Precise Fabrication of Gap-Tunable Nanoantennas for Plasmon-Enhanced Spectroscopy and Biosensing

This paper reports an arrayed nanometer precision gap-tunable bowtie nanoantennas fabricated by focused helium ion beam (HIB) milling. Plasmonic resonance is excited and tightly localized inside the nanogaps of the bowtie nanoantennas. Both numerical simulations and cathodoluminescence (CL) measurements manifest that the plasmon coupling resonance is significantly enhanced by decreasing the nanoantennas' gap width down to sub-10 nm scale. The stronger plasmon resonance also leads to a remarkable improvement of the spectral sensitivity to the surrounding media changes, which can be used to detect streptavidin with the concentration down to 100 ng/mL by simply monitoring the spectral shift.