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

A Zn 2+ -enhanced intelligent film was fabricated via a facile one-pot method. • The film shows enhanced mechanical strength and water resistance by metal cross-linking. • Dual-mode colorimetric/fluorescence response to ammonia enables real-time monitoring. • High sensitivity and accuracy in shrimp freshness detection were demonstrated. • Provides a intuitive solution for intelligent food packaging. This study innovatively employs Zn 2+ as a dual-functional enhancer to address the weak signal and single response of flavonoid-based smart packaging. A multifunctional film, SCP/QR/Zn 2+ (SCP represents sodium alginate/carboxymethyl cellulose/polyvinyl alcohol and QR denotes quercetin), was fabricated via a one-pot method. Zn 2+ significantly improved tensile strength (19.18 MPa), elongation (73.68%), water resistance (23.73% solubility), and antibacterial activity. Crucially, Zn 2+ 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 (R 2  > 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. Download: Download high-res image (216KB) Download: Download full-size image