Biology Reference
In-Depth Information
3.4.5
Electrochemical Genosensing Based on
Graphite-Epoxy Composite Modified with Gold
Nanoparticles (NanoAu-GEC) as Electrochemical
Transducer
Chemisorption based on self-assembled monolayers (SAMs) is
a single-point immobilization strategy that allows the oriented
attachment of a wide range of biomolecules on gold-based trans-
ducer surfaces. One of the main drawbacks of using SAMs for the
immobilization of biorreceptors in electrochemical biosensing is
that a compact layer is achieved which produces a dramatically
reduction of the diffusion of electroactive species toward the sur-
face of the transducer. Moreover, the tightly packed layer may also
produce steric hindrance and, as a consequence, lower rate of reac-
tion between the probe and the target. As such, a stringent control
ofthesurfacecoverageofthegold-basedtransducerisanimportant
factor, which can be performed by using auxiliary reagents such as
lateral spacer thiolsand mixedmonolayersto obtain bioactivegaps.
In order to avoid the stringent control of surface coverage para-
meters during immobilization of thiolated oligos on continuous
gold surface films, the use of gold NPs in a graphite-epoxy com-
posite (nano-AuGEC) has been proposed (Fig. 3.3D) [99]. In this
novel transductor, islands of chemisorbing material (gold NPs) sur-
rounded by rigid, non-chemisorbing, conducting, graphite-epoxy
composite are obtained, asshown in Fig. 3.7.
With this arrangement in the electrochemical transducer, the
resulting less-packed surface provides improved hybridization fea-
tures with a complementary probe minimizing steric and electro-
static repulsion. The spatial resolution of the immobilized thiolated
DNA was easily controlled by merely varying the percentage of gold
NPsin the composition of the composite (Fig. 3.8).
ForGECelectrodes,graphitepowder(particlesizebelow50
μ
m)
and epoxy resin (Epo-Tek, Epoxy Technology, Billerica, MA, USA) in
a 1:4 (w/w) ratio were thoroughly hand mixed to ensure the uni-
formdispersionofthegraphitepowderthroughoutthepolymer.For
nanoAu-GEC electrodes, the following ratios of gold NPs/graphite
powder/epoxy resin were prepared: 0.075:0.925:4 (w/w) for
nanoAu(7.5%)-GEC; 0.250:0.750:4 (w/w) for nanoAu(25%)-GEC;
