Page 424 - Organic Electronics in Sensors and Biotechnology

Electrochemical Surface Switches and Electronic Ion Pumps Based on Conjugated Polymers 401

Immediately after switching
Oxidized Reduced
o
o o os o – θ = 58.1° ± 5.5° θ = 30.1° ± 5.1°
θ
s n
PEDOT Tosylate

FIGURE 11.6 Left: The chemical structure of poly(3,4-ethylenedioxythiophene)
(PEDOT) and Tosylate. Middle: PEDOT:Tosylate has been chemically synthesized
along the surface of standard 12-well cell culture plates. Right: The water contact
angle of planar PEDOT:Tosylate surfaces switched to the oxidized and reduced
state, respectively.

growth. They found that cells preferred to adhere to and spread
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along the fibronectin-coated PPy electrodes that were switched to the
oxidized state. On the fibronectin-coated PPy electrodes switched to
the neutral state, cells obtained a rounded morphology and were less
prone to spread along the surface.
PEDOT can be chemically synthesized with Tosylate as the dop-
ing ion to form electrodes on various planar insulating carriers. These
films can be manufactured along the surfaces of wells in standard cell
culturing plates (Fig. 11.6). Electronically separated electrodes are
achieved by cutting the electrode films using a plotter knife or an
ordinary scalpel. The oxidation states of adjacent electronically iso-
lated PEDOT:Tosylate electrodes are controlled by biasing addressing
pads located outside the wells, while the cell medium serves as the
electrolyte.
We used the PEDOT:Tosylate electrodes to analyze whether the
electroactive surface could be used to direct stem cell differentiation.
Neuronal stem cells c17.2 were seeded onto the reduced and oxidized
electrodes. We found that the stem cells adhered to a much greater
extent to the oxidized surface compared to the reduced surface. Sur-
face spectroscopy studies and protein adsorption experiments
revealed that the amount of serum protein albumin differs vastly
between the reduced and oxidized surfaces. Such electronic control
of cell seeding and density may open possibilities for novel devices
that can be used to direct the differentiation of stem cells.

11.2 Electronic Ion Pumps Based on PEDOT:PSS
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In PEDOT:PSS -based (Fig. 11.7) thin-film EC devices, fast electro-
chemical switching throughout the bulk can occur because the polymer
film electrodes allow transport of both ionic and electronic species. In
the previously described surface switches, this may not be crucial