Biomedical Engineering Reference
In-Depth Information
Figure 10.9
LacI repressors bound to a DNA molecule stretched in a 200 nm wide nanochannel.
Both the LacI and the DNA are fluorescently labeled with different shades of gray. There are ~ 20 LacI
molecules in this particular case. From [27].
colors, a fluorescence image can reveal very rapidly and accurately the position of
this protein along the chain (Figure 10.9) [27].
In the same spirit, structures alternating micro- and nanoconstrictions respec-
tively 1.5-
m
m and 90-nm wide have been developed that induce different confine-
ment regimes for the DNA molecules [28]. Upon the application of the electric field,
molecules experience many transitions from thick regions to regions smaller than
the radius of gyration.
Although it was predicted that long molecules would be retarded by the con-
strictions by an entropic barrier, practically, their mobility turns out to be higher.
A qualitative interpretation involves a large deformation of the coil. Strong inter-
actions with the surface in these ultraconfined geometries are probably also to be
taken into account [29].
10.1.5 Electrophoresis of Proteins
After the genomics era and now that more and more genomes have been sequenced,
proteomics that aims at identify the proteins expressed in living organisms is the
next big challenge [30]. From a chemical physics point of view, proteins are not as
well defined as DNA as their characteristics of charge and hydrophilicity varies a
