Easy-to-manufacture confined silver nanoparticles via electrochemical synthesis enabling colorimetric peroxide detection in food

Solid-state colorimetric sensors are often constrained by nanoparticle instability and matrix interference in complex foods. Here, we report an easy-to-manufacture chitosan-κ-carrageenan-silver nanocomposite membrane fabricated through electrochemical in situ AgNP formation without an external reducing agent. The polyelectrolyte network confined AgNPs and enabled an H₂O₂-responsive color change through oxidation and partial dissolution of metallic Ag. After H₂O₂ exposure, TEM revealed residual Ag-containing domains of 4-16 nm, while XRD, SEM-EDS, AAS, and UV-Vis supported partial depletion of the plasmonically active Ag phase. RGB analysis showed a linear response from 1 to 100 μM H₂O₂, a 1.17 μM detection limit, and a 10 min response time. The membrane showed limited interference from several nonoxidizing food constituents but some cross-reactivity toward redox-active species. Refrigerated storage provided the best short-term stability. Recoveries in energy drink, tofu, and milk were 96.24-104.76%, with close agreement between RGB and HPLC.