Portable colorimetric probe based on high-entropy alloy nanozyme for rapid detection of fruit freshness

Freshness, crucial for quality, especially in nutrient-rich fruits and vegetables, declines with nutrient degradation during storage. Measuring antioxidant content effectively indicates freshness, but traditional methods like HPLC and MS are expensive and non-portable. Nanozyme-based colorimetric sensors offer a faster, cost-effective, and portable alternative. Here, five-element high-entropy (HE)-alloys were synthesized via a simple co-precipitation method, and their peroxidase-like catalytic properties were studied. Alloys containing Zn, Ni, and Fe showed notable activity, with CuZnCoNiFe performing best, followed by CuMgZnNiFe and CuZnMnNiFe. Activity was attributed to the high proportion of Cu²⁺ and the electrostatic effects, as indicated by zeta potential, ICP-MS, and XPS analyses. Then, CuZnCoNiFe was used to create a portable, smartphone-assisted colorimetric paper sensor, capable of rapid detecting antioxidant levels and distinguishing naturally or artificially ripened fruits, providing a practical tool for assessing food freshness.