Real-Time Tunable Colors from Microfluidic Reconfigurable All-Dielectric Metasurfaces.

Structural colors arising from all-dielectric nanostructures are very promising for high-resolution color nanoprinting and high-density optical storage. However, once the all-dielectric nanostructures are fabricated, their optical performances are usually static or change slowly, significantly limiting the practical applications in advanced displays. Herein, we experimentally demonstrate the real-time tunable colors with microfluidic reconfigurable all-dielectric metasurfaces. The metasurface is composed of an array of TiO2 nanoblocks, which are embedded in a polymeric microfluidic channel. By injecting solutions with a different refractive index into the channel, the narrow band reflection peak and the corresponding distinct colors of a TiO2 metasurface can be precisely controlled. The transition time is as small as 16 ms, which is orders of magnitude faster than the current techniques. By varying the lattice size of TiO2 metasurfaces, the real-time tunable colors are able to span the entire visible spectrum. Meanwhile, the injection and ejection of solvent have also shown the capability of the erasion and the restoration of information encoded in TiO2 metasurfaces. The combination of all-dielectric nanostructures with microfluidic channels shall boost their applications in functional color display, banknote security, anticounterfeiting, and point-of-care devices.