Exploiting polyphenol oxidation chemistry for colorimetric logic and encryption

Polyphenol oxidation governs color and browning in foods through structure-dependent redox reactions. Here we repurpose this chemistry to build an instrument-free colorimetric logic and encryption platform using plant polyphenols and praseodymium oxide nanorods (Pr₆O₁₁ NRs) as oxidase mimics. Five structurally distinct polyphenols underwent characteristic, pH-dependent oxidation, producing visually distinguishable colours, while radical-scavenging experiments indicated that hydroxyl radicals from Pr³⁺/Pr⁴⁺ redox cycling are the likely dominant oxidants. Using polyphenol identity, pH and Pr₆O₁₁ presence as orthogonal inputs, the system implemented AND- and IMP-type logic gates and 20 naked-eye-distinguishable states, which were mapped onto a color-wheel cipher for visual encryption. The gate operation proved robust across three fruit juices, where all 36 binary calls were correctly assigned, each matrix yielded a distinct colorimetric fingerprint, and thiol interference up to 10 mM did not flip the output. Built from food-derived molecules and earth-abundant catalysts, this strategy enables low-cost, non-direct-contact anti-counterfeiting and food authentication.