Dual-signal fluorescent test strips for spoilage sensing of packaged seafood: Visual monitoring of volatile basic nitrogens.

With the food safety issues abounding, exploring reliable and efficient methods for evaluating food safety is crucial. Herein, a ratiometric test strip was proposed by using green-yellow fluorescent d-penicillamine capped silver nanocluster (DPA-AgNCs) as indicator and red-emitting bimetallic gold/silver nanoclusters (AuAgNCs) as an internal reference, providing a real-time and visual monitoring system for food freshness. Results showed that the as-prepared DPA-AgNCs displayed an excellent response and good sensitivity for volatile basic nitrogens (VBNs), with a limit of detection (LOD) of 0.51 μM and 0.08 ppm for spermidine and ammonia hydroxide, respectively. Subsequently, a ratiometric test strip was developed to visually monitor ammonia vapour, displaying an obvious fluorescence colour variation from mustard to deep-red. Moreover, the presented ratiometric test strip was successfully applied for non-contact and visual evaluating and monitoring VBNs in the shrimp sample, showing high potential for in-situ monitoring.