Medical Design Briefs - September 2021 - 42

GlobAl
INNOVATIONS
Highly Accurate Test Quantifies Antibodies against SARS-CoV-2
Hokkaido University, Hokkaido, Japan
S
cientists have developed a rapid,
highly accurate test to detect antibodies
against the spike protein of
SARS-CoV-2 in human serum, opening a
new avenue for understanding the full
extent of the pandemic and evaluating
the effectiveness of vaccines.
In the 18 months since the emergence
of COVID-19 pandemic, great strides
have been made in discovering and
inventing various approaches to track
and control the spread of the SARS-CoV2
virus. The gold standard since the
beginning of the pandemic has been the
RT-PCR method.
A team of scientists from Japan,
including Prof. Manabu Tokeshi of
Hokkaido University's faculty of engineering,
have developed a 20-minute
test to detect and quantify antibodies
against SARS-CoV-2 in human serum.
Their
findings
were
published
Biosensors and Bioelectronics.1
It is estimated that between 40 and 45
percent of individuals infected with
SARS-CoV-2 are asymptomatic - despite
being infected, they do not develop any
symptoms of the disease. Identifying
individuals who may have had asymptomatic
COVID-19 is important to understanding
the full extent of the pandemic.
RT-PCR can only detect the presence
of the viral RNA in samples; individuals
who have recovered from the pandemic
will only have antibodies to the virus,
which RT-PCR cannot detect.
They developed a method of detecting
antibodies against SARS-CoV-2 in
human serum using a method called
non-competitive fluorescence
immunoassay (FPIA). This method can
also be used to quantify the antibodies.
The team has previously made many
innovations to the method and associated
equipment, including the development
of a portable fluorescence polarization
analyzer (see Figure 1).
FPIA requires fluorescently labeled
recombinant SARS-CoV-2 spike proteins
(F-RBD) and human serum to be mixed
together for the test. Individuals who
have been infected with or vaccinated
42
Intro
Cov
in
1. Mix sample and reagent
Serum
Reagent
(F-RBD)
Incubation
15 min
2. Inject Mixture
Mixture
3. Measure FP
Microdevice
Portable
FP analyzer
0 min
~20 min
Fig. 1 - The fluorescence polarization immunoassay developed to detect and quantify antibodies
against SARS-CoV-2. If present in a serum sample, antibodies against the SARS-CoV-2 virus will bind
to fluorescently labeled recombinant SARS-CoV-2 spike proteins (F-RBD); the antibody-bound proteins
emit polarized light, which is measured by a fluorescence polarization analyzer.
against SARS-CoV-2 will have anti-spike
protein antibodies in their serum. When
these antibodies bind to F-RBD, polarized
light is emitted, while F-RBD alone
emits depolarized light. By measuring
the degree of polarization using a fluorescence
polarization analyzer, the concentration
of antibodies can be determined.
The scientists optimized the test
and evaluated it using samples of human
serum from individuals diagnosed with
COVID-19 and from those who had not
been infected by SARS-CoV-2 (see
Figure 2).
The test was demonstrated to be highly
accurate, quick, and easy to perform,
Antibody detection by non-competitive FPIA
Low P
I
I
Polarized Excitation Light
Depolarized Emitted Light
High P
polarization
RBD
HiLyte Fluor 647-labeled
RBD
Anti-RBD Antibody
SARS-CoV-2
Spike Protein
Fig. 2 - The principle behind FPIA for detection
of antibodies against SARS-CoV-2. When free
fluorescently labeled recombinant SARS-CoV-2
spike proteins (F-RBD) are exposed to a specific
wavelength of polarized light, they emit depolarized
light. However, if F-RBD are bound to antiRBD
antibodies, they emit polarized light in -
stead, which can be measured.
www.medicaldesignbriefs.com
ToC
+
-
A
Polarized Emitted Light
with high throughput. This test requires
about 20 minutes to complete, compared
to about 2 hours for other tests;
furthermore, the equipment required
for the test is highly portable, weighing
only 4.3 kg. Taken all together, these features
make the test an excellent option
for detecting and quantifying antibodies
against SARS-CoV-2. The test can now be
used for two purposes: screening large
populations to determine the exact
extent of the pandemic, and for evaluating
the effectiveness of SARS-CoV-2 vaccines
based on the antibody response.
This work was supported by the Japan
Science and Technology Agency's JSTSENTAN
program (JPMJSN16A2); the
Nakatani Foundation for Advancement
of Measuring Technologies in Bio -
medical Engineering; the Japan Society
for the Promotion of Science (JSPS)
KAKENHI (JP20H02760), and Grant-inAid
for JSPS Fellows (20J11226); and the
Cooperative Research Program of the
Network Joint Research Center for Ma -
terials and Devices (NJRC Mat. & Dev.).
Reference
1. Keine Nishiyama, et al., " Facile and rapid
detection of SARS-CoV-2 antibody based
on a noncompetitive fluorescence
polarization immunoassay in human
serum samples, " Biosensors and
Bioelectronics, June 5, 2021, DOI:
10.1016/j.bios.2021.113414.
For more information, visit https://
www.global.hokudai.ac.jp.
Medical Design Briefs, September 2021
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Medical Design Briefs - September 2021

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