Organic field-effect transistor based sensors with sensitive gate dielectrics used for low-concentration ammonia detection

A novel organic field-effect transistor (OFET)-sensor concept is presented based on the application of an ion-conducting organic dielectric material, which is chemically adapted to change its electronic properties upon contact with an analyte, thereby generating an electrically detectable response. By employing pH-sensitive, ring-opening metathesis polymerized materials as gate dielectrics in bottom-contact OFETs with a meander-shaped top-gate structure, the concept was successfully realized and evaluated with ammonia (NH3) as gaseous analyte, easily providing distinct sensor response at concentration levels as low as 100 ppm. In addition to current-voltage OFET-analysis, optical spectroscopy and capacitance measurements were used to rationalize the underlying sensor mechanism, which is mainly attributed to a deprotonation of the pH-sensitive groups of the active-sensing dielectrics by NH3 and a resulting generation of mobile ions, leading to an increase of the charge carrier density within the OFET channel. The proposed concept provides several advantages over existing OFET-sensor detection principles, including the separation of the sensing mechanism from the charge-transport functionality of the semiconductor, inherent protection of the latter against air exposure and increased selectivity by the application of specific dielectric materials. It therefore offers a great deal of promise in contributing to the development of cheap, integrated, smart and flexible (bio)sensor systems. (C) 2012 Elsevier B.V. All rights reserved.