Biology Reference
In-Depth Information
mediators into DNA assemblies that activate bioelectrocatalytic
transformations, or the use of enzyme labels that yield an insoluble
product on electrode surfaces has been extensively used to amplify
biorecognition events. Due to the several problems associated with
these techniques and the fast development in nanotechnology,
nanoparticle-assisted signal enhancement for DNA biosensors has
been greatly developed in the last decade [7, 8, 9, 10, 11].
In electrochemical sensors, electrocatalytic procedures can be
approached in two ways, either by using an electrode that have
highly or moderately electrocatalytic properties, or by exploiting
a significant change in the electrocatalytic activity of an electrode
during the detection process. Gold and platinum are commonly
employed as highly electrocatalytic electrodes. Although these elec-
trodes allow fast electron-transfer kinetics for most electroactive
species, their background currents are high and fluctuate with the
appliedpotential,whichmaymakedi
culttoobtainthehighsignal-
to-background ratios, required to achieve low detection limits. In
recent years, moderately electrocatalytic electrodes have been used
to obtain high signal-to-background ratios. Such electrodes can be
obtainedbymodifyingapoorlyelectrocatalyticelectrodewithalow
coverage of a highly electrocatalytic material. For example, indium-
tin oxide (ITO) electrodes modified with a partial monolayer of
ferrocene, carbon nanotubes, or gold nanoparticles (Au-NPs) have
been employed [7, 11].
The actual knowledge concerning the special properties of NPs
arises from the numerous studies related to the effects of changes
in shape and size on the general properties of materials. From the
electroanalysispointofviewthemajorfeaturesresultingfromthese
studies are enhancement of mass transport, high catalytic activity,
higheffectivesurfacearea,andcontroloverlocalmicroenvironment
at the electrode surface [8, 12, 13, 14].
The development of nanotechnology during the last decades has
led scientists to fabricate and analyze catalysts at the nanoscale.
These nanostructured materials are usually high-surface-area met-
als or semiconductors in the form of NPs with excellent catalytic
properties due to the high ratio of surface atoms with free valences
to the cluster of total atoms. The catalysis takes place on the
active surface sites of metal clusters in a similar mechanism as the
