More Sensitive, Quicker Test Developed

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April 17, 2006

More Sensitive, Quicker Test Developed for Cholera and Botulism

http://www.sciam.com/article.cfm?chanID=sa003 & articleID=0007542C-

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The current test for botulin--the potent neurotoxin responsible for

paralyzing botulism--involves injecting a mouse with a suspicious

sample and waiting to see if it dies. The test is crude, imprecise

and can take up to three days to deliver results. But after 72 hours

death may have already come for victims of the deadly toxin. Now

researchers have discovered an exquisitely sensitive test that kills

no animals and takes just three hours to complete.

Biophysicists Mason of the Armed Forces Institute of

Pathology, O'Leary of the Veterans Health Administration and

their colleagues paired specific antibodies for botulin and cholera

with the crime scene DNA-amplification technique known as polymerase

chain reaction, or PCR. By combining the two, the scientists can

detect trace amounts of the biological agents in urine samples,

water or other mediums. " We can actually detect down to 10 molecules

of biotoxin in a sample, " Mason notes. " We're always below 500

molecules. "

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But the test also improves on its predecessors by delivering fewer

false positives. Previous attempts to couple antibodies and PCR

often led to incorrect results due to DNA contamination from the lab

or instruments involved. So the scientists encased the antibody and

DNA in a liposome, a man-made fat cell capable of sheltering up to

60 copies of DNA fragments. Since the important DNA is protected,

the entire sample can be subjected to rigorous cleaning to remove

any DNA contamination, Mason notes.

The new test is quick and as much as 1,000 times more sensitive in

detecting cholera or botulin than any other assay, according to the

paper presenting the research in yesterday's Nature

Biotechnology. " The goal is to develop something small and portable--

a lab on a chip version, " Mason adds.

It also holds wider promise: if antibodies can be found for other

biological agents, like the poison ricin, the same technique could

be employed. And, by modifying the liposome, it could even

potentially be useful in early detection of disease. " The goal is to

use this to detect disease biomarkers in [the bloodstream],

particularly cancer, " Mason says. " We're able to check such low

levels that this would be a very powerful technique, because most

cancer markers are only present in very low concentrations. " --

Biello