Nanopore-Based DNA Sequencing and DNA Motion Control - Nanopores: Sensing and Fundamental Biological Interactions - page 279

magnetic bead. As such, the speed of the end of the DNA moving out of the
nanopore can be estimated to be about 0.00316 nm/ s. This is

so because when the end of the DNA is in the nanopore, the net force on the DNA
is largest (the magnetic force is largest as the bead is closest to the magnetic
tweezers and the entropic force exerted by the random coil part of the DNA is
smallest as the DNA has been stretched), and in consequence the instant speed
of the DNA is the largest: thus the average speed of the DNA during the “pulling
out” process is actually slower than the instant speed of the end of DNA moving
out of the nanopore. By comparing to the average speed of the standard DNA
translocation [ 14 , 18 ], the average speed of this reverse DNA translocation
(by magnetic tweezers) is more than 2,000-fold slower than that of the standard
DNA translocation [ 14 , 18 ].

m s, or 0.0096 bases/ m

11.2.4 “DNA Transistor”

As experimentally demonstrated by Keyser et al . [ 34 ], the electrical force on
double-stranded DNA in a nanopore is proportional to the voltage bias across the
nanopore, about 0.24 pN/mV. This should allow the designing of a device to
electrically trap a single DNA in a nanopore against the thermal agitation, which
is exactly the idea of “DNA transistor” [ 45 ] of putting a stack of metal/dielectric/
metal/dielectric/metal layers into the membrane with the nanopore. As shown in
Fig. 11.28a , the “shaded” layers (thickness W ) are metal while the non-shaded
layers (thickness S ) are dielectric. The discrete negative charges of a DNA

Fig. 11.28 A schematic of the DNA transistor. The shaded regions in the sketch are metal layers,
while the non-shaded regions are dielectric layers. The negative charges of the ssDNA are
represented by the solid circles :(a) cross section and (b) top view. (Adapted from [ 45 ])