Structural Antagonism‐Aided Conformational Regulation Enables an Aptamer‐Loop G‐Quadruplex Modular Sensor of β‐Lactoglobulin

Abstract A simple, reliable method for identifying β‐lactoglobulin (β‐LG) in dairy products is needed to protect those with β‐LG allergies. A common, practical strategy for target detection is designing simplified nucleic acid nanodevices by integrating functional components. This work presents a label‐free modular β‐LG aptasensor consisting of an aptamer‐loop G‐quadruplex (G4), the working conformation of which is regulated by conformational antagonism to ensure respective module functionality and the related signal transduction. The polymorphic conformations of the module‐fused sequence are systematically characterized, and the cause is revealed as shifting antagonistic equilibrium. Combined with conformational folding dynamics, this helped regulate functional conformations by fine‐tuning the sequences. Furthermore, the principle of specific β‐LG detection by parallel G4 topology is examined as binding on the G4 aptamer loop by β‐LG to reinforce the G4 topology and fluorescence. Finally, a label‐free, assembly‐free, succinct, and turn‐on fluorescent aptasensor is established, achieving excellent sensitivity across five orders of magnitude, rapidly detecting β‐LG within 22‐min. This study provides a generalizable approach for the conformational regulation of module‐fused G4 sequences and a reference model for creating simplified sensing devices for a variety of targets.