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Cheap, Ultra-Sensitive Colour Test Spots Early HIV, Cancer

Researchers in the UK have developed a "naked eye" colour test for virus and disease biomarkers that is ten times more sensitive than current gold standard methods. They have tested it on HIV and prostate cancer biomarkers, and suggest it offers a cheap and simple way of spotting early onset of these and other diseases that could be of particular benefit in poorer countries.

In a paper published online in Nature Nanotechnology on 28 October, Roberto de la Rica and Molly Stevens, from Imperial College London, write how their prototype visual sensor technology detected an HIV biomarker called p24 in blood samples.

Stevens, a professor with Imperial's departments of Materials and Bioengineering, explains in a statement how important it is to keep testing patients on HIV treatment to assess the effectiveness of retroviral therapies and check for new infections, but:

"Unfortunately, the existing gold standard detection methods can be too expensive to be implemented in parts of the world where resources are scarce."

"Our approach affords for improved sensitivity, does not require sophisticated instrumentation and it is ten times cheaper, which could allow more tests to be performed for better screening of many diseases," she adds. Prostate Cancer, Other Diseases De la Rica and Stevens also report how they tested their method's ability to detect low levels of Prostate Specific Antigen (PSA), which can be an early indicator for prostate cancer.

They say the test can be reconfigured to detect known biomarkers of other viruses and diseases.

"We have developed a test that we hope will enable previously undetectable HIV infections and indicators of cancer to be picked up, which would mean people could be treated sooner," says de la Rica, from the Department of Materials at Imperial. Blue and Red Reactions Visible to Naked Eye The biosensor is so sensitive, it allows detection of a few molecules. It analyzes serum, derived from blood, in a disposable, see-through container.

If the result is positive for p24 or PSA, the solution inside the container turns blue, if it is negative, it turns red.

It works because of reactions with gold nanoparticles:

"The enzyme label of an enzyme-linked immunosorbent assay (ELISA) controls the growth of gold nanoparticles and generates coloured solutions with distinct tonality when the analyte is present," write the authors.

If the analyte (eg p24 or PSA) is present, the reaction generates irregular clumps of nanoparticles, and these give off a distinct blue hue in the solution inside the container.

If the analyte is absent, the nanoparticles separate into ball-like shapes, which give off a reddish hue. In both cases the reactions can be seen with the naked eye. Detecting Ultra-Low Levels of Biomarker In their paper, the authors describe how their test picked up minute levels of p24 and PSA. And in the case of HIV-infected patients with low viral loads, the prototype test detected p24 at levels undetectable by the current gold standard test:

"Prostate specific antigen (PSA) and HIV-1 capsid antigen p24 were detected in whole serum at the ultralow concentration of [1 x 10 to the minus 18 g per ml]. p24 was also detected with the naked eye in the sera of HIV-infected patients showing viral loads undetectable by a gold standard nucleic acid-based test," they write. Next Step The team now plans to approach not-for-profit global health organizations for funding and direction to move the test from the lab into manufacturing and distribution, especially in low income countries.

De la Rica says they "believe that this test could be significantly cheaper to administer, which could pave the way for more widespread use of HIV testing in poorer parts of the world".

Funds from the Engineering and Physical Sciences Research Council (EPSRC), the European Research Council (ERC), and a Marie Curie Intra European Fellowship within the 7th European Community Framework Programme, helped finance the study.

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