Abstract: In this work, we propose an electrical strategy to extract further more information on an electrolyte cation's nature than its concentration, out of a single organic electrochemical transistor (OECT): a biocompatible device which is nowadays attracting v ery much attention as a sensor platform for bioelectronics. Based on an optimized OECT structure,the systematic study by impedance spectroscopy of 6 different chloride salts over 12 different concentrations demonstrated that the impedance of the OECT dev ice is governed either by electrical or electrolytic transport mechanisms, depending on the frequency range of the study. From both of these ion-dependent impedances, on can extract either the conductance of the electrolytes or the one of the dedoped pol y(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). From the boundaries of both of these very different ion-limited mechanisms, we extracted two uncorrelated ion-dependent output, accessing to information on the electrolyte cation's nature apart from its concentration. This strategy can be implemented in dynamic analysis of complex ionic media, such as for cellular-activity sensing, in order to discriminate cationic flows, without introducing any foreign ion-selective material, which can t hreaten the biocompatibility.

Abstract: We report on hydrazine-sensing organic electrochemical transistors (OECTs) with a design consisting in concentric annular electrodes. The design engineering of these OECTs was motivated by the great potential of using OECT sensing arrays in fields such a s bioelectronics. In this work, PEDOT:PSS-based OECTs have been studied as aqueous sensors, specifically sensitive to the lethal hydrazine molecule. These amperometric sensors have many relevant features for the development of hydrazine sensors, such as a sensitivity down to 10^-5 M of hydrazine in water, an order of magnitude higher selectivity for hydrazine than for 9 other water soluble common analytes, the capability to recover entirely its base signal after water flushing and a very low v oltage operation. The specificity for hydrazine to be sensed by our OECTs is caused by its catalytic oxidation at the gate electrode and enables increasing the output current modulation of the devices. This has permitted the device-geometry study of the whole series of 80 micrometric OECT devices with sub-20-nm PEDOT:PSS layers, channel lengths down to 1 μm and a specific device geometry of coplanar and concentric electrodes. The numerous geometries unravel new aspects of the OECT mechanisms governi ng the electrochemical sensing behaviours of the device, more particularly the effect of the contacts which are inherent at the micro-scale. By lowering the device cross-talking, micrometric gate-integrated radial OECTs shall contribute to the diminishin g of the readout invasiveness and therefore promotes further the development of OECT biosensors.