Arriving at a rapid and accurate diagnosis is critical during flu outbreaks, but, until now, public health officials have had to choose between a highly accurate yet time-consuming test or a rapid but error-prone test.
‘We’ve known for a long time that you can use antibodies to capture viruses and that nanoparticles have different traits based on their size,’ said Ralph Tripp of University of Georgia, who led the team that developed the new technology. ‘What we’ve done is combine the two to create a diagnostic test that is rapid and highly sensitive.’
The team coated gold nanoparticles with antibodies that bind to specific strains of the flu virus and then measured how the particles scatter laser light.
The gold nanoparticle-antibody complex aggregates with any virus present in a sample and a commercially available device measures the intensity with which the solution scatters light. The clustering of the virus with the gold nanoparticles causes the scattered light to fluctuate in a predictable and measurable pattern.
‘The test is something that can be done literally at the point of care. You take your sample, put it in the instrument, hit a button and get your results,’ said Jeremy Driskell, another member of the Georgia team.
The current standard for definitively diagnosing flu is a test known as PCR, for polymerase chain reaction. PCR can only be done in highly specialised labs and requires that specially trained personnel incubate the sample for three days, extract the DNA and then amplify it many times. The entire process, from sample collection to result, takes about a week and is too costly for routine testing.
The alternative is a rapid test known as a lateral flow assay. The test is cost effective and can be used at the point of care, but it can’t identify the specific viral strain. It also misses up to 50 per cent of infections and is especially error-prone when small quantities of virus are present.
By overcoming the weaknesses of existing diagnostic tests, the researchers hope to enable more timely diagnoses that can help halt the spread of flu by accurately identifying infections and allowing physicians to begin treatment early, when anti-viral drugs, such as Tamiflu, are most effective.
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