Illustration of several SARS-CoV-2 virus particles in blue on a red background
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A novel test that shapes pathogen nucleic acid into nanoballs could provide a cheap, sensitive way to detect such infections without the need for laboratory analysis, making it particularly useful for low-resource settings.

The self-assembling nanoballs pass through a simple electrical detection system, where they disrupt the current to identify the type and concentration of pathogen.

The “one-pot” system was able to identify coronavirus, HIV, and tuberculosis bacteria, report researchers led by Vicent Pelechano, PhD, from the Karolinska Institute in Sweden.

“It potentially provides a sensitive (10 copies), cheap, fast (<60 min), and scalable POC system to help address the growing pathogen detection challenges in the coming decades,” they maintain in the journal Science Advances.

The system uses a modified form of loop-mediated isothermal amplification (LAMP) technology, which detects pathogen DNA rather than immune system antibodies.

The LAMP reaction uses four to six oligonucleotides to target a region of interest together with a strand-displacing polymerase, making it a simple, low-cost alternative to standard polymerase chain reactions.

The current technology used modified LAMP combined with a reverse transcriptase (RT-LAMP), which has been widely used for pathogen detection including SARS-CoV-2.

By creating nanoballs out of pathogen nucleic acid that are detected through electrical impedance, the new system circumvents the need for a laboratory to support diagnosis, as is necessary with traditional LAMP techniques or most existing high-quality antibody-based tests.

The team modified RT-LAMP reactions to self-nucleate the amplified DNA into nanoballs, which could be detected through the inexpensive electrical detection system.

Capillary-driven flow passively passed these self-assembling nanoballs through a microfluidic impedance cytometer, creating a compact system with no moving parts.

The movement of the nanoballs past two detection electrodes in the simple microfluidic channel generated spikes in the impedance signal.

Applying the technology to the coronavirus behind the COVID-19 pandemic, the researchers showed that the number of spikes corresponded to the amount of genetic information amplified and therefore higher viral concentrations.

The team subsequently detected multiple DNA and RNA pathogenic sequences including HIV, influenza, and Mycobacterium tuberculosis from various viral and bacterial sources from as little as 10 original target copies.

The system was also able to detect the presence of the β-lactamase gene, which has been associated with antimicrobial resistance.

“In summary, we demonstrated a passive flow impedance–based detection of novel label-free DNA nanoballs targeting SARS-CoV-2 and later various pathogens of both viral and bacterial origin,” the researchers conclude.

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