Biology Reference
In-Depth Information
detection of DNA [110]. It is convenient to immobilize these
complexes at the electrode surface using a polymer matrix. DNA
can be immobilized either with polymer [111] or redox polymer
electrodepositedontoaDNAlayer[112,113].Suchapolymerforms
a stable and reproducible surface and works as an electron-transfer
mediator.
10.4.3
Nonconducting Polymers
Nonconducting polymers are not so frequently used in DNA
biosensors as conducting ones. They have high resistivity, but
their permselectivity is very useful in preventing interferences
in electrochemical biosensors [114]. In this group of polymers,
polyethyleneimine(PEI)andchitosan(CHIT)areveryoftenusedfor
the preparation ofDNA biosensors.
CHIT is a pseudonatural polymer formed from chitin when
the degree of its deacetylation reaches 50% [115]. Both PEI and
CHIT are cationic polymers with good biocompatibility and high
positive charge density, which allows for easy electrostatic DNA
immobilization.StudyofinteractionbetweentheDNAmoleculeand
PEI-copper(II) complexes showed that together with electrostatic
interaction, van der Waals interactions and hydrogen binding are
also employed probably due to the presence of multiple copper(II)
complex molecular units and free amine groups of the polymer
[116, 117]. Electron-transfer kinetics at the PEI-DNA-modified
electrode was studied [118]. It was shown that the surface of
modified electrodes was homogeneous and electron transfer was
slower when PEI formed an external layer. Moreover, further
modification with PEI-gold nanoparticles enhanced the electron
transfer. PEI was used to disperse the MWCNTs, and the screen-
printedelectrode(SPCE)wasmodifiedwiththeresultingcomposite
[119]. MWCNT-PEI formed a layer suitable for the electrostatic
adsorptionofnegativelychargedDNA.DNA/MWCNT-PEI/SPCEwas
used for the detection of DNA damage by quinazolines. Interaction
of PEI and CHIT with plasmid DNA (pDNA) on a hanging mercury
drop electrode was compared [120]. Voltammetric studies showed
that each polymer interacts with pDNA by different mechanisms
and that a higher amount of PEI interacts with pDNA than was
