Liquid crystal-based immunoassay for detecting human serum albumin

Human serum albumin (HSA) is the most abundant protein in human blood plasma. It is commonly used as a biomarker in urine samples to identify the chronic kidney disease caused by high blood pressure or diabetes. In our research, a thin layer of liquid crystals (LCs) is used as a readout system for developing an immunoassay that reports the presence of HSA in the aqueous solution with optical signals. The detection principle of this assay is based on the variation of surface density of protein upon the specific binding of HSA on an anti-HSA immobilized surface, which leads a dark-to-bright transition of LC images under cross-polarizers. Our results show that the LC-based immunoassay can detect HSA at a concentration of 50 μg/mL. By using the slide with immobilized anti-HSA in array format, the concentration level of HSA can be simply determined by the number of LC spot shown on the slide.     

Electrochemically modified piezoelectric crystal biosensor for detection of Staphylococcus aureus

Electropolymerized o-phenylenediamine film is used as a functional coating for the immobilization of anti-S. aureus antibody on the surface of a gold-plated piezoelectric crystal, and this piezoelectric immunosensor is applied to detect S. aureus. The frequency shift (F = F20s - F380s, Hz) between the frequency at the 20th second (after the addition of sample, F20s) and that at 380 seconds later (F380s) was introduced to construct a calibration graph, and shortening of assay time was achieved. The S. aureus concentrations in the range of 105-109 cells/mL can be detected by this system.     

DNA-binding small-ligand-immobilized surface plasmon resonance biosensor for detecting thymine-related single-nucleotide polymorphisms

A surface plasmon resonance (SPR) biosensor that carries DNA-binding small ligands has been developed for the detection of single-nucleotide polymorphisms (SNPs). 3,5-Diaminopyrazine derivatives, with a hydrogen-bonding profile fully complementary to the thymine base, were utilized as recognition elements on the sensor surface, and a target single-stranded DNA sequence was hybridized with a DNA probe containing an abasic site to place this site opposite a nucleobase to be detected. In a continuous flow of sample solutions buffered to pH 6.4 (0.25 M NaCl), the 3,5-diaminopyrazine-based SPR sensor can detect an orphan nucleobase in the duplex with a clear selectivity for thymine over cytosine, guanine, and adenine (5'-GTT GGA GCT GXG GGC GTA GGC-3'/3'-CAA CCT CGA CNC CCG CAT CCG-5'; X=abasic site, N=target nucleobase G, C, A, or T). The SPR response was linear in the concentration range 10-100 nM. Allele discrimination is possible based on the combination of different binding surfaces in a flow cell of the SPR system, which is demonstrated for the analysis of the thymine/cytosine mutation present in 63-meric polymerase chain reaction (PCR) amplification products (Ha-ras gene, codon 12, antisense strand). Comparison with a bulk assay based on 3,5-diaminopyrazine/DNA binding shows that the immobilization of 3,5-diaminopyrazine derivatives on the SPR sensor allows more sensitive detection of the target DNA sequence, and binding selectivity can be tuned by controlling the salt concentration of sample solutions. These features of the DNA-binding small-molecule-immobilized SPR sensor are discussed as a basis for the design of SPR biosensors for SNP genotyping.     

Surface plasmon resonance biosensor for genetically modified organisms detection

The development of a surface plasmon resonance (SPR) affinity biosensor based on DNA hybridisation is described. This biosensor has been applied to genetically modified organisms (GMOs) detection. Single stranded DNA (ssDNA) probes were immobilised on the sensor chip of an SPR device and the hybridisation between the immobilised probe and the complementary sequence (target) was monitored. The probe sequences were internal to the sequence of 35S promoter and NOS terminator which are inserted sequences in the genome of GMO regulating the transgene expression. The system has been optimised using synthetic oligonucleotides, then applied to real samples analysis. Samples, containing the transgenic target sequences, were amplified by polymerase chain reaction (PCR) and then detected with the SPR biosensor.     

Quartz crystal biosensor for detection of sugars and glycated hemoglobin

3-Aminophenylboronic acid (APBA) was used for construction of affinity mass sensors for determination of saccharides and glycated hemoglobin using complexation reaction with diol groups. Two approaches were tested for the bioligand layer fabrication—incorporation of APBA inside a thicker matrix and immobilization as a self-assembled monolayer, respectively. The direct affinity sensor with APBA embeded in the structure of glutaraldehyde-crosslinked bovine serum albumine provided linear response to mono- and dissacharides in the range from 0.1 to 15.0 mg/ml. This biosensor was also used for kinetic analysis of the interaction of boronic acid with diols; the values of association and dissociation constants were determined. The sensors with a monolayer of boronic groups were better suited for binding of glycated hemoglobin, probably due to improved steric access to the ligand.     

Liquid crystal bridges

The liquid crystalline material octylcyanobiphenyl was studied in the form of bridges spanning the space between two solid supports in an immiscible water bath. In the nematic phase the bridge collapses above a certain length-to-diameter ratio, consistent with the behaviour of ordinary Newtonian liquid bridges. The smectic A phase, however, exhibited the formation of very long, stable columns as a consequence of its non-Newtonian behaviour.     

Electrochemical biosensor for detecting DNA sequences from the pathogenic protozoan Cryptosporidium parvum

An electrochemical hybridization biosensor was developed for the detection of short DNA fragments specific to the deadly waterborne pathogen Cryptosporidium. The sensor relies on the immobilization of a 38-mer oligonucleotide unique to the Cryptosporidium DNA onto the carbon-paste transducer, and employs a highly sensitive chronopotentiometric transduction mode for monitoring the hybridization event. Variables of the probe-immobilization, hybridization and indicator-detection steps are optimized to offer convenient quantitation of ng ml(-1) levels of the Cryptosporidium DNA target, in connection with short (3-15 min) hybridization times. The suitability for direct detection of the spiked Cryptosporidium DNA target in untreated drinking and river water samples is demonstrated. Similar performance characteristics are observed at DNA-coated microfabricated thick-film carbon strips. This and similar developments hold great promise for field screening of Cryptosporidium and other microorganisms in environmental samples.     

Reagentless biosensor for isocitrate using one step modified Pt-Ir microelectrode

The Pt-Ir microelectrode modified through one step electropolymerization is proposed for the isocitrate amperometric biosensor construction. The enzyme (isocitrate dehydrogenase-ICDH), coenzyme (NADP(+)) and mediator (Meldola's Blue) were immobilized onto the microelectrode surface in one step from a PIPES buffer solution containing pyrrole. The optimized experimental conditions were 25 cycles of cyclic voltammetric in a solution containing 3.58 10(-5) mol l(-1) of mediator, 3.51 10(-4) mol l(-1) of coenzyme and 2.68 U ml(-1) of enzyme. In contrast to the biosensor for isocitrate reported in literature, just one enzyme was immobilized and no coenzyme addition in the solution of analysis was necessary. Catalytic currents were proportional to the isocitrate concentration between 7.7 10(-6) and 1.04 10(-4) mol l(-1), showing good repeatability. The detection limit of the proposed biosensor was 3.50 10(-6) mol l(-1), the response time was lower than 20 s, the lifetime was about 30 determinations and no significant interference of sugars and citric acid was verified. Orange juice samples were analysed by both methodology biosensor and spectrophotometric commercial kit, and the obtained results presented a good correlation. The data demonstrated that the developed biosensor is suitable for isocitrate determination in orange juice without matrix interferences.     

Liquid crystal mixtures for potential infrared applications

Liquid crystals (LCs) with diazo linkages have high dielectric and optical anisotropy. Two newly synthesized liquid crystalline compounds were dissolved in room temperature LC hosts, E7 and PTTP-24/36, to assess their properties. It was found that these mixtures have higher birefringence, larger dielectric anisotropy, and better elastic properties than the hosts. Satisfactory viscoelastic coefficients were also obtained for these mixtures, showing that they are promising LC materials for applications in the near IR region.     

Liquid crystal mixtures for potential infrared applications

Liquid crystals (LCs) with diazo linkages have high dielectric and optical anisotropy. Two newly synthesized liquid crystalline compounds were dissolved in room temperature LC hosts, E7 and PTTP-24/36, to assess their properties. It was found that these mixtures have higher birefringence, larger dielectric anisotropy, and better elastic properties than the hosts. Satisfactory viscoelastic coefficients were also obtained for these mixtures, showing that they are promising LC materials for applications in the near IR region.     

Liquid crystal birefringence for millimeter wave radar

Abstract

Many liquid crystals are found to have relatively high birefringence (Δn) values in the microwave and millimeter wave regions, as calculated from the phase shift induced by their reorientation by magnetic or electric fields. At 30 GHz, Δn values were obtained in the range of 0.08 to 0.18 for eleven liquid crystal mixtures of various types. The most favourable liquid crystal structures for high millimeter wave birefringence are highly conjugated rod-like molecules containing biphenyl, terphenyl, phenylpyrimidine, biphenylpyrimidine, and tolane groups in nematics of positive dielectric anisotropy (Δε). However, other liquid crystal structures including Schiffs base, azoxybenzene, and aromatic ester groups also have substantial birefringence, including nematics with negative and crossover Δε, as well as cholesteric nematics. The Δn varied only slightly at different frequencies of microwave millimeter wave in the 15–94 GHz range. Studies on magnetic and electrical field liquid crystal orientation in specially designed waveguides provide a basis for new types of modulators and scanning array antennae in the millimeter wave region, where more compact liquid crystal modulation media can be used than in the microwave region. These scanners can be used for both sending and receiving radar signals for potentially low cost radar systems.     

Liquid crystal polymer optics

In this paper we give a concise overview of various optical applications of Liquid Crystalline side‐chain polymers. The possibility to tune the LC structure and phase‐diagrams, as well as the availability of methods to create specific structures in the director field, allows materials to be developed for data‐storage media and as optical compensation films for LC display applications.     

Acetylcholinesterase liquid crystal biosensor for identification of AChE inhibitors by a reactivator

An improved acetylcholinesterase liquid crystal(LC) biosensor has been developed for the identification of organophosphates(OPs) by using a reactivator. When the acetylcholinesterases(AChEs) inhibited by different kinds of OPs are reactived by a reactivator, the catalytic activity of AChEs can be recovered with different activation efficiency because of the different phosphorylation structures formed in the inhibited AChEs. Accordingly, the reactived AChEs can catalyze the hydrolysis of acetylthiocholine to generate thiocholine product in different degrees, which will result in different catalytic growth of AuNPs and further form distinct orientational response of LCs. Based on such a reactivation mechanism, the AChE LC biosensor with a simple, rapid and visual procedure achieves an obvious identification of three OPs pesticides, methamidophos, trichlorfon and paraoxon, by using a pralidoxime reactivator.     

Nano-ZnO微叉指电极生物传感器检测大肠杆菌

设计了一种基于纳米ZnO材料检测大肠杆菌(E.coli O157:H7)的微叉指阻抗生物传感器,利用电化学方法在氧化铟锡(ITO)叉指电极表面沉积上纳米ZnO,然后将链霉亲和素固定在纳米ZnO表面,利用生物素亲和素的高亲和性原理将大肠杆菌抗体绑定在传感器表面,完成传感器的构建。实验表明,传感器检测E.coli O157:H7线性范围为40~4×10^6cfu/mL,检出限为40 cfu/mL,传感器的特异性、重现性、实用性较好。     

Design of two-dimensional photonic crystal biosensor using DNA detection

Abstract

In this paper, the photonic crystal biosensor is investigated theoretically with, concomitantly, high quality factor, transmission and sensitivity. This biosensor is made out of two waveguide couplers and one L2 resonant cavity formed by removing two air holes. For biosensor analysis, the 2D finite difference time domain (FDTD) method and the plane-wave expansion (PWE) approach are applied. Four slots placed into the cavity and the three rows of functionalized holes nearby the resonant cavities are filled with DNA. For the optimized structure, the biosensor quality factor is found to be over 3.7468?×?10⁶ and the sensitivity is of order 460?nm/RIU. The designed structure has high sensitivity, which is an important parameter in biosensing applications.     

Liquid crystal compound anti-ice surface

In some cold areas/regions, ice accumulation is harmful to aircrafts, highways and power lines. To overcome this challenge, many researchers have focused on developing anti-icing surfaces. In this paper, liquid crystal compound Cholest-5-en-3-ol(3β)-4-(2-propenyloxy)benzoate was synthesised, and a liquid crystal surface (LC surface) is prepared by heating the liquid crystal compound to 250°C and then cooling it. We determined ice-phobic properties of LC surface using differential scanning calorimetry (DSC) and polarised optical microscope (POM). A phenomenon that the freezing of water droplet on the LC surface is delayed was found. Compared with the two measurement methods, we obtained similar result that water freezing temperature was delayed nearly by 8°C on average on the LC surface. A process of ice/frost formation is observed using POM. The results displayed that the glass wafer without LC was covered completely by ice/frost, whereas on the LC surface at the same temperature no ice/frost was formed. Characteristics of LC surface were observed by field emission scanning electron microscope (FESEM) and Fourier transform infrared (FT-IR) imaging system. We suggest that the reason behind anti-ice surface is related to surface molecules and this is an important factor which may have an effect on anti-icing property.     

Liquid crystal dimers and oligomers

A liquid crystal dimer is composed of molecules containing two mesogenic groups linked via a flexible spacer. Initial interest in these materials stemmed from their ability to act as model compounds for semi-flexible main chain liquid crystal polymers but are now of fundamental interest in their own right because their behaviour is significantly different to that of conventional low molar mass liquid crystals. Recently research has begun to focus also on higher monodisperse oligomers such as trimers and tetramers consisting of molecules containing either three or four mesogenic units, respectively, linked via flexible spacers. In this review the most recent developments in our understanding of structure–property relationships in liquid crystal dimers and higher oligomers is discussed.     

Liquid crystal chemistry and poetry

This paper comments on a recent article “Revolutionary poetry and liquid crystal chemistry: Herman Gorter, Ada Prins and the interface between literature and science” by Hub Zwart (Foundations of Chemistry, published online: 10 July 2020), in which the author explores the influence of the liquid crystal research of Ada Prins on the epic poem Pan written by her long-time lover Herman Gorter. The present paper reviews the basic science of liquid crystals and explains the connections between the work of Prins and its influence on the poem. Other examples of the use of “liquid crystal” as a literary device are identified from renaissance poetry, and the uses of the metaphor in these poems are analysed from a scientific perspective. From these examples it is suggested that creative concepts from poetry may contain elements of substance that appear in hitherto unrecognised scientific realities.