title: Hot-Volumes as Uniform and Reproducible SERS-Detection Enhancers in Weakly-Coupled Metallic Nanohelices.
abstract: Reproducible and enhanced optical detection of molecules in low concentrations demands simultaneously intense and homogeneous electric fields acting as robust signal amplifiers. To generate such sophisticated optical near-fields, different plasmonic nanostructures were investigated in recent years. These, however, exhibit either high enhancement factor (EF) or spatial homogeneity but not both. Small interparticle gaps or sharp nanostructures show enormous EFs but no near-field homogeneity. Meanwhile, approaches using rounded and separated monomers create uniform near-fields with moderate EFs. Here, guided by numerical simulations, we show how arrays of weakly-coupled Ag nanohelices achieve both homogeneous and strong near-field enhancements, reaching even the limit forreproducible detection of individual molecules. The unique near-field distribution of a single nanohelix consists of broad hot-spots, merging with those from neighbouring nanohelices in specific array configurations and generating a wide and uniform detection zone ("hot-volume"). We experimentally assessed these nanostructures via surface-enhanced Raman spectroscopy, obtaining a corresponding EF of ~107and a relative standard deviation <10%. These values demonstrate arrays of nanohelices as state-of-the-art substrates for reproducible optical detection as well as compelling nanostructures for related fields such as near-field imaging.
authors.affiliation: School of Physics and CRANN, AMBER Research Centre, Trinity College Dublin, College Green, Dublin 2, Ireland.
authors.forename: José M
authors.initials: JM
authors.lastname: Caridad
authors.affiliation: School of Chemistry and CRANN, AMBER Research Centre, Trinity College Dublin, College Green, Dublin 2, Ireland.
authors.forename: Sinéad
authors.initials: S
authors.lastname: Winters
authors.affiliation: School of Physics and CRANN, AMBER Research Centre, Trinity College Dublin, College Green, Dublin 2, Ireland.
authors.forename: David
authors.initials: D
authors.lastname: McCloskey
authors.affiliation: School of Chemistry and CRANN, AMBER Research Centre, Trinity College Dublin, College Green, Dublin 2, Ireland.
authors.forename: Georg S
authors.initials: GS
authors.lastname: Duesberg
authors.affiliation: School of Physics and CRANN, AMBER Research Centre, Trinity College Dublin, College Green, Dublin 2, Ireland.
authors.forename: John F
authors.initials: JF
authors.lastname: Donegan
authors.affiliation: School of Physics and CRANN, AMBER Research Centre, Trinity College Dublin, College Green, Dublin 2, Ireland.|Department of Physics, Chair for Applied Physics, Friedrich-Alexander-University Erlangen-Nürnberg (FAU), Staudtstr. 7, 91058 Erlangen, Germany.
authors.forename: Vojislav
authors.initials: V
authors.lastname: Krstić