Rapid detection of mercury ions in water using functionalized liquid crystal microdroplets

Abstract

In this study, we present a stimuli-responsive liquid crystal (LC) droplet-based sensor system coated with poly(ethylene imine) (PEI) and Tween-20 for the detection of mercury ions (Hg²⁺) in aqueous environments. Upon exposure to Hg²⁺, the LC droplets undergo a distinct orientational transition from radial (homeotropic) to bipolar (planar), which can be clearly visualized using polarized optical microscopy (POM). This response is attributed to the strong interaction between mercury ions and the amine groups present in the PEI coating. The sensor exhibits a rapid response time of approximately 10 s at a mercury ion concentration as low as 59 mM. The limit of detection (LOD) in distilled water is determined to be 4.71 mM using a sample volume of 160 μL. The sensitivity of the system is influenced by parameters such as the concentration and volume of the mercury ion solution and the number of LC droplets used. Furthermore, the sensor demonstrates reliable detection of Hg²⁺ in various water samples, including distilled and lake water, indicating its practical applicability. In addition to detection, the PEI/Tween-20-coated LC droplets show potential for reducing mercury ion concentration through surface adsorption. This approach offers a simple, cost-effective alternative to conventional instrumentation for on-site mercury detection in environmental samples.