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

Detection of glyphosate residues in agricultural products using liquid-crystal-based sensor exploiting competitive binding of glyphosate and Cu2+ at the aqueous/LC interface and capillary tube test strip

Glyphosate is a widely used herbicide that poses both health and environmental risks. In this study, we propose a liquid crystal (LC)-based assay for glyphosate detection that exploits the unique properties of LC materials. The nematic LC 4-cyano-4'-pentylbiphenyl (5CB) was employed as the sensing material and a self-assembled monolayer of octadecyltrichlorosilane (OTS) was used to modify glass substrates. The assay involved strong competition for coordination with Cu2+ for glyphosate, resulting in changes in the LC texture. By monitoring and analyzing the optical images of the LC film using polarizing microscopy, we detected and quantified the glyphosate concentrations. The proposed assay demonstrated high sensitivity and selectivity toward glyphosate in the detection range of 1-300 nM with a limit of detection of 0.26 nM. Moreover, the assay successfully applied to analyze glyphosate in spiked samples, including tap water, soil, and cabbage, and satisfactory recovery rates were achieved. Based on this detection principle, capillary tube test strips were developed for on-site applications. The detection thresholds of the test strips were controlled by varying the Cu2+ concentration. The developed LC-based assay is a rapid and reliable glyphosate detection method with potential applications in environmental monitoring and food safety.

Liquid crystal based sensor for antimony ions detection using poly-adenine oligonucleotides

Antimony is highly toxic and a key water pollutant, which needs to be monitored closely. To date, however, most analytical methods for antimony detection are quite limited because they are complicated, expensive, and not suitable for real-time monitoring of antimony. In this study, a label-free and rapid method for antimony ions (Sb3+) detection is developed based on liquid crystals and a 10-mer poly-adenine oligonucleotide as a specific recognition probe for the first time. The working principle is based on the binding of the oligonucleotide to Sb3+, which weakens the interaction between the oligonucleotide and cationic surfactants. As a result, the event induces a planar-to-homeotropic orientational change of liquid crystals and a bright-to-dark optical change under crossed polars. This liquid crystal-based optical sensor exhibits a rapid response to Sb3+ in 10 s, a detection range between 20 nM and 5 μM, and a detection limit at 6.7 nM calculated from 10-mins assay time. It also shows good selectivity against other metal ions including Ag+, Cd2+, Cu2+, Fe3+, K+, Mg2+, Mn2+, Na+, Pb2+, and Zn2+. Moreover, this system can be used to detect Sb3+ in aqueous solutions with different pH or ionic strengths. This simple, fast, and low-cost liquid crystal-based sensing approach with high sensitivity and selectivity has a high potential for detecting Sb3+ in natural environments and industrial wastewater.

Selective Ligand-Doped Liquid Crystal-Based Sensing Platform for Detection of ClO- Ions in Aqueous Media

The liquid crystal (LC) detection platform has been fabricated for the detection of hypochlorite ions (ClO^-) in aquatic solutions. In this system, an imine consisting of the ligand (E)-2-((4-(diethylamino)-2-hydroxybenzylidene)amino)-5-methoxybenzenesulfonic acid (MBA) was doped in 4-cyano-4'-pentyl biphenyl as a selecting LC for ClO^-. When immersing the platform in a solution containing ClO^-, hypochlorite appears to react with the imine bond in the MBA, and cause it to cleave, which eventually disrupts the direction of LC and causes a dark-to-bright conversion of the LC image. The detection limit for ClO^- is 0.05 μM. This sensory platform was unresponsive to NO₃ ^-, BrO₃ ^-, CH₃COO^-, CO₃ ^2-, and PO₄ ^3- ions. Our sensing platform also detected ClO^- in piped water. Since this sensory platform is colored under ambient light, it is easy for regular operators, and it can be used as a mobile tool for monitoring water quality anywhere.

A novel liquid crystal resonance Rayleigh scattering spectral probe for determination of trace Cr6

Hexavalent chromium (Cr⁶⁺) has strong oxidizing property and toxicity. It has been identified as a carcinogen with obvious carcinogenic effect by the International Anti-cancer Research Center. Therefore, it has a great significance to establish a simple and sensitive method for Cr⁶⁺. In the solution, liquid crystal (LC) trans, trans-4-(3,4-difluorophenyl)-4'-n-pentylbicyclohexyl (DP) exhibits strong resonance Rayleigh scattering (RRS) effect due to formation DP nanoparticles. It was used firstly as nanoprobe, to establish a simple and sensitive RRS energy transfer (RRS-ET) method for the determination of trace Cr⁶⁺ in water samples. The Cr⁶⁺ reacts with diphenylcarbazide (DCB) to produce purple complex. It is adsorbed on the nanoprobe surface, the purple complex as energy receptor and DP as energy donor to produce RRS-ET phenomenon, to make the RRS signal of 370 nm decreasing. In the range of 3-30 nmol/L Cr⁶⁺, with the increase of concentration, the RRS signal decreased linearly at 370 nm, with a detection limit of 0.49 nmol/L. This new RRS-ET method was applied to the determination of Cr⁶⁺ in water samples, with recovery of 96.0-104.7% and the relative standard deviation (RSD) of 4.44-9.98%.

Automated Calculation of Liquid Crystal Sensing Images Based on Deep Learning

Liquid crystal (LC)-based sensors have been extensively applied in the detection of chemical and biological events. However, the calculation of the optical images of the LC-based sensors is usually time-consuming and also might bring some errors due to the use of different judgment criteria by different users. In the present study, an automated calculation method for LC sensing images based on deep learning is provided. A convolutional network is trained with the prepared LC sensing images and their corresponding segmentation annotations to predict the positive responses. The ratio is calculated from the area of positive response to the total area selected by our image processing method. The robustness of the proposed algorithm is validated on both the test set and the label-free Cd²⁺ detection. The results show that the method based on deep learning can detect the positive response area in real time and the speed is much faster than the manual processing method. In addition, deep learning method can be directly applied to other label-free molecular detection assays.

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.

Liquid crystal microcapillary-based sensors for affordable analytical applications

Stimuli-responsive properties of liquid crystals (LCs), when combined with their optical properties, offer sensitive and rapid sensing applications. Here, we propose and demonstrate a microcapillary-based method to be applied for the online detection of amphiphilic species, which can be further used for tracking biological and chemical species in aqueous media. Specifically, we used compartments (300-1400 μm) of nematic 4-cyano-4'-pentylbiphenyl (5CB) that were positioned into cylindrical glass microcapillaries that promote homeotropic anchoring. The flat surfaces of the cylindrical LC compartments were in contact with an aqueous media. We characterized the equilibrium and nonequilibrium response of LCs upon a change in their anchoring at the aqueous interfaces. Upon anchoring transition, we observed the formation of a positively charged defect at the proximity of the interface that moved to the center of the LC compartment and reached equilibrium, a four-petal configuration. This transition was observed to take an average of 41 ± 19 min., which we related to the motion of the defect due to the imbalance of the elastic forces. During the transition, we observed metastable states which could be removed via thermal treatment. We showed the capillary sensors to be useful considering their ease of additional quantification. We also show that the sensors are reversible that facilitate temporal and cumulative quantification. The findings reported in this study can further be used to develop sensors for specific purposes that require continuous tracking of the chemical and biological species that is critical for the health and safety of the individuals and society.

Overview of Liquid Crystal Biosensors: From Basic Theory to Advanced Applications

Liquid crystals (LCs), as the remarkable optical materials possessing stimuli-responsive property and optical modulation property simultaneously, have been utilized to fabricate a wide variety of optical devices. Integrating the LCs and receptors together, LC biosensors aimed at detecting various biomolecules have been extensively explored. Compared with the traditional biosensing technologies, the LC biosensors are simple, visualized, and efficient. Owning to the irreplaceable superiorities, the research enthusiasm for the LC biosensors is rapidly rising. As a result, it is necessary to overview the development of the LC biosensors to guide future work. This article reviews the basic theory and advanced applications of LC biosensors. We first discuss different mesophases and geometries employed to fabricate LC biosensors, after which we introduce various detecting mechanisms involved in biomolecular detection. We then focus on diverse detection targets such as proteins, enzymes, nucleic acids, glucose, cholesterol, bile acids, and lipopolysaccharides. For each of these targets, the development history and state-of-the-art work are exhibited in detail. Finally, the current challenges and potential development directions of the LC biosensors are introduced briefly.

Enhancing the signal contrast ratio and stability of liquid crystal-based sensors by using fine grids made by photolithography of photoresists

We prepared fine grid patterns on a glass substrate through photolithography of photoresists; we filled photoresist grids with liquid crystals (LCs) to construct LC-based sensors. Scanning electron microscopy images revealed that the photoresist grids were flat, smooth, and 3.0-8.0 μm thick. In contrast to conventional LC-based sensors, in which LCs are filled in metal grids placed on glass substrates, our results proved that LC-based sensors constructed using photoresist grids exhibited a larger signal contrast ratio, better signal stability in aqueous solutions and lower limit of detection for mercuric ions. All these characteristics enhanced the performance of the LC-based sensors.

A Fluorescence Sensor for Pb2+ Detection Based on Liquid Crystals and Aggregation-Induced Emission Luminogens

Heavy metals, such as lead ions, are regarded as the main environmental contaminants and have a negative impact on human bodies, making detection technologies of lead ions critical. However, most existing detection methods suffer from time consumption, complicated sample pretreatment, and expensive equipment, which hinder their broad use in real-time detection. Herein, we show a new fluorescence sensor for detecting lead ions derived from liquid crystals doped with an aggregation-induced emission luminogen. The mechanism is based on the variation of fluorescence intensity caused by the disturbance of an ordered liquid crystal configuration in the presence of Pb²⁺, induced by DNAzyme and its catalytic cleavage. The proposed fluorescence sensor exhibits a low detection limit of 0.65 nM, which is 2 orders of magnitude lower than that previously reported in an optical sensor based on liquid crystals. The detection range of the Pb²⁺ fluorescence sensor is broad, from 20 nM to 100 μM, and it also selects lead ions from numerous metal ions exactly, resulting in a highly sensitive, highly selective, simple, and low-cost detection strategy of Pb²⁺ with potential applications in chemical and biological fields. This approach to designing a liquid crystal fluorescence sensor offers an inspiring stage for detecting biomacromolecules or other heavy metal ions by varying decorated molecules.

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.

Screening of Xanthine Oxidase Inhibitors by Liquid Crystal-Based Assay Assisted with Enzyme Catalysis-Induced Aptamer Release

Small-molecule drugs play an important role in the treatment of various diseases. The screening of enzyme inhibitors is one of the most important means in developing therapeutic drugs. Herein, we demonstrate a liquid crystal (LC)-based screening assay assisted with enzyme catalysis-induced aptamer release for screening xanthine oxidase (XOD) inhibitors. The oxidation of xanthine by XOD prevents the specific binding of xanthine and its aptamer, which induces a bright image of LCs. However, when XOD is inhibited, xanthine specifically binds to the aptamer. Correspondingly, LCs display a dark image. Three compounds are identified as potent XOD inhibitors by screening a small library of triazole derivatives using this method. Molecular docking verifies the occupation of the active site by the inhibitor, which also exhibits excellent biocompatibility to HEK293 cells and HeLa cells. This strategy takes advantages of the unique aptamer-target binding, specific enzymatic reaction, and simple LC-based screening assay, which allows high-throughput and label-free screening of inhibitors with high sensitivity and remarkable accuracy. Overall, this study provides a competent and promising approach to facilitate the screening of enzyme inhibitors using the LC-based assay assisted with the enzyme catalysis-induced aptamer release.

Using Diazotization Reaction to Develop Portable Liquid-Crystal-Based Sensors for Nitrite Detection

A liquid-crystal (LC)-based sensor for detecting nitrite in aqueous solutions was developed using a diazotization reaction as the sensing mechanism. First, tetradecyl 4-aminobenzoate (14CBA) was synthesized and doped into a nematic LC, i.e., 4-cyano-4'-pentylbiphenyl (5CB). When the LC mixture was cast on a glass substrate and then immersed into an aqueous solution without nitrite, the orientation of LC was planar and the LC image was bright. In the presence of nitrite, it reacted with alkylanilines to give corresponding diazonium ions with a positive charge, which aligned at the LC/aqueous interface to cause homeotropic orientation of LC. As a result, a bright-to-dark transition of the LC image was observed. The limit of detection (LOD) of this system for nitrite is 25 μM with high selectivity. In addition, this system can work in environmental water samples such as tap water and pond water. Finally, we demonstrated that the optical signals of LC can be measured and recorded using a built-in digital camera of a smartphone, suggesting the portability of this system for on-site applications.

Simultaneous Detection of Multiple Tumor Markers in Blood by Functional Liquid Crystal Sensors Assisted with Target-Induced Dissociation of Aptamer

Multiplex detection of tumor markers in blood with high specificity and high sensitivity is critical to cancer diagnosis, treatment, and prognosis. Herein, we demonstrate a strategy for simultaneous detection of multiple tumor markers in blood by functional liquid crystal (LC) sensors assisted with target-induced dissociation (TID) of an aptamer for the first time. Magnetic beads (MBs) coated with an aptamer (apt1) are employed to specifically capture target proteins in blood. After incubation of the obtained protein-coated MBs with duplexes of another aptamer (apt2) and signal DNA, sandwich complexes of apt1/protein/apt2 are formed on the MBs due to specific recognition of target proteins by apt2, which induces release of signal DNA into the aqueous solution. Subsequently, signal DNA is specifically recognized by highly sensitive DNA-laden LC sensors. Using this strategy, a 3D printed optical cell was employed to enable simultaneous detection of multiple tumor markers such as carcinoembryonic antigen (CEA), alpha-fetoprotein (AFP), and prostate specific antigen (PSA) with high specificity and high sensitivity. Overall, this effective and low-cost multiplex approach takes advantage of the easy separation of MBs, high specificity of aptamer-based recognition, and high sensitivity of functional LC sensors. Plus, it offers a performance that is competitive to that of commercial ELISA kits without potential interference from hemolysis, which makes it very promising in multiplex detection of tumor markers in clinical applications.

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

A new methodology involving the use of Bovine Serum Albumin (BSA) as a probe and liquid crystal (LC) as a signal reporter for the detection of heavy metal ions in water at neutral pH was developed. BSA acted as a multi-dentate ligand for the detection of multiple metal ions. The LC sensor was fabricated by immobilizing 3 µg mL-1 BSA solution on dimethyloctadecyl-[3-(trimethoxysilyl)propyl]ammonium chloride (DMOAP)-coated glass slides. In the absence of heavy metal ions, a dark optical image was observed, while in their presence, a dark optical image turned to bright. The optical response was characterized by using a polarized optical microscope (POM). The BSA based LC sensor selectively detected toxic metal ions as compared to s block metal ions and ammonium ions in water. Moreover, the limit of detection was found to be very low (i.e., 1 nM) for the developed new biosensor in comparison to reported biosensors.

A natural cyanobacterial protein C-phycoerythrin as an Hg2+ selective fluorescent probe in aqueous systems

C-phycoerythrin (CPE) as a natural protein-based fluorescence ‘turn off’ probe for Hg²⁺ in aqueous systems.

Real-time monitoring of the enzymatic reaction of urease by using whispering gallery mode lasing

A new strategy is reported here to monitor the enzymatic reactions in real time by using whispering gallery mode (WGM) lasing. The optical microcavity is formed via the self-assembly of an ultraviolet (UV)-treated nematic liquid crystal (LC) 4-cyano-4'-pentylbiphenyl (5CB). The single UV-treated 5CB microdroplet serves as both optical resonator and sensing reactor. The microdroplet configuration transitions induced wavelength shift in the WGM lasing spectra can be used as an indicator for the enzymatic reaction. The proposed sensor has a sub-microgram detection limit of urease (∼0.5 µg/ml), which is lower than the detection limit of currently available urease sensor based on LC materials. Our experimental results demonstrate that WGM lasing has unique advantages in the real-time monitoring of enzymatic reactions compared, for instance, with observation of the optical appearance under a polarized optical microscope.

Highly sensitive and selective optical sensor for lead ion detection based on liquid crystal decorated with DNAzyme

Lead ions (Pb²⁺) are one of the major environmental pollutants that are dangerous for human health, thus the detection methods of Pb²⁺ become very important as well. However, most reported techniques suffer from drawbacks such as long time, expensive equipment and complicated testing process, which prevent the use of real-time application. Herein, we demonstrate a novel liquid crystal optical sensor for detection of Pb²⁺ based on DNAzyme and its combined strand. The ordered and disordered configuration of liquid crystals, induced by complementary DNA strand and catalytically cleaved DNA in presence of lead ion separately, leads to dark and bright optical image under POM. The proposed naked-eye optical sensor possesses an extremely broad detection range of Pb²⁺ from 50 nM to 500 µM, with a low detection limit about 36.8 nM. The sensor also demonstrates high selectivity of Pb²⁺ from many other metal ions. The proposal LC sensor is highly sensitive and selective for Pb²⁺ detection, which provides a novel platform for other heavy metal, DNAs or antigen in biological and chemical fields by modifying sensing molecules.

Detection of Biomarkers in Blood Using Liquid Crystals Assisted with Aptamer-Target Recognition Triggered in Situ Rolling Circle Amplification on Magnetic Beads

Detection of biomarkers in body fluids is critical to both diagnosing the life-threatening diseases and optimizing therapeutic interventions. We herein report use of liquid crystals (LCs) to detect biomarkers in blood with high sensitivity and specificity by employing in situ rolling circle amplification (RCA) on magnetic beads (MBs). Specific recognition of cancer biomarkers, such as platelet derived growth factor BB (PDGF-BB) and adenosine, by aptamers leads to formation of a nucleic acid circle on MBs preassembled with ligation DNA, linear padlock DNA, and aptamers, thereby triggering in situ RCA. LCs change from dark to bright appearance after the in situ RCA products being transferred onto the LC interface decorated with octadecy trimethylammonium bromide (OTAB), which is particularly sensitive to the amplified DNA on MBs. Overall, this label-free approach takes advantages of high specificity of aptamer-based assay, efficient enrichment of signaling molecules on MBs, remarkable DNA elongation performance of the RCA reaction, and high sensitivity of LC-based assay. It successfully eliminates the matrix interference on the LC-based sensors and thus achieves at least 4 orders of magnitude improvement in sensitivity for detection of biomarkers compared to other LC-based sensors. In addition, performance of the developed sensor is comparable to that of the commercial ones. Thus, this study provides a simple, powerful, and promising approach to facilitate highly sensitive, specific, and label-free detection of biomarkers in body fluids.

Construction of a Liquid Crystal-Based Sensing Platform for Sensitive and Selective Detection of l-Phenylalanine Based on Alkaline Phosphatase

The detection of l-phenylalanine (l-Phe) has become one of the most pressing issues concerning diagnosis and treatment of phenylketonuria in neonates; however, a simple and robust methodology is yet to be developed. Here, the application of novel liquid crystals (LCs)-sensing platform for sensitive, selective, and label-free detection of l-Phe was reported at the first time. We devised a strategy to fabricate the sodium monododecyl phosphate (SMP)-decorated LC sensing platform with the appearance of dark. Then, a dark to bright (D-B) optical images alteration of LCs was observed after transferring alkaline phosphatase (ALP) to the interface, owing to cleavage of SMP induced by ALP. LCs remained dark images after the SMP-decorated interface in contact with the pre-incubated ALP and l-Phe. Such optical appearance resulted from the inhibition of ALP by l-Phe, which was further verified by the isothermal titration calorimetry (ITC). The strategy was applied to sensing l-Phe, which have been proven to allow for sensitively and selectively differentiation of l-Phe from interfering compounds with similar aromatic groups, as well as seven other essential amino acids. More importantly, the detection limit of l-Phe reached 1 pg/mL in urine samples, further demonstrating its value in the practical applications. Results obtained in this study clearly demonstrated the superiority of LCs toward the l-Phe detection, which can pave a way for the development of high performance and robust probes for l-Phe detection in clinical applications.

A liquid crystal based method for detection of urease activity and heavy metal ions by using stimulus-responsive surfactant-encapsulated phosphotungstate clusters

A liquid crystal (LC) based method is described for the sensitive determination of the activity of urease and of heavy metal ions which acts as inhibitors. Stimulus-responsive surfactant-encapsulated phosphotungstate clusters (SECs) were fabricated and deposited onto octadecyltrichlorosilane-coated glass. A copper TEM grid filled with LCs was placed on the substrate to construct the LC optical cell. Upon addition of water to the LC interface, the optical appearance of LCs on the glass undergoes a bright-to-dark shift due to an orientational transition of the LCs from a planar to a homeotropic state. However, the LCs display a bright appearance if they are pretreated with an aqueous solution containing urea and urease. This is caused by the disassemby of the SECs from the glass surface due to an increase of the pH value that is induced by the enzymatic hydrolysis of urea by urease. The method is highly sensitive and can detect urease activities as low as 0.03 mU/mL. It can also be applied to the determination of heavy metal ions which exert an inhibitory effect on the activity of urease. For example, Cu(II) can be quantified via urease inhibition in 1 nM concentration. Graphical abstract Schematic presentation of a liquid crystal-based sensor for detection of urease and heavy metal ions by using stimulus-responsive surfactant-encapsulated phosphotungstate clusters.

Fabrication of Liquid-Crystal-Based Optical Sensing Platform for Detection of Hydrogen Peroxide and Blood Glucose

Rapid and accurate determination of H₂O₂ is of great importance in practical applications. In this study, we demonstrate construction of liquid-crystal (LC)-based sensing platforms for sensitive and real-time detection of H₂O₂ with high accuracy for the first time. Single-stranded DNA (ssDNA) adsorbed onto the surface of nanoceria is released to the aqueous solution in the presence of H₂O₂, which disrupts arrangement of the self-assembled cationic surfactant monolayer decorated at the aqueous/LC interface. Thus, the orientation of LCs changes from a homeotropic to planar state, leading to change in the optical response from dark-to-bright appearance. As H₂O₂ can be produced during oxidation of glucose by glucose oxidase (GOx), detection of glucose is also fulfilled by employing the H₂O₂ sensing platform. Our system can detect H₂O₂ and glucose with concentrations as low as 28.9 nM and 0.52 μM, respectively. It shows high promise of using LC-based sensors for the detection of H₂O₂ and its relevant biomarkers in practical applications.

Directed Self-Assembly of C4-Symmetric, Oxidovanadate-Centered, Vanadyl(V) Quadruplexes for Ba2+- and Hg2+-Specific Recognition, Transport, and Recovery

Directed assembly of loosely, Na⁺-bound, oxidovanadate-centered quartets of C₄-symmetry from tailor-made chiral N-salicylidene-vanadyl(V) complexes, for the first time, allows for highly efficient Ba²⁺- or Hg²⁺-specific detection (by ⁵¹V NMR and VCD), transport (forming a unique helical capsule or a capped square planar complex, respectively), and green recovery from an aqueous phase containing 4 different alkaline earth ions or from at least 10 different metal ions of similar size and charge capacity into the CHCl₃ layer without interference from oxa- or oxophilic ions like Mg²⁺, Ca²⁺, Cu²⁺, Cd²⁺, and Pb²⁺.

Liquid crystal based sensing device using a smartphone

Liquid crystal (LC) based optical sensors have been found to be very promising for detecting aqueous biological samples due to the ease of optical detection, their cost effectiveness and the removal of the need for labelling biological species with fluorescent dyes. To date, all LC based sensors are studied in laboratories using conventional polarizing optical microscopy (POM), and no attention has been paid towards the fabrication of portable LC sensing devices for use in commercial purposes. Here, we designed and fabricated a 3D printed portable, lightweight, and inexpensive sensing device using a smartphone to detect the optical signal of LC based sensors. The accuracy of the optical signal using the fabricated sensing device is similar to that obtained using conventional POM. The fabricated sensing device, using a smartphone, gives a novel and new platform to LC based sensors for practical applications in the industrial world and people's daily lives.

Highly sensitive and selective liquid crystal optical sensor for detection of ammonia

Ammonia detection technologies are very important in environment monitoring. However, most existing technologies are complex and expensive, which limit the useful range of real-time application. Here, we propose a highly sensitive and selective optical sensor for detection of ammonia (NH₃) based on liquid crystals (LCs). This optical sensor is realized through the competitive binding between ammonia and liquid crystals on chitosan-Cu²⁺ that decorated on glass substrate. We achieve a broad detection range of ammonia from 50 ppm to 1250 ppm, with a low detection limit of 16.6 ppm. This sensor is low-cost, simple, fast, and highly sensitive and selective for detection of ammonia. The proposal LC sensing method can be a sensitive detection platform for other molecule monitors such as proteins, DNAs and other heavy metal ions by modifying sensing molecules.

Liquid crystals based sensing platform-technological aspects

In bulk phase, liquid crystalline molecules are organized due to non-covalent interactions and due to delicate nature of the present forces; this organization can easily be disrupted by any small external stimuli. This delicate nature of force balance in liquid crystals organization forms the basis of Liquid-crystals based sensing scheme which has been exploited by many researchers for the optical visualization and sensing of many biological interactions as well as detection of number of analytes. In this review, we present not only an overview of the state of the art in liquid crystals based sensing scheme but also highlight its limitations. The approaches described below revolve around possibilities and limitations of key components of such sensing platform including bottom substrates, alignments layers, nature and type of liquid crystals, sensing compartments, various interfaces etc. This review also highlights potential materials to not only improve performance of the sensing scheme but also to bridge the gap between science and technology of liquid crystals based sensing scheme.