Gold Sunflower Microelectrode Arrays with Dendritic Nanostructures on the Lateral Surfaces for Antireflection and Surface-Enhanced Raman Scattering

A facile method is presented for uniform electrochemical growth of dendritic gold nanostructures selectively at the lateral surfaces of conductor–dielectric disc arrays to obtain gold sunflower microelectrode arrays (SMA). The electrical anisotropicity of Au–SiO₂ disc arrays is leveraged to restrain the electrochemical growth to the lateral surfaces, while the enhanced electric field on the lateral surfaces due to the fringe effect facilitates growth of highly dendritic nanostructures in unprecedented growth regimes. Electrochemical growth of gold dendrites is performed on 200 nm thick gold lateral surfaces of Au–SiO₂ disc arrays with a disc diameter of 5 μm, a 50 nm SiO₂ thickness, and dendrite sizes controlled from 150 to 1400 nm in length. The fabricated SMA exhibit broadband antireflection characteristics for visible radiation, tunable photonic–plasmonic hybrid modes in the near-infrared region, strong electromagnetic (EM) field enhancements, and a high density of EM hotspots useful for surface-enhanced Raman scattering (SERS). The efficacy of developed gold SMA is demonstrated for SERS-based detection of an important Raman label 4-aminothiophenol (4-ATP), which is widely used for binding and detection of different biomarkers. The optimized SERS substrate exhibits an impressive limit of detection of 0.5 nM for 4-ATP with a relative standard deviation of only 6.74% and could be reused multiple times following the surface regeneration process.