridine molecules was found to be ∼10−11 mol/L. It is inferred that the multiple plasmonic resonances and coupling derived from the hybridization of Au nanoctahedrons and Ag NWs are vital in achieving broadband and high absorbance of UV–Vis spectrum, and the produced conspicuous E-field enhancements with high-density hotspots greatly enhance the SERS-sensing performance. These findings suggest the potential of such functional MAs as promising candidates for optical devices aimed at solar-energy harvesting or trace-substance detection.