Ligand-Doped Liquid Crystal Sensor System for Detecting Mercuric Ion in Aqueous Solutions

Abstract

We developed a liquid crystal (LC) sensor system for detecting mercuric ion (Hg(2+)) in aqueous solutions. In this system, 4-cyano-4'-pentyl biphenyl (5CB) was doped with a sulfur- and nitrogen-containing ligand 5-(pyridine-4-yl)-2-(5-(pyridin-4-yl)thiophen-2-yl)thiazole (ZT) as the Hg(2+) specific LCs. When the system was immersed in the solution containing Hg(2+), the complex of ZT and Hg(2+) formed, which disrupted the orientation of LC and lead to a dark-to-bright transition of the image of LCs. From mercuric binding titrations monitored by UV-vis spectroscopy, it was found that 1:1 Hg(2+)/ZT complexes were formed. The limit of detection (LOD) of the system to Hg(2+) is 10 μM, and it did not respond to Cd(2+), Zn(2+), Cu(2+), Pb(2+), Fe(+), Mg(2+), Ca(2+), Na(+), and K(+). Besides, we also demonstrated that this system is capable of detecting Hg(2+) in tap water and pond water. Because the signal of this system is colorful under ambient light, which is readily understood by normal users, it can be used as a portable device to monitor the water quality at any location.

Non-electronic gas sensors from electrospun mats of liquid crystal core fibres for detecting volatile organic compounds at room temperature

“…We are currently experiencing an increasing interest in gas sensors based on liquid crystals (LCs) [32][33][34][35][36][37][38][39][40][41], functioning at room temperature, requiring no energy supply as they are powered by thermal energy alone, and delivering a strong optical response that is easily detected without complex spectroscopic equipment. The response is due to the ability of certain gas molecules, even at low concentration, to strongly influence the liquid crystal self-assembly [40,[42][43][44][45], triggering a reorientation of the liquid crystal director [32,34,43,44], a change in period of the supramolecular helix of shortpitch cholesterics [19,36,42,[46][47][48], or even complete loss of long-range ordering [11].…”

“…In these cases the LC sensor response arises from an analyte-induced change of anchoring conditions, leading to a major change in director field geometry within the sample, which in turn results in a strong change in optical properties. Other researchers [37,38,41] have demonstrated alternative approaches for exploiting LCs as sensors to chemical agents, sensitised either through doping or other chemical modifications.…”

Bovine Serum Albumin Protein-Based Liquid Crystal Biosensors for Optical Detection of Toxic Heavy Metals in Water

“…Singh, et al [17] reported Selective detection of Hg 2+ up to 0.5 µM using thiocarbamate as a chemical probe. Similarly, Chen, et al [18] also detected Hg 2+ down to 10 µM using 5-(pyridine-4-yr)-2(5-(pyridine-4-yr)thiophen-yl) diazole. However, these molecular probes were chemically synthesized and used for the detection of a specific metal ion in water and have certain shortcomings such as the chemical synthesis of these probes being complicated; they also cannot be used for the detection and quantifications of heavy metal ions in body fluids.…”

All-Optically Controllable Photonic Crystals Based on Chiral-Azobenzene-Doped Blue Phase Liquid Crystals

“…Liquid crystals (LCs) have been widely applied to various fields, such as flat panel displays [1,2], electro-optical devices [3][4][5], biological [6,7] or environmental sensors [8,9], and topological defects [10,11] in a micrometer scale. Blue phase LCs (BPLCs) are among the most promising materials for advanced applications because of their superior characteristics, such as self-assembled three-dimensional (3D) photonic structure and fast response time [12][13][14][15].…”