How a rapid field testing device could help head off future epidemics
Mechanical engineer Juan
Santiago is an expert in microfluidics — compact chemistry labs
that are increasingly being used to test various liquids for toxins, pollution,
parasites, microbes and more.
Santiago and graduate student
Ashwin Ramachandran are working to adapt one of his microfluidic tests for
tuberculosis to detect the presence of the SARS-CoV-2 virus that causes
COVID-19. Here’s an excerpt of a conversation with him about his project.
What
is microfluidics?
Microfluidics is, essentially, a
tiny medical lab that fits in the palm of your hand. There are very small tubes
and pumps and so forth that move fluids — like those from a nasal swab, a
teardrop amount is all it takes — through a series of chemical reactions.
There’s a computer processor monitoring everything and a USB connection relays
information to and from a computer. In fact, our test can be controlled in the
field using a smartphone. It’s very mobile. Very compact. And very fast.
What is the advantage of your system
over existing tests?
The advantages are several. First,
it’s portable and could be used by any doctor, nurse or technician in the field
at the point of care. Second, it’s fast. Existing tests can take eight hours or
longer and samples must be sent to a central facility. No such point-of-care
assay currently exists for SARS-CoV-2.
Lastly, and perhaps most
importantly, our test can detect an active COVID-19 infection — which is key to
early detection and treatment. The current rapid assays are based on antibodies
to the virus, not the virus itself. So, those tests can tell the caregiver that
the person has had the infection. Ours will tell them whether the patient is
currently infected — and, therefore, infectious. This is a big distinction in
isolating people who can infect others.
How
does your test work?
In technical terms, the lab first
looks for traces of genetic material in the sample — a corollary to DNA known
as RNA. RNA is the protein that decodes DNA to create the proteins necessary
for life. Viruses leave little traces of themselves wherever they go in the
form of RNA.
If you find RNA, you can actually
recreate the DNA that produced it — a process known as reverse transcription.
Next, we need to create a lot of the DNA, that is we need to “amplify” it.
Then, we do another process where we tag the DNA from the virus with tiny
fluorescent molecules, so that when we illuminate the sample with an
ultraviolet light the samples with coronavirus glow green. That’s how we would
know the patient has the SARS-CoV-2 virus that causes COVID-19. In a sample
where no virus RNA is present, the sample does not glow.
It’s actually quite a bit more
complicated than this, because a sample always contains lots of RNA — from the
patient themselves, from any microbes present, even from other viruses that
aren’t life-threatening.
We want to know specifically that
the patient has SARS-CoV-2, and not the common cold or the flu. That’s quite
tricky as you can imagine, especially to do it fast enough to keep up with the
virus.
All that transcribing, amplifying
and tagging takes place in this compact package that can be taken into the
field pretty much anywhere. We hope to get the test down to under 45 minutes or
so, start to finish.
How
quickly do you think you can have test kits ready to go?
Well, we think the window is too
narrow to help out much with COVID-19, but we’re working as fast as we can.
However, a microfluidic test kit like this could be easily reconfigured to head
off future epidemics much more quickly than with COVID-19. You could quickly
email the new RNA you were looking for and the kits could be reconfigured on
the spot to look for any new virus or microbe of concern. We use the
tuberculosis bacterium in our test now — it’s not safe to use the SARS-CoV-2
virus at this time — but the technology is applicable to any RNA, so you can
imagine quick tests for bacteria like E. coli, MRSA, anthrax or viruses
like the flu, Ebola or HIV, even parasites like malaria, schistosomiasis and
others. It would be a very powerful tool.
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