Sensing of Biomolecules - Bionanoelectronics: Bioinquiring and Bioinspired Devices - page 75

I (a.u)

CTTGCA....

nanopore

DNA

F drag

F driving

time

I

-

+

trans

cis

V

Fig. 2.19 DNA sequencing using a nanopore

Fig. 2.20 A schematic
behavior of the DNA
blocking current

I

the blocking
current

t d

time

nucleotides inside the pore manifests as a blocking current (see Fig. 2.20 ). As a
result, the ionic current displays a sharp decrease with durations ranging from 300
to 1;300s( Zwolak and Di Ventra 2008 ). The blockade current offers information
about the length of the DNA sequence and about its base content, since each base
has its own geometrical dimensions, affecting t d in a quite different manner.
The voltage drop is located around the nanopore, which has a much higher
resistance than the ionic solution surrounding it, and the presence of DNA signifi-
cantly changes the voltage distribution, so that the applied bias drops mainly on the
nucleotides. Considering that the bias is applied only on the nanopore, there are two
forces acting in the two ionic chambers. The first is the driving force acting on DNA
in the pore region, given by

F driving Š 0:5 eNE ; (2.28)

where N is the number of folds in the pore region, and E is the applied electric
field. The DNA-pore interaction is modeled as a drag force expressed as

F drag Š N v ; (2.29)