Reorientation Of Liquid Crystal Research Articles

A novel liquid crystal aptasensor via DNA aptamer conformational change for on-site detection of cocaine in sewage

A novel one-step liquid crystal (LC)-based aptasensor has been developed for on-site detection of trace substances in sewage analysis. The platform utilizes different mechanisms to simultaneously trigger the upper and bottom layers of LC orientation. By employing trace amounts of CTAB in Tris-HCl buffer, the upper layer of LC is aligned, while DNA aptamers modified on a single glass induce the orientation of the bottom layer. When targeting cocaine, the asymmetric single-stranded DNA aptamers transition to a symmetric Y-shape, causing the reorientation of LCs from planar to homeotropic. This results in an optical change from bright to dark in the LC image. The sensing procedure involves adding pre-buffered samples at pH 7.4 to the system in one step. The platform requires only 10 ng of DNA aptamers, which can be kept dry. It enables on-site detection of cocaine in sewage, exhibiting a linear calibration curve from 1 pM to 15 µM in water (R2 = 0.997) with a limit of detection of 0.5 pM. The aptasensor demonstrates quantitative recoveries ranging from 89.6% to 110.9% in sewage samples. This sensitive, robust, and portable LC-based aptasensor shows promise as a tool for on-site detection of trace substances.

A cost-effective label-free biosensor for rapid detection of multiple viral respiratory infections base on liquid crystals: Fabrication and modeling

The high transmission rate and incurability of recurrent Herpes Simplex Virus (HSV) infection require an accurate and fast detection approach for its efficient prevention. In an attempt to find a novel sensitive and simple optical diagnostic technique which enables on-spot testing, here we developed label-free biosensors based on E7 nematic liquid crystals (LCs) for specific detection of HSV DNA. For this purpose, homeotropically oriented LCs as smart materials are spread on the textile grid to make their both upper and lower surfaces be in contact with ambient air. HSV DNA of concentration between 1.4 nM and 5.5 nM is added to the platform, and DNA elution buffer is used as a control. Then, the reorientation of LCs occurs due to the coupling of electrical dipoles between LCs and DNA molecules. Creating a unique pattern that is projected onto CCD by putting the sample in a cross-polarizer and using white light. To model the LC's director distribution, LC's free energy equation is solved using the variational method and finite difference method (FDM). Overall, our LC-based sensor is a user-friendly, cost-effective, highly sensitive, and fast way for specific detection of HSV without the need for experts and expensive equipment.

Unique Polymer-Stabilized Liquid Crystal Structure Prepared by Addition of a Reversible Addition-Fragmentation Chain Transfer Agent.

Polymer-stabilized liquid crystals (PSLCs) are important electrically switchable materials due to their superior electro-optical properties. Nevertheless, it remains a formidable challenge to balance PSLCs' instant electro-optical performance and long-term durability due to their relatively low polymer content and the related sensitivity to external force. Herein, we demonstrate the possibility of regulating the polymer network structure in PSLCs via reversible addition-fragmentation chain transfer (RAFT) polymerization reactions of acrylate monomers with a chain transfer agent (CTA). By controlling the concentration of CTA and conditions of photopolymerization, the kinetics of the polymerization reaction can be modified. Compared to conventional free-radical (FR) polymerization, the reduced chain growth rate leads to sufficient chain relaxation, reorientation of liquid crystal (LC) directors, and alleviation of shrinkage stresses in the RAFT polymerization process. This in turn produces an ordered polymer network structure in the vertical direction and a uniform distribution in the horizontal plane. As a result, the PSLC network presents increased elasticity with a lower hysteresis effect and greatly improved durability. Our research offers insightful guidance for the fine-tuning of polymer network structures to prepare advanced LC/polymer composite structures with outstanding performances.

Controlling Plasmon Resonance of Gold and Silver Nanoparticle Arrays with Help of Liquid Crystal

The tunability of plasmonic resonances in gold and silver nanosphere arrays on a glass substrate, embedded in a liquid crystal matrix, was explored. The calculations involving the finite element method revealed that the optical properties of these arrays can be modulated by reorienting the liquid crystal. When the liquid crystal director was reoriented between planar and homeotropic configurations in the plane containing the incident wave polarization vector, the plasmonic resonance wavelength shifted within an approximately 100 nm range. A reduced shift of about 40 nm was observed when the reorientation occurred in the plane perpendicular to the polarization. Both metal nanosphere arrays showed notable near-field amplification. Gold achieved up to 18 times the amplification of the incident wave electric field, while silver reached 16 times but showed a remarkable 40 times amplification at the inter-band transition resonance wavelength. This research underscores the potential of using liquid crystal reorientation for controlling the plasmonic lattice resonance in metal nanosphere arrays, opening up new possibilities for adaptable plasmonic devices.

A simple and robust aptasensor assembled on surfactant-mediated liquid crystal interface for ultrasensitive detection of mycotoxin

Here, a simple aptasensing approach is represented to sensitively detect ochratoxin A (OTA) as one of the most perilous mycotoxins with carcinogenic, nephrotoxic, teratogenic, and immunosuppressive sequels on human health. The aptasensor is based on the alteration in the orientational order of liquid crystal (LC) molecules at the surfactant-arranged interface. Homeotropic alignment of LCs is achieved by the interaction of the surfactant tail with LCs. By perturbing the alignment of LCs due to the electrostatic interaction of the aptamer strand with the surfactant head, a colorful polarized view of the aptasensor substrate is induced drastically. While OTA causes the re-orientation of LCs to a vertical state by forming an OTA-aptamer complex that induces darkness of the substrate. This study shows that the length of the aptamer strand impacts the efficiency of the aptasensor; longer strand results in the greater disruption of LCs, and therefore, increases the aptasensor sensitivity. Hence, the aptasensor can determine OTA in the linear concentration range of 0.1 fM-1 pM as low as 0.021 fM. The aptasensor is capable to monitor OTA in grape juice, coffee drink, corn, and human serum real samples. The proposed LC-based aptasensor provides a cost-effective, easy-to-carry, operator-independent, and user-friendly array with great potential to develop portable sensing gadgets for food quality control and health care monitoring.

Surface modification strategy of boronic acids on glass substrates and its application for detecting glycated hemoglobin by liquid crystal-based sensors

Surface modification is a fundamental technique in the development of chemical sensors and biosensors. In this work, we established a strategy to incorporate boronic acids into the structure of polyethylenimine (PEI) through a multi-component reaction under microwave conditions. The presence of boronic acids on PEI was identified by NMR and IR spectroscopy. This borylated PEI polymer was coated on the glass substrate and its binding activity was tested by using 5-(diethylamino)-2-((methylimino)methyl)phenol (DAHMI) as a fluorescence tag. Moreover, the boronic acid-modified surface was applied to construct a liquid crystal (LC)-based sensor system for detecting glycated hemoglobin (HbA1C). The specific binding of HbA1C to boronic acid on glass surface lead to the reorientation of LCs, such that a dark-to-bright optical transition was observed under polarized light. Based on this mechanism, the limit of detection of the LC-based sensor for HbA1C was 100 μg/mL with good specificity. Our results demonstrated the applicability of the surface modification strategy of boronic acids on glass substrates for developing chemical sensors and biosensors.

Electro-optic response of bipolar nematic liquid crystal confined in oblate spheroid

Electro-optic response of liquid crystals (LCs) relies on the molecular reorientation of LCs under external electric field and is important for a wide spectrum of applications. Here, we uncover an interesting electro-optic response of 5CB nematic LC confined in an oblate spheroid and subjected to external electric field. Under the planar anchoring, the nematic LC spheroid adopts a bipolar structure with the bipolar axis laid in the horizontal film plane. When a threshold electric field EF, is applied, the bipolar structure reorients from the horizontal configuration (LC molecules align along long axis direction) to the vertical configuration (LC molecules align along short axis direction), involving the competition of elastic energy, surface anchoring energy and electric field energy. In contrast to bipolar nematic LC droplets, the vertical configuration does not relax to the low-energy horizontal configuration after removing E; we argue that is due to the oblate shape of the nematic LC spheroid, which traps the bipolar structure in a local energy minimum. We use continuum simulation to demonstrate the detailed response and the reorientation dynamics of bipolar nematic spheroids under E field, showing consistent results with the experiments and confirming the proposed switching mechanism. Nevertheless, the vertical configuration of the bipolar structure could relax to the low-energy horizontal configuration by thermal cycling. Our studies provide clear experimental results that show the characteristics of the electro-optic response of oblate LC spheroids, which have both fundamental and practical implications.

Attomolar analyte sensing technique for detection of Pb2+ and Hg2+ ions based on liquid crystal

Detecting the ultra-low abundance of heavy metals in real samples remains challenging and it requires the development of high-performance biosensing modalities. This work describes a novel strategy for design an ultra-sensitive liquid crystal (LC) aptasensor, in which the LCs reorientation induced by conformational changes of a triple helix molecular switch (THMS) structure is utilized for the quantitative detection of Pb2+ and Hg2+ ions. The developed aptasensor exhibits a wide linear range with the ultralow detection limits as low as 0.021 aM and 0.068 aM for Pb2+ and Hg2+, respectively. Besides, the results show that other analytes cause no interference. Noteworthy, this sensing strategy is easy to expand for other targets by altering the aptamer sequence without change of the triple-helix structure and can be used for multiple analyte detection. The developed aptasensor is promising powerful platform as a LC AttoSens for precision screening of hazardous residues in food analysis.

Electro-Optical Modulation in High Q Metasurface Enhanced with Liquid Crystal Integration.

Electro-optical tuning metasurfaces are particularly attractive since they open up routes for dynamic reconfiguration. The electro-optic (EO) modulation strength essentially depends on the sensitivity to the EO-induced refractive index changes. In this paper, lithium niobate (LiNbO3) metasurfaces integrated with liquid crystals (LCs) are theoretically investigated. Cylinder arrays are proposed to support quasi-bound states in the continuum (quasi-BICs). The quasi-BIC resonances can significantly enhance the lifetime of photons and the local field, contributing to the EO-refractive index changes. By integrating metasurfaces with LCs, the combined influence of the LC reorientation and the Pockels electro-optic effect of LiNbO3 is leveraged to tune the transmitted wavelength and phase spectrum around the quasi-BIC wavelength, resulting in an outstanding tuning sensitivity up to Δλ/ΔV ≈ 0.6 nm/V and relieving the need of high voltage. Furthermore, the proposed structure can alleviate the negative influence of sidewall tilt on device performance. The results presented in this work can foster wide application and prospects for the implementation of tunable displays, light detection and ranging (LiDAR), and spatial light modulators (SLMs).

Dynamically color-changing polymer-dispersed liquid crystals containing ionic liquid for smart window applications

ABSTRACT In this work, we report a bifunctional dynamically colour-changing polymer-dispersed liquid crystals (PDLCs) for smart windows by doping a supporting electrolyte ionic liquid into the conventional PDLC system. The transmittance spectra were used to measure the electrically colour-changing properties of the system, while the electro-optical curves were employed to examine the electrically switchable performances. The SEM was used to observe the surface morphology of the polymer microstructure. The result obtained from this work suggested that such device could obtain four independent states under different electric fields. The initial state was opaque and colourless due to the randomly dispersed liquid crystal droplets. The transparent and colourless state was obtained as a result of reorientation of liquid crystal under alternative current (AC) electric field. The opaque and green state was achieved under direct current (DC) electric field owing to the oxidation reaction in the system. Besides, the transparent and green state was realised via applying DC and AC electric field simultaneously or in steps. The convenience and simplification of switching between the four states enable the system to provide some interesting applications for smart windows.

Light-induced Fredericks transition in the nematic liquid crystal cell with plasmonic nanoparticles at a cell bounding substrate.

The paper presents a theoretical description of the light-induced nematic liquid crystal reorientation in a cell with gold nanoparticles deposited on the surface of one of bounding substrates. It is shown that the surface plasmon resonance in the nanoparticles significantly affects the threshold of the director reorientation. The mathematical model of a surface free-energy density of nematic cell is given, which takes into account the influence of the local electric field on the near-surface nematic layer at the substrate with gold nanoparticles. The threshold intensity of a director orientation instability is calculated and its dependence on the wavelength of incident light and the degree of filling of the surface with gold nanoparticles is analyzed. Comparison of the theoretical calculations with experimental data confirms the full adequacy of the proposed theoretical model.

Surface Topographical Control of a Liquid Crystal Microlens Array Embedded in a Polymer Network

A novel approach for fabricating a microlens array with a tunable surface topographical structure and focal length is proposed in the present study. The microlens array was manufactured through the photoinduced molecular reorientation of nematic liquid crystals (LCs) stabilized by a polymer network. The fabricated microlens array had a mountain-shaped topographical structure due to the accumulation of polymers and LC molecules. The molecular orientation of the LC inside the microlens was disordered, while the outer side of the microlens was ordered. The thermal expansion of the polymer network and the phase transition of the LC molecules within the microlens array allowed the surface topographical structure and the focal length to be reversibly tuned under heat treatment. The results of this research work will enable future implementations to provide a thermally tunable microlens array.

Reconstruction of weak near-infrared images in methyl red-doped nematic liquid crystals via stochastic resonance.

We propose a near-infrared (NIR) image reconstruction method based on molecular reorientation of nematic liquid crystals (NLCs) doped with the azo-dye methyl red (MR). The signal can be recovered at the expense of noise via stochastic resonance. The numerical results show that image reconstruction based on the molecular reorientation in a magnetic field can be achieved when the input light intensity is 0.9W/cm2, this is due to the strong enhancement of the nonlinear optical response in MR doped-NLCs. The cross-correlation coefficient is increased from 0.26 to 0.54, and the maximum cross-correlation gain is 2.25. The results suggest a potential method in NIR weak optical image processing under noisy environments.

Magnetic tuning of liquid crystal dielectric metasurfaces

Abstract Dielectric metasurfaces hold an exceptional potential for the next generation of tunable optical systems that find applications in sensing, ranging, and imaging. Here, we introduce and demonstrate magnetic field tuning of dielectric metasurfaces infiltrated with liquid crystals. To illustrate this concept, we show how the reorientation of liquid crystal induced by the magnetic field changes the spectrum of the resonant dielectric metasurface. This new magnetic-field tuning approach offers significant advantages over other liquid crystal tuning methods since it does not require pre-alignment or the fabrication of structured electrodes, which are both challenging when dealing with metasurfaces. Furthermore, there are no strict limitations on the thickness of liquid crystal cells. Importantly, our approach allows for gradual tuning of the resonances by changing the magnetic-field orientation and, thereby, shows good promise for highly tunable optical metadevices.

Development of a novel liquid crystal Apta-sensing platform using P-shape molecular switch

Described herein is a liquid crystal (LC)-based aptasensor via employing the reorientation of LC triggered by the conformational changes of a P-shaped DNA structure. The structure consists of a short linker sequence as an immobilizer probe with ability to hybridize with the central part of the intact aptamer (Apt) sequence and an Apt terminal-locker (ATL) strand with complementary segments of the Apt terminal fragments. Bindings of two arm segments of the Apt sequence with the ATL strand enforces it to form a P-shaped configuration on the sensing platform. The selective interaction between the Apt strand and OTA leads to the disassembly of the Apt-ATL hybrid, collapse of the P-shaped structure, and consequently, transition of the optical appearance of the aptasensor texture. Determination of Ochratoxin A (OTA) in foods is an urgent demand in attempt to minimize food safety risks. To demonstrate the feasibility of our aptasensing design, the OTA specific aptamer was selected as a model. The developed LC aptasensor possesses a wide linear range from 0.01 aM to 100 pM, ultra-low limit of detection (LOD) of 0.0078 aM, and quantitative recoveries of 91–103.51% for OTA in rice and grape juice samples. This study proposes a novel and universal LC-based platform for facile, ultra-sensitive, and precision sensing of hazardous analytes in real samples.

Polymer Dispersed Liquid Crystals with elongated droplets as novel pressure sensors

ABSTRACT Polymer-Dispersed Liquid Crystals, PDLCs, are formed by liquid crystal droplets embedded in a polymer matrix, which can assume different liquid crystal director configurations. The transition from one configuration to another one by the application of an external field (electric, magnetic or mechanical) allows to exploit interesting applications such as electro-optical devices or to develop theoretical models in the soft matter field. Pressure sensors represent a recent and important application of PDLCs. In this work, PDLCs with elongated droplets and radial configuration were obtained during the phase separation of the liquid crystal component from an elastomeric polymer in the presence of an AC external electric field. The application of pressure to the device causes deformation in the droplets shape and liquid crystal reorientation with a consequent variation in the overall electric resistance of the sample.

Liquid Crystal Reorientation with Ultra-Low Driving Voltage between Strong and Weak Anchoring Surfaces

Liquid Crystal Reorientation with Ultra-Low Driving Voltage between Strong and Weak Anchoring Surfaces

Optofluidic Platform Based on Liquid Crystals in X-Cut Lithium Niobate: Thresholdless All-Optical Response

In this study, we present a new configuration of the recently reported optofluidic platform exploiting liquid crystals reorientation in lithium niobate channels. In order to avoid the threshold behaviour observed in the optical control of the device, we propose microchannels realized in a x-cut crystal closed by a z-cut crystal on the top. In this way, the light-induced photovoltaic field is not uniform inside the liquid crystal layer and therefore the conditions for a thresholdless reorientation are realized. We performed simulations of the photovoltaic effect based on the well assessed model for Lithium Niobate, showing that not uniform orientation and value of the field should be expected inside the microchannel. In agreement with the re-orientational properties of nematic liquid crystals, experimental data confirm the expected thresholdless behaviour. The observed liquid crystal response exhibits two different regimes and the response time shows an unusual dependence on light intensity, both features indicating the presence of additional photo-induced fields appearing above a light intensity of 107 W/m2.

Probing Nanoscale Lipid–Protein Interactions at the Interface of Liquid Crystal Droplets

Aqueous interfaces of liquid crystals (LCs) are widely explored in the design of functional interfaces to recapitulate the key aspects of biomolecular interactions in cellular milieu. Herein, using aqueous LC dispersions, we explore the interactions between mitochondrial cardiolipin and membrane-associated cytochrome c which play a pivotal role in the apoptotic signaling cascade. Conventional techniques used to decipher LC ordering at the droplet interface fail to give information about the interactions at a molecular level. Besides, owing to the complexity of LC systems and multiple determinants driving the LC reorientation, accurate analysis of the underlying mechanism responsible for the LC ordering transition remains challenging. Using a combination of atomistic simulations and microscopic and spectroscopic readouts, for the first time, we unveil the lipid-protein interactions that drive the reorientation at the LC droplet interface. The insights from our work are fundamental to the design of these interfaces for a spectrum of interfacial applications.

Reconfigurable Surfaces Using Fringing Electric Fields from Nanostructured Electrodes in Nematic Liquid Crystals

AbstractLiquid crystals with a varying phase profile enable reconfigurable and intelligent devices to be designed, which are capable of manipulating incident electromagnetic fields in display, telecommunications as well as wearable applications. The active control of defects in these devices is becoming more important, especially since the electrodes used to manipulate them are shrinking to nanometer length scales. In this paper, a simple subwavelength, 1D, interdigitated metal electrode structure that can be reconfigured using nematic liquid crystals aligned in the homeotropic, planar, and hybrid methods are demonstrated. Accurate electro‐optic modeling of the directors and the defects are shown, which are induced by the fringing electric fields. Applied voltages result in liquid crystal reorientation near the bottom surface, such that defects are induced between the electrodes. The height of the electrodes does not affect the lateral position of these defects. Rather, this can be achieved by increasing the biasing voltage on the top electrode, which also leads to greater splay‐bend in the bulk of the material. These results therefore aim to generalize the control of defects in complex anisotropic nematic liquid crystals using simple interdigitated structures for a range of reconfigurable intelligent surface applications.