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 × 10 6 . 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.

Dendritic Forest-Like Ag Nanostructures Prepared Using Fluoride-Assisted Galvanic Replacement Reaction for SERS Applications

“…High-quality anisotropic Ag nanostructures can be obtained through many methods, including photolithography and template growth from electrodeposition, in which the surface roughness of Ag nanostructure can be precisely controlled during fabrication to yield a greatly enhanced SERS signal for highly sensitive detection of brilliant cresyl blue, benzenethiol, and adenine [ 10 , 11 , 12 , 13 , 14 , 15 , 16 ]. Both photolithography and template growth from electrodeposition require sophisticated surface patterning steps and a time-consuming bottom-up approach to build nanostructures on the substrate.…”

Electrochemically deposited silver nanostructures for use as surface‐enhanced Raman scattering (SERS) substrates in point‐of‐need diagnostic devices

“…[ 8–10 ] Recently, Raveendran et al have developed a technique to form novel SERS substrates by electrochemically reducing silver ions (Ag + ) from solution to form plasmonically active, dendritic silver (Ag) nanostructures. [ 11,12 ] The reduction process takes place through gold (Au) electrodes fabricated onto a silicon (Si) microchip (Si‐Au chip). Unlike typical electroreduction processes, these Ag nanostructures grow laterally from the edge of the electrodes along the insulating Si surface.…”

“…As these substrates were only recently developed, much of the work to date has been focused on understanding the fundamentals of nanostructure growth. [ 11–13 ] Raveendran's most recent work presents the underlying electrochemical reactions and several reaction parameters that are critical to Ag nanostructure formation. [ 11 ] Ag + reduction at the cathode is balanced by the oxidation of citrate (provided in the form of trisodium citrate) at the anode, as shown in Equations () and (), respectively.…”

“…[ 11–13 ] Raveendran's most recent work presents the underlying electrochemical reactions and several reaction parameters that are critical to Ag nanostructure formation. [ 11 ] Ag + reduction at the cathode is balanced by the oxidation of citrate (provided in the form of trisodium citrate) at the anode, as shown in Equations () and (), respectively. [ 11 ] In addition to being oxidized, trisodium citrate (Na 3 C 6 H 5 O 7 ) was found to provide several functions within the formation process, including supporting anisotropic crystal growth and decreasing ionic migration within the local environment.…”

“…[ 11 ] Ag + reduction at the cathode is balanced by the oxidation of citrate (provided in the form of trisodium citrate) at the anode, as shown in Equations () and (), respectively. [ 11 ] In addition to being oxidized, trisodium citrate (Na 3 C 6 H 5 O 7 ) was found to provide several functions within the formation process, including supporting anisotropic crystal growth and decreasing ionic migration within the local environment. [ 11 ] The latter helps to create the diffusion‐limiting reaction conditions necessary to achieve fractal Ag nanostructure morphologies.…”