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Abstract
A force microscope operated with an amplitude modulation feedback (usually known as
tapping-mode atomic force microscope) has two tip-sample interaction regimes, attractive
and repulsive. We have studied the performance of those regimes to imaging single
antibody molecules. The attractive interaction regime allows determination of the
basic morphologies of the antibodies on the support. More importantly, this regime
is able to resolve the characteristic Y-shaped domain structure of antibodies and
the hinge region between domains. Imaging in the repulsive interaction regime is associated
with the irreversible deformation of the molecules. This causes a significant loss
in resolution and contrast. Two major physical differences distinguish the repulsive
interaction regime from the attractive interaction regime: the existence of tip-sample
contact and the strength of the forces involved.