Development of a rapid and sensitive quantum dot nanobead-based double-antigen sandwich lateral flow immunoassay and its clinical performance for the detection of SARS-CoV-2 total antibodies

Abstract

Owing to the over-increasing demands in resisting and managing the coronavirus disease 2019 (COVID-19) pandemic, development of rapid, highly sensitive, accurate, and versatile tools for monitoring total antibody concentrations at the population level has been evolved as an urgent challenge on measuring the fatality rate, tracking the changes in incidence and prevalence, comprehending medical sequelae after recovery, as well as characterizing seroprevalence and vaccine coverage. To this end, herein we prepared highly luminescent quantum dot nanobeads (QBs) by embedding numerous quantum dots into polymer matrix, and then applied it as a signal-amplification label in lateral flow immunoassay (LFIA). After covalently linkage with the expressed recombinant SARS-CoV-2 spike protein (RSSP), the synthesized QBs were used to determine the total antibody levels in sera by virtue of a double-antigen sandwich immunoassay. Under the developed condition, the QB-LFIA can allow the rapid detection of SARS-CoV-2 total antibodies within 15 min with about one order of magnitude improvement in analytical sensitivity compared to conventional gold nanoparticle-based LFIA. In addition, the developed QB-LFIA performed well in clinical study in dynamic monitoring of serum antibody levels in the whole course of SARS-CoV-2 infection. In conclusion, we successfully developed a promising fluorescent immunological sensing tool for characterizing the host immune response to SARS-CoV-2 infection and confirming the acquired immunity to COVID-19 by evaluating the SRAS-CoV-2 total antibody level in the crowd.

Keywords: Fluorescent detection; Lateral flow immunoassay; Quantum dot nanobeads; SARS-CoV-2; Total antibodies.

Graphical abstract

Scheme 1

(A) Schematic representation of the developed QB-based double-antigen sandwich lateral flow immunoassay and (B) the corresponding test results.

Fig. 1

Characterization of QBs. (A) High-resolution transmission electron microscope image of the QBs. The inset shows the image of individual QB at high magnification. (B) The average hydrodynamic diameter distribution of the QBs by DLS measurement. (C) UV–vis absorption spectra of QBs and QDs, respectively. (D) Comparison of fluorescence intensities of oleic acid-functionalized CdSe/ZnS QDs and the resultant QBs. The maximum emission wavelength of QBs is 618 nm, while that of QDs in ethanol is 616 nm. The particle concentrations of QDs in ethanol and QBs in pure water are 25 nM and 8.9 pM, respectively.

Fig. 2

Parameter optimization for the fabrication of QB-LFIA. (A) The solution pH for the conjugation of QBs and RSSP. (B) The saturated labeling content of RSSP on the surface of QBs. (C) The spayed concentration of RSSP on the T line.

Fig. 3

The dynamic monitoring of serum total antibody level in 12 SARS-CoV-2-infected patients at different disease stages by the proposed QB-LFIA.