Tunable Fractal Nanostructures for Surface-Enhanced Raman Scattering via Templated Electrodeposition of Silver on Low-Energy Surfaces

Abstract

Here, we demonstrated a facile method for growing nanofeatured silver (Ag) structures on a planar microelectrode platform. The nanostructures were assembled along the electrically insulating substrate, growing from the microelectrode edge with the electrodes acting as the template. This was done by (a) limiting the nucleation to the edges of the electrodes and (b) chemically functionalizing the insulating substrate to promote an interaction between itself and the growing metallic structures. These structures were able to reach lateral lengths greater than 100 μm. Additionally, we performed an extended investigation into how the nanostructure morphology can be changed from spherical aggregates to fractal dendrites by altering the electrical signal and solution composition. We determined citrate to be a necessary additive and showed that it acts as a supporting electrolyte, capping agent, and oxidizing/complexing agent. Next, using optimal deposition conditions, we assembled Ag surface-enhanced Raman scattering (SERS) substrates with an enhancement factor up to 4.55 × 106. Finally, we demonstrated how these SERS nanostructures can also serve as concentration amplification devices, accelerating analyte deposition onto the detection site by means of electrohydrodynamics.