only one small opening through which DNA travels, i.e., single capillary and
the separation takes place in the similar way.
(c) Surface electrophoresis
This technique of electrophoresis is mainly used for handling longer strands
of DNA. If the DNA strands are long, there is the problem of making them to
travel along agarose or so. Hence to handle the heavier molecules, mainly of
the size above 10 kbp (kilo base pair), this technique is used. In this case the
friction between surface and DNA strand plays a very major role, while
making DNA to move on the surface. Li et al. has reported that the mobility
of dsDNA, while moving along the surface is influenced by intensity of the
electric field, ionic strength and the migration distance [ 79 ]. Going with the
modifications, gel free microchannel electrophoresis has also been fabricated
by Lee and Kuo [ 80 ] for fractionating larger DNA. It was observed that the
channel’s bottom surface was modified in this process. This process helped in
fractionating molecules of size 3.5–21.2 kbp. Ghosh et al. [ 81 ] fabricated
PDMS micro-channels to make dsDNA to travel along. It was observed that
the dsDNA travels along the corner rather than the channel base, with the fast
speed. The physics behind the movement in such case was also optimized
using molecular dynamics simulation. Hence it was remarked that the orthog-
onally placed pair of surface channel corners is a more favourable option
rather than the flat base. Figure2.26shows the schematic of the fabricated
device.
Fig. 2.26 Color online Schematic of the SE device, (dimensions: reservoirs diameter¼3 mm,
width of channel¼ 400 μm, depth of features¼ 250 μm) (Reproduced from Ghosh et al. [ 81 ] with
permission from the American Institute of Physics)
64 G. Bhatt et al.