Surface-Programmable Carbon Dots Dispersed in a Hydrophobic Polymer Film for In Situ Dynamic Sensing of Volatile Fatty Acids

Wireless passive optical gas sensors reduce food waste by providing real-time freshness information through continuous biomarker analysis. However, their practical use remains limited by high cost, strict environmental requirements, poor stability, and device rigidity. Here, programmable carbon dots (CDs) were incorporated into a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) electrospun film to monitor volatile fatty acid (VFA) levels in dairy products via fluorescence color changes. While the rational design of carboxylic and amino groups on the CD surface ensures wide-range pH sensitivity, the hydrophobic polymer matrix enables a self-cleaning mechanism for dynamic sensing. This colorimetric readout is further enhanced by a convolutional neural network model integrated into a mobile app, achieving over 98% accuracy in VFA assessment and providing a precise “best-before date.” The simplicity and integrable design of this VFA sensor make it well suited for incorporation into dairy packaging, where it can reduce food waste and uphold safety standards. Broadly, this dynamic in situ pH sensor with a regenerable surface is effective in both liquid and vapor phases, offering diverse potential practical applications.