The ability to detect dissolved species in liquids is crucial for applications ranging from healthcare diagnostics to environmental monitoring. Traditional methods often require complex, resource-intensive setups, limiting their accessibility. Inverse opals, a class of nanoporous materials characterized by their 3D interconnected, periodic pore structures, offer a cost-effective and straightforward alternative as sensor materials for on-site applications. They exhibit vibrant structural coloration which disappears upon liquid infiltration into the pores, providing a clear and unambiguous visual readout.

So far, wetting transitions in wetting-based inverse opal sensors have relied on the physical properties of liquids, such as surface tension. However, this approach cannot detect soluble species within the same liquid, as most analytes do not significantly alter surface tension. Our research focuses on a different strategy: inducing wetting transitions through changes in surface chemistry rather than the liquid itself. By functionalizing the pore surfaces with selective recognition units, the binding of an analyte triggers a change in wettability, allowing the liquid to penetrate previously unwetted pores. This enables inverse opals to act as autonomous sensors for detecting dissolved species with high specificity and simplicity.