Biomedical Engineering Reference
In-Depth Information
studies of neurotransmitter release in brain slices. Nanoelectrodes described below in detail form
an array on a planar insulating substrate suitable for holding a brain slice under an optical micro-
scope.
50,51
Electrical simulation and detection of neurotransmitter release at individual neurons over
large sample area can therefore be easily carried out with the fast response and high-sensitivity
characteristic of nanosized electrodes and without the requirement of individual electrode fabrication
and positioning.
Template synthesis of gold (Au) and conducting polymer nanostructures using template syn-
thesis techniques has been reported previously
20
and was adopted here with an addition of a mask-
ing step to reduce the density of deposited nanostructures (Figure 13.28). An alumina membrane
with 20 nm pore size was used as a template for Au-electrode electroplating.
Polystyrene beads of 0.5 µm diameter were used as a mask to create a pattern in the sputtered
SiO
2
where gold electrodes could be electroplated and then coated with
o
-PPY. A series of SEM
images showing various stages in the fabrication procedure are shown in Figure 13.29. The result-
ing nanoelectrodes are composed of an array of 20 nm Au posts, providing a large surface area
for increased current response with a small overall diameter of 500 nm. By varying the size and
the concentration of the beads in the suspension when deposited onto the alumina membrane,
(A)
Polystyrene bead
Alumina membrane
(B)
SiO
2
film
(C)
Au/Ti seed layer
(D)
Au electroplating
in nanopores with
exposed seed
layer
(E)
Electroplated Au posts
(F)
o
-PPy coating
FIGURE 13.28
Fabrication sequence for making nanoelectrodes: (A) polystyrene bead suspension is
deposited onto an alumina membrane; (B) SiO
2
fi lm is deposited by ion sputtering; (C) beads are removed
by ultrasonication, and Ti/Au seed layer is sputtered onto the substrate; (D) gold is electroplated through the
alumina pores where the seed layer is exposed to solution; (E) alumina membrane is dissolved; and (F) PPy is
electropolymerized and oxidized to form
o
-PPy coating on Au nanoelectrodes.
