  Red blood cells (RBC) are known to form aggregates in the forms of rouleaux
due to the presence of plasma proteins under physiological conditions. Rouleaux
formation can be also induced in vitro by the addition of macromolecules to the
RBC solution. Current data on the adhesion strength between red blood cells in
their natural discocyte shapes mostly rely on indirect measurements like flow
chamber experiments, but on the single cell level data is lacking. Here we
present measurements on the dextran induced aggregation of red blood cells by
use of atomic force microscopy based single cell force spectroscopy (SCFS). The
effects of dextran concentration and molecular weight on the interaction energy
of adhering RBCs was determined. The results are in good agreement with a model
based on the depletion effect and former experimental studies.
