Paper-based electrochemical biosensor for diagnosing COVID-19: Detection of SARS-CoV-2 antibodies and antigen

Abstract

Coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is emerging as a global pandemic outbreak. To date, approximately one million deaths and over 32 million cases have been reported. This ongoing pandemic urgently requires an accurate testing device that can be used in the field in a fast manner. Serological assays to detect antibodies have been proven to be a great complement to the standard method of reverse transcription-polymerase chain reaction (RT-PCR), particularly after the second week of infection. We have developed a specific and sensitive immunosensor for immunoglobulin detection produced against SARS-CoV-2. Unlike other lateral flow-based assays (LFAs) involving the utilization of multiple antibodies, we have reported a label-free paper-based electrochemical platform targeting SARS-CoV-2 antibodies without the specific requirement of an antibody. The presence of SARS-CoV-2 antibodies will interrupt the redox conversion of the redox indicator, resulting in a decreased current response. This electrochemical sensor was proven effective in real clinical sera from patients with satisfactory results. In addition, the proposed format was also extended to antigen detection (the spike protein of SARS-CoV-2), which presents new possibilities for diagnosing COVID-19.

Keywords: COVID-19; Electrochemical detection; Paper-based sensors; SARS-CoV-2.

Fig. 1

Schematic illustration of the (A) device components, (B) detection principle and (C) detection procedure of the COVID-19 ePAD.

Fig. 2

(A) SEM images of the bare paper (i), the GO modified paper (ii), and its corresponding cross-sectional image (iii). Characterization results of each fabrication step using the EIS (B) and CV (C) techniques. Note that all EIS Nyquist plots were fitted with the Randles equivalent circuit.

Fig. 3

SWV responses of the COVID-19 ePAD tested with different concentrations of SARS-CoV-2 IgG (A) and SARS-CoV-2 IgM (B) in the presence of 5 mM [Fe(CN)₆]^3-/4-. (C) A linear relationship between $\Delta$ current vs logarithmic concentration of SARS-CoV-2 IgG and IgM and its corresponding relationship between $\Delta$ current and concentration of SARS-CoV-2 IgG and IgM. The threshold line was estimated based on an LOD (3SD_blank/slope) and the starting point of the calibration plots.

Fig. 4

(A) Schematic illustration of the in-house LFA colorimetric test strips for detecting SARS-CoV-2 IgG and IgM. (B) and (C) represent the calibration plots of $\Delta$ color intensity in the red channel as a function of the logarithmic concentration of SARS-CoV-2 IgG and IgM (n = 3). Illustrated in the insets of each calibration plot are the photographic images of the LFA device after loading different concentrations of IgG and IgM. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

Fig. 5

(A) SWV responses of the COVID-19 ePAD tested with different concentrations of the SARS-CoV-2 spike protein in the presence of 5 mM [Fe(CN)₆]^3-/4-. (B) The relationship between $\Delta$ current and concentration of SARS-CoV-2 spike protein; the inset shows its corresponding calibration plotted between the $\Delta$ current and logarithmic concentration of the SARS-CoV-2 spike protein.