High Performance CO 2 Gas Sensing Using Plasmonic Bowtie and Fan-Shaped Nanoantennas

This work introduces two plasmonic nanoantenna designs, bowtie-shaped and fan-shaped, integrated within a metasurface for highly sensitive carbon dioxide (CO 2 ) gas detection in the visible and short-infrared regions. Both designs employ silver (Ag) nanoantennas deposited on a multilayer structure incorporating a polyhexamethylene biguanide (PHMB) polymer film, which undergoes refractive index (RI) changes upon CO 2 absorption, producing a redshift in resonance wavelengths. The optical performance of both designs was analyzed under identical conditions. The bowtie structure achieved a maximum figure of merit (FOM) of 33.278% −1 , while the fan-shaped design reached 19.54% −1 , benefiting from enhanced field localization due to its sharper geometry. The fan-shaped nanoantenna demonstrates enhanced resolution, attributed to its reduced resonance line widths and improved electromagnetic field confinement within the nanogap. Both sensors demonstrated distinct multimodal absorption peaks and exhibited high sensitivity within a 0–524 ppm CO 2 concentration range, confirming their suitability for miniaturized, high-performance gas sensing applications.