A diagnostic "cocktail" containing a single drop
of blood, a dribble of water, and a dose of DNA powder with gold particles
could mean rapid diagnosis and treatment of the world's leading diseases in the
The cocktail diagnostic is a home-grown brew being developed
by University of Toronto's Institute of Biomaterials and Biomedical Engineering
(IBBME) PhD student Kyryl Zagorovsky and Professor Warren Chan that could
change the way infectious diseases, from HPV and HIV to malaria, are diagnosed.
And it involves the same technology used in over-the-counter
"There's been a lot of emphasis in developing simple
diagnostics," says IBBME Professor and Canada Research Chair in
Nanobiotechnology, Warren Chan. "The question is, how do you make it
simple and portable enough?"
Particles used are
The recent winner of the NSERC E.W.R. Steacie Memorial
Fellowship, Professor Chan and his lab study nanoparticles: in particular, the
use of gold particles in sizes so small that they are measured in the
nanoscale. Chan and his group are working on custom-designing nanoparticles to
target and illuminate cancer cells and tumours, with the potential of one day
being able to deliver drugs to cancer cells.
But it's a study recently published in Angewandte Chemie, a top chemistry journal published out of
Germany, that's raising some interesting questions about the future of this
relatively new frontier of science.
Zagorovsky's rapid diagnostic biosensor will allow
technicians to test for multiple diseases at one time with one small sample,
and with high accuracy and sensitivity. The biosensor relies upon gold
particles in much the same vein as your average pregnancy test. With a
pregnancy test, gold particles turn the test window red because the particles
are linked with an antigen that detects a certain hormone in the urine of a
"Gold is the best medium," explains Chan,
"because it's easy to see. It emits a very intense colour."
How the new process
Currently scientists can target the particular disease they
are searching for by linking gold particles with DNA strands: when a sample
containing the disease gene (ie. Malaria) is present, it clumps the gold
particles, turning the sample blue. Rather than clumping the particles
together, Zagorovsky immerses the gold particles in a DNA-based enzyme solution
(DNA-zyme) that, when the disease gene is introduced, 'snip' the DNA from the
gold particles, turning the sample red.
"It's like a pair of scissors," Zagorovsky
explains, "and the target gene activates the scissors that cut the DNA links
holding gold particles together."
The advantage is that far less of the gene needs to be
present for the solution to show noticeable colour changes, amplifying
detection. A single DNA-zyme can clip up to 600 "links" between the
Just a single drop from a biological sample such as saliva
or blood can potentially be tested in parallel, so that multiple diseases can
be tested for in one sitting.
But the team has also demonstrated that they are able to
transform the testing solution into a powder, making it light and far easier to
ship than solutions, which degrade over time. Powder can be stored for years at
a time, and offers hope that the technology can be developed into efficient,
cheap, over-the-counter tests for diseases such as HIV and malaria for
developing countries, where access to portable diagnostics is a necessity.
"We've now put all the pieces together," says