Biology Reference
In-Depth Information
procedure led to the synthesis of a Ppy film bearing covalently
linked ODN. The hybridization event was detected using a quartz
crystal microbalance method (QCM) [60-63]. This method was also
applied to prepare silicon DNA chip containing 48 or 128 gold
microelectrodes, where the hybridization reaction was evaluated
using fluorescence [60, 62, 64, 65]. A similar procedure was
described for the preparation of biotinylated Ppy film at the
surface of gold quartz crystals as well as silicon chip containing
48 gold microelectrodes [66-68], where biotin was used for the
immobilization of avidin. Then biotinylated ODN was immobilized
viathe biotin/avidina
nity bond.
Polypyrrole can also be functionalized with the electrochemical
indicator of DNA, such as ferrocenyl groups bearing an active ester
group used for the covalent binding of amino-labeled ODN probe
[69]. Hybridization with complementary ODN caused a decrease in
thecurrentdensityandashiftoftheoxidationwaveoftheferrocenyl
group because of the decrease of polymer permeability. This was
explained by the change of the conformation along the conjugated
backbone of the polymer. The prepared DNA biosensor was able to
detect less than 1 pmol oftarget ODN.
The gold electrode was modified with a copolymer using
the monomers 3-acetic acid pyrrole and 3-
N
-hydroxyphthalimide
pyrrole [36, 70]. This copolymer contained activated ester groups
used for covalent grafting of an ssDNA probe bearing a terminal
amino group. It was found that porous Ppy led to a higher density
of immobilized DNA probes and improved the detection of the
hybridization reaction. The same copolymer was used for the
preparation of a multiplot DNA biosensor based on microelec-
trodes deposited on the chip [71]. The polymer offered direct
transduction of the recognition process into an electrochemical
signal because its signature varied according to a hybridization
event. Another copolymer-based DNA biosensor was prepared
by electropolymerization of Py in the presence of 4-(-3-pyrrolyl)
butanoic acid [29]. Ppy was also used as an electrostatic adsorption
matrix, which allowed immobilization of DNA onto the porous
silicon substrate without using covalent bonds [72]. Polypyrroles
are reported as a convenient matrix for the immobilization of
nanomaterials at the surface of an electrode [73]. In this case the
