Mapping Magnetic Near-Field Distributions of Plasmonic Nanoantennas

We present direct experimental mapping of the lateral magnetic near-field distribution in plasmonic nanoantennas using aperture scanning near-field optical microscopy (SNOM). By means of full-field simulations it is demonstrated how the coupling of the hollow-pyramid aperture probe to the nanoantenna induces an effective magnetic dipole which efficiently excites surface plasmon resonances only at lateral magnetic field maxima. This excitation in turn affects the detected light intensity enabling the visualization of the lateral magnetic near-field distribution of multiple odd and even order plasmon modes with subwavelength spatial resolution

Development of Bright and Biocompatible Nanoruby and Its Application to Background-Free Time-Gated Imaging of G‑Protein-Coupled Receptors

At the forefront of developing fluorescent probes for biological imaging applications are enhancements aimed at increasing their brightness, contrast, and photostability, especially toward demanding applications of single-molecule detection. In comparison with existing probes, nanorubies exhibit unlimited photostability and a long emission lifetime (∼4 ms), which enable continuous imaging at single-particle sensitivity in highly scattering and fluorescent biological specimens. However, their wide application as fluorescence probes has so far been hindered by the absence of facile methods for scaled-up high-volume production and molecularly specific targeting. The present work encompasses the large-scale production of colloidally stable nanoruby particles, the demonstration of their biofunctionality and negligible cytotoxicity, as well as the validation of its use for targeted biomolecular imaging. In addition, optical characteristics of nanorubies are found to be comparable or superior to those of state-of-the-art quantum dots. Protocols of reproducible and robust coupling of functional proteins to the nanoruby surface are also presented. As an example, NeutrAvidin-coupled nanoruby show excellent affinity and specificity to μ-opioid receptors in fixed and live cells, allowing wide-field imaging of G-protein coupled receptors with single-particle sensitivity

Near-Field Mapping of Optical Fabry–Perot Modes in All-Dielectric Nanoantennas

Subwavelength optical resonators and scatterers are dramatically expanding the toolset of the optical sciences and photonics engineering. By offering the opportunity to control and shape light waves in nanoscale volumes, recent developments using high-refractive-index dielectric scatterers gave rise to efficient flat-optical components such as lenses, polarizers, phase plates, color routers, and nonlinear elements with a subwavelength thickness. In this work, we take a deeper look into the unique interaction of light with rod-shaped amorphous silicon scatterers by tapping into their resonant modes with a localized subwavelength light sourcean aperture scanning near-field probe. Our experimental configuration essentially constitutes a dielectric antenna that is locally driven by the aperture probe. We show how leaky transverse electric and magnetic modes can selectively be excited and form specific near-field distribution depending on wavelength and antenna dimensions. The probe’s transmittance is furthermore enhanced upon coupling to the Fabry–Perot cavity modes, revealing all-dielectric nanorods as efficient transmitter antennas for the radiation of subwavelength emitters, in addition to constituting an elementary building block for all-dielectric metasurfaces and flat optics