Development and Application of Liquid Crystals as Stimuli-Responsive Sensors

Abstract

This focused review presents various approaches or formats in which liquid crystals (LCs) have been used as stimuli-responsive sensors. In these sensors, the LC molecules adopt some well-defined arrangement based on the sensor composition and the chemistry of the system. The sensor usually consists of a molecule or functionality in the system that engages in some form of specific interaction with the analyte of interest. The presence of analyte brings about the specific interaction, which then triggers an orientational transition of the LC molecules, which is optically discernible via a polarized optical image that shows up as dark or bright, depending on the orientation of the LC molecules in the system (usually a homeotropic or planar arrangement). The various applications of LCs as biosensors for glucose, protein and peptide detection, biomarkers, drug molecules and metabolites are extensively reviewed. The review also presents applications of LC-based sensors in the detection of heavy metals, anionic species, gases, volatile organic compounds (VOCs), toxic substances and in pH monitoring. Additionally discussed are the various ways in which LCs have been used in the field of material science. Specific attention has been given to the sensing mechanism of each sensor and it is important to note that in all cases, LC-based sensing involves some form of orientational transition of the LC molecules in the presence of a given analyte. Finally, the review concludes by giving future perspectives on LC-based sensors.

Liquid crystal droplet design by using pseudopeptidic bottlebrush polymer additives

“…S17c and f, ESI †) due to the homeotropic alignment of LC molecules in the low surface anchoring area. 77 The obtained results show that the formed PDLC samples are equally sensitive to pH solutions of different compositions. This demonstrates that pseudopeptidic polymer confined LC droplets are suitable for fabricating pH sensing devices with enhanced mechanical strength.…”

“…The isotropic black texture in low surface anchoring area (away from the polymer) due to homeotropic alignment in the presence of basic solution, results in pattern formation in the sample. 77 In order to investigate the effect of the composition of pH buffer solutions on obtained pH response, three more solutions of pH 4, 7, and 10 with different compositions (Table S5, ESI †) are tested on PFO5 and PEO5 samples. The obtained experimental results show consistency with the previously obtained results.…”

“…The isotropic black texture in low surface anchoring area (away from the polymer) due to homeotropic alignment in the presence of basic solution, results in pattern formation in the sample. 77…”

Liquid Crystal Biosensors: Principles, Structure and Applications

“…The anisotropy in the refractive index is the most commonly used optical birefringence characteristic. Plane polarized light is decomposed into two linearly polarized rays with different propagation rates, which are called ordinary ( ) and extraordinary ( ) rays, respectively [ 56 ]. The birefringence property of LC can be described as the difference between the refractive indices of and .…”

Dissipative Particle Dynamics Simulation of the Sensitive Anchoring Behavior of Smectic Liquid Crystals at Aqueous Phase

“…In recent years, intense research efforts have been directed to the development and applications of thermotropic liquid crystal (LC)-based sensors, especially for systems involving aqueous-LC interface (thin films or droplets) [ 1 , 2 , 3 , 4 ]. As first proposed by Abbott et al [ 5 ], it is essentially designed on the basis of an unique combination of the sensitive alignment responsiveness to interfaces and orientation-dependent optical texture of LCs as well as the fluid feature of aqueous-LC interfaces.…”