Archives
Scientists design simple dipstick test for cocaine, other drugs
James E. Kloeppel, Physical Sciences Editor
217-244-1073; kloeppel@uiuc.edu
11/13/2006
|
CHAMPAIGN, Ill.
— Researchers at the University of Illinois at Urbana-Champaign
have developed a simple “dipstick” test for detecting
cocaine and other drugs in saliva, urine or blood serum. The test
is based upon DNA-gold nanoparticle technology, and can be packaged
in user-friendly kits similar to those used for home pregnancy
tests.
“Building upon our earlier work with lead (Pb) sensors, we constructed
colorimetric sensors that are based on the lateral flow separation
of aptamer-linked nanostructures,” said Yi Lu, a chemistry professor
at the U. of I., and a researcher at the Beckman
Institute for Advanced Science and Technology.
“The new sensors offer a quick and convenient test that can
be utilized by first responders or emergency room staff to quickly
screen individuals for a variety of drugs and other chemicals.”
Lu said.
Aptamers are single-stranded nucleic acids that can bind to specific
molecules in three-dimensions. For each molecular target, such as
cocaine, a corresponding aptamer can be selected from a large DNA
library.
By using lateral flow devices as platforms to separate aptamer-linked
nanoparticle aggregates, Lu, postdoctoral researcher Juewen Liu and
graduate student Debapriya Mazumdar created highly sensitive and selective
colorimetric sensors that mimic litmus paper tests. The researchers
describe their work in a paper accepted for publication in the journal
Angewandte Chemie International Edition, and posted on its Web site.
“Our lateral flow devices take advantage of the difference in
size between dispersed and aggregated gold nanostructures,”
Lu said. “This provides critical control for the performance
of the devices.”
The lateral flow device consists of four overlapping pads –
wicking, conjugation, membrane and absorption. The appropriate aptamer-linked
nanoparticle aggregates are placed on the conjugation pad, streptavidin
is applied as a thin line to the membrane pad, and the device is then
dried.
When dipped into a solution, or swabbed with a sample, the wicking
pad carries the fluid to the nanoparticle aggregates on the conjugation
pad. The rehydrated aggregates then migrate to the edge of the membrane,
which they cannot penetrate because of their large size.
The aptamers quickly bind to any targeted molecules that are present,
freeing some of the gold nanoparticles. The red-colored nanoparticles
then migrate along the membrane, where they are captured by the streptavidin
and form a red line. The intensity of the line is an indicator of
how much of the targeted molecule was in the sample solution.
So far, the researchers have successfully demonstrated their dipstick
technology on both adenosine (a nucleotide consisting of adenine and
ribose) and cocaine, in human blood serum.
“Our results show that the aptamer-based dipstick is compatible
with biological samples, making applications in medicinal diagnostics
possible,” Lu said.
The work was funded by the U. S. Department of Energy, the National
Science Foundation, and the U.S. Army Research Laboratory.
Editor’s note: To reach Yi Lu, call 217-333-2619;
e-mail: yi-lu@uiuc.edu
