Layer-by-Layer Assembly Monitored by PEDOT-Polyamine-Based Organic Electrochemical Transistors

In this work, we present the fabrication of PEDOT–PAH-based organic electrochemical transistors (OECTs), that are employed to monitor the deposition of polyelectrolyte multilayers on their surface. We first explore different synthesis conditions in order to optimize the electrical characteristics of the devices, such as threshold voltage and voltage of maximum transconductance. Next, the transistors showing the desired features are chosen to investigate the process of the layer-by-layer (LbL) assembly through (i) the analysis of the transfer characteristics curves and (ii) the changes in the registered drain–source current. It is demonstrated that the OECTs are able to monitor the assembly of the different polyelectrolyte layers in real time in both modes of operation, yielding information about conductivity and surface potential changes in the channel. Next, the transient characteristics of the devices are studied upon the assembly of the different layers, providing information about the changes in the ionic transport through the whole film during the ON and OFF switching. Finally, the kinetic response of the OECTs toward the monitoring of charged macromolecules is fitted to a two-step adsorption model and compared against graphene field-effect transistors and surface plasmon resonance. The monitoring of the LbL assembly by the changes in the PEDOT–PAH OECT response illustrates the use of these transistors for sensing interactions with charged species in solution and supports the development of sensing platforms by integration of specific recognition elements on the conducting polymer channel.