A comparison of simulated and fabricated gold bowtie nanoantennas for molecular fingerprinting

Abstract

The use of nanoantennas to enhance molecular fingerprinting has an important application in the field of biomolecular reaction sensing. Nanoantennas, which are plasmonic metastructures that manipulate light to generate a localized electric field, or hotspot, can be scaled and coupled with Raman spectroscopy and surface enhancement also known as surface enhanced Raman spectroscopy (SERS) to achieve single molecule structural changes, such as signal transduction mechanisms in eukaryotic cells. In this work, we explore an optimal design of nanoantennas in the bowtie configuration using computer simulation technology (CST) microwave studio and simulate gold-contact bowtie nanoantennas with varying fabrication parameters. Simulated gold-contact bowtie nanoantennas are designed with varying tip-to-tip gap distances ranging from 20-100 nm, contact thicknesses ranging from 15-45 nm, and side lengths ranging from 20-300 nm based on the protein chain lengths involved in post translational modifications within eukaryotic cells. Based on our current Jobin Yvon BX41 Confocal Raman microscope configuration, the bowtie antennas are modeled using a one-micron diameter spot and a 532 nm light source to achieve an optimized design. The nanoantenna is fabricated using electron beam lithography (EBL), electron beam evaporation and deposition (EBED), and metal lift-off process. In comparison with other demonstrations of nanoantenna-enhanced Raman spectroscopy, our design is unique for measuring protein phosphorylated events in eukaryotic cells. Based on the optimized design, electric field intensities in the gap were estimated at 7.30 V/m.