Comparison of polymer-based 1D and 2D plasmonic metasurfaces for refractive index sensing

Abstract Polymer-based plasmonic metasurfaces containing subwavelength features arranged in one dimension (1D) and two dimensions (2D) are compared for their application in refractive index sensing. The 1D metasurface has parallel linear grooves with a sinusoidal surface profile, while the 2D metasurface has hexagonally periodic nanobumps. Both have a thin gold film on the top for plasmonic effect. Both the designs were optimized using numerical computations. The 1D metasurface exhibits only one plasmonic mode while the 2D metasurface exhibits multiple plasmonic modes for normal incidence of light. For refractive index sensing, both the metasurfaces can be used over a broad range. But in comparison, the 1D metasurface is found to be better in the low- and intermediate-index ranges, and the 2D metasurface works better in the higher-index range. In the low-index range, the 1D metasurface has a sensitivity of 766 nm RIU −1 , whereas the mode-1 of the 2D metasurface has a sensitivity of 633 nm RIU −1 . In the intermediate-index region, the sensitivity of the 1D metasurface is 714 nm RIU −1 , while the sensitivity values of mode-2 and mode-3 of the 2D metasurface are 428 nm RIU −1 and 238 nm RIU −1 , respectively. At the higher-index range, the width of the plasmonic mode for 1D metasurfaces widens, thus lowering its figure of merit and quality factor for sensing, but mode-3 of 2D metasurface detects the analyte efficiently. Both the metasurfaces were fabricated using a low-cost two-step soft lithography approach using easily available economical masters, and the label-free sensing ability of the 1D metasurface is experimentally tested using a biomolecular interaction which establishes that micromolar concentrations of the analyte can be detected unambiguously.