Electrochemically engineered hierarchical flower-like Ag nanostructures within Al2O3 honeycomb microchannel periodic arrays for ultra-sensitive SERS detection†

Sensitive surface-enhanced Raman scattering (SERS) substrates were fabricated by electrodeposition of silver (Ag) nanostructures into aluminum oxide (Al₂O₃) honeycomb microchannel periodic arrays (HMPAs). The spatial confinement and morphology of Ag nanostructures were precisely tuned by varying different deposition parameters. The SERS performance of the as-prepared Ag nanostructures was evaluated. The hierarchical flower-like Ag nanostructures demonstrated the highest Raman signal enhancement as compared to other nanostructures electrodeposited 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, is responsible for the Raman signal enhancement. The hierarchical flower-like Ag nanostructure array achieved a limit of detection of 9.3 × 10⁻¹¹ M for rhodamine 6G and an enhancement factor of 6.99 × 10⁷. This work highlights the significance of nanostructures' 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.