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The red blood cell (RBC) viscoelastic membrane contains proteins and glycolproteins embedded in, or attached, to a
fluid lipid bilayer and are negatively charged, which creates a repulsive electric (zeta) potential between the cells
and prevents their aggregation in the blood stream. The basis of the immunohematologic tests is the interaction
between antigens and antibodies that causes hemagglutination. The identification of antibodies and antigens is of
fundamental importance for the transfusional routine. This agglutination is induced by decreasing the zeta-potential
through the introduction of artificial potential substances. This report proposes the use of the optical tweezers to
measure the membrane viscosity, the cell adhesion, the zeta-potential and the size of the double layer of charges
(CLC) formed around the cell in an electrolytic solution. The adhesion was quantified by slowly displacing two
RBCs apart until the disagglutination. The CLC was measured using the force on the bead attached to a single RBC
in response to an applied voltage. The zeta-potential was obtained by measuring the terminal velocity after releasing
the RBC from the optical trap at the last applied voltage. For the membrane viscosity experiment, we trapped a bead
attached to RBCs and measured the force to slide one RBC over the other as a function of the relative velocity. After
we tested the methodology, we performed measurements using antibody and potential substances. We observed that
this experiment can provide information about cell agglutination that helps to improve the tests usually performed in
blood banks. We also believe that this methodology can be applied for measurements of zeta-potentials in other kind of samples.
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