Affinity Imaging of Red Blood Cells Using an Atomic Force MicroscopeMichel Grandboisa, Wolfgang Dettmannb, Martin Benoitb, and Hermann E. Gaubba Department of Physics and Astronomy, University of MissouriColumbia, Columbia, Missouri b Lehrstuhl für Angewandte Physik, Universität München, München, Germany Correspondence to: Michel Grandbois, Dept. of Physics and Astronomy, U. of MissouriColumbia, 318 Physics Bldg., Columbia, MO 65211. E-mail: grandboism@missouri.edu We used an atomic force microscope (AFM) to produce an image of a mixed layer of group A and O red blood cells with a contrast based only on the measured strength of a specific receptorligand pair. The image was obtained by measuring and plotting for each image pixel the adhesion force between the mixed RBC layer and the AFM tip functionalized with Helix pomatia lectin. The high specificity of that lectin for the N -acetylgalactosamine-terminated glycolipids present in the membrane of group A RBCs enabled us to discriminate between the two cell populations 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. The mean rupture force was found to be 65 pN when measured on the group A RBCs and 35 pN on the agarose beads. These results show that the adhesion, mediated by only a few receptorligand pairs, produces sufficient contrast for the affinity image formation. (J Histochem Cytochem 48:719724, 2000) Key Words: atomic force microscope (AFM), affinity, recognition, glycocalix, lectin
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