Nanofiber films based on colourimetric and fluorescent dual channels for visual monitoring of shrimp freshness

Food freshness indication labels have a broad application prospect in the field of food safety because of monitoring the freshness of food and its environment in real time, which can assist consumers in identifying the freshness of food. Herein, large-area nanofiber films with colourimetric and fluorescent dual-channel indication were prepared via electrospinning technology using fluorescein isothiocyanate (FITC) with biogenic amine response as the indicator. FITC/PVA nanofiber films resulted in enhanced thermal stability and mechanical properties. With the increase of ammonia concentration in the atmosphere, the FITC/PVA composite films exhibited a gradual change in colour from grey to orange under daylight conditions. Furthermore, the green fluorescence was observed to gradually intensify under ultraviolet (UV) light. The results of shrimp freshness monitoring demonstrated obvious colour changes under both daylight and UV light condition, which the colour of the nanofiber films underwent a transformation from yellow to dark orange (ΔE = 46.18) under daylight and from green to bright yellow-green (ΔE = 41.77) under UV light after 1 day at 25 °C. The principal reason for the colour change of the films is the release of organic amine molecules during the spoilage process of fresh shrimp, leading the deprotonation of FITC under alkaline atmosphere and the change in its molecular conformation, resulting in the colour change and fluorescence enhancement of FITC under daylight. This colourimetric and fluorescent dual-channel response nanofiber films has the potential to be utilized in the field of food freshness monitoring to ensure the safety of the food supply.