Guiding light in monolayers of sparse and random plasmonic meta-atoms.

Encouraged by the capacity of surface plasmons to confine and propagate electromagnetic fields, waveguiding concepts have been developed, including combinations of continuous metal films or ordered arrays of metal nanoparticles. So far, waveguiding in the latter systems has been based on near-field or diffractive coupling. Herein, we show that monolayers of sparse and disordered gold nanoparticles support a novel transverse-electric guided mode that, contrary to previous work, relies on the strong enhancement of the polarizability upon excitation of the nanoparticle LSPR, creating an effective refractive index sufficiently high to support light guidance over a large range of frequencies. Excitation of this guided mode offers interesting nanophotonics features and applications such as a tunable total absorption spectral band, attractive for light harvesting applications, or the generation of a large amplification of the sensitivity to changes of refractive index accompanied with striking enhancement of the limit of detection in real biosensing experiments.

Suitable combination of noble/ferromagnetic metal multilayers for enhanced magneto-plasmonic biosensing.

We present a theoretical and experimental study on the biosensing sensitivity of Au/Co/Au multilayers as transducers of the magneto-optic surface-plasmon-resonance (MOSPR) sensor. We demonstrate that the sensing response of these magneto-plasmonic (MP) transducers is a trade-off between the optical absorption and the magneto-optical activity, observing that the MP multilayer with larger MO effect does not provide the best sensing response. We show that it is possible to design highly-sensitive MP transducers able to largely surpass the limit of detection of the conventional surface-plasmon-resonance (SPR) sensor. This was proved comparing the biosensing performance of both sensors for the label-free detection of short DNA chains hybridization. For this purpose, we used and tested a novel label-free biofunctionalization protocol based on polyelectrolytes, which increases the resistance of MP transducers in aqueous environments.