United Kingdom

Blood tests for Covid-19 could be made 'up to 100,000 times more sensitive' by using nanodiamonds

Pregnancy-style tests for diseases such as Covid-19 and HIV could soon be upgraded with embedded 'nanodiamonds' that improve their sensitivity up to 100,000 times. 

While PCR swabs are currently the most common way to test for coronavirus infection, other diagnostic methods are also being developed.

These include 'lateral flow' tests that work in the same way as pregnancy tests, in that they can detect the virus proteins in bodily fluids, such as blood or urine. 

Traditionally, lateral flow tests use gold nanoparticles, which absorb light and produce a red line to indicate a positive result. 

However, the researchers claim that replacing gold with diamond nanoparticles would result in this line emitting a bright fluorescent light, which is easier to detect, making the test up to 100,000 times more sensitive.   

UCL researchers working on the project say this method, which is still in its early stages, could allow for earlier diagnosis and rapid treatment.  

This artist's impression reveals how the nanodiamonds glow when they come into contact with a predetermined compound, which could be the antigens of a virus

Paper-based lateral flow tests using gold nanoparticles are already in use as a method of quickly diagnosing HIV, and are in the early stages of a preliminary study to see if they can spot SARS-CoV-2, the virus which causes Covid-19 infection.  

It is hoped that these will be able to to rapidly provide a positive or negative result without the need for complex laboratory analysis. 

However, diamonds can be engineered to have a very slight and precise defect in their rigid structure. 

This deliberate 'mistake' creates a so-called nitrogen-vacancy centre, which allows the diamond particle to glow. This unique property is currently being investigated by several fields, including for biomarking and quantum computers. 

In disease tests, these light-emitting voids glow brightly in a straight line when the diamond bonds to a target molecule — for example the viral antigen. 

This glowing is far brighter than the line made by gold-imbued tests, but it has another advantage; the nanodiamond's quantum glow can also be easily distinguished from background fluorescence. 

This filters out noise and amplifies the diamond's signal, making the tests up to 100,000 times more sensitive than current methods in early tests, researchers say.  

UCL scientists found a positive result can be given by the diamonds from just a single molecule of HIV genetic material after ten minutes amplification.  

Pictured, a graphic showing how the lateral flow assays with nanodiamonds work. They are fixed in a paper strip and designed to bind to markers of disease. If they do, they fluoresce and this indicates a positive test result 

Lead author Professor Rachel McKendry at UCL said: 'We have focused on the detection of HIV, but our approach is very flexible and can be easily adapted to other diseases and biomarker types. 

'We are already working on adapting our approach to Covid-19. We believe that this transformative new technology could benefit patients and protect populations from infectious diseases through much earlier disease diagnosis.'

The current methods are right at the forefront of scientific innovation, but the researchers hope to miniaturise the tech so it can be made easily accessible. 

They are now focusing on allowing the glowing diamond tests to be read with a smartphone or portable fluorescence reader.

First author Dr Ben Miller at UCL said: 'Paper-based lateral flow tests with gold nanoparticles do not require laboratory analysis, making them particularly useful in low resource settings and where access to healthcare is limited. 

'They are low cost, portable, and user friendly. However, these tests currently lack the sensitivity to detect very low levels of biomarkers.

'By replacing commonly used gold nanoparticles with fluorescent nanodiamonds in this new design, and selectively modulating their (already bright) emission of light, we have been able to separate their signal from the unwanted background fluorescence of the test strip, dramatically improving sensitivity.'

Coronavirus remains infectious on surfaces for DAYS by transforming into a pancake-like film 

Particles containing the coronavirus that land on a surface remain infectious for several days by transforming into a microscopic, pancake-like film after the water in the droplet has evaporated.

This conversion sees more than 99.9 per cent of the droplet's liquid vanish in the space of minutes, but the virus survives in a protective film of the remaining fluid.  

Tiny forces keep the film, which is just nanometres thick, clinging to a surface and slows down the evaporation process.  

The film fully evaporates at different times, depending on the material it has landed on, with a large droplet on stainless steel and copper lasting just 24 and 16 hours, respectively. 

But it can survive for more than 150 hours on polypropylene. A smaller droplet, just one-tenth of the size, lasts for more than 80 hours on glass.

These figures based on experiments conducted in lab conditions, and are likely lower in the real world where there are variable amounts of heat and air flow — factors which boost evaporation. 

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