Ultrasensitive refractometric sensing via centimeter-scale metasurfaces with spatially gradient geometry generated by elastomer mechanical stretching.

Plasmonic metasurfaces with gradient geometry are emerging two-dimensional optical elements with unique capabilities, such as manipulating light by imparting local, space-variant phase changes to an incident electromagnetic wave, eliminating the chromatic aberration. However, the costly and time-consuming fabrication process and the requirement of sophisticated optical characterization instruments restrict practical applications of plasmonic metasurfaces. Herein, we present a novel nanofabrication method to generate centimeter-scale metasurface with spatially gradient geometry over the whole metasurface by directional stretching of a trapezoid elastic carrier patterned with regular metallic nanostructures. This strategy eases the requirement of time-consuming and expensive lithographic techniques in conventional methods. The spatially gradient plasmonic metasurface exhibit variable transmittances under monochromatic and polar light illumination, resulting in grayscale patterns with different transmittance intensity distributions. An ultrahigh imaging-based sensitivity of 1495 pixel/refractive index unit (RIU) and a detection limit of 0.00068 RIU can be achieved based on the spatially gradient plasmonic metasurface, which is superior to the performance of the regular metasurface before stretching. This novel strategy is expected to be promising for fabrication of gradient metasurfaces to be employed in many fields of nanophotonics.