Ionic thermophoresis and its application in living cells

Although thermophoresis, i.e. the directed movement of molecules in
a temperature gradient, was discovered more than 150 years ago, its
molecular origin is not jet fully understood. Nonetheless
thermophoresis is used as a principle in biomolecular binding
measurements. Both topics are interesting and worth a scientific
discussion. In this thesis, systematic experiments over a large
parameter space were conducted. From these measurements a
combination of different theories about its molecular origin could
be verified. Thus, the first result of this thesis is that the
phenomenon thermophoresis consists of different additive
contributions. Some of them relate to the ionic nature of the
molecule and are non-existent when the molecule is electrically
neutral. The microscopic mechanism of these ionic contributions to
thermophoresis is discussed in the first part. It continues the
work on the capacitor model and explains a further contribution,
which we call Seebeck effect in analogy to solid state physics.
Through the different contributions we bridge the gap between local
thermodynamic equilibrium approaches and non-equilibrium theories.
Several applications will greatly benefit from understanding the
molecular physics of thermophoresis. Pharmacological screens are
conducted to determine the binding affinity of a whole molecular
library to a target molecule and thus to identify the best
candidates for a new drug. These screens will be improved when
thermophoresis can be predicted and for example the influence of
the buffer can be determined. Binding measurements of biomolecules
can already be conducted in cell lysate. The second part of this
thesis will show thermophoresis measurements inside living cells
for the first time. This paves the way for in vivo binding
measurements inside cells. To make thermophoresis measurements
compatible to cell culture, the setup was changed in great parts,
now using total internal reflection fluorescence (TIRF) microscopy.