Test Strips For The Rapid Detection Of Cocaine
"Our method is based on tiny gold spheres and aptamers," reports Lu. Aptamers are single-stranded nucleic acid molecules that bind to certain target molecules with the same strength and specificity as antibodies. From a large number of DNA strands with random sequences (a library), it is basically possible to find a suitable aptamer for almost every target molecule. Says Lu: "The broad practical application of aptamers has thus far not realized its promise in practical diagnostics because the corresponding tests could not be made sufficiently user-friendly for the average user, who has not had laboratory training."
The new test strips for cocaine are different. When the end of the strip is dipped into a sample, the liquid travels along the strip to reach a zone with small gold-aptamer clumps. The trick lies in the special structure of these clumps: they are aggregates of nanoscopic gold spheres coupled to short DNA strands, some containing the biomolecule biotin. The DNA sequences are complementary to two regions of the cocaine-specific DNA aptamer. The aptamers bind to these strands, linking the gold spheres into larger aggregates. When the cocaine-containing liquid reaches these aggregates, the cocaine molecule instantly binds to the aptamers and removes them from the network; the aggregates fall apart into individual gold spheres. These free spheres are red. When the liquid travels further along the strip, it reaches a membrane. While the larger gold aggregates are stopped by the membrane, the red gold spheres are small enough to pass through it. They end up stuck to a narrow strip of streptavidin, a biomolecule that grabs onto the biotin on the gold surface like a hook onto an eye. The gold spheres get concentrated on the narrow strip and become visible as a distinct red stripe on the test strip.
"Our method is universal," stresses Lu. "Based on this principle, we should be able to develop rapid tests for the emergency diagnosis of a large number of drugs and poisons, as well as physiological molecules. The same method is also applicable to environmental monitoring."
Contact: Yi Lu
John Wiley & Sons, Inc.
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