Chemically Tunable, Biocompatible, and Cost-Effective Metal–Insulator–Metal Resonators Using Silk Protein and Ultrathin Silver Films

Responsive optical resonators are used in chemical and biological sensing applications because their optical properties can be tuned by interactions with their environment. The use of non-nanostructured designs and biological materials expands the applications of these resonators because of their biocompatibility and low cost. Natural silk protein enables designing cost-effective, biocompatible, and chemically tunable metal–insulator–metal (MIM) resonators for color filters and superabsorbers. Our resonant silk MIM exhibited a red shift of the resonance through swelling, which could be controlled by stimuli such as pH and alcohol concentration. The absorption could be detected even in highly scattering biological tissues. Additionally, deep UV light was applied to generate arbitrary patterns with a different color than the background. The proposed silk MIM resonator, which was tunable, biocompatible, and cost-effective, would be useful as a spectral signature in chemical and biological sensing applications.