Label-free optical detection of thrombin using a liquid crystal-based aptasensor

We describe a real-time, label-free aptasensor that utilizes the orientational properties of nematic liquid crystals (LCs) for detection of thrombin. The imaging principle is based on the homeotropic orientation of LC films, which can be influenced by thrombin-specific aptamers and N,N-dimethyl-N-(3-(trimethoxysilyl)propyl)-1-octadecanaminiuchloride (DMOAP) immobilized on glass slides. The interactions between thrombin and its specific aptamer, including ionic and hydrogen bonds, can interfere with the homeotropic alignment of LCs, leading to changes from 'dark' to 'bright' responses that can be visualized simply using crossed polarizers. We describe the condition for maintaining the homeotropic state of LCs, which are suitable for thrombin-specific aptamer experiments, and reactions between aptamer and several enzymes, including thrombin. This novel simple LC-based aptasensor has not only high specificity, but also high sensitivity (low detection limit of 1 pg/mL (26.7 fM)). We also note the blood coagulation reaction between fibrinogen and thrombin, which confirms that the aptamer-bound thrombin is auto-enzymatic. Our result shows that the sensitivity of the proposed sensor increases (1 pg/mL to 0.1 pg/mL) using fibrinogen.