Corn Starch/Polyvinyl Alcohol Composite Film With pH-Mediated Fluorescent Sensing: Carbon Quantum Dot Incorporation for Film Stability and Efficient Food Freshness Monitoring

There is an urgent need in the food packaging sector to develop smart packaging systems to cope with various scenarios, such as pH-indicating smart packaging systems. This study aims to explore the effect of incorporation of carbon quantum dots (CDs) into a corn starch/polyvinyl alcohol matrix to develop pH-mediated fluorescent sensing smart films. CDs with an average particle size of 5.496 nm were successfully prepared using a hydrothermal method incorporating citric acid and urea as raw materials, which are rich in hydrophilic groups, especially nitrogen-containing groups, and exhibit pH fluorescence response characteristics. The CDs presented hydrogen bonding–dominated interactions with the film while having no significant effect on the microstructure and crystal structure. They were uniformly dispersed in the films, and the loading of CDs endowed the films with UV-shielding ability, excellent mechanical properties and thermal stability. The pH-mediated fluorescence sensing function of the film was verified by simulating pH changes in a high-protein food storage environment using acetic acid and ammonia, showing a 62.91% increase in fluorescence intensity from pH 3.5 to 8.5. This work provided an idea for developing a new smart packaging system.