Liquid Crystal-Based Droplet Sensor for the Detection of Hg(II) Ions Using an Aptamer as the Recognition Element

Abstract

Herein, we report the development of a simple liquid crystal (LC)-based droplet sensor for the specific detection of mercury ions (Hg2+) in an aqueous medium, using trimethyl octadecyl ammonium bromide (OTAB) and an Hg2+-binding aptamer. In terms of the mechanism, the system senses the homeotropic orientation of the LCs at the LC–aqueous interface that is induced by the self-assembled monolayer of positively charged OTAB molecules. In the absence of Hg2+, electrostatic interactions between the positively charged OTAB and negatively charged aptamer molecules disturb the organization of the OTAB monolayer, causing the LCs to adopt a planar orientation. By contrast, an aptamer hairpin structure formed in the presence of Hg2+ weakens the interactions between the OTAB and aptamer molecules, causing the OTAB monolayer to self-reassemble and the LCs to consequently adopt a homeotropic orientation. These LC orientational transitions are observable under a polarized optical microscope. This sensor had a low limit of detection of 100 and 250 pM for buffer and tap water samples, respectively. Therefore, our LC-based droplet sensor is a suitable platform for the simple, specific, and convenient detection of Hg2+ in an aqueous medium. © 2021, The Korean BioChip Society.