Tunable, cost-effective, and scalable structural colors for sensing and consumer products

The cost-effective colorimetric detection of chemicals can be a potential substitute for expensive spectrometers. Here, a structural color sensor is presented that can distinguish seven different organic solvents through a timed sharp color change. The color sensor is based on interference effects in a metal–insulator–metal Fabry–Perot (FP) cavity with polydimethylsiloxane (PDMS) serving as the dielectric layer. By tuning the cross-linker to monomer ratio of PDMS and employing a porous nickel (Ni) top layer, the PDMS films experience shrinkage that results in substantial color changes. The time-dependent color change can be used to indicate the type of solvent that the sensor was exposed to. When the sensor is immersed in a solvent, the PDMS diffuses through the porous Ni film at different rates depending on the solvent, resulting in a shrinkage of the PDMS and resonance shift of the FP cavity. Materials used in this single-use sensor are cost effective (≈0.28 USD m⁻²), and the fabrication process requires no lithography and is scalable. Moreover, the FP configuration produces vibrant colors that cover ≈50% of the standard Red Green Blue (sRGB) color space and is suited for decorative purposes and consumer products as well.