Upconversion Lateral Flow Test for A1 Beta‐Casein Protein in Milk and Infant Formulas

A1 and A2 β‐casein are two major genetic variants of β‐casein in cow milk, possessing similar structures but distinct health effects. A1 beta‐casein has been linked to increased disease risk, digestive disruption, and inflammatory processes. To address the need for on‐site milk quality control by the dairy industry and food safety management by consumers, we developed a rapid lateral flow test. In our approach, the high sensitivity is addressed by utilizing lanthanide‐doped upconversion nanoparticles (UCNPs). We demonstrated the test can quantify A1 protein in a range of 0.001–10 ng/mL, with a limit of detection of 61 pg/mL, and the test results can be reliably returned within 10 min. Moreover, we applied this method to identify the A1 concentration across a series of milk and infant formula samples, indicating its potential as a rapid screening method for point‐of‐field testing outside of well‐equipped laboratories in food industry settings.