Cross-Validation of ELISA and a Portable Surface Plasmon Resonance Instrument for IgG Antibodies Serology with SARS-CoV-2 Positive Individuals

Abstract

We report on the development of surface plasmon resonance (SPR) sensors and matching ELISAs for the detection of nucleocapsid and spike antibodies specific against the novel coronavirus 2019 (SARS-CoV-2) in human serum, plasma and dried blood spots (DBS). When exposed to SARS-CoV-2 or a vaccine against SARS-CoV-2, the immune system responds by expressing antibodies at levels that can be detected and monitored to identify the fraction of the population potentially immunized against SARS-CoV-2 and support efforts to deploy a vaccine strategically. A SPR sensor coated with a peptide monolayer and functionalized with various sources of SARS-CoV-2 recombinant proteins expressed in different cell lines detected human anti-SARS-CoV-2 IgG in the nanomolar range. Nucleocapsid expressed in different cell lines did not significantly change the sensitivity of the assays, whereas the use of a CHO cell line to express spike ectodomain led to excellent performance. This bioassay was performed on a portable SPR instrument capable of measuring 4 biological samples within 30 minutes of sample/sensor contact and the chip could be regenerated at least 9 times. Multi-site validation was then performed with in-house and commercial ELISA, which revealed excellent cross-correlations with Pearson’s coefficients exceeding 0.85 in all cases, for measurements in DBS and plasma. This strategy paves the way to point-of-care and rapid testing for antibodies in the context of viral infection and vaccine efficacy monitoring.

Cross-reactivity of antibodies from non-hospitalized COVID-19 positive individuals against the native, B.1.351, B.1.617.2, and P.1 SARS-CoV-2 spike proteins

“…Sensing techniques such as surface plasmon resonance (SPR) provide complementary biochemical data to ELISA. SPR has been used to conduct serological tests 37 and to measure various biochemical parameters influencing the strength of the humoral response, including the binding constant of the antibodies to spike or its subunits 38 , the inhibition of the spike protein:ACE-2 interaction by neutralizing antibodies 39 , 40 and the equilibrium dissociation constant (K D ) of recombinant human ACE-2 with the RBD of spike protein 41 .…”

Cross-reactivity of antibodies from non-hospitalized COVID-19 positive individuals against the native and B.1.351 SARS-CoV-2 spike proteins

“…Antigen-down colorimetric ELISA and SPR assays were adapted from the previously reported protocols (11,30,35,36) to detect IgGs targeting the B.1.351 spike protein. ELISA operates at a greater dilution factor (1:50) compared to SPR (1:5).…”

“…Semi-quantitative ELISA was performed based on the protocols of Krammer and of Finzi and Bazin (11,36,57), as recently reported (30). The sera were heat inactivated for 60 minutes at 55 o C in a heating block and diluted 1:50 before use.…”

“…Sera from the same cohort of individuals as previously reported were used in this study. (30) Adult volunteers (14 males and 18 females) were recruited after written informed consent by the Centre Hospitalier Universitaire de Québec -Université Laval (CHUL, ethics registration number 2021-5241) in Quebec City, Canada. Volunteers recruited in each age group were 18-49, 50-59, 60-69 and 70+ years of age at the time of enrollment and had received a PCR-positive diagnostic for COVID-19 four weeks prior to serum collection.…”

“…Sensing techniques such as surface plasmon resonance (SPR) provide complementary biochemical data to ELISA. SPR has been used to conduct serological tests (30) and to measure various biochemical parameters in uencing the strength of the humoral response, including the binding constant of the antibodies to spike or its subunits (31), the inhibition of the spike protein:ACE-2 interaction by neutralizing antibodies (32,33) and the equilibrium dissociation constant (K D ) of recombinant human ACE-2 with the RBD of spike protein (34).…”