ELISAs were performed with the human ACE2-Fc chimera protein (GenScript). Flat-bottom, 96-well plates (Thermo Fisher Scientific) were coated with 416 nM of each polyP. After blocking with 5% nonfat dry milk in phosphate-buffered saline (PBS) for 1 hour at 37°C, the plates were incubated with the ACE2-Fc chimeric protein used at increasing concentrations (0.1 to 2 μM) in 3% bovine serum albumin (BSA)–PBS for 1 hour at room temperature with gentle shaking. In parallel assays, the ACE2-Fc chimeric protein was tested under the same conditions on uncoated wells after blocking, as a negative control. The plates were then washed with PBS and incubated with an anti-human HRP-conjugated antibody (AP113P, Sigma-Aldrich, USA) for 1 hour at room temperature with gentle shaking. The remaining steps were performed as previously described (51 (link)). Absorbance at 450 nm was measured with a plate reader (EnVision; 2102, PerkinElmer), and the binding values are reported as the means of at least three determinations.