A card instead of a lab: A ligand embedded in a bio-composite of starch/gelatin intelligent film for milk quality test followed by colorimetric analysis

Milk adulteration analysis at different stages of the production chain, which profiteers widely use to mask milk quality parameters, is problematic. We prepared selective intelligent thin bio-films and a dedicated app to test milk adulteration in an out-of-lab setting. In this regard, each reagent is immobilized on a piece of starch/gelatin film as color-changeable polymeric support, which is then pasted onto a transparent test card. Incorporating starch and gelatin as the backbone of these composite films can significantly improve the mechanical properties, color, and potential applications in real-time monitoring. After 5 min floating of the card on the surface of the milk, our developed software as a Progressive Web Application can be used to locate and read the QR codes of the samples to estimate qualitative and quantitative information about the presence of some preservatives. These preservatives ranged from 0.1 to 200.0 mg/L, 1.0-100.0 mg/L, 0.001-0.05 mol/L in 10 mL of milk with the LODs of 0.1, 1.0 mg/L, and 0.001 mmol/L, for H₂O₂, Cr(VI), and salicylic acid, respectively. The pH monitoring film also indicates the freshness/spoilage of the milk. The portability, ease of use, and low cost of testing coupled with the app, make it an attractive alternative to lab-based analysis.