Semiconductor-Bimetallic Plasmonic Heterojunction ZnO-Ag-Cu as Reusable SERS Substrate with Attomolar Detection Limit

Semiconductor-bimetallic ZnO-Ag-Cu (ZAC) heterojunction of different compositions were fabricated as highly sensitive SERS substrates. ZnO nanorods were synthesized using a facile hydrothermal route. ZAC composites were synthesized via impregnation method by keeping ZnO content same and varying the mole fractions of Ag and Cu. The ZnO matrix, known for its stability and photocatalytic properties, was decorated with Ag and Cu nanoparticles to enhance plasmonic activity and boost SERS. Introducing semiconductor oxide as SERS substrate reduces the substrate cost due to its self-cleaning property upon exposure to UV light. When SERS activity of ZAC composites were compared with either ZnO-Ag (ZA) or ZnO-Cu (ZC) composites, the best SERS performance was recorded with ZAC55, where the Ag and Cu content are same. ZAC55 produced a SERS enhancement factor of 6.2×10⁶ and a limit of detection of 10^-18 M and 10^-15 M for the analyte molecules Rhodamine 6 G (R6G) and Methylene Blue (MB), respectively, using 532 nm laser excitation. The enhanced SERS performance is attributed to the synergistic effects of ZnO, Ag, and Cu, unveiling ZAC55 as a promising next-generation SERS substrate. Along with remarkable sensitivity, ZAC55 showed promising reusability and reproducibility, indicating its potential for practical applications in chemical sensing.