Figure 1.

Isoelectric point determination using CFM. (A) Inactivated SARS-CoV-2 particles were covalently immobilized on a Au-coated slide that contained a self-assembled monolayer that presented COOH and CH₃ functional groups. NHS/EDC chemistry covalently bound the virus to the COOH groups [16,17]. Au tips were functionalized to provide either negatively charged carboxyl (COO⁻) or positively charged quaternary amine (NR₄⁺) groups. Changes in the mean adhesion forces were measured with respect to pH with (B) a NR₄⁺ probe or (C) a COO⁻ probe. The data points of the mean adhesion force vs. pH were fit to a sigmoidal curve and the IEP was determined to be the infection point. Each data point represents 450 force curves and the histogram for each individual point can be found in Figure S2. * p < 0.05 from student’s t-test. Image A was made with BioRender.com.