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.