A Highly Directive Ultraviolet Plasmonic “Antenna‐on‐Reflector” for Single‐Molecule Detection

Abstract

Single‐molecule detection (SMD) has been a hot topic for decades due to its extensive implementation in biomedical, chemical, physical, and material sciences. The methods used for single‐molecule detection are generally variants of fluorescence and Raman spectroscopy, which employs plasmonic particles for hot‐spot generation upon illumination. The signal generated by molecules in the hot spot is strong but not directive, so, <in most contemporary works, a nanomolar concentration is required to suppress noise from background molecules. However, at extremely low concentrations, biological samples vary with regard to conformation and interaction dynamics, so the most suitable dilution is micromolar. Thus an optical antenna that can both focus incident light at tight spots and be highly directive for the efficient collection of fluorescence is demanded. Herein, a nanoantenna in the shape of an aluminium hemisphere on a parabolic reflector providing both incident wave enhancement and efficient directive signal outcoupling is proposed and simulated. To achieve this feat, the focus of the parabolic reflector coincides spatially with the hot spot created by the plasmonic gap antenna. The structure shows broadband () escalation in directivity, 24–28 dB. The calculated incident field enhancement in the detection volume of the plasmonic gap is up to .