A New Saliva-Based Lateral-Flow SARS-CoV-2 IgG Antibody Test for mRNA Vaccination

Abstract

Sensitive detection of IgG antibodies against SARS-CoV-2 is important to assessing immune responses to viral infection or vaccination and immunity duration. Antibody assays using non-invasive body fluids such as saliva could facilitate mass testing including young children, elderly and those who resist blood draws, and easily allowing longitudinal testing/monitoring of antibodies over time. Here, we developed a new lateral flow (nLF) assay that sensitively detects SARS-CoV-2 IgG antibodies in the saliva samples of vaccinated individuals and previous COVID-19 patients. The 25-minute nLF assay detected anti-spike protein (anti-S1) IgG in saliva samples with 100% specificity and high sensitivity from both vaccinated (99.51% for samples ≥ 19 days post 1st Pfizer/BioNTech or Moderna mRNA vaccine dose) and infected individuals. Antibodies against nucleocapsid protein (anti-NCP) was detected only in the saliva samples of COVID-19 patients and not in vaccinated samples, allowing facile differentiation of vaccination from infection. SARS-CoV-2 anti-S1 IgG antibody in saliva measured by nLF demonstrated similar evolution trends post vaccination to that in matching dried blood spot (DBS) samples measured by a quantitative pGOLD lab-test, enabling the nLF to be a valid tool for non-invasive personalized monitoring of SARS-CoV-2 antibody persistence. The new salivary rapid test platform can be applied for non-invasive detection of antibodies against infection and vaccination in a wide range of diseases.

Quantification of a COVID-19 Antibody Assay Using a Lateral Flow Test and a Cell Phone

“…Our calculated detection limit (4 ng/mL) was three orders of magnitude below this level and lower than the limit of detection for pre-existing saliva-based antibody LFAs for SARS-CoV-2 [34]. Table 1 shows a comparison between the proposed assay and other LFAs previously reported in the literature for the detection of SARS-CoV-2 IgG antibodies in different samples [13][14][15][16][17][18][19][20][21]34,35]. Our method exhibited a lower limit of detection than other quantitative LFAs based on an image analysis and magnetic measurements [16,17,34].…”

“…After exposure to COVID-19, the concentration of SARS-CoV-2 IgG antibodies in saliva reaches 25.5 ± 47.7 µg/mL [46]. Our calculated detection limit (4 ng/mL) was three orders of magnitude below this level and lower than the limit of detection for pre-existing saliva-based antibody LFAs for SARS-CoV-2 [34]. Table 1 shows a comparison between the proposed assay and other LFAs previously reported in the literature for the detection of SARS-CoV-2 IgG antibodies in different samples [13][14][15][16][17][18][19][20][21]34,35].…”

“…Table 1 shows a comparison between the proposed assay and other LFAs previously reported in the literature for the detection of SARS-CoV-2 IgG antibodies in different samples [13][14][15][16][17][18][19][20][21]34,35]. Our method exhibited a lower limit of detection than other quantitative LFAs based on an image analysis and magnetic measurements [16,17,34]. Other tests based on surface-enhanced Raman spectroscopy, fluorescence spectroscopy, and reflectance measurements showed lower limits of detection [13][14][15]19].…”

“…Our lateral flow assay (LFA) is advantageous because it is cost-effective, simple, and can be administered without elaborate instrumentation. Table 1 compares the proposed assay with the pre-existing LFAs for antibodies against SARS-CoV-2 [13][14][15][16][17][18][19][20][21]34,35]. Of these pre-existing assays, only two use saliva samples [34,35].…”

“…Table 1 compares the proposed assay with the pre-existing LFAs for antibodies against SARS-CoV-2 [13][14][15][16][17][18][19][20][21]34,35]. Of these pre-existing assays, only two use saliva samples [34,35]. Our method offers unique advantages due to a combination of a quick processing time (10 min) and low detections limits.…”