Using liquid crystals to detect DNA hybridization on polymeric surfaces with continuous wavy features

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 cationic surfactant-decorated liquid crystal-based sensor for sensitive detection of quinoline yellow

Quinoline yellow (QY) is one of the popular synthetic food colorants and in food industry greatly used. Developing accurate and simple QY detection procedures is of major considerable importance in ensuring food safety. Hence, it is important to detect this food colorant effectively to reduce risk. Herein, an innovative liquid crystal (LC)-based sensor was designed for the label-free and ultra-sensitive detecting of the QY by means of a cationic surfactant-decorated LC interface. The nematic liquid crystal in touch with CTAB revealed a homeotropic alignment, when QY was injected into the LC-cell, the homeotropic alignment consequently altered to a planar one by electrostatic interactions between QY and CTAB. The designed LC-based sensor detected QY at the too much trace level as low as 0.5 fM with analogous selectivity. The suggested LC-based sensor is a rapid, convenient and simple procedure for label-free detection of QY in food industrial and safety control application.

Liquid-Crystal-Based Immunosensor for Diagnosis of Tuberculosis in Clinical Specimens

Tuberculosis (TB) is a serious global health problem, although it is easily preventable and curable. The prevalence of TB is caused by a lack of simple, rapid, cheap, and effective TB diagnostic tests. In this study, we have established a novel liquid crystal (LC)-based immunosensor to diagnose TB in clinical specimens. The clinical serum samples were incubated on a TB antigen-immobilized substrate, and their optical LC responses were observed using a polarized light microscope. Specific binding of anti-TB antibodies to the TB antigen-immobilized surface only occurred in clinical specimens from TB patients, inducing the disruption of the orientation of LCs. This was followed by the distinctive change in the optical appearance of LCs from uniform to random. However, when clinical serum samples from healthy people or latent TB patients were incubated, the orientation of LCs remained uniform. Through the change of optical LC images, in 76% of TB patients, this essay correctly identified the patients as having antibodies to TB in their serums. 91% of healthy people free of TB were correctly identified as not having antibodies to TB. Thus, this LC-based immunosensor is a promising platform, particularly in clinical TB diagnostics, which does not require complicated preparation of clinical specimens or complex instrumentation.

Label-free detection of viruses on a polymeric surface using liquid crystals

In this study, we demonstrated a label-free detection of viruses using liquid crystals (LCs) on a polymeric surface with periodic nanostructures. The polymeric nanostructures, which hold sinusoidal anisotropic patterns, were created by a sequential process of poly-(dimethylsiloxane) buckling and replication of the patterns on a poly-(urethane acrylate) surface containing a film of gold. After immobilization of human cytomegalovirus- and adenovirus-antibodies onto the polymeric surface treated with a mixed self-assembled monolayer, a uniform appearance reflecting the uniform orientation of 4-cyano-4'-pentylbiphenyl (5CB) was observed. Conversely, binding of viruses to their antibody decorated surface induced a random appearance of 5CB from the random orientation of 5CB. The uniform to random orientational transition of 5CB indicates that the anisotropic topography of the polymeric surface was masked after specific binding of viruses to the antibody decorated surface. We evaluated the specificity of the binding events by confirming topographical changes and optical thickness using atomic force microscopy and ellipsometry, respectively. These results demonstrate that polymeric surfaces with continuous anisotropic patterns can be used to amplify the presence of nanoscopic virions into an optical response of LC, as well as expand the scope of LC-based biological detection on polymeric solid surfaces.

Imaging trypsin activity through changes in the orientation of liquid crystals coupled to the interactions between a polyelectrolyte and a phospholipid layer

In this study, we developed a new type of liquid crystal (LC)-based sensor for the real-time and label-free monitoring of enzymatic activity through changes in the orientation of LCs coupled to the interactions between polyelectrolyte and phospholipid. The LCs changed from dark to bright after an aqueous solution of poly-l-lysine (PLL) was transferred onto a self-assembled monolayer of the phospholipid, dioleoyl-sn-glycero-3-phospho-rac-(1-glycerol) sodium salt (DOPG), at the aqueous/LC interface. Interactions between the positively charged PLL and the negatively charged DOPG drove the reorganization of the phospholipid membrane, which induced an orientational transition in the LCs from a homeotropic to planar state. Since the serine endopeptidase trypsin can enzymatically catalyze the hydrolysis of PLL, the dark-to-bright shift in the optical response was not observed after transferring a mixed solution of PLL and trypsin onto the DOPG-decorated LC interface, indicating that no orientational transitions in the LCs occurred. However, the optical response from dark to bright was observed when the mixture in the optical cell was replaced by an aqueous solution of PLL. Control experiments with trypsin or an aqueous mixture of PLL and deactivated trypsin further confirmed the feasibility of this approach. The detection limit of trypsin was determined to be ~1 μg/mL. This approach holds great promise for use in the development of LC-based sensors for the detection of enzymatic reactions in cases where the biological polyelectrolyte substrates of enzymes could disrupt the organization of the membrane and induce orientational transitions of LCs at the aqueous/LC interface.