Nanoelectrochemistry: Fundamentals and Applications in Biology and Medicine - Applications of Electrochemistry and Nanotechnology in Biology and Medicine - page 52

tially, they will allow measurements of release at single-vesicle
resolution. Wu et al. have already observed dopamine release from
single living vesicles using carbon-fiber nanoelectrodes. 213 With
sufficient miniaturization they may also enable measurements in
the synaptic clefts, thereby directly probing neuronal communica-
tion. Smaller electrodes also have potential for lesser tissue dam-
age in in-vivo studies. Much of the work to date has been per-
formed with carbon fiber microelectrodes. This is because carbon
fiber microelectrodes are biocompatible and more resistant to foul-
ing than noble metal electrodes. Since most efforts in making
nanoelectrodes have hitherto focused on noble-metal electrodes, a
key challenge will be to make similar carbon-based nanoelectrodes.
Chen et al. have fabricated carbon-fiber electrodes (100-300 nm
diameter) covered with sheets of SWNTs that increase the surface
area, while remaining nanometric in overall dimensions. These
modified electrodes lowered the detection limit of select neuro-
transmitters 10-fold compared to the unmodified electrodes. 214 An
alternative approach would be to utilize surface-modification of
noble-metal electrodes to increase sensitivity and selectivity.
However, these modifications can compromise the response time
of the electrodes, thus lowering the time resolution. 215 They might
also complicate the inherent uncertainties in the exact geometry of
the electrode, especially in context of quantitative studies involv-
ing spatial resolution.
With the ability to make structures that are much smaller than
an average mammalian cell (ca. 10-20 ȝm), the field is approach-
ing a point at which it is possible to insert nanosized electrochemi-
cal probes inside cells. Recently, Sun et al. demonstrated electro-
chemical measurements obtained inside of a cell. 216 A 42 nm Pt,
pulled glass electrode, was used to successfully penetrate a human
epithelial cell and measure intracellular redox species. A schematic
diagram of the measurement concept is shown in Fig. 10 . The de-
crease in size of electrochemical tranducers corresponds with de-
velopments in the semiconductor industry, thus smaller electrode
structures that permit measurements of still unknown exocytosis
properties can be anticipated. Future application of nanostructures
and electroanalytical measurements on living systems will necessi-
tate investigating and answering questions associated with how
nondestructive they really are and how the penetration of nano-