Silver nanodesert rose as a substrate for surface-enhanced Raman spectroscopy.

Silver galvanic displacement on silicon has been employed to produce large-area reproducible substrates, with morphology similar to that of the natural desert rose but on the micrometer scale. The process is based on an extremely simple wet chemistry approach using only AgF and KF, as silver and fluoride sources. A key element is the absence of HF in the deposition solution, which has been commonly used in previous silver galvanic displacement processes. The new process affords a higher degree of control in the redox reaction than those reported previously. The structures formed in this manner possess a large area-to-volume ratio with a high density of rough silver flakes uniformly distributed across the substrate. The silver morphology on the nanometer scale is shown to provide an excellent platform for surface-enhanced Raman spectroscopy (SERS), yielding detection levels for trans-1,2-bis(4-pyridyl)ethylene, 4-mercaptopyridine, and Rhodamine 6G in solution down to ppb, ppt, and ppq limits, respectively. The SERS reproducibility on the substrate was verified by monitoring the signal intensity variations across the sample. The simplicity of the substrate fabrication process, as well as the excellent uniformity, opens up opportunities for the quantitative and in-field chemical trace analysis using these substrates.