Analytical Instrumentation : Biodefense


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.

Robust Biological and Chemical Detection Method and Microfluidic Device with Liquid Crystal Sensing Element

UW-Madison researchers have now developed an improved method for autonomously generating stabilized liquid crystal thin films and two microfluidic devices that employ the technique for detecting trace amounts of biological agents and chemical compounds.  The handheld microfluidic devices each contain a microchannel defined by grooved polymer materials sandwiched between glass substrates.  Priming the device involves filling the microchannel with liquid crystal material, which fills specific nickel-plated structures in the channel, and flushing the liquid crystals outside the container with the laminar flow of an aqueous solution.  This method allows for automatic formation and rapid regeneration of the stable aqueous/liquid crystal interface. 

In the presence of a target compound the orientation of the liquid crystals changes, altering optical properties of the liquid crystals through a phenomenon known as optical birefringence.  After the analyte has been introduced into the channel, a white light is passed through a first polarizing lens, the microfluidic device, and a second orthogonally oriented polarized lens.  The intensity of the light, determined by the degree of optical birefringence, is detected by a microscope to confirm the presence or absence of the specific target in the aqueous solution.

The microfluidic biological and chemical detection device with a liquid crystal sensing element allows for automatic formation of the sensing interface through its design and operation.  The device design also provides better control of the interaction between the aqueous target containing solution and liquid crystal region.  By providing a robust device and method, as well as reducing the need for advanced technical training, the improved detection apparatus will greatly enhance in-field applicability of biological and chemical sensor technologies.

Detecting and Determining the Concentration of a Target Bioagent

UW-Madison researchers have now developed an improved sensor that requires only one membrane to determine target concentration. The membrane is fabricated from a polymeric material that dissolves when exposed to a particular biological agent. To detect the agent, the membrane is contacted with a sample of fluid. If the target bioagent is present in the fluid, the membrane dissolves at a speed dependent on the concentration of the agent. A beam of light with a specific wavelength is passed through the membrane to determine the degree of dissolution, and a detector generates an output voltage in response to the intensity of light transmitted. The change in voltage can be monitored to determine the concentration of the target agent.

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.

Bioagent Detection Device

UW-Madison researchers have developed an inexpensive, real-time wireless microsensor for detecting biological agents in water supply networks and other aqueous environments such as the milk supply. This system includes a microdevice composed of a sampling chamber and a capacitor chamber connected by a channel. A biosensitive membrane blocks the channel between the two chambers.

To detect a biological agent, a sample of fluid is introduced into the sampling chamber and contacts the membrane. If a target bioagent is present in the fluid, it causes the membrane to become permeable or even to dissolve. When this occurs, fluid flows from the sampling chamber into the capacitor chamber, creating a very large change in impedance and an extremely large electrical output signal. The output signal is then wirelessly transmitted to a device that alerts the user to the presence of the target bioagent.

Method and Compositions for Detecting Botulinum Neurotoxin

UW-Madison researchers have developed a fluorescence resonance energy transfer (FRET) method for the sensitive detection of botulinum neurotoxin. The assay uses two fluorescent proteins, such as cyan fluorescent protein (CFP) and yellow fluorescent protein (YFP), which are linked together by a molecule that can be recognized and cleaved by botulinum neurotoxin. The emission spectrum of CFP partially overlaps with that of YFP. As a result, when CFP and YFP are very close together, excitation of CFP results in FRET-YFP emission and partial quenching of CFP emission. When botulinum neurotoxin cleaves the linker molecule separating these two fluorescent proteins, FRET is eliminated, i.e., excitation of CFP no longer results in YFP emission and partial quenching of CFP emission.

To detect botulinum neurotoxin, a sample is exposed to the CFP and YFP construct. The FRET signals are measured and compared before and after exposure, with a decrease in FRET after exposure indicating the toxin’s presence. This method is useful for detecting botulinum toxin both in vitro and in living cells.