<p>There is intense interest
in utilizing the redox activity of Organic Mixed Ionic Electronic Conductors
for faradaic chemical sensing. In particular, the investigation of organic
electrochemical transistors (OECTs) as biosensors due to their low operational
potentials, ease of fabrication (e.g. by inkjet printing), biocompatibility,
and large transconductance. </p>
<p>It has become common
practice in the OECT community to combine both chemical detection and
transistor function within the same compartment, assuming that the sensor
signal is amplified seamlessly by the sensing OECT. These devices however routinely
encounter several challenges whose origins often remained unclear. Some of
these challenges are 1) small changes in drain current, contradicting OECT’s oft-touted
current-amplifying abilities. 2) Irreversible chemical changes to the
semiconducting polymer electrodes. 3) Parasitic side reactions convoluting the
sensing signal, exacerbated by applied voltages.</p>
<p>In this manuscript, we
show that optimization of OECT-based sensors requires more rigorous
characterization of electrode potentials to elucidate electrochemical phenomena,
a practice that is often largely absent in current reports. Our analysis of fundamental
device physics of various OECT architectures shows that despite what a large
fraction of the organic bioelectronics community still believes, amperometric OECTs either 1) do not display
any transistor behavior, and in fact operate merely as electrodes or 2) Undergo
irreversible changes and are extremely complex to calibrate, or both 1) and 2).
</p>
<p>Indeed, to fully utilize
the OECT’s large transconductance, a separate 2-electrode Reaction Cell which
is utilized to gate a separate OECT is needed (RC-OECT). In this manuscript, in
addition to showing that the RC-OECT resolves the fundamentally and
irreconcilably contradicting design principles of amperometric OECTs, we demonstrate
that it provides great device and materials design flexibility. Finally, we elucidate
the basic principles on how to further optimize the RC-OECT.</p>
<p>We believe that our
findings will be of great interest to researchers in the fields of
bioelectronics as a call to action to re-evaluate present approaches of
utilizing OECTs for chemical detection and to help practitioners select
materials and designs to optimize redox sensors based on organic semiconductors.
</p>
Nanofiber Channel Organic Electrochemical Transistors for Low‐Power Neuromorphic Computing and Wide‐Bandwidth Sensing Platforms
