A liquid crystal-based biosensor for detection of insulin driven by conformational change of an aptamer at aqueous-liquid crystal interface

Insulin is a critical predictor for the function of pancreatic islet beta cells, which plays a crucial role in diagnosing diabetes and diabetes-related disorders. Herein, we propose and validate a label-free and cost-effective aptamer-based optical LC biosensor for detection of insulin based on the directional recognition of biomolecular binding events at a responsive aqueous-liquid crystal (LC) interface. The binding of insulin and aptamer adsorbed on CTAB triggers a conformational change of the aptamer from G-quadruplex to stretched structure, inducing homeotropic to planar alignment and correspondingly dark to bright optical image change of the LC films. The molecular dynamic (MD) simulation validates that the orientational transition is associated with the interaction energy changes at the interface, which is in coordination with the optical observation. This LC biosensor takes advantages of simple preparation, easy operation, rapid sensing, high specificity for insulin determination in the range of 0.1-1.0 nM within 5 min. This sensor is also applicable for insulin detection in diluted human urine and serum. Additionally, the optical cell arrays allow to detection multiple samples of the same/different biomarkers at the same time. Such a strategy offers a potential basis for monitoring other clinical biomarkers, and for point-of-care testing (POCT) as well.