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

Tests for diseases such as Covid-19 and HIV could soon be upgraded to include nanodiamonds that improve their sensitivity by up to 100,000 times.  

Besides the PCR swabs to spot Covid-19, hailed as the ‘gold standard’ for spotting coronavirus infection, other diagnostic methods are also being developed.

They work in the same way to pregnancy tests and identify infection in bodily fluids such as blood and urine. 

These so-called lateral flow assays use gold nanoparticles which absorb light and produce a red line to indicate a positive result. 

But by switching to carefully engineered tiny diamonds, a positive test result would glow thanks to a quirk of quantum mechanics.

In a lab study designed as a proof-of-concept, the nanodiamond method proved to be up to 100,000 times more sensitive than the gold technique currently used. 

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 diagnostics for diseases called lateral flow assays work in a similar way to pregnancy tests and require a liquid sample from a patient such as blood or urine.

These are currently used to quickly diagnose HIV and are in the early stages of a preliminary study to see if they spot SARS-CoV-2, the virus which causes Covid-19, infection. 

But current tests use gold nanoparticles which absorb light when they detect a tell-tale sign of infection and form a red line. 

This can be used to rapidly give a positive or negative result without the need for complex laboratory analysis. 

Diamonds however 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 fluoresce. This unique property is currently being investigated by several fields, including for biomarking and quantum computers. 

For disease tests, these light-emitting voids are used to glow brightly in a straight line when the diamond has bonded 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

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.’

The full findings are published in the journal Nature.  

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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