Imaging of red blood cells based on recognition forces

We have measured and mapped the adhesion between an atomic force microscope (AFM) tip functionalized with helix pomatia lectin (HPL) and a mixed layer of red blood cells (RBC) of group A and O. The high specificity of that lectin for the N-acetylgalaclosamine terminated glycolipids present on the membrane of the group A RBC allowed us to discriminate between the two differents RBC and to produce an image based on affinity contrast. The rupture force of the adhesion events leading to the image formation were quantitatively analyzed and compared to rupture forces measured with the same AFM tip on N-acetylgalactosamine tethered to agarose beads. Measurement of rupture force shows that the adhesion, mediated by only few receptor-ligand pairs, produces a sufficient contrast for the affinity image formation.