Biomedical Engineering Reference
In-Depth Information
2.3 Imprinted Electropolymerized Au NPs Composites Based on Ligand-Analyte
Complexation Processes for Sensing ................................................ 204
3 Conclusions and Perspectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
1
Introduction
During the past several decades, and in accord with the rapidly growing field of
nanotechnology, a considerable amount of scientific efforts has been directed toward
research that includesmetal nanoparticles (NPs). Due to the quantum-size dimensions,
metallic NPs offer unique electrical [ 1 - 3 ], optical [ 4 ], and catalytic functions [ 5 ],
which allow their diverse applications in many different fields. For example, metallic
NPs were recently reported as promising building blocks of enhanced sensing
platforms [ 6 ], or nanoscale devices [ 7 ], or as catalysts for a variety of chemical
reactions [ 8 ]. Among the different metallic NPs, Au NPs are most extensively
investigated. The aggregation of Au NPs as a result of sensing events, and the
subsequent formation of interparticle coupled plasmon excitons were used for the
development of colorimetric sensors [ 9 , 10 ]. For example, the red-to-blue color
changes arising from the aggregation of Au NPs were used to detect phosphatase
activity [ 11 ], polynucleotides [ 12 ], or alkali ions [ 13 ]. Also, the occurrence of shifts in
the plasmon absorption bands of Au NPs upon binding of different analytes, and due
to the consequent emergence of dielectric changes on the surface, was used in the
development of optical sensors, such as for dopamine [ 14 ], adrenaline [ 15 ], choles-
terol [ 16 ], pH [ 17 ] and biosensors that probed DNA hybridization [ 18 ], or the
formation of aptamer-substrate [ 19 ] or antigen-antibody [ 20 , 21 ] complexes.
In recent years electropolymerized films on electrodes have played a key role as
functional materials for sensing [ 22 - 25 ], in the actuation of a mechanical motion in
microdevices [ 26 , 27 ], in the fabrication of solar cells [ 28 , 29 ] or light-emitting diodes
[ 30 , 31 ], and for the bioelectrocatalytic activation of enzymes [ 32 - 34 ]. The method-
ology of imprinting organic or inorganic polymer matrices is known since the
twentieth century, and has been extensively developed by Mosbach [ 35 - 37 ]and
Wulff [ 38 - 40 ]. This technology still constitutes a simple, yet a solid means, for
generating specific molecular recognition sites in polymer systems [ 41 - 43 ]. Over
the years, a broad range of applications based onmolecularly imprinted polymers have
been demonstrated, including their use as separation and controlled release matrices
[ 44 ], as catalytic supports [ 45 , 46 ], or as sensing materials [ 47 ]. In this context,
particularly interesting is the application of imprinted polymers immobilized on
electrodes for sensing. Despite the inherent advantages provided by the imprinted
sensing electrodes, which are primarily associated with the formation of molecular
templates for the selective binding of analytes, several fundamental limitations related
to these electrodes are often encountered; (1) The density of the imprinted sites is
typically low, and thus relatively thick polymer interfaces are required. This results in
a slow diffusion of the analyte into the thick sensing matrix, leading to long response
times for the sensor devices. (2) The need for a thick sensing layer often perturbs the
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