Liquid crystal sensor for the detection of acetylcholine using acetylcholinesterase immobilized on a nanostructured polymeric surface

In this study, we report on a label-free biosensor for the detection of acetylcholine (ACh) and an acetylcholinesterase (AChE) inhibitor, utilizing liquid crystals (LCs) on a polymeric surface with periodic nanostructures. The polymeric nanostructures, which hold sinusoidal anisotropic patterns, were fabricated by a sequential process of poly(dimethylsiloxane) buckling and replication of these patterns on a poly(urethane acrylate) surface where a film of gold was deposited. AChE was then covalently immobilized onto the gold surface. Optical images of nematic 4-cyano-4′-pentylbiphenyl (5CB) revealed that it aligned parallel to the plane of the enzyme-decorated surface. However, AChE-mediated hydrolysis of ACh resulted in a plume of choline, acetate, and unreacted ACh, which in turn produced a distinctive optical transition of 5CB (from uniform to random) by masking the anisotropic surface topography. The hydrolysis of ACh was inhibited in the presence of a carbamate insecticide (AChE inhibitor), which prevented the orientational transition of 5CB by decreasing the enzymatic activity of AChE. These results suggest that this LC-based enzymatic sensor is highly sensitive to ACh and the AChE inhibitor, with a detection limit of 10 and 1 nM, respectively. This study demonstrates that polymeric surfaces with continuous wavy features can be used as LC-based biosensors to amplify the existence of ACh and an AChE inhibitor without labeling or an additional amplification strategy.