Biomedical Engineering Reference
In-Depth Information
thioaniline monolayer-modified Au-coated glass surface. Due to the electronic
conductivity of the Au NPs, the electropolymerization process yields a three-
dimensional film that is being gradually deposited on the surface of the electrode.
An AFM analysis corresponding to the border region between the electropo-
lymerized surface and the bare Au support reveals a complex morphology
(Fig.
1b
). Evidently, the composite consists of aggregated domains exhibiting an
average thickness of ca. 30 nm and a nonhomogenous topography. A cyclic
voltammetry analysis of the bis-aniline-cross-linked Au NPs deposit at pH
7.2
reveals a quasi-reversible redox wave around 0.1 V vs. Ag QRE (Fig.
1c
) consistent
with the electrochemical transformation of the bridging units between the reduced
bis-aniline and the oxidized quinoid states.
The simplicity associated with the one-step electrochemical synthesis of the
bis-aniline-cross-linked Au NPs composite, the ability to control its electrochemical
preparative conditions, and the diversity in the functionalization of the Au NPs
building blocks suggested the application of the electrodes as attractive host
materials for molecular imprinting. Upon their synthesis, the imprinted electrodes
were applied in different fields, including the sensitive and selective detection of
different target analytes [
49
-
56
], as photochemically and/or electrochemically
triggered “sponges” [
57
,
58
], the signal-controlled wettability of surfaces [
59
,
60
],
and for the generation of enhanced photoelectrochemical cells [
61
].
By the incorporation of a substrate that demonstrates high structural and/or
chemical analogy to the selected target analyte in the electropolymerization mixture,
and by designing high affinity interactions between the substrate and the bis-aniline-
bridging units (or the capping of the Au NPs, for further information
vide infra
),
specific imprinted sites for the target analyte in the Au NPs composite can be
generated (Fig.
2
). Different host-guest interactions between the matrix and
the template molecule facilitate the imprinting process, and these include
donor-acceptor, ionic (acid-base) interactions, hydrogen bonds, and ligand
complexation. It should be noted that the analog imprint molecules are often
significantly more soluble in the electropolymerization medium in comparison to
the target analytes themselves. This enhanced solubility is essential for increasing
the density of imprinted sites in the electro-synthesized matrices. Following the
entrapment of the imprint analog molecule in the matrix, it can be removed away by
weakening the associative interactions. This process is typically carried out by
rinsing off the composite for an appropriate time-interval with the pure background
buffer solution, by using a chemical agent, or by the application of an external
potential on the composite-modified electrode, allowing the transformation of the
bridging units between their oxidized and reduced states. The extraction process
yields a matrix containing high affinity imprinted sites with a remarkable similarity
¼
Fig. 1 (continued) corresponding to the bis-aniline-cross-linked Au NPs composite, recorded in a
0.1 M, pH
7.2 HEPES buffer at 100 mV s
1
. Part B - Reprinted with permission from ref. 59.
Copyright 2011, American Chemical Society. Part C - Reprinted with permission from ref. 57.
Copyright 2010, American Chemical Society
¼
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