The cover picture highlights an inverse opal photonic gel (IOPG) sensor that exhibits a structural color change through Bragg diffraction of light. This occurs when glucose binds to a phenylboronate group within the IOPG, stabilized by a neighboring trimethylamino group. The formation of a 2:1 boronate-glucose complex causes the IOPG to shrink, changing its structural color from red to green. This innovative glucose-sensing IOPG was developed and studied by Wonmok Lee and coworkers, as detailed in article no. 1800416. This article is part of a special issue featuring five contributions on “Green Photonics.” -Scientific Journal cover design by scapiens

https://onlinelibrary.wiley.com/doi/abs/10.1002/pssr.201970013