SARS-CoV-2 Antibody Profiling: Spike S2 Antigen

This workflow and its products described here are for research use only and is not to be used for any other purposes, including, but not limited to, in vitro diagnostics, clinical diagnostics, or use in humans. The document and its content are proprietary to Fluidic Analytics and is intended for use only in connection with the products described herein and for no other purposes.

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1. Intended use

This user guide describes affinity-based antibody profiling against the SARS-CoV-2 Spike S2 protein directly in serum samples by use of the Fluidity One-W Serum instrument.

2. Background

COVID-19 is a respiratory disease caused by the coronavirus SARS-CoV-2 that produces mild symptoms in most individuals. However, dependent on underlying health issues and other factors such as age, gender, or genetic makeup, symptoms can vary dramatically in severity. A complete and accurate immune response assessment of COVID-19 patients or vaccinated individuals based on the two key determining factors, namely antibody concentration and affinity, is key to:

  • Assessing the strength and duration of acquired immunity
  • Evaluating the mechanisms and immunological effects of virus-neutralizing antibodies
  • Characterizing cross-reactivity with other, less harmful, coronaviruses

This user guide describes microfluidic affinity antibody profiling (MAAP) against the SARS-CoV-2 Spike S2 for a comprehensive immune response assessment in COVID-19 patients or vaccinated individuals.

3. Microfluidic affinity antibody profiling – assay principle 

This user guide describes all steps required to characterize the immune response against the SARS-CoV-2 Spike S2 (S2) directly in minimally diluted serum samples. After S2 labeling, three independent serum titration curves are measured to enable the simultaneous determination of antibody affinity and concentration.

Flow Diagram WI-0037v2

4. Before you start

Good laboratory practice when working with serum samples

For use of this user guide, we recommend working with serum rather than plasma. Serum collected from COVID-19 patients (whether newly infected or recovered), and uninfected people who could still harbour infectious agents must be handled using a high level of precaution and at the required biosafety level for your country’s regulations. In addition, all serum samples should be handled as if capable of transmitting infectious agents.

 For the full protocol download the user guide below                            Download User Guide

7.2. Results

After data submission, background subtraction will be performed for each measurement and the resulting data for all three titration series subjected to a global, non-linear fit to determine the following parameters:

Parameter Definition Constraints
Rh, free Hydrodynamic radius of the unbound
Alexa Fluor™ 647–S2 (nm)
Shared, must be greater than zero
Rh, complex Hydrodynamic radius of the antibody-bound Alexa Fluor™ 647–S2 (nm) Shared, must be greater than zero
A Antibody concentration in the sample serum (nM) Shared, must be greater than zero
n Stoichiometry factor Fixed to 1.0
P Concentration of Alexa Fluor™
647–S2 in each experiment (nM)
Fixed to 10, 40 and 100 nM respectively
KD Dissociation constant (nM) Shared, must be greater than zero
FA0003_user guide_example figure_CoV2-S2Concentration of antibody binding sites: [ab] = 133 nM, 95% CI (111 – 162)
KD = 2.0 nM, 95% CI (0.6 – 4.5)
Please note: The shape of the binding curves will vary between patient samples. If neither of the three curves reaches a plateau at the highest serum concentrations, samples might contain low amounts of antibodies. Please contact
technical support for more information.

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