In the wake of the COVID-19 pandemic, millions of confirmed
cases
and deaths have been reported around the world. COVID-19 spread can
be slowed and eventually stopped by a rapid test to diagnose positive
cases of the disease on the spot. It is still important to test for
COVID-19 quickly regardless of the availability of the vaccine. Using
the binding-induced folding principle, we developed an electrochemical
test for detecting SARS-CoV-2 with no RNA extraction or nucleic acid
amplification. The test showed high sensitivity with a limit of detection
of 2.5 copies/Ī¼L. An electrode mounted with a capture probe
and a portable potentiostat are used to conduct the test. To target
the N-gene of SARS-CoV-2, a highly specific oligo-capturing probe
was used. Based on the binding-induced āfoldingā principle,
the sensor detects binding between the oligo and RNA. When the target
is absent, the capture probe tends to form a hairpin as a secondary
structure, retaining the redox reporter close to the surface. This
can be seen as a large anodic and cathodic peak current. When the
target RNA is present, the hairpin structure will open to hybridize
with its complementary sequence, causing the redox reporter to pull
away from the electrode. Consequently, the anodic/cathodic peak currents
are reduced, indicating the presence of the SARS-CoV-2 genetic material.
Validation of the test performance was performed using 122 COVID-19
clinical samples (55 positives and 67 negatives) and benchmarked to
the gold standard reverse transcription-polymerase chain reaction
(RT-PCR) test. As a result of our test, the accuracy, sensitivity,
and specificity have been measured at 98.4%, 98.2%, and 98.5%, respectively.