Zn2+-enhanced dual-mode intelligent film based on natural polysaccharides and quercetin for real-time visual monitoring of shrimp freshness.

This study innovatively employs Zn2+ as a dual-functional enhancer to address the weak signal and single response of flavonoid-based smart packaging. A multifunctional film, SCP/QR/Zn2+(SCP represents sodium alginate/carboxymethyl cellulose/polyvinyl alcohol and QR denotes quercetin), was fabricated via a one-pot method. Zn2+ significantly improved tensile strength (19.18 MPa), elongation (73.68%), water resistance (23.73% solubility), and antibacterial activity. Crucially, Zn2+ coordination synergistically enhanced the film's dual-mode (colorimetric/fluorescent) response to pH/ammonia, improving reliability over single-mode systems. The film exhibited a rapid, reversible response to ammonia with a 4.87 ppm detection limit. Color/fluorescence changes highly correlated (R2 > 0.98) with shrimp TVB-N, providing a clear visual spoilage alert beyond the safety threshold (25 mg/100 g). This work offers an effective strategy to overcome natural indicators' limitations, creating a high-performance, multifunctional active packaging system.