Lu Xiaoyuan, Gautam Vini, Shishmarev Dmitry, Daria Vincent R
Opt Express. 2020 Oct 12;28(21):31594-31602. doi: 10.1364/OE.402259.
Metasurfaces exhibit unique optical properties that depend on the ratio of their refractive index and that of their surroundings. As such, they are effective for sensing global changes in refractive index based on the shifts of resonances in their reflectivity spectra. However, when used as a biosensor, the metasurface can be exposed to a spatial distribution of biomolecules that brings about gradients in refractive index along the plane of the metasurface. Such gradients produce complex global reflectivity spectrum but with distinct optical enhancements in localized areas along the metasurface. Here, we propose a unique sensing paradigm that images and maps out the optical enhancements that are correlated with the spatial distribution of the refractive index. Moreover, we designed a metasurface whose resonances can be tuned to detect a range of refractive indices. Our metasurface consists of silicon nanopillars with a cylindrical nanotrench at their centers and a metal plane at the base. To assess its feasibility, we performed numerical simulations to show that the design effectively produces the desired reflectivity spectrum with resonances in the near-infrared. Using an incident light tuned to one of its resonances, our simulations further show that the field enhancements are correlated with the spatial mapping of the gradients of refractive indices along the metasurface.
超表面展现出独特的光学特性，这些特性取决于其折射率与周围环境折射率的比值。因此，基于其反射光谱中共振的移动，超表面对于感应折射率的整体变化是有效的。然而，当用作生物传感器时，超表面可能会暴露于生物分子的空间分布中，这会在超表面平面上产生折射率梯度。这种梯度会产生复杂的整体反射光谱，但在超表面沿线的局部区域具有明显的光学增强。在这里，我们提出了一种独特的传感范式，该范式可以对与折射率空间分布相关的光学增强进行成像和映射。此外，我们设计了一种超表面，其共振可以被调谐以检测一系列折射率。我们的超表面由中心带有圆柱形纳米沟槽且底部有金属平面的硅纳米柱组成。为了评估其可行性，我们进行了数值模拟，结果表明该设计有效地产生了具有近红外共振的所需反射光谱。使用调谐到其共振之一的入射光，我们的模拟进一步表明，场增强与沿超表面的折射率梯度的空间映射相关。
