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DNA ‘Cocktail’ Could Change Way Infectious Diseases Are Diagnosed

Single drop of blood or saliva can be tested for multiple diseases (Feb. 28)

According to researchers at the University of Toronto, a diagnostic “cocktail” containing a single drop of blood, a dribble of water, and a dose of DNA powder with gold particles could one day mean rapid diagnosis and treatment of the world's leading diseases — from human papillomavirus (HPV) and human immunodeficiency virus (HIV) infections to malaria. The new “cocktail” involves the same technology used in over-the-counter pregnancy tests.

Professor Warren Chan and his colleagues have developed a rapid-diagnostic biosensor that will allow technicians to test for multiple diseases at one time with one small sample, with a high degree of accuracy and sensitivity. The biosensor relies on gold particles in much the same way as a standard pregnancy test. In pregnancy tests, 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 pregnant woman.

Currently, scientists can target a particular disease by linking gold particles with DNA strands. When a sample containing a disease gene — such as the gene for malaria — is present, it clumps the gold particles, turning the sample blue.

Rather than clumping the particles together, Chan and his colleagues immerse the gold particles in a DNA-based enzyme solution that, when the disease gene is introduced, “snip” the DNA from the gold particles, turning the sample red.

The advantage of this process is that far less of the gene needs to be present for the solution to show noticeable color changes, amplifying detection. A single DNA-based enzyme can clip up to 600 “links” between target genes.

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 in one sitting, the researchers say.

The team has also transformed the testing solution into a powder, making it easier to ship than solutions, which degrade over time. The powder can be stored for years 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,” Chan said.

Source: University of Toronto; February 28, 2013.

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