Abstract
This study presents an eco-friendly synthesis of bimetallic silver-copper nanoparticles (Ag-Cu NPs) using food-grade d-mannitol as a reducing agent, demonstrating their dual-mode sensing mechanism for detecting sulfides and biogenic amines in meat freshness monitoring. The Ag-Cu NPs exhibit distinct optical responses through two mechanisms: (1) For biogenic amines (e.g., dimethylamine), selective silver enrichment occurs via amine-mediated reduction while copper undergoes dissolution, resulting in the formation of stable Ag-N surface complexes. (2) For sulfides (e.g., Na₂S), low concentrations (0-130 μM) enhance Ag/Cu plasmonic peaks through sulfur-metal coordination, whereas higher concentrations induce oxidative etching, causing structural collapse and subsequent signal quenching. The nanoparticles demonstrate high sensitivity and selectivity with minimal interference from common volatiles (VOCs) and ionic species. Validation studies using whiteleg shrimp and pork samples confirmed accurate detection of critical freshness thresholds, establishing the method's reliability in complex food matrices. The sensing platform maintained consistent performance across a wide temperature range (4-15°C), exhibiting accelerated response kinetics under temperature-abuse storage conditions. This work presents a sustainable nanotechnology platform that enables real-time monitoring for next-generation intelligent food packaging systems.