We fabricated hollow nanoantennas with varying inner channels sizes on a gold-covered silicon nitride membrane. Our fabrication technique allowed us to narrow the size of the inner channels down to 15nm. We managed to exclusively decorate the tips of the antennas with thiol-conjugated dyes by creating a concentration gradient through the nanoantennas. Finally, we characterized the antennas in terms of their effect on the lifetime of dyes. We used Atto 520 and Atto 590 for the experiments. We carried out experiments with the antennas decorated with Atto 520, with Atto 590 as well as with the two Atto dyes at the same time. The experiments carried out with the antennas decorated with Atto 520 only and Atto 590 only yielded a lifetime reduction with respect to the confocal case. Interestingly, their lifetime reductions were significantly different. Then, we decorated the antennas with the two dyes at the same time. Even though we could not control the distance between the two dyes, FRET effects were clearly observed. The FRET effects were found to be dependent on the size of the inner channel. We believe that our tip decorated hollow nanoantennas could find application in FRET-based single molecule nanopore technologies.
Modulating the fractal dimension of nanoporous gold is possible to tune the effective dielectric response over a wide spectral range of infrared wavelengths. The plasma edge and effective plasma frequency depend on the fractal dimension, which can be controlled by varying the preparation condition. The fractal porous metal has superior plasmonic properties compared to bulk gold. The long skin depth of porous metal on the order of 100-200 nm, enables the penetration of optical energy deep into the nanopores where molecules can be loaded, thus achieving more effective light-matter coupling. These findings may open new pathways to engineering the optical response of fractal-like or selfsimilar metamaterials.
Surface plasmon waves carry an intrinsic transverse spin angular momentum, which is locked to their propagation direction. On the other hand, helical plasmonic distributions may also carry an orbital angular momentum that is linked to the field topology. Apparently, when such a singular plasmonic mode propagates on a surface or is guided on a conic structure its helicity and the transverse spin can be coupled to the far-field spin and orbital angular momentum. We discuss the mechaism of such a coupling by using 2D and 3D guiding architetures. We analyze the coupling eﬃciency in each case as well as the intriguing spin-locking phenomenon occurring in our system. Finally we experimentally demonstrate the eﬃcient beaming of a single-handed mode decorated by a desired orbital angular using accurately fabricated nanostructures.
Nanoporous gold is a very promising material platform for several plasmonic applications. Nanoporous gold can be
formed by dealloying Au–Ag alloys, previously grown by means of Ag-Au co-sputtering. The optical response is
completely determined by the nanostructured film features, that only depend on the initial alloy composition. It has been
extensively used as SERS substrate both as thin film and nanofabricated fancy designs. Here we explore the potential
application of nanoporous gold as SERS substrate as it is coupled and decorated with Ag nanoparticles. Significant
enhancement has been observed in comparison with bare nanoporous film.