Page 425 - Organic Electronics in Sensors and Biotechnology

402 Chapter Eleven

PEDOT PSS
O O n

S n
H
SO 3
FIGURE 11.7 Left: Chemical structure of PEDOT and PSS. Middle: The conjugated
PEDOT:PSS-based ion pump made of patterned, adjacent PEDOT:PSS electrodes
+
(A through D). Right: By addressing the electrodes ions (M ) migrate from the source
to the target electrolytes through the nonconducting PEDOT:PSS channel (pink).
(See also color insert.)

since all desired action specifically occurs along the outermost sur-
face. But in other conjugated polymer-based EC devices (e.g., dis-
17
plays and transistors), switching of the bulk is crucial. For instance,
in a polymer EC transistor, the electronic current between drain and
5
source is controlled by the impedance state, which is further con-
trolled by the EC state, within the channel. Conversely, it would be of
great interest to enable electronic control of the migration of (charged)
biosignaling molecules for a variety of bioapplications.
Electronic ion pumps were recently constructed using adjacent
electrodes of PEDOT:PSS and separated source and target electro-
18
lytes (Fig. 11.7). The two aqueous electrolytes are connected via a
PEDOT:PSS channel, in which the PEDOT phase has been made per-
manently nonconducting (for electronic currents) by electrochemical
over-oxidation. Thus, the channel can only conduct ionic species,
19
primarily throughout the polyelectrolyte PSS phase in the channel.
As the electrodes are addressed, ions are first forced to enter the B
electrode. Then the biased B-C electrode configuration drives ions
from the source compartment toward the target electrolyte. Finally,
the C-D electrode configuration promotes launching of ions away
from the C-electrode surface to enter the target medium.

11.2.1 Electronic Control of Proton Oscillations
Initially, we studied the transport of positively charged ions, primarily
+
protons and different alkali metal ions such as K . As protons are
pumped from the A-B electrolyte to the C-D target electrolyte, they
enter the target electrolyte along the border at which the PEDOT:PSS
channel contacts the target electrolyte. To study the overall efficiency
and the charge transport characteristics of this ion pump device, sev-
eral different experiments were performed. First, proton migration was
recorded using a HCl aqueous source electrolyte of pH = 0 and a target
electrolyte based on a CaCl aqueous solution of pH = 7. At V = 5 V
2 BC