Colour-changing sensor could enable cheaper HIV detection

Scientists have developed a way of testing for HIV with a colour-changing sensor they claim is 10 times cheaper than current similar technology.

The team from Imperial College London claims that the device, which detects molecules in the blood known as biomarkers that indicate the presence of conditions including HIV and cancer, could enable cheaper and simpler disease detection in poorer countries.

The sensor works in a similar way to other biomarker diagnostic technology, using antibodies to target and bind with specific biomarkers in blood serum, which produces a detectable reaction. In this case, a positive result turns the sample blue and a negative one turns it red.

Prof Molly Stevens, co-author of a paper on the sensor published today in the journal Nature Nanotechnology, said the new disposable test could be 10 times cheaper and much more sensitive than similar existing methods.

‘The main difference is that the difference between blue and red colour can be detected with the naked eye, therefore circumventing the utilization of sophisticated instruments for the detection,’ she told The Engineer via email.

The sensor can be reconfigured to test for different biomarkers but the researchers have demonstrated its use diagnosing HIV and prostate cancer.

It works using enzymes attached to the biomarker-seeking antibodies, said Stevens. These enzymes affect the production of nanoparticles in the sample, which then determine its colour.

‘When the antibodies recognize the molecule, the enzyme consumes the reactant hydrogen peroxide, which promotes the slow growth of irregular clumps of nanoparticles (blue colour).

‘In the absence of the target molecule there is no enzyme, and the abundant concentration of hydrogen peroxide favours the fast growth of spherical non-aggregated nanoparticles (red colour).’

She added that the biggest challenge had been working out how to cause the colour change by altering the concentration of peroxide within a very narrow concentration range. It took one year of “trial and error” experiments: trying different conditions until we narrowed down the optimal ones,’ she said.

The team reported in their paper that the sensor was so sensitive that it could detect minute levels of the HIV biomarker p24 in samples where patients had viral loads so low they could not be diagnosed using existing tests such as the enzyme-linked immunosorbent assay (ELISA) test and the gold-standard nucleic-acid-based test.

The study’s other co-author, Dr Roberto de la Rica, said in a statement: ‘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.

‘We also 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.’

The team now plans to approach non-profit global health organisations for direction and funding to commercialise the sensor and make it suitable for use by non-experts.

The research was funded by the EPSRC and by a European Research Council starting investigator grant.