Cellulose nanofibrils/AgNP nanostructured coating on smart packaging for indication of H₂O₂ in milk

Colorimetric sensors offer user-friendly means of analysis, and do not require wired connections or antennas. These attributes make them suitable for integration into intelligent packaging systems, which enables real-time monitoring of product quality throughout the production and logistics chain, extending to the end consumer. Here we developed colorimetric sensors for detecting H₂O₂ adulteration in milk with a simple and cost-effective approach. Specifically, the sensor was manufactured using paper and can be adapted for use as labels or seals for commercial packaging. A nanohybrid formulation comprising TEMPO-oxidized cellulose nanofibrils and silver nanoparticles (AgNP) was used to modify the paper surface via bar coating technique. Nanocellulose acted as a stabilizer and nucleating site for the synthesis of AgNP and facilitated the homogeneous deposition of the nanohybrid formulation onto the paper. Applying CNF/AgNP improved the paper's roughness and porosity, resulting in homogeneous samples with stable optical properties. The developed platform demonstrated visible bleaching in the presence of H₂O₂ within a concentration range of 100 μM to 1 mM, with a detection limit of 74 μM, good selectivity against common interfering molecules found in milk, and suitable response in recovery tests using whole, semi-skimmed and skimmed milk, demonstrating its potential for real samples analysis.