New paper published in ACS Applied Polymer Materials. This joint work with Markus Gallei from Saarland University has developed smart core–shell particles with imidazole-functionalized shells that respond to acidic solutions and hydrophobic anions, forming viscoelastic opal films with tunable structural colors. These films serve as affordable optical sensors, changing color in response to environmental stimuli, with potential applications in life sciences, environmental monitoring, and electrochemistry.