Liquid crystal-based detection of thrombin coupled to interactions between a polyelectrolyte and a phospholipid monolayer

Optical sensing of tetracycline concentration using a liquid crystal-based platform targeting the chelating properties of tetracycline

In this study, a liquid crystal (LC)-based assay for the real-time detection of tetracycline (Tc) was developed. The sensor was constructed by implementing an LC-based platform that utilized the chelating properties of Tc to target Tc metal ions. This design enabled Tc-dependent induction of changes in the optical image of the LC; these modifications could then be observed in real-time with the naked eye. The performance of the sensor in detecting Tc was investigated with various metal ions to identify the most effective metal ion for Tc detection. In addition, the selectivity of the sensor was evaluated using different antibiotics. A correlation between Tc concentration and the optical intensity of the LC optical images was established, which enabled the quantification of Tc concentrations. The proposed method can detect Tc concentrations with a detection limit as low as 2.67 pM. Tests were conducted on milk, honey, and serum samples, which demonstrated that the proposed assay is highly accurate and reliable. The high sensitivity and selectivity of the proposed method make it a promising tool for real-time Tc detection, with potential applications in fields ranging from biomedical research to agriculture.

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.

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.

Development and Application of Liquid Crystals as Stimuli-Responsive Sensors

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.

Applications of liquid crystals in biosensing

Liquid crystals (LCs), as a promising branch of highly-sensitive, quick-response, and low-cost materials, are widely applied to the detection of weak external stimuli and have attracted significant attention. Over the past decade, many research groups have been devoted to developing LC-based biosensors due to their self-assembly potential and functional diversity. In this paper, recent investigations on the design and application of LC-based biosensors are reviewed, based on the phenomenon that the orientation of LCs can be directly influenced by the interactions between biomolecules and LC molecules. The sensing principle of LC-based biosensors, as well as their signal detection by probing interfacial interactions, is described to convert, amplify, and quantify the information from targets into optical and electrical parameters. Furthermore, commonly-used LC biosensing targets are introduced, including glucose, proteins, enzymes, nucleic acids, cells, microorganisms, ions, and other micromolecules that are critical to human health. Due to their self-assembly potential, chemical diversity, and high sensitivity, it has been reported that tunable stimuli-responsive LC biosensors show bright perspectives and high superiorities in biological applications. Finally, challenges and future prospects are discussed for the fabrication and application of LC biosensors to both enhance their performance and to realize their promise in the biosensing industry.

Effect of Single/Mixed Surfactant Systems on Orientations of Liquid Crystals and Interaction of Proteins with Surfactants at Fluid Interfaces

A series of single surfactant systems, i.e, quaternary ammonium-based gemini surfactants with different spacers and alkyl chain lengths (m-n-m; m=12, n=2, 3, 4, 6; n=3, m=12, 14, 16), halogen-free surface-active ionic liquid (HF-SAILs) with different symmetries ([Cnmim][C12H25SO4]; n=6, 8, 10, 12), and single-chain cationic surfactants including 1-dodecyl-3-methylimidazolium bromide ([C12mim]Br) and dodecyltrimethylammonium bromide (DTAB), along with certain combinations of different surfactants (12-3-12/[C12mim]Br and 12-3-12/DTAB) were applied to an aqueous/liquid crystal interface (ALI). All the surfactants could induce an orientational transition of liquid crystals (LCs) from a planar to homeotropic state, which caused a bright-to-dark optical shift. It was proved that double-chain surfactants and the mixed surfactants inclined to adsorb at the ALI triggering the orientational transition. Inspiringly, a quicker and more sensitive dark-to-bright optical response was observed for mixed surfactant system-decorated interfaces in contact with proteins (such as bovine serum albumin (BSA), lysozyme, and trypsin) as opposed to the single surfactant systems. The ALI decorated by the 12-3-12/[C12mim]Br system was particularly efficient and exhibited the most sensitive optical response for BSA (0.01ngmL−1). The order parameters (SCD) of surfactants tails at the interface and the free energy of proteins with 12-3-12 and [C12mim]Br were calculated, respectively. The results explain that the 12-3-12/[C12mim]Br-laden ALI shows a quicker and more sensitive optical response for BSA. This work inspired us to study mixed surfactant systems-decorated LC interfaces and further provides new insights for different chemical and biological applications.

Sensitive and label-free liquid crystal-based optical sensor for the detection of malathion

In this paper, we report the development of a rapid and simple, liquid crystal (LC)-based aptasensor that enables the detection of malathion (MA) using the orientation properties of liquid crystals. This sensor is composed of aptamers immobilized on a surface decorated with a self-assembled monolayer of (3-glycidyloxypropyl)trimethoxysilane (GOPS) and dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride (DMOAP). When MA interacts with the immobilized aptamers, an orientational change in the LCs, from homeotropic to random, is induced. This orientational change generates visible optical responses observed as shifts from dark to bright images under a polarized optical microscope (POM). This sensing system has a linear detection range from 0.8 to 50 pM, with a correlation coefficient of 0.9922, and a limit of detection (LOD) of 2.5 pM (≈0.826 pg/mL). Our proposed aptasensor has good specificity and sensitivity to MA in tap water and soil. Moreover, this sensor suggests a promising strategy for simple, rapid testing for various insecticide residues.

Preparation of DNA-functionalized surfaces for simultaneous homeotropic orientation of liquid crystals and optical recognition of analytes: application to the determination of progesterone

The work describes a simplified method for the preparation of liquid crystal (LC) bioassay using DNA-based capture molecules and having lower detection limits. The capture DNA probes of the stem-loop structure were immobilized on the surface of a glass slide. A homeotropic orientation of LC molecules can be obtained with the proper surface coverage of capture DNA probes. In the presence of analytes (specifically shown here for the progesterone as a model analyte), the molecular binding between capture DNA probes and progesterone opens the loop of the capture DNA probes. The opened sequence is then amenable to hybridization with a reporter DNA probe that is immobilized on gold nanoparticles. This changes the surface microstructure, disrupts the orientation of LC molecules, and results in an enhanced optical response, expressed as the average grey value of the images. This new kind of surface treatment for simultaneous recognition of target molecules and homeotropic anchoring of LCs reduces the number of preparation steps and makes the process of LC bioassay easier. This method has a detection limit as low as 0.1 pmol·L^-1 of progesterone. Graphical abstract Schematic presentation of the liquid crystal-based DNA assay. DMOAP: Dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride; TEA: Triethoxsilylbutyraldehyde; 5CB: 4-cyano-4'-pentylbiphenyl; P4: progesterone.

Conjugation of Nanomaterials and Nematic Liquid Crystals for Futuristic Applications and Biosensors

The established role of nematic liquid crystals (NLCs) in the recent rapid development of displays has motivated researchers to modulate the electro-optical properties of LCs. Furthermore, adding nanomaterials into NLCs has led to enhancements of the properties of NLCs, like reduced threshold of the operating voltage, variation in pretilt angle, reduced switching time, etc. These enhanced properties, due to interfacial dynamics, are enabling wider applications of NLCs and nanomaterials. The recent literature of nanomaterial-doped NLCs is rich with various kinds of nanomaterials in a variety of NLCs. The light has been focused on the most widely used and studied gold nanoparticles in NLCs. The intrinsic inherent property of easy excitation of surface plasmons polaritons (SPP) is the mediating interaction of NLC electric dipoles and the polarization of charges in the GNP surface. The concepts and methods for the application of metal nanomaterials as dopants in NLCs are discussed for future applications, especially biosensors. The biosensing application of NLCs alone has already been proven in the literature. However, it is always desirable to further enhance the detection efficiency and selectivity, which have been achieved by the conjugation of GNPs and nickel nanoparticles with NLCs and their compatibility with biological materials. This aspect of future application of nanoparticles and NLC makes the point more selective to be included in the present manuscript.

Liquid-Crystal Biosensor Based on Nickel-Nanosphere-Induced Homeotropic Alignment for the Amplified Detection of Thrombin

A new liquid-crystal (LC)-based sensor operated by nickel nanosphere (NiNS)-induced homeotropic alignment for the label-free monitoring of thrombin was reported. When doped with NiNSs, a uniform vertical orientation of 4-cyano-4'-pentylbiphenyl (5CB) was easily obtained. A sandwich system of aptamer/thrombin/aptamer-functionalized gold nanoparticles (AuNPs) was fabricated, and AuNPs-aptamer conjugation caused the disruption of the 5CB orientation, leading to an obvious change of the optical appearance from a dark to a bright response to thrombin concentrations from 0.1 to 100 nM. This design also allowed quantitative detection of the thrombin concentration. This distinctive and sensitive thrombin LC sensor provides a new principle for building LC-sensing systems.

Design of bio-molecular interfaces using liquid crystals demonstrating endotoxin interactions with bacterial cell wall components

Liquid crystals offer a promising approach to study and quantify the interactions between different bacterial cell membrane components with endotoxin at an aqueous interface.