Tunable protein color micropixels for sensing and imaging of transparent objects

Abstract

Controlling and manipulating light–matter interactions, along with realizing unprecedented performance and cost-effective fabrication, are essential for environmental and biological applications. Although biomaterial-based planar optical devices can be suitable candidates, device microscaling and unlocking the potential of biomaterials are challenging. Here, we report a silk-protein-based microscale color filter based on the Fabry–Pérot etalon and its application to detect and image transparent objects. The etalon consists of a silk fibroin layer sandwiched by two 30-nm-thick Ag layers, and the resonant wavelength is determined by the thickness of the silk layer. Large-sized submicrometer color filters can be fabricated using the in-lab photolithography and lift-off processes. Patterning of color filters and their inherent responsivity to water facilitate detection and imaging of transparent liquids and solids, which cannot be easily distinguished by the human eye. The patterned color filter, featuring a QR code, can serve as a water sensor when scanned underwater as well as allows tracking of water droplets. Water concentrations in alcohol–water mixtures can be estimated by adjusting the swelling ratio. Additionally, incorporation of transparent polymeric materials induces additional resonance, revealing morphology information. This device offers a cost-effective and efficient sensing and imaging platform for various environmental and biological applications.