Safe and accurate diagnostic testing for COVID-19 at a population scale has been deemed crucial to breaking the chain of infections. Whilst it was hoped by many that antibody tests would provide the answer, it seems the challenges associated with developing and validating point-of-care testing kits may have been underestimated.
The fourth article in our COVID-19 series relates to diagnostic testing for the SARS-CoV-2 virus and its characterisation, which may aid our understanding of its mechanism of action in the future.
The gold standard technique for sensitive and specific COVID-19 diagnosis remains quantitative reverse transcription PCR (RT-PCR) - adapted to detect the SARS-CoV-2 virus. However, RT-PCR is not applicable for the large-scale processing that would be required to achieve population-scale testing.
One potential high-throughput testing method is the barcoded Reverse-Transcription Loop-mediated Isothermal Amplification (RT-LAMP) protocol, which has been proposed by the Broad Institute of MIT and Harvard. This method involves tagging individual samples with a unique DNA sequence allowing thousands of ‘barcoded’ samples to be analysed en masse.
In theory, if clinically validated, this technique could prove a practical tool to enable rapid and sensitive detection of individuals infected with SARS-CoV-2, with population-scale testing becoming an attainable goal using existing sequencing facilities and instruments.
As noted above, serological tests to determine whether a subject has been infected with SARS-CoV-2 are considered to be of great importance to aid a gradual return to normality. So-called “immunity passports” have been mooted to enable those who have been infected with the virus and recovered to no longer be restricted in their movement and to be able to return to work in certain circumstances.
The “holy grail” of serological test would be a home-administered device e.g. based on a lateral flow assay (LFA) system which identifies anti-SARS-CoV-2 antibodies present in a subject’s blood. So far, the existing LFA devices have not exhibited sufficient accuracy to enable them to be used with confidence. However, Roche is currently applying for emergency use authorisation from the FDA with a view to market a serological test from early May. There are currently a handful of serological tests which have FDA authorisation, each of which require a sample to be tested in a laboratory setting even if the sample is taken in a home environment.
Understandably, much of the current scientific research in respect of SARS-CoV-2 relates to testing for COVID-19 and for researching potential treatments and vaccines to the disease. In future however, it is likely that more peripheral avenues of research into the virus will gain traction. Particularly, it is envisaged that the utilisation of biophysical techniques such as atomic force microscopy (AFM) and force spectroscopy (FS) may aid in the characterisation of, and long-term response effort against, the virus.
AFM and FS make use of the atomic force microscope to build up an image, or assess particular properties of, a surface by contacting the surface with a probe, of radius typically in the order of tens of nanometres, and assessing how a laser, incident on the probe, deviates as the probe deflects due to certain properties of the surface. Such techniques allow for ultra-high-resolution imaging of a surface, going way beyond the diffraction limited technique of conventional optical microscopy, and for the precise determination of interactive forces between the probe and the surface. By employing biologically active surfaces and coatings for the probe, one can extract detailed information relating to properties of biological matter including unbinding forces and, length scales and elasticity.
AFM and FS research has previously been conducted in relation to a wide variety of viruses, including SARS coronavirus. Such studies have determined, for example, the structure of SARS and the physical effect of infection at a cellular level. Furthermore, these techniques have previously been utilised to identify the isoelectric point of individual virus molecules. Such research, if applied to SARS-CoV-2, may aid in the development of potential therapies and vaccines to COVID-19.
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