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Piezoelectric crystals enhance detection of biologicals.

Piezoelectric quartz crystal microbalance (QCM) systems are becoming an increasingly accepted tool for researchers seeking a fast, direct and relatively inexpensive method for real-time measurement of biomolecular reactions.

QCMs have been used to detect pollutants from wastewater effluents in mine tailings, as well as to detect pesticides, notably organophosphorus-based products.

They can also detect antibodies, explosives, and chemicals or other biologicals used in warfare and can assay for volatiles in air, such as benzene or toluene.

Selling points Some advantages of PZ crystals are that they:

* Work in air or solution--in the field or in the lab

* Provide noninvasive measurement of molecular interactions

* Offer fast, direct measurement at concentrations as low as [10.sup.-10] M

* Require no labeling, elaborate sample preparation, or specimen purification

* Can be reused several times

* Yield reproducible results, with a coefficient of variation of [is less than] 5%

* Permit the study of immunochemical reactions with affinities of 104 to [10.sup.10] [M.sup.-1]

New techniques Universal Sensors Inc., of Metairie, La., is finding new ways to use biological polymers as adhesives on the PZ transducers.

The company, founded in 1981 by Univ. of New Orleans chemistry professor George Guilbault, has been using Protein A, polysaccharides, and latex on the transducer surfaces. These include mussel-adhesive protein (MAP), glucosamine polymer (GAP), and carboxy-modified latex (CML).

The advantage of CML over the polysaccharides is that the analyte can be removed, or "chaotroped," fairly easily without harming the capture antibody. The crystal can then be reused.

With passive adsorption, says Robert Carter, the company's immunology and microbiology director, "antibodies are randomly scattered every which way, like trees knocked down in a windstorm."

This can retard or block some of the antibody binding sites from being able to contact the antigen.

But MAP, GAP, and CML create a more favorable orientation toward the analyte, he says, "as if the trees are standing up and better spaced, so that analyte can bind more readily."

Carter says his group has also reversed the technique: "We put antigen on the surface of the PZ transducer and assay for antibody in solution, in real time."

New developments In recent months, Carter has been using polyacrylonitrile as a substitute for antibody attachment. PAN, as the polymer is known, differs from the adhesives in that it can be spun onto the surface of the crystals (a technique developed by Cliff Renschler at Sandia National Labs, Albuquerque, N.M.)

When spun in a humid atmosphere, PAN forms a foam-cell matrix with a large surface area that allows for direct covalent attachment of antibodies.

This results in greater amounts of capture antibody per crystal, which lowers the minimum detection level.

RELATED ARTICLE: How PZ Biosensors Work

In piezoimmunosensors, quartz crystals are coated with antibodies, specific for the antigen to be assayed. Upon interaction with the antigen, the crystal undergoes a frequency change, whose magnitude indicates the concentration of the antigen by a frequency-to-mass ratio.

Due to the high specificity of the interaction, little frequency change is observed unless the antigen-antibody immunocomplex is formed.

No labeling reagents are needed, and little if any sample preparation or pretreatment is required. Signal generation is usually not affected by a dirty matrix. The crystal can be chaotroped--in effect, cleaned--and reused several times.

Contact: Universal Sensors Inc., phone or fax: 504-885-8443.

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Author:Cassidy, Robert
Publication:R & D
Date:Jan 1, 1995
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