Detection of pesticides using an optical biosensor based on liquid crystal microdroplets

This study presents a label-free optical biosensor based on fully spherical liquid crystal (LC) microdroplets for the simple and sensitive pesticide detection. The LC-water interface was modified with myristoylcholine chloride (Myr), a cationic surfactant, resulting in a radial molecular configuration of the LC microdroplets, in which LC molecules orient perpendicularly to the droplet surface. Upon the introduction of acetylcholinesterase (AChE), enzymatic hydrolysis of Myr is triggered, inducing a transition to a bipolar configuration, where LC molecules align parallel to the droplet interface. Conversely, the presence of AChE inhibitors, such as dimethoate and fenobucarb, suppresses this hydrolysis, thereby preserving or restoring the droplets to a radial configuration. Experimental results reveal that the detection limits for fenobucarb and dimethoate reach 1 × 10-8 mg/mL and 1 × 10-9 mg/mL, respectively, both well below the maximum permissible levels specified by water quality regulations. This platform exhibits a sensitivity improvement of approximately two orders of magnitude compared to systems utilizing hemispherical LC microdroplets. Additionally, successful application to real water samples from Heilongjiang River validates its practical utility. Overall, this label-free, simple, and highly sensitive LC microdroplet-based biosensor represents a promising approach for environmental pesticide monitoring.