title: Matching Nanoantenna Field Confinement to FRET Distances Enhances Förster Energy Transfer Rates.
abstract: Förster resonance energy transfer (FRET) is widely applied in chemistry, biology, and nanosciences to assess distances on sub-10 nm scale. Extending the range and applicability of FRET requires enhancement of the fluorescence energy transfer at a spatial scale comparable to the donor-acceptor distances. Plasmonic nanoantennas are ideal to concentrate optical fields at a nanoscale fully matching the FRET distance range. Here, we present a resonant aluminum nanogap antenna tailored to enhance single molecule FRET. A 20 nm gap confines light into a nanoscale volume, providing a field gradient on the scale of the donor-acceptor distance, a large 10-fold increase in the local density of optical states, and strong intensity enhancement. With our dedicated design, we obtain 20-fold enhancement on the fluorescence emission of donor and acceptor dyes, and most importantly up to 5-fold enhancement of the FRET rate for donor-acceptor separations of 10 nm. We also provide a thorough framework of the fluorescence photophysics occurring in the nanoscale gap volume. The presented enhancement of energy transfer flow at the nanoscale opens a yet unexplored facet of the various advantages of optical nanoantennas and provides a new strategy toward biological applications of single molecule FRET at micromolar concentrations.
authors.affiliation: CNRS, Aix-Marseille Université, Centrale Marseille, Institut Fresnel, UMR 7249, 13013 Marseille, France.
authors.forename: Petru
authors.initials: P
authors.lastname: Ghenuche
authors.affiliation: ICFO-Institut de Ciencies Fotoniques, Mediterranean Technology Park, 08860 Castelldefels, Spain.
authors.forename: Mathieu
authors.initials: M
authors.lastname: Mivelle
authors.affiliation: CNRS, Aix-Marseille Université, Centrale Marseille, Institut Fresnel, UMR 7249, 13013 Marseille, France.
authors.forename: Juan
authors.initials: J
authors.lastname: de Torres
authors.affiliation: CNRS, Aix-Marseille Université, Centrale Marseille, Institut Fresnel, UMR 7249, 13013 Marseille, France.
authors.forename: Satish Babu
authors.initials: SB
authors.lastname: Moparthi
authors.affiliation: CNRS, Aix-Marseille Université, Centrale Marseille, Institut Fresnel, UMR 7249, 13013 Marseille, France.
authors.forename: Hervé
authors.initials: H
authors.lastname: Rigneault
authors.affiliation: ICFO-Institut de Ciencies Fotoniques, Mediterranean Technology Park, 08860 Castelldefels, Spain.|ICREA-Institució Catalana de Recerca i Estudis Avançats, Barcelona 08010, Spain.
authors.forename: Niek F
authors.initials: NF
authors.lastname: Van Hulst
authors.affiliation: ICFO-Institut de Ciencies Fotoniques, Mediterranean Technology Park, 08860 Castelldefels, Spain.|ICREA-Institució Catalana de Recerca i Estudis Avançats, Barcelona 08010, Spain.
authors.forename: María F
authors.initials: MF
authors.lastname: García-Parajó
authors.affiliation: CNRS, Aix-Marseille Université, Centrale Marseille, Institut Fresnel, UMR 7249, 13013 Marseille, France.
authors.forename: Jérôme
authors.initials: J
authors.lastname: Wenger
keywords: FRET; LDOS; aluminum; fluorescence enhancement; nanoantenna; plasmonics