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In this study, we demonstrate the detection of mRNA from Escherichia coli in drinking water using thermotropic liquid crystals (LCs). After hybridization of complementary mRNA with the single-stranded DNA immobilized on a polymer substrate containing periodic sinusoidal wave patterns, the orientation of LCs transits from a uniform to a non-uniform state, thereby inducing a change in the optical response of LCs. The periodic sinusoidal features of the polymer substrate are obtained through buckling the poly-(dimethylsiloxane) slide on a cylindrical surface, followed by replicating the associated relief structures on a poly-(urethaneacrylate) surface, where a film of gold was deposited. Then, thiol-modified single-stranded DNA was functionalized on the gold film as an mRNA receptor. The formation of mRNA-single-stranded DNA complex, which covers the sinusoidal nanostructures on the surface, induces the orientational transition of LCs. This result indicates that LCs can be used to report the specific hybridization of mRNA with single-stranded DNA, which holds promise for the sensitive and label-free detection of viable bacterial pathogens in drinking water. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

In this study, we demonstrate a real-time and sensitive strategy for monitoring of lipase activity using liquid crystal (LC) droplets with micrometre scales supported on solid surfaces. The LC droplet pattern was formed by evaporating a solution of nematic LC, 4-cyano-4′-pentylbiphenyl (5CB) dissolved in heptane. The surface-anchored LC droplets displayed a bright fan-shaped appearance in buffer solution, while they exhibited a dark cross appearance when they were in contact with an aqueous mixture of glycerol trioleate (GT) and lipase. Due to adsorption of the released oleic acid generated from the enzymatic reaction between GT and lipase, LCs adopted a perpendicular orientation instead of planar orientation at the aqueous/LC droplet interface, resulting in contrasting optical response. Using this approach, the presence of 0.1 μg/mL lipase in the aqueous solution could be detected within 6 min. When compared to previously reported LC-based sensors for the detection of lipase, this simple and convenient method has the advantage of real-time monitoring of lipase activity with high sensitivity. In addition, this strategy also has high potential for application of the LC droplet pattern for sensing applications. [ABSTRACT FROM AUTHOR]

Highlights: [•] Investigation of the interactions between chitosan and phospholipid membranes using liquid crystals. [•] A distinctive orientational transition of LCs was obtained after transferring lysozyme onto the chitosan-disrupted membrane. [•] Polyelectrolytes-disrupted lipid membranes at the aqueous–LC interface could be used to build LC-based sensors. [Copyright &y& Elsevier]

In this study, we employed a simple liquid crystal (LC)-based system to dynamically image enzymatic events at the aqueous/LC interface decorated with polyelectrolyte-disrupted phospholipid membranes. Since polyelectrolytes were shown to disrupt the arrangement of the self-assembled phospholipid monolayer and induced a dark-to-bright shift in the optical response of LCs that support the phospholipid membrane, we observed that the transfer of an aqueous solution of protease onto the polyelectrolyte-disrupted phospholipid membrane resulted in a gradual recovery of the optical response of LCs from bright to dark appearance. Due to the enzymatic event that occurs at the aqueous/LC interface, the generated polyelectrolyte fragments desorbed from the interface to the bulk solution. This led to the restoration of the disrupted phospholipid monolayer, which resulted in recovery of the optical response. These results suggest that the polyelectrolyte-decorated membrane-supported LCs could be potentially used to examine a range of biological interactions that involve polyelectrolytes. Furthermore, the LC-based system holds great promise for label-free and real-time investigation and detection of biomolecular interactions coupled to membrane disruption and restoration, which might have potential utility in the clinical diagnosis and treatment of membrane-associated disease. [ABSTRACT FROM AUTHOR]

Abstract: In this study, we developed a simple label-free technique for monitoring the enzymatic activity of lipase using liquid crystal (LC)-based sensors. The optical response of LCs changed from a bright to dark appearance when an aqueous solution of lipase was in contact with a nematic LC, 4-cyano-4′-pentylbiphenyl (5CB), that was doped with glyceryl trioleate, which is a glyceride that can be enzymatically hydrolyzed by lipase. Since the oleic acid released from the enzymatic reaction could spontaneously form a self-assembled monolayer at the aqueous/LC interface due to its amphiphilic property, the orientation of the LCs transited from a planar to homeotropic state, which induced a change in the optical response of the LCs. We did not observe a bright-to-dark shift in the optical appearance of LCs when pure 5CB was immersed into the lipase solution. Moreover, we further confirmed the specificity of the enzymatic reaction by transferring an aqueous buffer solution not containing an analyte, or with bovine serum albumin (BSA) or trypsin onto the interface of aqueous solutions and the glyceryl trioleate-doped 5CB, which did not produce any distinctive contrast in the optical appearance. These results suggest the feasibility of measuring the enzymatic activity of lipase using the LC-based sensing technique. Furthermore, our strategy could also be used for the preparation of a self-assembled monolayer of carboxylates at the aqueous/LC interface. [Copyright &y& Elsevier]

In this study, we developed a simple and label-free liquid crystal (LC)-based biosensor for real-time screening of the presence of urease in aqueous solutions. Nematic liquid crystal, 4-cyano-4′-pentylbiphenyl (5CB), when treated with ultraviolet light, showed a bright to dark optical response to the emergence of ammonia in the aqueous phase, indicating a planar to homeotropic alignment of LC. The ammonia-driven optical signal could be ascribed to the orientational transition of 5CB, caused by the deprotonation of 4-cyano-4′-biphenylcarboxylic acid (CBA), which was the main product of UV-treatment and the screening of the electrostatic interactions at the aqueous/LC interface. Due to the high spatial resolution and fast response, this method was successfully used to detect urease belonging to the family of amidohydrolase, which hydrolyzes urea into ammonia and carbon dioxide. A urease concentration as low as 1 nM could be detected and monitored in real-time. Moreover, no signal was detected when a divalent copper ion, which blocks the active sites of urease, was used. This result further confirmed our initial hypothesis that orientational transitions of LC were induced from the enzymatic reaction. The results reported in this article suggest that our method may potentially have clinical utility for the specific detection of Helicobacter pylori. In addition, this ammonia-based LC biosensor may be used for the sensitive detection of other amidohydrolases. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract: In this study, we developed a simple label-free method for the detection of catalase (CAT) using liquid crystals (LCs). The optical appearance of LCs changed from bright to dark when hydrogen peroxide was in contact with the dodecanal-doped nematic LC, 4-cyano-4′-pentylbiphenyl (5CB). Since hydrogen peroxide can oxidize aldehyde into carboxylic acid, an orientational transition of the LC from the planar to homeotropic state was induced by the self-assembled carboxylate monolayer formed at the aqueous/LC interface. The optical response of LCs exhibited a higher sensitivity to the presence of hydrogen peroxide in an alkaline solution. A new type of LC-based sensor was developed to monitor the presence of CAT in the aqueous phase. Due to the enzymatically catalytic hydrolysis of hydrogen peroxide, the bright-to-dark shift in the optical signal did not take place in the aqueous mixture of hydrogen peroxide and catalase. In contrast, the optical response changed from bright to dark when the mixture in the optical cell was replaced with an aqueous solution of hydrogen peroxide. Considering the optical response of LCs related to the absence and presence of hydrogen peroxide, the aldehyde-doped 5CB might have potential utility in real-time recognition and detection of chemical and biological events associated with hydrogen peroxide. [Copyright &y& Elsevier]

Abstract: In this study, a new method for the detection of heavy metals in aqueous phase was developed using liquid crystals (LCs). When UV-treated nematic LC, 4-cyano-4′-pentyl biphenyl (5CB) that was confined in the urease-modified gold grid was immersed in a urea solution, an optical response from bright to dark was observed under a polarized microscope, indicating that a planar-to-homeotropic orientational transition of the LC occurred at the aqueous/LC interface. Since urease hydrolyzes urea to produce ammonia, which would be ionized into ammonium and hydroxide ions, the main product of the photochemically degraded 5CB, 4-cyano-4′-biphenylcarboxylic acid (CBA), was deprotonated and self-assembled at the interface, inducing the orientational transition in the LC. Due to the high sensitivity and rapid response of this system, detection of heavy metal ions was further exploited. The divalent copper ion, which could effectively inhibit the activity of urease, was used as a model heavy metal ion. The optical appearance of the LC did not change when urea was in contact with the copper nitrate hydrate-blocked urease. After the copper-inhibited urease was reactivated by EDTA, a bright-to-dark shift in the optical signal was regenerated, indicating an orientational transition of the LC. This type of LC-based sensor shows high spatial resolution due to its optical characteristics and therefore could potentially be used to accurately monitor the presence of enzyme inhibitors such as heavy metal ions in real-time. [Copyright &y& Elsevier]

In this study, we examined the anchoring behaviour of the ultraviolet (UV)-tailored nematic liquid crystal (LC) 4-cyano-4'-pentylbiphenyl (5CB) at the aqueous/LC interface. A range of photochemical reaction products are generated when 5CB is exposed to UV light, including the main product 4-cyano-4'-biphenylcarboxylic acid (CBA). When UV-treated 5CB is in contact with an aqueous sodium hydroxide or sodium chloride solution, the optical appearance of the LC undergoes a bright-to-dark shift, which indicates an orientational transition in the 5CB from a planar to homeotropic (perpendicular to the surface) state. Moreover, when the photochemically degraded 5CB was immersed in an aqueous mixture of hydroxide ions and electrolytes, the optical response was even more sensitive, which was associated with the deprotonation of CBA and the screening of electrostatic repulsion between the carboxylate head groups at the interface. In this study, the competitive orientational behaviour of LC in relation to biomolecular conjugation and ionic interaction at the interface was examined. When biomacromolecules, such as urease, were conjugated to a mixed monolayer of tetra(ethylene glycol)-terminated lipid and carboxylic acid-terminated lipid at the interface, UV-treated 5CB exhibited an ordering transition from a homeotropic to planar state. However, when a sodium hydroxide solution was in contact to the urease-decorated interface, the LC reverted back to its homeotropic state. By exploiting the orientational behaviour of the UV-treated 5CB at the aqueous/LC interface, we concluded that the acid-doped LC could potentially be used for the sensitive screening of pathogens and biomolecules. [ABSTRACT FROM AUTHOR]