Highly Sensitive Humidity-Responsive Photonic Films Integrated with MATLAB Programs for an Advanced Security Authentication System

The proliferation of counterfeit products has created an urgent demand for advanced authentication technologies. Herein, a humidity-responsive photonic crystal (HPC)-based advanced security authentication system was developed, which can be triggered by human breath and serve as a high-security label for use in combination with a MATLAB application. We fabricated a series of HPC films by infiltrating hydrophilic copolymers of poly(ethylene glycol) methyl ether acrylate (OEGA480) into self-assembled ZnS@SiO2 opaline templates. Across 11-90% relative humidity (RH), the HPC films exhibited a reflection wavelength shift of 150 nm with distinct color variation from bluish-purple to orange-red. Notably, the HPC films reached sensing balance in 150 ms, making them suitable for real-time colorimetric humidity sensing. Furthermore, by controlling monomer composition and ratios, the HPC films demonstrated a remarkable reflection wavelength shift exceeding 400 nm upon exposure to moist air and could achieve multilevel humidity responsiveness. Finally, an anticounterfeiting code label with multilevel information was developed, whose information is concealed in ambient humidity and can be revealed by human breath. Notably, we integrated the label with a MATLAB application to enable a two-step security function that encompassed verifying RGB color values and ensuring the accuracy of digital encoding, thereby enhancing security authentication capabilities.