Aptamer-based sensitive fluorescence β-lactoglobulin food allergen bioassay via dual and cyclic bidirectional strand displacement amplifications.

β-Lactoglobulin (β-Lg) is a prevalent allergenic protein found in most dairy products, which poses great food safety risks for individuals with allergies, especially for infants. Sensitive and effective detection methods for such allergens are essential to reduce the risk of allergies in daily life. Herein, a fluorescent aptamer bioassay based on a dual and cyclic bidirectional strand displacement means is developed for the sensitive detection of β-Lg in infant rice porridge and milk. The aptamer in the duplex DNA probe binds β-Lg to release the assistance strand to further hybridize with two hairpins, which triggers the initiation of two cyclic amplification cycles through the polymerization, displacement, and nicking of the strands under the action of DNA polymerase and endonuclease restriction enzymes. The amplification cycles lead to the unfolding of many fluorescently quenched signal probes to exhibit substantially enhanced fluorescence recovery for detecting β-Lg. The assay can realize detection of β-Lg in concentrations as low as 4.41 pM within the range of 0.01 to 10 nM. Furthermore, our sensing method has the capability to discriminate β-Lg from other proteins with high selectivity, resulting in low levels of β-Lg detection in rice porridge and milk samples, demonstrating promising potentials of the developed sensing method for monitoring various food allergens.