A label-free photoelectrochemical aptasensor utilizing Ag2S quantum dot-sensitized In2O3/BiOBr heterojunction for β-lactoglobulin detection in milk samples

Cow’s milk allergy is a prevalent food allergy, with β-lactoglobulin (β-Lg) identified as one of the major allergenic proteins in cow’s milk. The accurate detection of β-Lg is crucial for reducing the risk of allergic reactions. In this study, a novel label-free photoelectrochemical (PEC) aptasensor was developed for the detection of β-Lg in milk, utilizing an In₂O₃/BiOBr heterojunction composite material. Sensitization of the heterojunction with Ag₂S quantum dots (QDs) enhanced the photosensitivity, leading to a significant increase in photocurrent response. The In₂O₃/BiOBr heterojunction improved solar energy utilization and enhanced light absorption across the visible spectrum. The photocurrent signal intensity decreased proportionally with increasing β-Lg concentration due to the specific binding with the aptamer. Under optimized experimental conditions, the PEC aptasensor exhibited a wide linear detection range from 0.001 ng/mL to 100 ng/mL and achieved a detection limit of 2.31 pg/mL. The sensor proved excellent selectivity, stability, reproducibility, and a broad linear range, offering a promising method for β-Lg detection in real milk samples.