A compound-eye-shaped photonic crystal SERS substrate for synergistic enhancement of Raman scattering

Solid-state SERS substrates are favored for their portability in point-of-care testing, but achieving both high sensitivity and superior signal uniformity remains challenging. We report a biomimetic Au@Ag/OPC film through self-assembling a Au@Ag nanoparticle layer on a three-dimensional opal photonic crystal (OPC). The key innovation lies in the design of a compound-eye-shaped structure, where the face-centered cubic OPC surface serves as a precise physical template, which forces the nanoparticles into a densely packed configuration with short-range disorder and long-range order, creating uniform SERS hotspots. Simultaneously, the 3D OPC structure modulates the excitation light field, enhancing local optical intensity. This synergistic combination of structural confinement and optical field modulation yields exceptional sensitivity (a detection limit of 10^-13 M for CV and an enhancement factor of 8.2 × 10⁹) and high uniformity. The practical utility is demonstrated by the direct identification of Staphylococcus aureus at 10³ CFU mL^-1 on an apple surface without pretreatment, showcasing its great potential for practical point-of-care diagnostics.