Rapid label-free colorimetric dual-functional aptasensor for β-lactoglobulin detection based on a rational tailoring strategy

β-lactoglobulin (β-LG) is a nonnegligible allergenic protein found in cow milk. A label-free, enzyme-free, dual-functional aptameric sensor was constructed based on rational aptamer tailoring for β-LG detection. Via an established three-step rational tailoring strategy, the original aptamer was transformed from an inflexible antiparallel topology into the flexible, antiparallel/parallel hybrid topology, enlg2-pl3. enlg2-pl3 displayed the dual-functionality of not only binding with β-LG via the antiparallel conformation but also outputting signals via the parallel type. The dual-functionality depended on the conformational conversion of enlg2-pl3. The β-LG-driven conformational conversion to antiparallel type was the detection basis of aptasensor. The detection conditions were optimized regarding ions, hemin, chromogenic substrate, pH levels, and detection time. Furthermore, the aptasensor offered advantages, such as cost-efficiency, simple operation, 40 min rapid detection, excellent specificity, and a sensitivity of a three-orders of magnitude linear range and an 8.23-fold linear curve slope, meeting the point-of-care testing (POCT) requirements for dairy analysis.