The device – Minimally Instrumented SHERLOCK (miSHERLOCK) renders precise results that can be verified simply with a smartphone app in one hour. It is assembled using a 3D printer and commonly available components for about $15.

Re-using this hardware cuts down the cost of individual assays further to $6. The test provides substantial differences between three different variants of coronavirus. It can also be reconfigured to identify additional strains like Delta variants.

miSHERLOCK – Diagnostic Tool for COVID-19

The pandemic led to a shortage of simple things that earlier used to be ubiquitous in the hospital. One of these includes nasopharyngeal swabs that suddenly became hard to be obtained.

The study team thereby strived to design a diagnostic tool that may overcome the shortcomings of the global supply chains as well as provide accurate detection of the emerging COVID-19 variants.

“miSHERLOCK eliminates the need to transport patient samples to a centralized testing location and greatly simplifies the sample preparation steps, giving patients and doctors a faster, more accurate picture of individual and community health, which is critical during an evolving pandemic,” says co-first author Helena de Puig, Ph.D., a Postdoctoral Fellow at the Wyss Institute and MIT.

The Minimally Instrumented (mi) SHERLOCK (specific high sensitivity enzymatic reporter unlocking) utilizes CRISPR’s “molecular scissors” to slice DNA or RNA at a specific target and its surrounding locations. A fluorescent signal is produced to symbolize the successful cut, nucleoprotein (specific region of a gene) in the case of SARS-CoV-2 RNA.

Diagnostic Challenge

With the advent of this economic and reliable diagnostic for coronavirus, the team now concentrates on resolving sample preparation – the most complex challenge in diagnostics.

Sample preparation requires mandatory steps to preserve and prepare all the samples in a non-infectious way to further extract and amplify the nucleic acids (RNA or DNA) of the virus.

The tool thereby had to be simplified to a greater extent as possible. This allowed the researchers to use saliva rather than nasopharyngeal swab samples, as the former is detectable for a greater number of days post-infection.

However enzymatic degradation of the untreated saliva sample is one of the greatest loopholes to produce a high rate of false positives. This was overcome by adding two specific chemicals – DTT and EGTA to saliva and then heating it to 95°C for 3 minutes.

The sample preparation and the SHERLOCK reaction were blended into one diagnostic using a simple battery-powered device. This consisted of two chambers – a heated sample prep chamber, and an unheated reaction chamber.

How to Use the miSHERLOCK?

• The user has to first spit into the sample prep chamber.
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  Then the heat is turned on.
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  The user has to wait for the next 3-6 minutes for the saliva to be wicked into the filter.
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  Following this, the filter is then removed and transferred into the reaction chamber column.
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  Then the plunger is pushed to deposit the filter into the chamber and puncture a water reservoir to activate the SHERLOCK reaction.
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  After 55 minutes, the user has to look through the tinted transilluminator window (into the reaction chamber) to confirm the presence of a fluorescent signal.
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  One can also use an accompanying smartphone app to confirm the presence of the signal.
• The app analyzes the pixels being registered by the smartphone’s camera to provide a clear positive or negative diagnosis.

Proof for Efficacy of the Tool

The study team validated their results from 27 COVID-19 patients and 21 healthy patients using saliva samples.

It was found that miSHERLOCK correctly identified the COVID-19-positive patients 96% of the time. Among the healthy patients, the prediction was correct 95% of the time. The performance of the test was also proven effective against the Alpha, Beta, and Gamma variants of SARS-CoV-2.

“One of the great things about miSHERLOCK is that it’s entirely modular. The device itself is separate from the assays, so you can plug in different assays for the specific sequence of RNA or DNA you’re trying to detect. The device costs about $15, but mass production would bring the housing down to about $3. Assays for new targets can be created in about two weeks, enabling the rapid development of tests for new variants of COVID-19 and other diseases,”says co-first author Devora Najjar, a Research Assistant at MIT Media Lab and in the Collins Lab.

Set for the Launch

The miSHERLOCK device was created with an aim to utilize low-resource settings as the pandemic contributed to the vast inequalities in healthcare across the world. The files and circuitry designs of the device are made publicly available online. Thus, with access to a 3D printer, one can easily assemble this device for diagnosis.

The study team is now anticipating collaboration with various industrial partners to make the miSHERLOCK commercially available for global distribution. This combination of cutting-edge biotechnology with low-cost materials has contributed a powerful diagnostic device amidst this pandemic for mass benefit.

Tips to Slow the Spread of COVID-19

• 
  With an alarming warning against the third wave of coronavirus, safety practices have to be still incorporated to evade the severity of COVID-19 infection.
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  This includes wearing a mask, cleaning your hands, and coughing into a bent elbow or tissue along with physical distancing (6 feet about 2 arm’s length)
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  Avoid the crowd and poorly ventilated spaces.
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  Eat healthily and maintain your immune system.
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  Even after getting vaccinated, follow the COVID-appropriate safety measures
• Seek medical advice at the earliest if any symptoms are suspected of COVID-19.

References:

1. Minimally instrumented SHERLOCK (miSHERLOCK) for CRISPR-based point-of-care diagnosis of SARS-CoV-2 and emerging variants
   – (https://advances.sciencemag.org/content/7/32/eabh2944)
2. A test that detects COVID-19 variants in your spit
   – (https://wyss.harvard.edu/news/a-test-that-detects-covid-19-variants-in-your-spit/)
3. Coronavirus disease (COVID-19) advice for the public
   – (https://www.who.int/emergencies/diseases/novel-coronavirus-2019/advice-for-public)
4. How to Protect Yourself & Others
   – (https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/prevention.html)

Source: Medindia