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Mass spectrometry, long used to analyse what a stuff is made up of, is emerging as a major diagnostics too; there is a pretty good case for using it to detect Covid-19.
At the Indian Institute of Science, Bengaluru, scientists recently used mass spectrometry (MS) for the proteomic analysis — identification and quantification of the full set of proteins, or proteome, in a biological system such as a cell, tissue or organ — of the SARS-CoV-2 virus.
The use of MS for proteomic analysis is not uncommon. Proteins are more reliable markers of infections; they are more abundant and stable as compared with RNA molecules, which the prevalent RT-PCR tests rely on, says Dr Utpal Tatu of the Department of Biotechnology, the lead scientist in the research.
What is mass spectrometry? Unlike techniques such as Raman Spectroscopy, which throws a beam of light at the analyte sample and divines what it is made of from the light that bounces off the molecules, MS uses the mass of the atomic particles to study the sample. Simply, the analyte is first vaporised, transferred to a chamber and bombarded with high-speed electrons. The electrons knock off the electrons in the sample; having lost the negatively charged electrons, the atoms of the sample become positively charged cations. The cations are pushed (accelerated) through a tube kept in an electrical field; their path gets deflected by the electrical field and the extent of the deflection depends on the mass of the particle — hence mass spectroscopy. A detector measures the deflection, which gives an idea of the mass of the particle, and hence the composition of the sample.
Tatu told Quantum that MS has several advantages over the RT-PCR method. First, the results arrive much faster. Tatu envisions airports having this equipment — a nasal swab is taken when you join the security check queue; the results are out by the time you complete the security check. Moreover, while RT-PCR looks at the RNA of the virus, MS takes a peek at its proteins and can, therefore, detect variants right away. In the case of an RT-PCR test, to detect the variant you would need to send the sample to another lab for genome sequencing. Also, because MS looks for peptides (short chains of proteins), it is more accurate than RT-PCR — no false positives or false negatives.
Yet, India and the rest of the world still choose RT-PCR over MS because the former is well established, while MS is still emerging as a diagnostic tool. Laboratories were more equipped and trained for the RT-PCR test. However, MS has tremendous potential, says Tatu. He sees it evolving as the primary diagnostic tool for all diseases in the future.
Gaining ground
A number of scientific publications have, in the last few months, highlighted the application of MS in diagnostics. It’s efficacy for testing Covid-19 is now well established.
In December, a group of scientists from Sao Paulo, Brazil, put out a paper in Nature titled ‘Establishing a mass spectrometry-based system for rapid detection of SARS-CoV-2 in large clinical sample cohorts’. The paper noted that, when applied to several hundred clinical samples, the MS assay detects up to 84 per cent of the SARS-CoV-2 positive cases (already) identified by an in-house real-time PCR method, “demonstrating the utility of this MS-based approach for high-volume SARS-CoV-2 testing”.
Opportunity for industry
If MS’s effectiveness is well established, how amenable is it for large-scale adoption? Tatu, for one, feels that with the government’s support, it needn’t take more than a year — in fact, it can be much quicker. He sees no hardware challenge. MS is therefore an opportunity for the industry. Enough expertise exists in India to produce mass spectrometers.
Today, MS is more expensive than other diagnostic tools, but that is only because the market is small; they would become pretty affordable when scaled up.
“The best thing we can hope to see in this century is the use of MS as a basic technique for diagnostics,” says Sheetal Tushir, a researcher who works with Tatu.
M Ramesh
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