Biomedical Engineering Reference
In-Depth Information
Here, our primary focus will be on the fundamental and prac-
tical consequences of working with electrode systems with lateral
dimensions that are below 100 nm. In some instances we will also
consider nano-gap electrodes, where although the electrodes them-
selves are micrometer scale, they are separated from another elec-
trode by distances < 100 nm. We will only deal with systems that
involve some manner of
electron transfer
between molecules in
solution and an electrode.
Therefore, although they may, in a sense, be considered
elec-
trochemical
, we will refrain from considering advances in areas
such as nanowires
1-3
and other low-dimensional nanomaterials
4-6
and nanopores
7
—areas which have witnessed great fundamental
advances in the last decade and hold tremendous potential for ana-
lytical, biological, bio-medical and energy-related applications.
We will also refrain from addressing the areas of solid-state elec-
trochemistry as applicable in battery and fuel-cell research. The
progress in using nanostructured materials as electrodes in these
areas holds great promise, but again lies outside the scope of this
chapter.
8-12
Finally, also omitted for purposes of brevity are elec-
trodes based on arrays of nanoparticles or carbon nanotubes. In the
last two decades carbon nanotubes as electrode materials of na-
noscale dimensions and as components of sensing systems (for
example, field-effect transistors (FETs) etc.) have received consid-
erable attention, perhaps more than any other material. The accu-
mulated body of literature is hence enormous and the interested
reader is again referred to more specialized reviews.
13-16
The underlying motivation for many researchers exploring
nanoelectrochemistry is that shrinking the dimensions of elec-
trodes is rife with many unexplored and potentially exciting fun-
damental phenomena that are, in principle, inaccessible to electro-
chemistry done on the macro-scale. Therefore, we attempt to pro-
vide a general appraisal of the promises inherent in nanoelectro-
chemistry, the progress made towards the realization of some of
these goals, and finally the challenges that lie ahead.
The efforts to shrink dimensions of electrodes down to the na-
noscale regime can be considered the logical denouement of a pro-
cess than began nearly three decades ago with the introduction of
microelectrodes and ultramicroelectrodes (UMEs). The expecta-
tion is that the key advantages of enhanced mass-transport and
relatively easy access to the steady-state regime (on account of the
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