A rapid
and accurate method for detection of virus (SARS-CoV-2)-specific
antibodies is important to contain the 2019 coronavirus disease (COVID-19)
outbreak, which is still urgently needed. Here, we develop a colorimetric-fluorescent
dual-mode lateral flow immunoassay (LFIA) biosensor for rapid, sensitive,
and simultaneous detection of SARS-CoV-2-specific IgM and IgG in human
serum using spike (S) protein-conjugated SiO2@Au@QD nanobeads
(NBs) as labels. The assay only needs 1 μL of the serum sample,
can be completed within 15 min, and is 100 times more sensitive than
the colloidal gold-based LFIA. Two detection modes of our biosensor
are available: the colorimetric mode for rapid screening of the patients
with suspected SARS-CoV-2 infection without any special instrument
and the fluorescent mode for sensitive and quantitative analyses to
determine the concentrations of specific IgM/IgG in human serum and
detect the infection early and precisely. We validated the proposed
method using 16 positive serum samples from patients with COVID-19
and 41 negative samples from patients with other viral respiratory
infections. The results demonstrated that combined detection of virus-specific
IgM and IgG via SiO2@Au@QD LFIA can identify 100% of patients
with SARS-CoV-2 infection with 100% specificity.
Sensitive
point-of-care methods for detecting severe acute respiratory
syndrome coronavirus 2 (SARS-CoV-2) antigens in clinical specimens
are urgently needed to achieve rapid screening of viral infection.
We developed a magnetic quantum dot-based dual-mode lateral flow immunoassay
(LFIA) biosensor for the high-sensitivity simultaneous detection of
SARS-CoV-2 spike (S) and nucleocapsid protein (NP) antigens, which
is beneficial for improving the detection accuracy and efficiency
of SARS-CoV-2 infection in the point-of-care testing area. A high-performance
magnetic quantum dot with a triple-QD shell (MagTQD) nanotag was first
fabricated and integrated into the LFIA system to provide superior
fluorescence signals, enrichment ability, and detectability for S/NP
antigen testing. Two detection modes were provided by the proposed
MagTQD-LFIA. The direct mode was used for rapid screening or urgent
detection of suspected samples within 10 min, and the enrichment mode
was used for the highly sensitive and quantitative analysis of SARS-CoV-2
antigens in biological samples without the interference of the “hook
effect.” The simultaneous detection of SARS-CoV-2 S/NP antigens
was conducted in one LFIA strip, and the detection limits for two
antigens under direct and enrichment modes were 1 and 0.5 pg/mL, respectively.
The MagTQD-LFIA showed high accuracy, specificity, and stability in
saliva and nasal swab samples and is an efficient tool with flexibility
to meet the testing requirements for SARS-CoV-2 antigens in various
situations.
The rapid and accurate diagnosis of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) at the early stage of virus infection can effectively prevent the spread of the virus and control the epidemic. Here, a colorimetric and fluorescent dual-functional lateral flow immunoassay (LFIA) biosensor was developed for the rapid and sensitive detection of spike 1 (S1) protein of SARS-CoV-2. A novel dual-functional immune label was fabricated by coating a single-layer shell formed by mixing 20 nm Au nanoparticles (Au NPs) and quantum dots (QDs) on SiO
2
core to produce strong colorimetric and fluorescence signals and ensure good monodispersity and high stability. The colorimetric signal was used for visual detection and rapid screening of suspected SARS-CoV-2 infection on sites. The fluorescence signal was utilized for sensitive and quantitative detection of virus infection at the early stage. The detection limits of detecting S1 protein via colorimetric and fluorescence functions of the biosensor were 1 and 0.033 ng/mL, respectively. Furthermore, we evaluated the performance of the biosensor for analyzing real samples. The novel biosensor developed herein had good repeatability, specificity and accuracy, which showed great potential as a tool for rapidly detecting SARS-CoV-2.
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