Hierarchically Structured Plasmonic Nanoparticle Assemblies with Dual-Length Scale Electromagnetic Hot Spots for Enhanced Sensitivity in the Detection of (Bio)Molecular Analytes

High sensitivity in plasmon-enhanced spectroscopies results not only from high electromagnetic (EM) field enhancements at the vicinity of nanostructured metal surfaces but also the ability to leverage on these enhancements via analyte colocalization with the EM hot spots. However, promising configurations for EM hot spots such as metal nanogaps are spatially restrictive for adsorption of larger analytes such as proteins. This results in an adverse spatial trade-off in the design of EM hot spots, viz., increasingly confined geometries sought to drive high EM enhancements and space necessary to accommodate binding of large biomolecular analytes. In this direction, we demonstrate gold nanoparticle cluster arrays (NCAs) exhibiting interparticle (