Real-time optical detection of mercury contamination in drinking water using an amphiphilic recognition probe at liquid crystal/aqueous interfaces

Abstract

Mercury contamination is a global environmental issue due to its toxicity and persistence in ecosystems. It poses a particular risk in aquatic systems, where it bioaccumulates and biomagnifies, leading to serious health impacts on humans. Therefore, effective detection technologies for mercuric ions in natural water resources are highly desirable. However, most existing detection methods are time-consuming, require complicated sample pre-treatment, and rely on expensive equipment, which hinders their widespread use in real-time detection. Here, we present a convenient, rapid, portable, user-friendly, and cost-effective sensing system for detecting Hg²⁺ ion contamination in water. This system utilizes a highly selective, amphiphilic, and structurally simple molecular probe, N-dodecylamine-di-thiocarbamate (DDC). DDC molecules align at the interface between the liquid crystal (LC) and water, inducing a homeotropic LC orientation. In water samples contaminated with Hg²⁺, a bright optical texture is observed, indicating the alignment of the 5CB LC in a planar manner at the LC/aqueous boundary. The minimum detectable concentration (LOD) for Hg²⁺ ions is 5.0 μM in distilled water, with a broad detection range from 5.0 μM to 2 mM. The sensor selectively detects Hg²⁺ ions over other common interfering metal ions, including Pb²⁺, Co²⁺, Ni²⁺, Cu²⁺, Cd²⁺, Zn²⁺, Cr²⁺, Mg²⁺, Na⁺, K⁺, and Ca²⁺. Boolean logic gates, bar graphs, and truth tables are employed to explain the selectivity of this liquid crystal-based sensor. This work demonstrates the significant potential of the sensor for monitoring mercuric ions in natural water resources, offering a promising strategy for controlling mercury pollution.