Noncontact Atomic Force Microscopy - Yale School of Engineering ...

Dynamic Force Spectroscopy of Single Chain-like Molecules
Daniel Ebeling 1 , Harald Fuchs 1 , Filipp Oesterhelt 2 , and Hendrik Hölscher 3
Tu-1120
1
Center for Nanotechnology (CeNTech), Heisenbergstrasse 11, 48149 Münster, Germany and
Physikalisches Institut, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Strasse 10, 48149
Münster, Germany
2
Institut für Physikalische Chemie II, Heinrich-Heine-Universität Düsseldorf, Universitätsstrasse 1,
40225 Düsseldorf, Germany
3
Institute for Microstructure Technology (IMT), Forschungszentrum Karlsruhe, P.O. box 36 70, 76021
Karlsruhe, Germany
In order to measure forces acting on a single chain-like molecule during a stretching
experiment in liquid, we introduce a dynamic approach based on the frequencymodulation
technique with constant-excitation. In difference to the classical approach
where the force is recorded as a conventional force vs. distance curve in a static
measurement, we are able to detect simultaneously the conservative force as well as the
energy dissipation during the elongation of a chain-like molecule.
Therefore the amplitude and the frequency shift of an oscillating cantilever are measured
during the retraction from the surface (Fig. 1a and b) [1]. The tip-sample force (Fig. 1c)
and the energy dissipation (Fig. 1d) can be reconstructed from these data sets via an
analytical approach. We apply this technique to dextran monomers and demonstrate the
agreement of the experimental force curves with a ``single-click'' model [2].
Figure 1: a) Amplitude and b) frequency shift curves measured during approach to and retraction
from the surface covered with dextran molecules. c) Force acting on the dextran molecule as a
function of the actual tip position. The experimental result is well described by a ``single-click''
model (solid line) d) Energy dissipation per oscillation cycle.
[1] D. Ebeling, F. Oesterhelt, H. Hölscher (submitted).
[2] R. G. Haverkamp, A. T. Marshall, and M. A. K. Williams, Phys. Rev. E 75, 021907 (2007).
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