Controlling Atomic-Scale Restructuring and Cleaning of Gold Nanogap Multilayers for Surface-Enhanced Raman Scattering Sensing

We demonstrate thereliable creation of multiple layersof Au nanoparticlesin random close-packed arrays with sub-nm gaps as a sensitive surface-enhancedRaman scattering substrate. Using oxygen plasma etching, all the originalmolecules creating the nanogaps can be removed and replaced with scaffoldingligands that deliver extremely consistent gap sizes below 1 nm. Thisallows precision tailoring of the chemical environment of the nanogapswhich is crucial for practical Raman sensing applications. Becausethe resulting aggregate layers are easily accessible from oppositesides by fluids and by light, high-performance fluidic sensing cellsare enabled. The ability to cyclically clean off analytes and reusethese films is shown, exemplified by sensing of toluene, volatileorganic compounds, and paracetamol, among others.