As the COVID-19 pandemic continues to spread across the world, testing remains
a key strategy for tracking and containing the virus. Bioengineering graduate
student, Maha Alafeef, has co-developed a rapid, ultrasensitive test using a
paper-based electrochemical sensor that can detect the presence of the virus
in less than five minutes. The team led by professor Dipanjan Pan reported
their findings in ACS Nano.
"Currently, we are experiencing a once-in-a-century life-changing event,"
said Alafeef. "We are responding to this global need from a holistic
approach by developing multidisciplinary tools for early detection and
diagnosis and treatment for SARS-CoV-2."
There are two broad categories of COVID-19 tests on the market. The first
category uses reverse transcriptase real-time polymerase chain reaction
(RT-PCR) and nucleic acid hybridization strategies to identify viral RNA.
Current FDA-approved diagnostic tests use this technique. Some drawbacks
include the amount of time it takes to complete the test, the need for
specialized personnel and the availability of equipment and reagents.
The second category of tests focuses on the detection of antibodies.
However, there could be a delay of a few days to a few weeks after a person
has been exposed to the virus for them to produce detectable antibodies.
In recent years, researchers have had some success with creating
point-of-care biosensors using 2D nanomaterials such as graphene to detect
diseases. The main advantages of graphene-based biosensors are their
sensitivity, low cost of production and rapid detection turnaround. "The
discovery of graphene opened up a new era of sensor development due to its
properties. Graphene exhibits unique mechanical and electrochemical
properties that make it ideal for the development of sensitive
electrochemical sensors," said Alafeef. The team created a graphene-based
electrochemical biosensor with an electrical read-out setup to selectively
detect the presence of SARS-CoV-2 genetic material.
There are two components to this biosensor: a platform to measure an
electrical read-out and probes to detect the presence of viral RNA. To
create the platform, researchers first coated filter paper with a layer of
graphene nanoplatelets to create a conductive film. Then, they placed a gold
electrode with a predefined design on top of the graphene as a contact pad
for electrical readout. Both gold and graphene have high sensitivity and
conductivity which makes this platform ultrasensitive to detect changes in
electrical signals.
Current RNA-based COVID-19 tests screen for the presence of the N-gene
(nucleocapsid phosphoprotein) on the SARS-CoV-2 virus. In this research, the
team designed antisense oligonucleotide (ASOs) probes to target two regions
of the N-gene. Targeting two regions ensures the reliability of the senor in
case one region undergoes gene mutation. Furthermore, gold nanoparticles
(AuNP) are capped with these single-stranded nucleic acids (ssDNA), which
represents an ultra-sensitive sensing probe for the SARS-CoV-2 RNA.
The researchers previously showed the sensitivity of the developed sensing
probes in their earlier work published in ACS Nano. The hybridization of the
viral RNA with these probes causes a change in the sensor electrical
response. The AuNP caps accelerate the electron transfer and when
broadcasted over the sensing platform, results in an increase in the output
signal and indicates the presence of the virus.
The team tested the performance of this sensor by using COVID-19 positive
and negative samples. The sensor showed a significant increase in the
voltage of positive samples compared to the negative ones and confirmed the
presence of viral genetic material in less than five minutes. Furthermore,
the sensor was able to differentiate viral RNA loads in these samples. Viral
load is an important quantitative indicator of the progress of infection and
a challenge to measure using existing diagnostic methods.
This platform has far-reaching applications due to its portability and low
cost. The sensor, when integrated with microcontrollers and LED screens or
with a smartphone via Bluetooth or wifi, could be used at the point-of-care
in a doctor's office or even at home. Beyond COVID-19, the research team
also foresees the system to be adaptable for the detection of many different
diseases.
"The unlimited potential of bioengineering has always sparked my utmost
interest with its innovative translational applications," Alafeef said. "I
am happy to see my research project has an impact on solving a real-world
problem. Finally, I would like to thank my Ph.D. advisor professor Dipanjan
Pan for his endless support, research scientist Dr. Parikshit Moitra, and
research assistant Ketan Dighe for their help and contribution toward the
success of this study."
Reference:
Maha Alafeef, Ketan Dighe, Parikshit Moitra, Dipanjan Pan. Rapid,
Ultrasensitive, and Quantitative Detection of SARS-CoV-2 Using Antisense
Oligonucleotides Directed Electrochemical Biosensor Chip. ACS Nano, 2020;
DOI: 10.1021/acsnano.0c06392
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