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

In a world that increasingly demands answers in real-time, there exists a distinct need for chemical sensors that can quickly and efficiently detect substances with high sensitivity and selectivity. To address this need, we use surface-enhanced Raman scattering (SERS) as a powerful analytical technique that can provide ultrasensitive and versatile chemical detection on a mobile platform when implemented on a handheld Raman spectrometer. However, the large laser spot size of handheld Raman spectrometers requires SERS substrates of sufficient surface area. Here, we present a facile method for electrodepositing nanostructured silver (Ag) SERS substrates onto silicon microchips. In this method, silver ions are continuously reduced from a large volume of solution in an apparatus resembling a batch electrochemical reactor. The straightforward protocol is scalable, fast, and reproducible. Further, we investigate the influence of temperature and fluid agitation on the growth of Ag nanostructures with the intention of maximizing surface area coverage. We observe an increase in lateral nanostructure growth from heating due to an increase in the diffusion coefficient. However, no significant increase in lateral nanostructure growth is observed from stirring the reagent solution. Despite the absence of trends in lateral growth, we find that high agitation levels promote the growth of extraneous Ag structures on top of the nanostructured film, indicating the presence of a boundary layer at the silicon surface. Further, we find that increased diffusion rates at high temperatures shift the reaction towards the limits of the mass transfer-controlled regime.