Analytical Instrumentation : Liquid crystals

Analytical Instrumentation Portfolios


Liquid Crystal Sensors for Detecting Nerve Toxins and Other Dangers

UW–Madison researchers have developed LC-based sensor devices that are more sensitive and selective, and can be used to detect a wide variety of target compounds.

The new sensors contain mixed metal salts. Each salt includes one type of metal cation and a combination of weakly coordinating (stable) and strongly coordinating (unstable) anions. For example, the anions could be ClO4- and acetylacetonate, respectively. The interaction between the metal salt and LCs is enhanced by these mixed anions, resulting in a more sensitive device.

Liquid Crystal Device for Identifying and Validating Cleaning Processes for Biofouling

UW–Madison researchers have developed a model liquid crystal-based system for studying the behavior and conformation of proteins at a surface or other interface. The system can be used to rapidly assess cleaning compositions for removing proteins or biofilms, agents for preventing adsorption of proteins and other molecules to surfaces and potential protein stabilizing agents.

The system includes one or more protein molecules disposed at a liquid crystal-aqueous interface. As proteins are removed from the interface, the liquid crystal surprisingly undergoes a continuous orientational ordering transition, which is correlated to the extent and speed of protein removal. By measuring this ordering transition, the model system can be used to rapidly assay the effectiveness of a given cleaning composition in removing proteins or biofilms from a surface.

In the model system, proteins that have aged or deformed are more difficult to remove from the interface and proteins that are crowded on the interface (i.e., less likely to be deformed) are easier to remove. Accordingly, the system also can be used to assay the state or conformation of proteins.

Devices and Methods for Immobilizing Liquid Crystal Droplets onto a Chemically Functionalized Substrate Surface

UW–Madison researchers have developed devices and methods for immobilizing micrometer-sized liquid domains such as liquid crystal or isotropic oil droplets on a variety of chemically-functionalized surfaces. A multifunctional polymer, which may be a polyamine, is adsorbed at the surface interface of the liquid crystal droplets. Then the droplets are immobilized by covalent bonding, electrostatic interactions or other interactions between the adsorbed polymer and the functionalized substrate surface. The immobilized droplets can be used, for example, in liquid crystal droplet-based sensing devices or devices engineered to possess optical band gaps.

Liquid Crystal Devices for Detecting and Quantifying Endotoxin

UW–Madison researchers have developed methods and devices for detecting and quantifying endotoxin using micrometer-sized droplets of liquid crystal dispersed in aqueous solution.  The researchers found that LPS triggers anchoring configuration transitions on contact with liquid crystals by changing the energies of topological point defects generated within the liquid crystal microdomains.

In a preferred embodiment, a sensor contains liquid crystal droplets that have a bipolar alignment with two point defects.  When the device is exposed to a solution that contains LPS, the alignment of the liquid crystals quickly changes from bipolar (LPS negative) to radial (LPS positive) with one point defect.  This change in alignment can be detected easily using polarized light or other means.   

Robust, Moldable Colloidal Liquid Crystal Gels Provide User-Friendly, Portable Sensors

UW-Madison researchers have developed self-supporting and mechanically robust gels that can be molded, easily handled and processed yet retain their responsiveness to chemical and biological species.  These colloidal liquid crystal gels can be used to produce improved liquid crystal-based devices, including wearable, personalized sensors.

The gels are produced by dispersing liquid crystals into colloids, which spontaneously form a network.  The combination of colloids and liquid crystals yields a visco-elastic gel that has high mechanical strength because of the network of colloids.  The high strength allows the gels to be molded into any desired shape, making the detection of chemicals and biochemicals much easier than previous methods using liquid crystals.

Automated System Measures Changes in Liquid Crystal Orientation to Detect and Quantify Biomolecules

UW-Madison researchers now have developed an automated system for precisely determining the in-plane orientation of liquid crystals with high spatial resolution to sensitively and quantitatively detect biomolecules.  This system, which allows variations in the anchoring strength of liquid crystals to be measured easily, consists of a modified liquid crystal cell and an automated image recording and analysis system. 

The liquid crystals can be oriented by a variety of mechanisms.  In one embodiment, a liquid crystal cell is composed of two functionalized thin films of gold, which face each other and are separated by a mylar spacer.  One surface orients the liquid crystal with an in-plane anchoring, which is not parallel to the in-plane anchoring of the opposing surface.

Then a series of images are acquired of the liquid crystal film that contacts the surface to be analyzed.  The images are analyzed to yield maps of the twist angle and thus anchoring energy of the liquid crystal across the surface.  This technique effectively condenses a large data set of images into a compact map to reveal features on the analytic surface that were not apparent in the individual images.

Varied Monodisperse Oil or Liquid Crystal Emulsion Droplets for Improved Nanoviewing, Sensing and Biosensors

UW-Madison researchers have developed a versatile, scalable and highly parallel method of producing monodisperse emulsion droplets in a range of predetermined sizes.  The oil emulsion droplets, in which the oils can be liquid crystal molecules, can be prepared with or without polymeric shells or capsules.

This method is based on templating polyelectrolyte multilayer (PEM) capsules formed by the layer-by-layer adsorption of polyelectrolytes on sacrificial particles.  A polymeric shell is formed around a sacrificial particle, such as silica.  Then the silica is etched away and the shell is infiltrated with an oil.  The shell then can be removed to reveal monodisperse oil or liquid crystal emulsion droplets of a uniform, predetermined size.  These droplets could be used as biosensors to detect enzymatic activity or target analytes, such as bacteria or viruses, in a sample.

Methods of Manufacturing and Using Beta-Peptide Lyotropic Liquid Crystals

UW-Madison researchers have developed liquid crystals based on relatively short beta-peptide scaffolds that can be tailored to have unique properties for use in biological assays. Beta-peptides differ from conventional peptides in that certain beta-peptides form stable helices at short, oligomeric lengths, giving rise to robust, asymmetric structures. These helical beta-peptides can self-assemble to form lyotropic liquid crystals in aqueous environments.

To give the liquid crystals more desirable properties, a variety of functional groups can be added to the beta-peptides. The liquid crystals can then be used, for example, to detect an analyte, such as a protein, in a biological sample.

Liquid Crystalline Substrates for Culturing Cells

UW-Madison researchers have developed a method of culturing cells, including hES cells, on liquid crystalline substrates to provide a new means of visualizing developmental changes that occur in the cells. A thin protein layer, such as Matrigel, is deposited on the surface of a thermotropic liquid crystal. Then cells are seeded onto the Matrigel.

As the cells grow and differentiate, they impart subtle structural changes to the protein gel layer. Because the liquid crystal layer is in direct contact with the protein layer, these changes are amplified and transduced by the liquid crystals, where they may be observed easily.

To induce changes in the cells, a stimulus may be introduced to alter the orientation of the liquid crystals. This imparts changes to the structure of the Matrigel, which in turn alters the cellular environment.

Device and Methods for Liquid Crystal-Based Bioagent Detection

UW-Madison researchers have developed a sensitive, selective and efficient liquid crystal-based device and method for detecting bioagents and other biological molecules. The device uses membranes that are comprised of a polymerized antigen or substrate of an enzyme, such as botulinum toxin (BoNT). A liquid crystal is in contact with one surface of the membrane. To detect a bioagent, the other membrane surface is contacted with an aqueous solution suspected of containing the antibody or enzyme. If the bioagent is present in the solution, the membrane containing the substrate degrades, leading to a detectable change in the orientation of the liquid crystal.

Devices and Methods for Analyte Detection Using Distorted Liquid Crystals

UW-Madison researchers have developed an alternative means of detecting liquid crystal signals in response to biomolecular interactions. This technique involves determining the anchoring strength of a constrained liquid crystal as a function of the molecules bound to the substrate surface. In the absence of any external force, liquid crystals align along the surfaces of a sample with their optical axis along one direction, defined as the “easy axis.” Anchoring strength can be defined as the amount of force required to cause the liquid crystal to not lie along the easy axis. When a liquid crystal is constrained between two surfaces that have their easy axes in two different directions, the liquid crystal is distorted and strained. In that case, the orientation of the liquid crystal is a compromise between two opposing forces: the anchoring strength and the elastic torque resulting from the strain.

To evaluate the anchoring strength of liquid crystals, the researchers developed a slightly modified version of the optical cells typically used to detect biomolecular interaction using liquid crystals. Previous optical cells included two glass substrates separated by thin spacers on each end. One of the surfaces is a reference surface that the liquid crystal is strongly anchored to. The analyte is placed in or on the other substrate surface. In the modified version, a “wedge” optical cell is created by including a spacer on only one end. The easy axis of the substrate surface and the easy axis of the reference surface are rotated from one another by a known angle. If the analyte is present, the orientation of the liquid crystal deviates from the easy axis of the substrate surface in an analyte-dependent manner. The wedge configuration allows the angle of deviation to be measured, enabling the detection and quantification of the analyte.

Polyelectrolyte Multilayer Films at Liquid-Liquid Interfaces

UW-Madison researchers have developed a method for providing a PEM film at a liquid-liquid interface, such as the interface between a liquid crystal (LC) and an aqueous solution. A PEM can be incorporated between an LC and an aqueous solution by sequentially depositing layers of anionic and cationic polyelectrolytes at the interface. This modifies the interface and effectively functionalizes the LC layer. If the appropriate adducts and excipients are in the PEM, the PEM can transduce signals from the aqueous solution to the LC. For example, receptors incorporated in the PEM can recognize and bind ligands in the aqueous solution, resulting in changes that alter the orientation of the LC. This alteration can then be easily observed to determine if the ligand is present in the solution.

Using Liquid Crystals to Detect Post-Translationally Modified Peptides

UW-Madison researchers have developed devices and methods that use liquid crystals to distinguish between post-translationally modified peptides and unmodified peptides. A sample containing a post-translationally modified peptide, an unmodified peptide, or a mixture of both is bound to a substrate surface. The surface then is contacted with a recognition agent, such as an antibody, that specifically binds to or forms a complex with the post-translationally modified protein in the sample. A liquid crystal is contacted with the surface, and its orientation is observed. Disruptions in the uniform anchoring of the liquid crystal indicate the presence of post-translationally modified protein.

Liquid Crystals with Reduced Toxicity Toward Living Cells

UW-Madison researchers have now developed liquid crystal compositions that exhibit little or no toxicity towards cells. The compositions include at least two different liquid crystal compounds with chemical functional groups such as fluorine atoms, fluorophenyl groups or difluorophenyl groups. The liquid crystals may be added directly to cell culture media or to components of culture media to enable their use in counting cells.

Low-Power Liquid Crystal Switching Mechanism

A team of UW-Madison chemical engineers has now created a device and mechanism for switching the orientation of liquid crystals in displays operating at low potentials, e.g., less than 200 mV. The device is an electro-optical cell consisting of a liquid crystal layer doped with a salt, which is sandwiched between a counter electrode and a working electrode supported by a substrate. The researchers demonstrated the switching mechanism by building a device that contained a working electrode made of self-assembled monolayers of alkanethiols supported by a gold surface. These monolayers present ferrocene groups at the surface, which can be reversibly oxidized to ferrocenium. As the ferrocene groups are chemically or electrochemically oxidized to ferrocenium, an electrical double layer forms at the surface of the working electrode. The electrical field localized within the double layer then changes the orientation of the liquid crystals sitting on top.

Using Liquid Crystals to Detect Interactions at Biomimetic Interfaces

UW-Madison researchers have developed devices and methods for detecting interactions between proteins at interfaces between liquid crystals and aqueous solutions. They discovered it is possible to form biomimetic membranes from phospholipids that spontaneously assemble at the liquid crystal-aqueous interface. These membranes then can be used to detect protein binding and enzymatic activity at the interface.

An aqueous solution containing a surfactant and a receptor molecule, such as a phospholipid, is contacted with the top surface of a liquid crystal. The liquid crystal is in a well or other holding compartment on a substrate like a glass slide, and the aqueous solution may be passed over the surface of the liquid crystal in a flowing stream. The receptor molecule is adsorbed on the top surface of the liquid crystal, forming an interface between the crystal and the solution. If a target compound is present in the solution, it binds to the liquid crystal or the receptor molecule, causing an easily observable change in the orientation of the liquid crystal. Alternatively, a change in the orientation of the liquid crystal may indicate that a reaction of interest, such as enzymatic cleavage or hydrolysis, has occurred.

Detecting Compounds with Liquid Crystals

UW-Madison researchers have developed a novel method and device for detecting the presence of gas phase chemical compounds such as environmental contaminants with liquid crystals. The device consists of a thin film of liquid crystals overlaying a nanostructured surface that hosts receptors for binding a chemical compound of interest. When the target compound is present in a sample, it diffuses through the film of liquid crystals and binds to the receptors on the surface. Binding of the compound causes the liquid crystals to change their orientation, a shift that is readily observed with the naked eye.

Detecting Microscopic Pathogens with Liquid Crystals

UW-Madison researchers have developed a liquid crystal-based device for simple, efficient and accurate detection of pathogenic microbes. The device consists of a micro-structured surface containing depressions that match the size and contours of a specific bacterial species or viral type. The surface is also treated to bind a specific pathogen of interest and to block non-specific binding.

When the substrate is exposed to a water or soil sample from the field, the pathogen, if present, attaches to the surface and occupies the depressions. Next, a liquid crystal surface is laid over the micro-structured surface. If the pathogen is present, the liquid crystal layer will respond by changing its color or brightness, allowing easy visual read-out by an observer. In the absence of the pathogen, the liquid crystal layer appears dark. The device surface may also be designed as an array, so that clinical or environmental samples can be probed for multiple pathogens simultaneously.

Rubbed Substrates for Liquid Crystals

UW-Madison researchers have developed rubbed substrates for liquid crystals. These substrates are easy to prepare. They uniformly align liquid crystals and resist non-specific adsorption of proteins and other contaminants.

The substrates include a blocking compound, such as bovine serum albumin (BSA), which is immobilized on one side of a support to form a biochemical blocking layer. A bifunctional spacer and a surface modifying compound may be used to bind the blocking compound to the surface of the support. An immunoglobulin, peptide, nucleic acid sequence or other agent that is capable of specifically recognizing the target species is also immobilized on the side of the support with the blocking layer. The surface on that side is then mechanically rubbed, so liquid crystals become uniformly anchored when contacted with the substrate.

To detect the presence of a target species, the substrate is incubated with the sample to be tested. Then the liquid crystal is added. Disruptions in the uniform anchoring of the liquid crystal indicate the presence of the target.

Quantitative Characterization of Obliquely-Deposited Gold Substrates in Liquid Crystal Devices

A UW-Madison researcher has developed quantitative methods for analyzing the anisotropy of obliquely deposited metal films. The methods use scanning probe microscopic techniques, such as scanning tunneling and atomic force microscopy. They can be used to characterize the metal films and predict the orientation of liquid crystals supported on the films. They also can be used to design surfaces that differ systematically in their anisotropy, thereby allowing analytes to be detected at different threshold concentrations.

Liquid Crystal Device for Detecting Molecular Interactions

A UW-Madison researcher has developed a liquid crystal device for simply, inexpensively and reliably detecting the presence of an analyte. The device consists of one or more substrates, which can be made from almost any physio-chemically stable material, including inorganic crystals, glasses or oxides; metals; or organic polymers. A recognition element, such as an immunoglobulin, peptide, nucleic acid sequence or other agent capable of specifically recognizing the target analyte, is immobilized on the substrate surface. This moiety may be bound directly to the substrate or through an organic layer deposited on the surface. A liquid crystal then is coupled to the substrate surface.

To detect the analyte, the device is exposed to a sample that may contain it. If the analyte is present, it binds or otherwise interacts with the recognition moiety, causing an easily observable change in the orientation of the liquid crystal.