An Optically Responsive Soft Etalon Based on Ultrathin Cellulose Hydrogels

Stimuli-responsive optical etalons are an exciting class of next-generation sensors because they are scalable, cost-effective and offer tunability of their optical response across the entire UV–vis–NIR wavelength range. In this study, double-network cellulose hydrogels are used as a soft, responsive medium and are incorporated into Fabry–Perot optical etalons. The thin cellulose hydrogel layer can be solution processed. The hygroscopic hydrogel undergoes both refractive index and thickness changes in response to changes in humidity. This leads to strong changes in reflection due to optical interference within the metal–insulator–metal (MIM) cavity. The response can be optimized by adjusting the chemical crosslinker ratio. These flexible MIM structures provide a robust platform for optically based chemical sensors.