Citation: Venugopalan, P.; Kumar, S. Highly Sensitive Plasmonic Sensor with Au Bow Tie Nanoantennas on SiO 2 Nanopillar Arrays. Chemosensors 2023, 11, 121. https://doi.org/10.3390/ chemosensors11020121 Academic Editor: Brian Cullum Received: 29 November 2022 Revised: 12 January 2023 Accepted: 20 January 2023 Published: 7 February 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). chemosensors Communication Highly Sensitive Plasmonic Sensor with Au Bow Tie Nanoantennas on SiO 2 Nanopillar Arrays Priyamvada Venugopalan 1, * and Sunil Kumar 1,2 1 Faculty of Engineering, New York University, Saadiyat Island, Abu Dhabi P.O. Box 129188, United Arab Emirates 2 Department of Mechanical Engineering, New York University, Brooklyn, NY 11201, USA * Correspondence: pv33@nyu.edu Abstract: We report on plasmonic sensors based on arrays of metallic bow tie nanoantennas with high sensitivity and an enhanced figure of merit. In the present sensing device, each gold nanoantenna is positioned on the upper surface of a SiO 2 nanopillar that is placed on a quartz substrate. The presence of the nanopillar significantly reduces the coupling of the enhanced electromagnetic field generated at the plasmon resonance to the substrate. The simulated results show that the sensitivity of the device to refractive index sensing is 612 nm/RIU, calculated by the resonance wavelength shift per refractive index unit due to the change in the ambient medium index, while the full width at half maximum is calculated at around 10 nm with a figure of merit of 61. The proposed sensor thus has a great potential for sensing and detection applications. Keywords: plasmonic lattice resonance; plasmonic sensors; sensitivity 1. Introduction When light is incident on a metal nanoparticle at the resonant frequency, the conduc- tion electrons are excited, resulting in collective oscillations known as localized surface plasmon resonances (LSPR) [1,2]. The excitation of LSPRs enables the subwavelength local- ization and enhancement of electromagnetic fields, which are determined by the dielectric properties of the metal and the surrounding medium [3] and by the nanoparticle size and shape [4,5]. Metallic nanoantennas have recently gained much popularity due to their potential to localize and trap electromagnetic fields in nano regimes, attained by the cou- pling of LSPRs [6]. The recent development in micro-nano fabrication and characterization technologies has led to rapid advancement in improving the performance of the nanoan- tennas for a variety of applications, such as biological and chemical sensing with enhanced efficiency and sensitivity [7–9], wireless communication in nanophotonic chips [10], energy harvesting [11], nanoscale nonlinear optics [12], etc. Single or paired metallic nanoparticles are the most fundamental geometry of a plasmonic antenna. Amongst the other designs, bow tie nanoantennas, made of two gold triangles in a tip-to-tip configuration, provide much stronger electric field localization and enhancement because of the coupling across the gap and the lightning rod effect [13–15]. Periodic arrays of metal nanoantennas can generate plasmonic lattice resonances (PLR), arising from the coupling between diffracted waves from the periodic array and the localized surface plasmons of the metal nanoantennas [16–22]. The coupling generates an enhanced electric field around the nanostructures that can be employed in plasmonic sensors that rely on shifts in their lattice resonant wavelength prompted by an alteration in the refractive indices of the ambient media [23–27]. The performance of a sensor based on such periodic metal arrays is determined by the figure of merit (FOM), which is the ratio of the sensitivity, defined as the shift in the wavelength of PLR per refractive index unit (RIU) to the full width at half maximum (FWHM) [28]. There have been several such geometries arranged in a periodic manner, like L-shaped gold nanobars [29,30], MIM Chemosensors 2023, 11, 121. https://doi.org/10.3390/chemosensors11020121 https://www.mdpi.com/journal/chemosensors