Polydiacetylenes (PDAs) are a class of conjugated polymers with unique optical properties that make them excellent materials for the construction of colorimetric sensors. Amphiphilic diacetylene (DA) monomers self-assemble to form vesicular structures in aqueous solution, and in organized structures, neighboring DA monomers polymerize when exposed to 254 nm UV light to form alternating ene-yne polymer chains. Polymerization typically yields blue-phase PDAs with a characteristic absorption peak at ∼640 nm. Chemical and biological recognition events can induce a blue-to-red color transition of PDA (absorption peak of red-phase PDAs at ∼540 nm), which can be easily detected by the naked eye. In this work, we report the synthesis and applications of PDA on food packaging that enables low-cost, easy monitoring of food (including milk spoilage, meat spoilage, fruit ripening) without the need of specialized equipment. We investigated a range of DA monomers with different lengths of alkyl spacer and alkyl tail. To fabricate the film sensors, we stabilized PDA vesicles in polymer matrix. By optimizing the film fabrication process, we were able to increase the local concentration of PDA vesicles at the surface of the film, thus enhancing response time and sensitivity of PDA to byproducts of bacteria. We successfully demonstrated the application of this method as colorimetric food sensors by integrating them into the plastic packaging of food container stored at -20 °C, 4 °C, and room temperature. At all temperatures, the sensors exhibited a distinctive blue-to-red color transition to indicate food spoilage. The PDA sensors will provide a real time indication of actual food quality, surpassing the function of traditional date marking tools that provide an indication of expected shelf life.

Polydiacetylene-based sensors to detect food spoilage

ACS Spring 2022

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