a Binding of S-glycoprotein subunit 1 (S1) is probed on A549 and A549–ACE2 cells. b Confocal microscopy (z stack) of A549–ACE2–eGFP (green) cell transduced with plasma membrane BFP (blue). c Overlay of eGFP and DIC images of a mixed culture of A549 and A549–ACE2–eGFP cells. d, e Force–distance (FD)-based AFM topography image (d) and the corresponding adhesion map (e) in the specified area in (c). The frequency of adhesion events is indicated. f Box plot of the binding probability between S1 and A549 cells (gray) or A549–ACE2 cells (green) without and after injection of cyclic RGD (cRGD, checked boxes) or sialic acid (SA, dashed boxes), respectively. The square in the box indicates mean, the colored box indicates the 25th and 75th percentiles, and the whiskers indicate the highest and the lowest values of the results. The line in the box indicates median. g Force versus time curves showing either a nonadhesive curve (bottom) or specific adhesive curves acquired at different LRs (LR1–LR3). h DFS plot showing the distribution or the rupture forces measured either between the S1 subunit and the ACE2 on model surfaces (black dots, extracted from Fig. 2e), and between the S1 subunit and ACE2-overexpressing A549 cells acquired at three different LRs (blue and red dots) (N = 403). Blue dots belong to a data set acquired in fast-force volume mode, with a retraction velocity of 20 µm s−1 (LR1). Red dots belong to data sets acquired in peak force tapping mode with 0.125 kHz peak force frequency and 375-nm amplitude (LR2) or at 0.25 kHz and 750 nm (LR3), respectively. The error bar indicates s.d. of the mean value. Histograms of force distribution on A549–ACE2 cells for LR1–LR3 are shown on the side. For experiments without injection of cRGD or SA, data are representative of at least N = 11 cells from N = 6 independent experiments. The data for blocking experiments with cRGD or SA were acquired for at least N = 4 cells from N = 2 independent experiments. P values were determined by two-sample t test in Origin. Source data are provided as a Source Data file.