Hydrogel-polymersome composites as a sensing platform for monitoring food spoilage

The development of advanced functional soft materials for applications in preserving food quality and detecting spoilage is in focus today. While various smart food packaging options are available, there are still challenges to be addressed due to several limitations of current food quality sensors, such as a lack of multifunctionality, use of potentially harmful synthetic sensing molecules or short shelf life of natural analogues. Herein, we present a dual-functional hydrogel-polymersome composite (HPC) system that integrates two complementary sensing functionalities into a single platform. As a model for dual-functionality, we successfully incorporated dye-loaded polymersomes into a poly(N-isopropylacrylamide)-based hydrogel. This approach enables temperature-triggered cargo release, while the encapsulated dyes serve as pH-reporting molecules for monitoring food freshness. The first functionality was demonstrated by hydrogel shrinkage and subsequent release of dye upon increasing the temperature from 25 °C to 40 °C. The second functionality was probed by decreasing the pH to 6.2 or exposure to methylamine (MA), a representative volatile amine, which shifted the local pH to basic values. The HPCs remained stable under hydrated conditions, and their dual-functionality was proved using fluorescence spectroscopy and light scattering. Our system exhibited a detection limit of 1 mM MA-2.5 times lower than the threshold classified as acutely toxic by the Centers for Disease Control and Prevention-highlighting its relevance for spoilage detection. These findings demonstrate that combining functional polymersomes with stimuli-responsive hydrogels offers a promising approach for developing multifunctional, compartmentalized composite sensors suitable for integration into food packaging to efficiently monitor its freshness.