The National Institutes of Health (NIH) recently announced that they have developed a platform capable of detecting small amounts of nucleic acid (DNA and RNA) sequences, something that can be incredibly beneficial in the health sector—especially when it comes to detecting viral or bacterial infections within a population during infectious disease outbreaks. The best part? It’s quick and
it’s cheap. Its name? SHERLOCK
James J. Collins, PhD, and Feng Zhang, PhD, from the Broad Institute of MIT and Harvard developed the approach, basing it off of the CRISPR
system, which is used by bacteria “to defend themselves from other microbes, according to a press release
. The project is funded by the NIH’s National Institute of Allergy and Infectious Diseases as well as the National Institute of Mental Health.
CRISPR enzymes can identify “specific target sequences” to slice, through the help of “guide RNAs.” In past research, Dr. Zhang’s team found that Cas13a, a CRISPR enzyme, had “an interesting collateral effect,” meaning that once its activated by its target RNA sequence, it “goes on to indiscriminately slice other non-targeted RNA nearby.”
It was this collateral effect that was used to design the nucleic acid detection platform, dubbed SHERLOCK (Specific High Sensitivity Enzymatic Reporter UnLOCKing). For their approach, the researchers added “reporter RNA,” designed to release a signal when sliced, to detect if a target sequence was present. Whenever Cas13a was activated, it would go on to cut the reporter RNA and emit a signal,” according to the press release.
In their study
, published on April 13, 2017 in the journal Science
, the scientists looked at Cas13a enzymes from several types of bacteria to gauge which ones “had the best RNA-guided cutting activity.” Using recombinase polymerase amplification, the scientists were able to “amplify” nucleic acids—this is especially important since the amount of DNA and RNA within samples is usually quite small. “Another enzyme could also be added to the reaction to convert DNA to RNA for Cas13a detection,” the NIH reports.
Further testing found that SHERLOCK was capable of detecting RNA or DNA molecules at attomolar, or tiny, levels. Some approaches that are more established for detecting nucleic acid are sensitive enough to detect RNA or DNA at minute levels, however, “SHERLOCK gave more consistent results.”
So, what can SHERLOCK potentially be used for? According to the press release, it is capable of a number of things:
- Detecting specific strains of Zika virus or Dengue virus
- Detecting Zika virus in semen, urine, and saliva of patients
- Distinguishing pathogenic strains of bacteria
- Distinguishing single base differences in DNA extracted from human saliva
- Detecting cancer mutations in DNA fragments at levels like that found in patient blood
The researchers also found that the components could be freeze-dried and reconstituted on glass fiber paper. In fact, the scientists estimated that within only a few days, and for as little as $0.61 per test, paper diagnostic tests could be designed and developed. The fact that it is consistent, quick, and cost-effective underscores its potential to be used within the diagnostic field.
“We can now effectively and readily make sensors for any nucleic acid, which is incredibly powerful when you think of diagnostics and research applications,” Dr. Collins concluded. “The scientific possibilities get very exciting very quickly.”
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