Using DNA powder and gold nanoparticles, an innovative diagnostic method could enable rapid point-of-care diagnosis of the world's leading infectious diseases including STDs in the near future, replacing currently needed expensive and time consuming tests in labs. The new method is under development by scientists at the University of Toronto's Institute of Biomaterials and Biomedical Engineering, who successfully tested their method on several sexually transmitted diseases (STD) and malaria.

A fast working diagnostic biosensor that is set to allow technicians to test for multiple diseases at once with one tiny sample, and with high accuracy and sensitivity, was developed by BBME PhD student Kyryl Zagorovsky. The biosensor works with color changing gold nanoparticles, and was demonstrated to work by experimentally testing and rapidly detecting gonorrhea, syphilis, malaria, and hepatitis B infections.

Until now, scientists were able to target just one specific disease by linking gold particles with DNA strands: when certain disease genes like Malaria are present, it clumps the gold nanoparticles which colors the sample blue. But beside detecting only a single disease agent, this method also uses fluorescence as the readout, which is not an optimal detection method to use anywhere because it requires access to a fairly complex fluorometer, the researchers note.

So instead of clumping the particles together, Zagorovsky immerses the gold nanoparticles in a DNA-based enzyme solution (DNAzyme - a synthetic DNA enzyme that can catalyze the cleavage or "snip" of another nucleic acid molecule). When a disease gene is introduced, the DNA is snipped from the gold nanoarticles, which turns the sample visibly red.

Another significant advantage of the method is that far less of the gene needs to be present for the solution to show noticeable color changes, amplifying detection. A single DNAzyme can clip up to 600 "links" between the target genes.

This also opens up the multi-test capability, since a single drop from a biological sample such as saliva or blood can potentially be tested in parallel, so that the results for multiple diseases will show up at once. The team even succeeded in transforming the testing solution into a powder, making it light and far easier to ship than solutions, which degrade over time.

Because powder can be stored for years at a time, it suggests that the technology can be developed into efficient, cheap, over-the-counter tests for diseases such as HIV and malaria for both developing countries, where access to portable diagnostics is a necessity, but also as a means to lower both risk and cost anywhere in the world.


    Kyryl Zagorovsky and Warren C. W. Chan, A Plasmonic DNAzyme Strategy for Point-of-Care Genetic Detection of Infectious Pathogens, Angewandte Chemie, 2013, DOI: 10.1002/ange.201208715

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