pH-Responsive strips integrated with resazurin and carbon dots for monitoring shrimp freshness

Carbon dots (CDs) were synthesized via a one-step hydrothermal approach using tangerine peel (Tan) and resazurin (Res) to fabricate biocompatible indicators for food freshness. The CDs' pH-responsive mechanism, morphology, zeta potential, XPS, and optical and fluorescence analysis were investigated. The as-prepared tangerine peel/resazurin carbon dots (Tan/Res CDs) exhibited pH-responsive emission that changed from yellow to orange as the pH value increased. The Tan/Res CDs showed the sensing ability of ammonia with a detection limit of 0.84 μM by proportionally losing fluorescence intensity as the concentration increased from 1 to 100 μM. The CDs were coated onto paper strips to impart biogenic amine (BAs) detection for pH-responsive intelligent monitoring of packaged foods. The Tan/Res CDs paper-based indicator exhibited an impressive color change from yellow to brown during the detection of ammonia vapor. The indicator also showed the ability to detect BAs through a color change, demonstrating the ability to monitor the freshness of shrimp in situ. Additionally, the efficacy of the Tan/Res CDs indicator is validated by total volatile basic nitrogen (TVB-N), providing customers and suppliers with a simple, inexpensive, and portable tool to monitor the freshness of seafood in real-time.