Electrochemically Engineered Hierarchical Flower-like Ag Nanostructures within Al2O3 Honeycomb Microchannel Periodic Arrays for Ultra-Sensitive SERS Detection

In this study, we present a simple and facile synthesis approach to fabricate highly sensitive surface-enhanced Raman scattering (SERS) substrates by electrodeposition of silver (Ag) nanostructures into aluminum oxide (Al2O3) honeycomb microchannel periodic arrays (HMPAs). The spatial confinement and morphology of Ag nanostructures was precisely tuned by varying different deposition parameters. The SERS performance of the as prepared Ag nanostructures were evaluated. The hierarchical flower-like Ag nanostructures demonstrated the highest Raman signal enhancement as compared to other nanostructures electrodepsosited in the HMPAs. The densely packed network of plasmonic "hot spots" generated by the hierarchical flower-like Ag nanostructures, as well as the confinement of analyte molecules near the metal surface in Al2O3 HMPAs, are responsible for Raman signal enhancement. The hierarchical flower-like Ag nanostructure array achieved a limit of detection (LOD) of 9.3 × 10⁻11 M for rhodamine 6G (R-6G) and an enhancement factor (EF) of 6.99 × 107. This work highlights the significance of nanostructure’s precision over a large area and spatial confinement of analyte molecules in or near "hot spots", for enhanced SERS sensitivity and broad applicability in chemical analysis.