Continuous monitoring of temperature and freshness in cold chain transport based on the dual-responsive fluorescent hydrogel

Comprehensive attention should be paid to the potential food spoilage in food transport. However, there is a problem of freshness destruction by repeated freezing and thawing during the cold chain transport. Herein, a fluorescent hydrogel with N-doped green-emitting carbon dots (N-GCDs), bovine serum albumin-gold nanoclusters (BSA-AuNCs) as fluorescent probes and polyvinyl alcohol-sodium alginate hydrogel as carrier matrix was developed to continuously detect temperature and freshness. Due to the solvatochromic effect of N-GCDs, when the temperature surpassed the threshold, the mixture of water and dimethyl sulfoxide underwent a phase transition and melted into the gel, changing the fluorescence color to realize the temperature monitoring. Then, due to the pH effect of BSA-AuNCs, the gel could respond to pH changes in food deterioration to monitor the food freshness. Thus, the changes of both fluorescence color and intensity of the hydrogel provides a new method for visual and portable authenticity of food freshness.