Rapid and Low-Cost Detection of Oxytetracycline in Raw Bovine Milk Using a Copper Nanoparticle-Functionalized μPAD

Abstract Tetracycline antibiotics are widely used in cattle to treat and prevent bacterial infections, including enteric and systemic diseases. They are also used to treat bovine mastitis, which affects milk quality and productivity. Improper or excessive use can leave antibiotic residues in animal products, posing a public health risk and promoting antimicrobial resistance. In this study, we examined oxytetracycline (OTC) residues in raw cow’s milk from the semi-arid region of Alagoas, Northeastern Brazil. We used a paper-based microdevice (μPAD) with copper nanoparticles (CuNPs). Milk samples were collected from all four teats of 30 randomly selected Girolando cows across different rural properties. The method performed well, showing a linear response from 1 to 25 μg mL⁻ 1 and a high correlation coefficient ( R 2 = 0.99946). The recovery rate was 94.70%, indicating good accuracy with national regulations. The detection and quantification limits were 0.47 and 1.56 μg mL⁻ 1 . Overall, μPAD is an effective, sensitive, low-cost, and portable tool to detect oxytetracycline in raw milk. Graphical Abstract