Poly(2-isoproprenyl-2-oxazoline)-Based Reactive Hydrophilic Cross-Linked Nanofiber Networks as the Basis for Colorimetric Continuous Meat Freshness Monitoring Sensors
Ronald Merckx, Jana Becelaere, Ella Schoolaert, Olmo Frateur, Meike N. Leiske, Daniël Peeters, Florica Adriana Jerca, Valentin Victor Jerca, Karen De Clerck, Richard Hoogenboom
Abstract
Global food waste is a cross-cutting issue that ranges from agricultural production to storage in households and leads to the loss of one-third of produced food products. Although the currently depicted static expiry, best-by, and due-by dates provide accurate information on when to consume the food product, these time indications are only valid under ideal storage conditions. Therefore, there is a stringent need for easy-to-use sensor applications that allow continuous monitoring of food freshness. This work showcases a straightforward and effortless approach to obtain highly porous cross-linked water-stable and reactive hydrophilic nanofiber membranes based on electrospinning of poly(2-isoproprenyl-2-oxazoline) (PiPOx) with succinic acid as the cross-linker. Subsequent thermal treatment of the produced succinic acid-containing PiPOx nanofiber networks generated sufficient cross-linking to preserve the fibrous morphology in an aqueous environment while retaining the hydrophilic character of the scaffold. The remaining 2-oxazoline side chains of PiPOx are stable at room temperature but provide reactivity for post-cross-linking modification with carboxylic acid-containing compounds, as exploited here for continuous food monitoring by incorporating acid-functionalized dyes to yield a colorimetric sensor for biogenic food spoilage indicators, such as thiol- and amine-containing small molecules.