Abstract

Organic electrochemical transistors (OECTs) are now well-known, robust and efficient as amplification devices for redox reactions, typically biologically ones. In contrast, electrolyte-gated organic field-effect transistors (EGOFETs) have never been described for that kind of application because field-effect transistors are known as capacitive coupled devices, i.e., driven by changes in capacitance at the electrolyte/gate or electrolyte/semiconductor interface. For such a kind of transistors, any current flowing at the gate electrode is seen as a drawback. However, we demonstrate in this paper that not only the gate potential can trigger the source-drain current of EGOFETs, which is the generally accepted mode of operation, but that the current flowing at the gate can also be used. Because EGOFETs can work directly in water, and as an example of application, we demonstrate the possibility to monitor microalgae photosynthesis through the direct measurement of photosynthetic O2 production within the transistor’s electrolyte, thanks to its electroreduction on the EGOFET’s gate. This paves the way for the use of EGOFETs for environmental monitoring.

Highlights

  • Electrolyte-Gated Organic Field-Effect Transistors Electrolyte-Gated Organic Field Effect Transistors (EGOFETs) are original organic transistors for which the dielectric material in-between the gate and the semiconductor, mandatorily present in ISOFETs (Ion-Sensitive OFETs) is absent, so that the electrolyte is in direct contact with the semiconductor

  • We measured a parallel change of the drain current, with an amplitude of ca. 1000 nA. This experiment demonstrated that the EGOFET is able to amplify the current of a redox reaction occurring at the gate, into a more intense drain current

  • Under the same conditions as above, the drain and gate currents were recorded under alternated dark and illuminated periods (Figure 1, left). This result shows that oxygen produced under illumination by the cyanobacteria is reduced at the gate electrode, leading to a gate current to a drain current increase

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Summary

Introduction

Electrolyte-Gated Organic Field-Effect Transistors EGOFETs are original organic transistors for which the dielectric material in-between the gate and the semiconductor, mandatorily present in ISOFETs (Ion-Sensitive OFETs) is absent, so that the electrolyte is in direct contact with the semiconductor. Its absence allows low operating potentials, of a few hundreds of millivolts Another characteristic of EGOFETs compared to ISOFETs is that the gate is not necessarily a pseudo-reference electrode such as Ag/AgCl; it could be a simple metal wire such as Ti, Pt or Au, or even a carbon electrode. The current flowing through the semiconductor of these devices, called drain current and noted ID, is directly proportional to the overall capacitance CG_OSC between the gate and the semiconductor. This capacitance CG_OSC comes from the series capacitances of both the gate/electrolyte (G_ELEC) and electrolyte/semiconductor (ELEC_OSC) interfaces, i.e., 1/CG_OSC = 1/CG_ELEC + 1/CELEC_OSC. Because the gate electrode and the OSC are dipping in an electrolyte, they are both subject to electrochemical

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