Pocket test for instantaneous quantification of starch adulterant in milk using a counterfeit banknote detection pen

This work presents a paper-based analytical device for instantaneous detection of adulterant starch in commercial milk. A highly efficient strategy was based on the well-established starch/iodine complex formation reaction by using a commercial counterfeit detection pen (CDP). Employing the CDP as a user-friendly and reagent-free approach to modify confined regions of a paper substrate readily promotes the reaction with starch in milk. The resulting color change can be analyzed by a digital scanner or via portable smartphone cameras. The proposed device provided a linear behavior in the concentration range between 0.05 and 1 %, with limits of detection and quantification equal to 0.05 % and 0.17 %, respectively. The sensor shows a very stable readout for many interferents, except for sodium hydroxide at higher concentrations (>1.0 %). Recovery tests performed at different concentration levels yielded values from 96.2 to 116.8 %, demonstrating its potential for quantitative analysis.