Sensitive liquid crystal-based sensor for monitoring the enzymatic activities of trypsin

In this study, a highly sensitive and label-free method was developed to monitor the enzymatic activities of trypsin via orientational transition of liquid crystals (LCs) coupled to the interactions between the polyelectrolyte and phospholipid monolayer. Generally, the positively charged polyelectrolyte interacted with the negatively charged phospholipid monolayer by electrostatic interaction, which caused reorganization of the phospholipid membrane and induced a homeotropic to planar orientational transition of LCs. Enzymatic cleavage of the polyelectrolyte, which was caused by trypsin, eliminated the electrostatic interaction that occurred at the aqueous/LC interface and restored the LC alignment. The optical response of the LC changed in a way that corresponded with the LC molecular arrangement, which enables naked-eye detection under polarized optical microscopy. A rather low detection limit, down to 10 ng/mL, was achieved for trypsin activity detection by applying the proposed method