This communication demonstrates a facile method for naked-eye detection of urea based on the structure color change of pH-sensitive photonic crystals. The insertion of urease provides excellent selectivity over other molecules. The detection of urea in different concentration ranges could be realized by changing the molar ratio between the functional monomer and cross-linker.

A facile method to realize photo-responsive inverse opal photonic crystal polymer (IOPP) films with an adjustable broad-wavelength-range photonic band gap (PBG) was demonstrated in this communication. When immersing the IOPP film in malachite green carbinol base (MGCB) solution, under light irradiation, the MGCB released hydroxide ions. In this way, optical signals were converted to chemical signals. As a result, the pH sensitive IOPP film expanded and the PBG changed. The band gap movement of the IOPP films with different monomer to cross-linker ratios was studied in this work.