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

Abstract

We demonstrate the reliable creation of monolayers of Au nanoparticles in random close-packed arrays with sub-nm gaps as a sensitive SERS substrate. Using oxygen plasma etching, all the original molecules creating the nanogaps can be removed and replaced with scaffolding ligands that deliver extremely consistent gap sizes below 1 nm. This allows precision tailoring of the chemical environment of the nanogaps which is crucial for practical Raman sensing applications. Because the resulting aggregate monolayers are easily accessible from opposite sides by fluids and by light, high performance fluidic sensing cells are enabled. The ability to cyclically clean off analytes and reuse these films is shown, exemplified by sensing of toluene, volatile organic hydrocarbons, and paracetamol, among others.