Biology Reference
In-Depth Information
voltammetry(NPV)inordertoprepareelectrochemicalDNAbiosen-
sors were compared [49]. The NPV method enabled to prepare Ppy
nanofiber films with higher electroactivity due to higher specific
surface area. The potentiostatic and potentiodynamic method of
electropolymerization was used to prepare Ppy nanofibers [50].
Electrodes prepared bythepotentiostaticprocedure showedhigher
responses to the oxidation of dsDNA than the electrodes prepared
by potentiodynamic methods.
Ppycanbeelectropolymerizedfrombothaqueousandnonaque-
oussolvents[12].ForDNAbiosensorsthebiocompatabilityofPpyis
important as well as the fact that it can also be electropolymerized
from neutral aqueous solutions. Different conditions affecting DNA
adsorption onto conducting Ppy, including pH, buffer nature, ionic
strength, and substrate, were studied [22]. Maximum amount of
DNA was adsorbed from a solution of pH 5.1 because of the
high density of positive charge of Ppy, and also positive effect
of ionic strength was reported. DNA adsorbed at the Ppy surface
decreases the ionic conductivity of the polymer, but on the other
hand maintains the mobility of the dopant anions within the bulk
Ppy [23]. Anions incorporated as dopants into the Ppy during the
process of electropolymerization have a positive effect on polymer
stability [12]. Anions from the supporting electrolyte incorporated
into the polymer achieve its electroneutrality. However, other
anions can also be used as counterions. Large polymeric anions,
such as polyvinyl sulfonate, were used as counterions in the
preparation of DNA biosensors [40, 51]. Such doped Ppy can
displace negative PVS with PO
4
of DNA [24]. It was found
that the adsorption of DNA onto electropolymerized Ppy-PVS
reached the maximum at pH 6.0, and FTIR studies showed the
electrostatic interaction between the DNA and polymeric film. A
Ppy-PVS film was prepared at the surface of ITO electrodes by
chronopotentiometrical electropolymerization from the solution
containing pyrrole and PVS [51]. DNA was then physisorbed onto
the polymer, and the resulting biosensor had improved sensitivity
to 3-chlorophenol (0.1-25 ppm) and 2-aminoanthracene (0.01-15
ppm). The response time was about 30 seconds. Incorporation
of the DNA into the polymeric layer during electropolymerization
led to increased sensitivity to both 3-chlorophenol (0.01-55 ppm)
