Application and Technique of Liquid Crystal-Based Biosensors

Recent advances in gold nanoparticles-based biosensors for tuberculosis determination

Tuberculosis (TB) is one of the major killer diseases affecting lung parenchymal tissues. Mycobacterium tuberculosis (Mtb) is the bacterium that causes it. It most commonly affects the lungs, although it can affect any part of the body, including the stomach, glands, bones, and nervous system. Although anti-mycobacterial drugs are available, it remains a major threat to public health due to the rise of drug-resistant strains, and early and accurate diagnosis is very important. Currently, research science and medical communities are focusing on the use of cost-effective biosensors to manage human biological processes and assess accurate health diagnostics. Due to their high sensitivity in chemical and biological assays, nanomaterials have been considered in the field of biosensors for better diagnosis, and among them, gold nanoparticles (AuNPs) can play an important role in accelerating the diagnosis of TB. Superior biocompatibility, conductivity, catalytic properties, high surface-to-volume ratio, and high density enable their widespread use in the fabrication of biosensors. This review evaluates the diagnostic accuracy of AuNP-based biosensors for the detection of Mtb. According to different transducers of biosensors, their structure, performance, advantages and limitations are summarized and compared. Moreover, the upcoming challenges in their analytical performance have been highlighted and the strategies to overcome those challenges have been briefly discussed.

An emerging assay for rapid diagnosis of live Salmonella Typhimurium by exploiting aqueous/liquid crystal interface

The rapid and accurate identification of live pathogens with high proliferative ability is in great demand to mitigate foodborne infection outbreaks. Herein, we have developed an ultrasensitive image-based aptasensing array to directly detect live Salmonella typhimurium (S.T) cells. This method relies on the long-range orientation of surfactant-decorated liquid crystals (LCs) and the superiority of aptamers (aptST). The self-assembling of hydrophobic surfactant tails leads to a perpendicular/vertical ordered film at the aqueous/LC interface and signal-off response. The addition of aptST perturbed LCs' ordering into a planar/tilted state at the aqueous phase due to electrostatic interactions between the surfactant with the aptST, and a signal-on response. Following the conformational switch of aptST in the presence of live S. typhimurium, a relative reversing signal-off response was observed upon the target concentration. This aptasensor could promptly confirm the presence of S. typhimurium without intricate DNA-extraction or pre-enrichment stats over a linear range of 1-1.1 × 106 CFU/mL and a detection limit of 1.2 CFU/mL within ∼30 min. These results were successfully validated using molecular and culture-based methods in spiked-milk samples, with a 92.61-104.61 % recovery value. Meanwhile, the flexibility of this portable sensing platform allows for its development and adoption for the precise detection of various pathogens in food and the environment.

Real-Time pH Sensor in Bacterial Microenvironments Using Liquid Crystal Core-Shell Microspheres

It is well-known that the bacterial microenvironment imposes restrictions on the growth and behavior of bacteria. The localized monitoring of microenvironmental factors is appreciated when consulting bacterial adaptation and behavior in the presence of chemical or mechanical stimuli. Herein, we developed a novel liquid crystal (LC) biosensor in a microsphere configuration for real-time 3D monitoring of the bacteria microenvironment, which was implemented by a microfluidic chip. As a proof of concept, a LC gel (LC-Gel) microsphere biosensor was prepared and employed in the localized pH changes of bacteria by observing the configuration change of LC under polarized optical microscopy. Briefly, the microsphere biosensor was constructed in core-shell configuration, wherein the core contained LCE7 (a nematic LC) doped with 4-pentylbiphenyl-4'-carboxylic acid (PBA), and the shell encapsulated the bacteria. The protonation of carboxyl functional groups of the PBA induced a change in charge density on the surface of LCE7 and the orientation of E7 molecules, resulting in the transitions of the LC nucleus from axial to bipolar. The developed LC-Gel microspheres pH sensor exhibited its dominant performance on localized pH real-time sensing with a resolution of 0.1. An intriguing observation from the prepared pH biosensor was that the diverse bacteria impelled distinct acidifying or alkalizing effects. Overall, the facile LC-Gel microsphere biosensor not only provides a versatile tool for label-free, localized pH monitoring but also opens avenues for investigating the effects of chemical and mechanical stimuli on cellular metabolism within bacterial microenvironments.

Specific Condis Crystal-like Mesophase of Poly(butylene succinate-co-butylene adipate)

Understanding the properties of polymers, such as their crystallinity, is crucial for their material performance and predicting their behavior during and after use, especially in the case of environmentally friendly (bio)degradable polymers, enabling optimized design. In this work, for the first time, a pressure-induced condis crystal-like mesophase of poly(butylene succinate-co-butylene adipate) (PBSA) is presented. The phase behavior of pressed films obtained from commercial PBSA with 25% butylene adipate units is investigated at various processing temperatures from room temperature to 100 °C, pressed at a pressure of the press jaws and at 2-5 t for 1-5 min. The characterization and quantification evaluation of the condis crystal-like mesophase of pressed PBSA formed at temperatures above the glass transition is investigated by X-ray diffraction, polarized optical microscopy (POM), and differential scanning calorimetry (DSC) methods. Our results demonstrate that pressed PBSA films at 60 °C show a condis crystal-like mesophase, characterized by the presence of reflections at wide angles, birefringence by POM, as well as a higher melting point (endotherm) by DSC. The resulting oriented mesomorphic green polymer can, in a sustainable manner, expand further technological applications of (bio)degradable polymers, especially in the medical field, and open up opportunities for further research that could provide such polymers with tailored persistence and degradation, thus changing the shelf life.

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.

Lyotropic liquid crystalline phases: Drug delivery and biomedical applications

Liquid crystal (LC)-based nanoformulations may efficiently deliver drugs and therapeutics to targeted biological sites. Lyotropic liquid crystalline phases (LLCPs) have received much interest in recent years due to their unique structural characteristics of both isotropic liquids and crystalline solids. These LLCPs can be utilized as promising drug delivery systems to deliver drugs, proteins, peptides and vaccines because of their improved drug loading, stabilization, and controlled drug release. The effects of molecule shape, microsegregation, and chirality are very important in the formation of liquid crystalline phases (LCPs). Homogenization of self-assembled amphiphilic lipids, water and stabilizers produces LLCPs with different types of mesophases, bicontinuous cubic (cubosomes) and inverse hexagonal (hexosomes). Moreover, many studies have also shown higher bioadhesivity and biocompatibility of LCs due to their structural resemblance to biological membranes, thus making them more efficient for targeted drug delivery. In this review, an outline of the engineering aspects of LLCPs and polymer-based LLCPs is summarized. Moreover, it covers parenteral, oral, transdermal delivery and medical imaging of LC in targeting various tissues and is discussed with a scope to design more efficient next-generation novel nanosystems. In addition, a detailed overview of advanced liquid crystal-based drug delivery for vaccines and biomedical applications is reviewed.

Alkylbenzoic and Alkyloxybenzoic Acid Blending for Expanding the Liquid Crystalline State and Improving Its Rheology

Thermotropic mesogens typically exist as liquid crystals (LCs) in a narrow region of high temperatures, making lowering their melting point with the temperature expansion of the mesophase state an urgent task. Para-substituted benzoic acids can form LCs through noncovalent dimerization into homodimers via hydrogen bonds, whose strength and, consequently, the temperature region of the mesophase state can be potentially altered by creating asymmetric heterodimers from different acids. This work investigates equimolar blends of p-n-alkylbenzoic (kBA, where k is the number of carbon atoms in the alkyl radical) and p-n-alkyloxybenzoic (kOBA) acids by calorimetry and viscometry to establish their phase transitions and regions of mesophase existence. Non-symmetric dimerization of acids leads to the extension of the nematic state region towards low temperatures and the appearance of new monotropic and enantiotropic phase transitions in several cases. Moreover, the crystal-nematic and nematic-isotropic phase changes have a two-step character for some acid blends, suggesting the formation of symmetric and asymmetric associates from heterodimers. The mixing of 6BA and 8OBA most strongly extends the region of the nematic state towards low temperatures (from 95-114 °C and 108-147 °C for initial homodimers, respectively, to 57-133 °C for the resulting heterodimer), whereas the combination of 4OBA and 5OBA gives the most extended high-temperature nematic phase (up to 156 °C) and that of 6BA and 9OBA (or 12OBA) provides the existence of a smectic phase at the lowest temperatures (down to 51 °C).

Preparation and Orthogonal Analysis for Dual-Responsive Electrochromic Polymer Dispersed Liquid Crystal Devices

In this work, we provide a fabrication method for dual-responsive electrochromic (EC) polymer dispersed liquid crystal (PDLC) devices. The EC PDLC device was developed by combing the PDLC technique and a colored complex formed via a redox reaction without a specific EC molecule in a simple preparation method. The mesogen played dual roles in the device for scattering in the form of microdroplets and participating in the redox reactions. Orthogonal experiments were performed with the acrylate monomer concentration, the ionic salt concentration, and the cell thickness as factors to investigate the electro-optical performance for the achievement of optimized fabrication conditions. The optimized device presented four switchable states modulated by external electric fields. The light transmittance of the device was changed by an alternative current (AC) electric field while the color change was realized by a direct current (DC) electric field. Variations of mesogen and ionic salt species can modulate the color and hue of devices, which solves the disadvantage of a single color for traditional EC devices. This work lays the foundation for realizing patterned multi-colored patterned displays and anti-counterfeiting via screen printing and inkjet printing techniques.

An optical aptasensor for real-time quantification of endotoxin: From ensemble to single-molecule resolution

Endotoxin is a deadly pyrogen, rendering it crucial to monitor with high accuracy and efficiency. However, current endotoxin detection relies on multistep processes that are labor-intensive, time-consuming, and unsustainable. Here, we report an aptamer-based biosensor for the real-time optical detection of endotoxin. The endotoxin sensor exploits the distance-dependent scattering of gold nanoparticles (AuNPs) coupled to a gold nanofilm. This is enabled by the conformational changes of an endotoxin-specific aptamer upon target binding. The sensor can be used in an ensemble mode and single-particle mode under dark-field illumination. In the ensemble mode, the sensor is coupled with a microspectrometer and exhibits high specificity, reliability (i.e., linear concentration to signal profile in logarithmic scale), and reusability for repeated endotoxin measurements. Individual endotoxins can be detected by monitoring the color of single AuNPs via a color camera, achieving single-molecule resolution. This platform can potentially advance endotoxin detection to safeguard medical, food, and pharmaceutical products.

Zinc Oleate Nanorod-Induced Vertical Alignment of Nematic Liquid Crystal

Nanocomposite zinc oxide nanorods capped with oleic acid (ZOR) with positive dielectric anisotropy liquid crystal (LC) 4'-octyl-4-biphenylcarbonitrile (8CB) filled in unaligned cells exhibit homeotropic alignment of host LC molecules. Further, systematic investigation of the textural, dielectric, and conductivity properties of nanocomposites filled in planar cells is performed with increasing concentration of nanorods. At a nanorod concentration ≤0.2 wt % in 8CB, the order parameter of nanocomposite samples is found to be increasing and ionic conductivity is found to be decreasing as compared to pure LC. Beyond 0.3 wt % concentration of nanorods in 8CB, vertical alignment (VA) of host LC is observed even in a planar aligned cell. The VA of LC molecules in ZOR nanocomposites is confirmed through attenuated total reflection-Fourier transform infrared absorption spectra studies.

UV light sensing and switching applications of dimeric smectic liquid crystals: comparative calculations

Two dimeric smectic molecules, namely α-ω-bis (4-n-pentylanilinebenzylidene-4'-oxy) butane (PABO4) and α-ω-bis (4-n-pentylanilinebenzylidene-4'-oxy) pentane (PABO5), have been considered for sensing UV light. The compounds' optimization process has been performed through B3LYP hybrid functional together with basis set 6-31+G (d) using the input parameters from the crystallographer. The absorption of UV analysis of these compounds has been estimated, and the configuration interaction single-level method has been used to analyse the electronic transition features coupled with the calculation of excited states using semi-empirical Hamiltonian ZINDO. The CNDO/S, INDO/S together with CI approaches, has been utilized for comparative evaluation. The spectral-associated parameters have been summarized. The molecules discussed in this manuscript present several features, viz. the absorption range of the molecules that is sensitive to different wavelengths, the usage in flexible devices, offering the prospect for UV sensors. Further, the switching applications have been explored based on the oscillator strength data in various regions of wavelengths.

Rapid and Label-Free Methanol Identification in Alcoholic Beverages Utilizing a Textile Grid Impregnated with Chiral Nematic Liquid Crystals

Methanol contamination of alcoholic drinks can lead to severe health problems for human beings including poisoning, headache, blindness, and even death. Therefore, having access to a simple and inexpensive way for monitoring beverages is vital. Herein, a portable, low cost, and easy to use sensor is fabricated based on the exploitation of chiral nematic liquid crystals (CLCs) and a textile grid for detection of methanol in two distinct alcoholic beverages: red wine and vodka. The working principle of the sensor relies on the reorientation of the liquid crystal molecules upon exposure to the contaminated alcoholic beverages with different concentrations of methanol (0, 2, 4, and 6 wt %) and the changes in the observed colorful textures of the CLCs as well as the intensity of the output light. The proposed sensor is label free and rapid.

State-of-the-Art Development in Liquid Crystal Biochemical Sensors

As an emerging stimuli-responsive material, liquid crystal (LC) has attracted great attentions beyond display applications, especially in the area of biochemical sensors. Its high sensitivity and fast response to various biological or chemical analytes make it possible to fabricate a simple, real-time, label-free, and cost-effective LC-based detection platform. Advancements have been achieved in the development of LC-based sensors, both in fundamental research and practical applications. This paper briefly reviews the state-of-the-art research on LC sensors in the biochemical field, from basic properties of LC material to the detection mechanisms of LC sensors that are categorized into LC-solid, LC–aqueous, and LC droplet platforms. In addition, various analytes detected by LCs are presented as a proof of the application value, including metal ions, nucleic acids, proteins, glucose, and some toxic chemical substances. Furthermore, a machine-learning-assisted LC sensing platform is realized to provide a foundation for device intelligence and automatization. It is believed that a portable, convenient, and user-friendly LC-based biochemical sensing device will be achieved in the future.

Chiral nematic liquid crystal droplets as a basis for sensor systems

For a series of phospholipid coated calamitic nematic liquid crystal droplets (5CB, 6CB, 7CB, E7 and MLC7023) of diameter ∼18 μm, the addition of chiral dopant leaves the sign of surface anchoring unchanged. Herein we report that for these chiral nematic droplets an analyte induced transition from a Frank-Pryce structure (with planar anchoring) to a nested-cup structure (with perpendicular anchoring) is accompanied by changes in the intensity of reflected light. We propose this system as both a general scheme for understanding director fields in chiral nematic liquid crystal droplets with perpendicular anchoring and as an ideal candidate to be utilised as the basis for developing cheap, single use LC-based sensor devices.

Structural properties and ring defect formation in discotic liquid crystal nanodroplets

In this work, we performedNpTMonte Carlo simulations of a Gay-Berne discotic liquid crystal confined in a spherical droplet under face-on anchoring and fixed pressure. We find that, in contrast to the unbounded system, a plot of the order parameter as function of temperature does not show a clear evidence of a first-order isotropic-nematic transition. We also find that the impossibility of simultaneously satisfy the uniform director field requirement of a nematic phase with the radial boundary conditions, results in the appearance of a ring disclination line as a stress release mechanism in the interior of the droplet. Under further cooling, a columnar phase appears at the center of the droplet.

Partial induced reorientation of 5CB in a liquid crystal microarray and a signal-on sensing assay for the detection of aflatoxin B1

Herein, a signal-on liquid crystal microarray (LCM) sensor is designed for the first time with a micro-spectral optical sensing signal. Depending on the change of the orientation of the LC molecules in the LCM films and the intensity of the spectral peaks of the PhCs, the signal-on LCM biosensor achieves the detection of AFB1 and the Partial Response Mechanism (PSM) of the LCM films is discovered.

Quantitative Biosensing Based on a Liquid Crystal Marginally Aligned by the PVA/DMOAP Composite for Optical Signal Amplification

The working principle for a liquid crystal (LC)-based biosensor relies on the disturbance in the orderly aligned LC molecules induced by analytes at the LC-aqueous or LC-solid interface to produce optical signals that can be typically observed under a polarizing optical microscope (POM). Our previous studies demonstrate that such optical response can be enhanced by imposing a weak electric field on LCs so that they are readily tilted from the homeotropic alignment in response to lower concentrations of analytes at the LC-glass interface. In this study, an alternative approach toward signal amplification is proposed by taking advantage of the marginally tilted alignment configuration without applying an electric field. The surface of glass substrates was modified with a binary aligning agent of poly(vinyl alcohol) (PVA) and dimethyloctadecyl[3-(trimethoxysilyl)propyl] ammonium chloride (DMOAP), in which the amount of PVA was fine-tuned so that the interfacing LC molecules were slightly tilted but remained virtually homeotropically aligned to yield no light leakage under the POM in the absence of an analyte. Two nematic LCs, E7 and 5CB, were each sandwiched between two parallel glass substrates coated with the PVA/DMOAP composite for the detection of bovine serum albumin (BSA), a model protein, and cortisol, a small-molecule steroid hormone. Through image analysis of the optical appearance of E7 observed under the POM, a limit of detection (LOD) of 2.5 × 10−8 μg/mL for BSA and that of 3 × 10−6 μg/mL for cortisol were deduced. Both values are significantly lower than that obtained with only DMOAP as the alignment layers, which correspond to signal amplification of more than six orders of magnitude. The new approach for signal amplification reported in this work enables analytes of a wide range of molecular weights to be detected with high sensitivity.

Technological Advancements in Bio‐recognition using Liquid Crystals: Techniques, Applications, and Performance

The application of liquid crystal (LC) materials has undergone a modern-day renaissance from its classical use in electronics industry as display devices to new-fangled techniques for optically detecting biological and chemical analytes. This review article deals with the emergence of LC materials as invaluable material for their use as label-free sensing elements in the development of optical, electro-optical and electrochemical biosensors. The property of LC molecules to change their orientation on perturbation by any external stimuli or on interaction with bioanalytes or chemical species has been utilized by many researches for the fabrication of high sensitive LC-biosensors. In this review article we categorized LC-biosensor based on biomolecular reaction mechanism viz. enzymatic, nucleotides and immunoreaction in conjunction with operating principle at different LC interface namely LC-solid, LC-aqueous and LC-droplets. Based on bimolecular reaction mechanism, the application of LC has been delineated with recent progress made in designing of LC-interface for the detection of bio and chemical analytes of proteins, virus, bacteria, clinically relevant compounds, heavy metal ions and environmental pollutants. The review briefly describes the experimental set-ups, sensitivity, specificity, limit of detection and linear range of various viable and conspicuous LC-based biosensor platforms with associated advantages and disadvantages therein.

Liquid Crystals: Versatile Self-Organized Smart Soft Materials

Smart soft materials are envisioned to be the building blocks of the next generation of advanced devices and digitally augmented technologies. In this context, liquid crystals (LCs) owing to their responsive and adaptive attributes could serve as promising smart soft materials. LCs played a critical role in revolutionizing the information display industry in the 20th century. However, in the turn of the 21st century, numerous beyond-display applications of LCs have been demonstrated, which elegantly exploit their controllable stimuli-responsive and adaptive characteristics. For these applications, new LC materials have been rationally designed and developed. In this Review, we present the recent developments in light driven chiral LCs, i.e., cholesteric and blue phases, LC based smart windows that control the entrance of heat and light from outdoor to the interior of buildings and built environments depending on the weather conditions, LC elastomers for bioinspired, biological, and actuator applications, LC based biosensors for detection of proteins, nucleic acids, and viruses, LC based porous membranes for the separation of ions, molecules, and microbes, living LCs, and LCs under macro- and nanoscopic confinement. The Review concludes with a summary and perspectives on the challenges and opportunities for LCs as smart soft materials. This Review is anticipated to stimulate eclectic ideas toward the implementation of the nature's delicate phase of matter in future generations of smart and augmented devices and beyond.

A Single-Substrate Biosensor with Spin-Coated Liquid Crystal Film for Simple, Sensitive and Label-Free Protein Detection

A liquid crystal (LC)-based single-substrate biosensor was developed by spin-coating an LC thin film on a dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride (DMOAP)-decorated glass slide. Compared with the conventional sandwiched cell configuration, the simplified procedure for the preparation of an LC film allows the film thickness to be precisely controlled by adjusting the spin rate, thus eliminating personal errors involved in LC cell assembly. The limit of detection (LOD) for bovine serum albumin (BSA) was lowered from 10-5 g/mL with a 4.2-μm-thick sandwiched cell of the commercial LC E7 to 10-7 g/mL with a 4.2-μm-thick spin-coated E7 film and further to 10-8 g/mL by reducing the E7 film thickness to 3.4 μm. Moreover, by exploiting the LC film of the highly birefringent nematic LC HDN in the immunodetection of the cancer biomarker CA125, an LOD comparable to that determined with a sandwiched HDN cell was achieved at 10-8 g/mL CA125 using a capture antibody concentration an order of magnitude lower than that in the LC cell. Our results suggest that employing spin-coated LC film instead of conventional sandwiched LC cell provides a more reliable, reproducible, and cost-effective single-substrate platform, allowing simple fabrication of an LC-based biosensor for sensitive and label-free protein detection and immunoassay.

Label-Free Detection and Spectrometrically Quantitative Analysis of the Cancer Biomarker CA125 Based on Lyotropic Chromonic Liquid Crystal

Compared with thermotropic liquid crystals (LCs), the biosensing potential of lyotropic chromonic liquid crystals (LCLCs), which are more biocompatible because of their hydrophilic nature, has scarcely been investigated. In this study, the nematic phase, a mesophase shared by both thermotropic LCs and LCLCs, of disodium cromoglycate (DSCG) was employed as the sensing mesogen in the LCLC-based biosensor. The biosensing platform was constructed so that the LCLC was homogeneously aligned by the planar anchoring strength of polyimide, but was disrupted in the presence of proteins such as bovine serum albumin (BSA) or the cancer biomarker CA125 captured by the anti-CA125 antibody, with the level of disturbance (and the optical signal thus produced) predominated by the amount of the analyte. The concentration- and wavelength-dependent optical response was analyzed by transmission spectrometry in the visible light spectrum with parallel or crossed polarizers. The concentration of CA125 can be quantified with spectrometrically derived parameters in a linear calibration curve. The limit of detection for both BSA and CA125 of the LCLC-based biosensor was superior or comparable to that of thermotropic LC-based biosensing techniques. Our results provide, to the best of our knowledge, the first evidence that LCLCs can be applied in spectrometrically quantitative biosensing.

Functional liquid droplets for analyte sensing and energy harvesting

Over the past century, rapid miniaturization of technologies has helped in the development of efficient, flexible, portable, robust, and compact applications with minimal wastage of materials. In this direction, of late, the usage of mesoscale liquid droplets has emerged as an alternative platform because of the following advantages: (i) a droplet is incompressible and at the same time deformable, (ii) interfacial area of a spherical droplet is minimum for a given amount of mass; and (iii) a droplet interface allows facile mass, momentum, and energy transfer. Subsequently, such attributes have aided towards the design of diverse droplet-based microfluidic technologies. For example, the microdroplets have been utilized as micro-reactors, colorimetric or electrochemical (EC) sensors, drug-delivery vehicles, and energy harvesters. Further, a number of recently reported lab-on-a-chip technologies exploit the motility, storage, and mixing capacities of the microdroplets. In view of this background, the review initiates discussion by highlighting the different attributes of the microdroplets such as size, shape, surface to volume ratio, wettability, and contact line. Thereafter, the effects of the surface or body forces on the properties of the droplets have been elaborated. Finally, the different aspects of such liquid droplet systems towards technological adaptations in health care, sensing, and energy harvesting have been presented. The review concludes with a tight summary on the potential avenues for further developments.

From n-layer planar ordering to the monolayer homeotropic structure of confined hard rods: The effect of shape anisotropy and wall-to-wall separation

Using the Parsons-Lee theory, we examined the effect of shape anisotropy and the wall-to-wall separation (H) on the phase behavior of the hard parallelepiped rods with dimensions L, D, and D (L>D) in such narrow slitlike pores which only one homeotropic layer can form. The phase structures, including biaxiality, planar nematic layering transition as well as planar to homeotropic, were studied for some separations in the range 2.5D≤H≤10.0D for H-D≤L<H.

Optical fiber bio-sensor for phospholipase using liquid crystal

A cost-effective and label-free optical fiber sensor was proposed to detect phospholipase A₂ (PLA₂) in nM concentration. The sensor is made of an alkoxysilane-modified side-polished fiber (SPF) coated with 4'-pentyl-4-cyanobiphenyl (5CB) and self-assembled phospholipid (L-DLPC). It is found that the relative transmission optical power (RTOP) of the fiber sensor decreases due to the 5CB realignment and redistribution induced by the PLA₂ hydrolysis of L-DLPC. The response-time at 5 dB RTOP variation exhibits an exponential dependence on PLA₂ concentration, allowing us to detect the PLA₂ by the 5 dB-response time. This detection method can reduce the detection time. Compare with the traditional copper-grid sensor, the proposed novel fiber sensor has a lower detection limit (<1 nM). Furthermore, the sensor has good repeat-ability and specificity.The sensor's RTOP variation for PLA₂ detection at 1 nM is ~21 times higher than that for five other enzymes (trypsin, amylase, thrombin, glucose oxidase, pepsin) at 1000 nM and lipase at 50 nM. This confirms the sensor's excellent PLA₂ specificity. The fiber sensor provides a potential way to be incorporated into micro-flow chips to quantitatively detect biological molecules in a real-time and online manner.

Novel Trends in Lyotropic Liquid Crystals

We introduce and shortly summarize a variety of more recent aspects of lyotropic liquid crystals (LLCs), which have drawn the attention of the liquid crystal and soft matter community and have recently led to an increasing number of groups studying this fascinating class of materials, alongside their normal activities in thermotopic LCs. The diversity of topics ranges from amphiphilic to inorganic liquid crystals, clays and biological liquid crystals, such as viruses, cellulose or DNA, to strongly anisotropic materials such as nanotubes, nanowires or graphene oxide dispersed in isotropic solvents. We conclude our admittedly somewhat subjective overview with materials exhibiting some fascinating properties, such as chromonics, ferroelectric lyotropics and active liquid crystals and living lyotropics, before we point out some possible and emerging applications of a class of materials that has long been standing in the shadow of the well-known applications of thermotropic liquid crystals, namely displays and electro-optic devices.