Bilayer pH-sensitive colorimetric films with light-blocking ability and electrochemical writing property: Application in monitoring crucian spoilage in smart packaging.

• ZnO nanoparticles improved the UV-blocking property and color stability of the bilayer film. • Different patterns could be printed on the bilayer colorimetric film by electrochemical writing. • The bilayer colorimetric film showed a limit of detection of 0.01 mM to NH 3. • The bilayer colorimetric film with written patterns can monitor crucian freshness in real-time. Bilayer colorimetric films were developed for monitoring fish spoilage by using gelatin (GN) incorporated with ZnO nanoparticles as the upper layer (GN-ZnO), and gellan gum (GG) incorporated with mulberry anthocyanins (MBA) as the lower layer (GG-MBA). The color stability of the bilayer colorimetric films under visible and ultraviolet light was improved with the increase of ZnO nanoparticles content. Meanwhile, the bilayer films had good NH 3 sensitivity. The limit of detection of the GG-MBA/GN-2.0% ZnO film to NH 3 was 0.01 mM. The electrochemical writing ability of the bilayer films was also identified, indicating the feasibility of inks-free printing on biopolymer films. Finally, the GG-MBA/GN-2.0% ZnO film with an electrochemical writing pattern was used to monitor crucian spoilage. The GG-MBA/GN-2.0% ZnO film with electrochemical writing pattern showed visible color changes with the crucian spoilage. In conclusion, the bilayer colorimetric film was expected to be a good fish spoilage indicator in smart packaging. [ABSTRACT FROM AUTHOR]