A photoelectrochemical aptasensor based on in-situ grown Ag2S quantum dot-sensitized Bi2MoO6/BiOBr heterojunction for α-lactalbumin detection

α-Lactalbumin (α-La), a major allergenic protein in milk, requires ultrasensitive detection to address food safety concerns and mitigate allergic risks. This study introduces a novel label-free photoelectrochemical (PEC) aptamer sensor for α-La detection in dairy products, utilizing a Bi 2 MoO 6 /BiOBr heterojunction substrate sensitized with in-situ synthesized Ag 2 S quantum dots (QDs). The heterojunction platform enhances visible-light absorption and photocurrent generation, while the in-situ Ag 2 S QDs optimizes interfacial charge transfer and surface reactivity. Systematic optimization of experimental parameters such as heterojunction composition, pH, ascorbic acid (AA) concentration, and Ag 2 S QDs conditions enabled precise tuning of the sensor’s performance. The aptamer-functionalized electrode selectively recognized α-La through specific binding interactions, with photocurrent signal attenuation proportional to α-La concentration. The sensor demonstrated a linear response from 0.005 to 50 ng/mL, described by the equation I (μA) = 56.81 − 9.796 lg c , ( R 2 = 0.9934), and achieved an ultralow detection limit of 0.106 pg/mL, surpassing existing methods. The sensor exhibited remarkable stability, reproducibility, and selectivity in complex milk matrices, underscoring its practical utility. This work advances PEC sensing by rationally combining heterojunctions and QDs, providing a robust platform for allergen monitoring in food safety applications.