title: Unveiling the correlation between nanometer-thick molecular monolayer sensitivity and near-field enhancement and localization in coupled plasmonic oligomers.
abstract: Metal nanoclusters, sometimes called metamolecules or plasmonic oligomers, exhibit interesting optical properties such as Fano resonances and optical chirality. These properties promise a variety of practical applications, particularly in ultrasensitive biochemical sensing. Here we investigate experimentally the sensitivities of plasmonic pentamers and quadrumers to the adsorption of self-assembled nanometer-thick alkanethiol monolayers. The monolayer sensitivity of such oligomers is found to be significantly higher than that of single plasmonic nanoparticles and depends on the nanocluster arrangement, constituent nanoparticle shape, and the plasmon resonance wavelength. Together with full-wave numerical simulation results and the electromagnetic perturbation theory, we unveil a direct correlation between the sensitivity and the near-field intensity enhancement and spatial localization in the plasmonic "hot" spots generated in each nanocluster. Our observation is beyond conventional considerations (such as optimizing nanoparticle geometry or narrowing resonance line width) for improving the sensing performance of metal nanoclusters-based biosensors and opens the possibilities of using plasmonic nanoclusters for single-molecule detection and identification.
authors.affiliation: Department of Physics, Imperial College London , London SW7 2AZ, United Kingdom.
authors.forename: Matthias
authors.initials: M
authors.lastname: König
authors.forename: Mohsen
authors.initials: M
authors.lastname: Rahmani
authors.forename: Lei
authors.initials: L
authors.lastname: Zhang
authors.forename: Dang Yuan
authors.initials: DY
authors.lastname: Lei
authors.forename: Tyler R
authors.initials: TR
authors.lastname: Roschuk
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Giannini
authors.forename: Cheng-Wei
authors.initials: CW
authors.lastname: Qiu
authors.forename: Minghui
authors.initials: M
authors.lastname: Hong
authors.forename: Sebastian
authors.initials: S
authors.lastname: Schlücker
authors.forename: Stefan A
authors.initials: SA
authors.lastname: Maier
keywords: Fano resonance; monolayer sensing; near-field enhancement; plasmonic oligomers