A Cationic Surfactant-Decorated Liquid Crystal-Based Aptasensor for Label-Free Detection of Malathion Pesticides in Environmental Samples

Abstract

We report a liquid crystal (LC)-based aptasensor for the detection of malathion using a cationic surfactant-decorated LC interface. In this method, LCs displayed dark optical images when in contact with aqueous cetyltrimethylammonium bromide (CTAB) solution due to the formation of a self-assembled CTAB monolayer at the aqueous/LC interface, which induced the homeotropic orientation of LCs. With the addition of malathion aptamer, the homeotropic orientation of LCs changed to a planar one due to the interactions between CTAB and the aptamer, resulting in a bright optical image. In the presence of malathion, the formation of aptamer-malathion complexes caused a conformational change of the aptamers, thereby weakening the interactions between CTAB and the aptamers. Therefore, CTAB is free to induce a homeotropic ordering of the LCs, which corresponds to a dark optical image. The developed sensor exhibited high specificity for malathion determination and a low detection limit of 0.465 nM was achieved. Moreover, the proposed biosensor was successfully applied to detect malathion in tap water, river water, and apple samples. The proposed LC-based aptasensor is a simple, rapid, and convenient platform for label-free monitoring of malathion in environmental samples.

Liquid Crystal Biosensors: Principles, Structure and Applications

“…Jang et al developed a novel label-free LC biosensor to detect malathion insecticides [ 97 ]. DNA aptamers were used as sensing probes, specifically bound to malathion molecules, and the positively charged hexadecyltrimethylammonium bromide (CTAB) was chosen as the cationic surfactant.…”

“…The aforementioned conventional LC–aqueous interface in glass-substrate-based biosensors employs a manual approach to pipette LCs into TEM grids [ 97 , 98 , 99 , 100 ]. In spite of the simple design and the mature technology, the implementation of such conventional sensors still requires the manual operation, which is laborious and time-consuming.…”

“… ( a ) Schematic of LC sensor device for malathion detection [ 97 ]; copyright with permission from Nguyen et al ( b ) Diagram of the LC sensor configuration for the detection of acetylcholine (b1) Dark appearance associated with homeotropic orientation caused by Myr layer formation; (b2) enzymatic hydrolysis of Myr layer by AChE causes a bright appearance associated with a plane orientation; (b3) the competitive enzymatic hydrolysis of Myr and ACh by AChE is associated with homeotropic orientation and dark appearance [ 98 ]; reproduced with permission from Elsevier. ( c ) Optical images of LC sensor in the presence of various hydrogen peroxide concentrations [ 99 ]; reproduced with permission from Elsevier.…”

State-of-the-Art Development in Liquid Crystal Biochemical Sensors

“…Moreover, as some biomolecules show good affinity with surfactants, they can disrupt the balance between the surfactants and LCs and trigger the orientation transition from homotropic to planar. Based on this principle, more sensors can be designed for the detection of various targets, such as single-strand DNA, metal ions, and toxins, and so on [ 34 , 35 , 36 ]. Therefore, the LC–aqueous interface provides a functional, flexible, and real-time sensing platform for biochemical sensors.…”

“…LC exhibited planar alignment under the interaction between malathion aptamer and CTAB. With the addition of malathion, the orientation transferred towards a homeotropic state due to the appearance of an aptamer–malathion complex [ 36 ].…”