Analogue voltage inverter from electrolyte-gated graphene field-effect transistors for ion-sensing applications in aqueous media

Overview & Synopsis

Ion Sensitive Membranes (ISM) and their integration into Electrolyte-Gated Field Effect Transistors (EGFETs) based devices have been widely described in literature to perform sensing in solution. Interest of graphene and graphene-based materials (GBM) for such application has increased lately since it is considered as being a highly conductive material stable in aqueous media. While voltage inverters operated as logic gates from graphene-EGFET have already been designed and reported, no work is relating to their use as ion sensors. The presented work is targeting to combine ISM working principle with GBM-EGFET technology in order to build a device able to detect a certain threshold ion concentration with a direct numerical or voltage readout method, which is conforming to the emerging field of Chemical Logic, and that is less resources-consuming regarding the integration of such sensor in electronic circuits. A noteworthy effort of the presented work is concerning the use of low-cost techniques and materials for a large-scale production perspective of plastic electronics devices. Therefore, polyimide substrates are used and conductive channel of the transistors are built from a home-made graphene oxide formulation deposited from drop-casting or printing techniques. Furtherly GO is turned into rGO (reduced Graphene Oxide) by an in situ electroreduction step able to tune the doping level of the material. While the usual complementary Inverter is composed of two transistors connected in series: an n-type and a p-type one, We have shown that it is still possible to create a functional inverter out of p-doped rGO-based transistors.. The working principle of the rGO-EGFET inverter is close to the one of a voltage divider bridge. We developed a toy-model in order to have a better understanding on the electric behavior obtained from our ambipolar rGO-based inverters. We designed afterwards an ion-sensor based on the rGO-inverter. The selectivity toward potassium ion has been investigated by the deposition of a potassium ionophore III ISM on the device's channel. The working principle of the detection is based on a shift of the electrical characteristics of the modified transistor while the whole device is being immersed in an electrolyte containing the target ion.