In biological systems many tissue types have evolved a barrier function to selectively allow the transport of matter from the lumen to tissue beneath. Characterization of these barriers is very important as their disruption or malfunction is often indicative of toxicity/disease. The degree of barrier integrity is also a key indicator of the appropriateness of in vitro models for use in toxicology/drug screening. The advent of organic electronics has created a unique opportunity to interface the worlds of electronics and biology, using devices such as the organic electrochemical transistor (OECT), that provides a very sensitive way to detect minute ionic currents. This proposal aims to integrate the barrier function of biological systems with OECTs to yield devices that can detect minute disruptions in barrier function. Specifically, OECTs will be integrated with cell monolayers that form tight junctions and with membranes that incorporate ion channels. A disruption in tight junctions or a change in permeability of ion channels will be detected by the OECT. These devices will have unprecedented sensitivity, in a format that can be mass produced at low-cost. The potential benefits of this multidisciplinary project are numerous: It will be a vehicle for fundamental research in life sciences and the development of new in vitro models for toxicology screening of disruptive agents and the development of drugs to treat disorders linked with barrier tissue malfunction (e.g. mutations in ion channels). Moreover, through the use of various cell lines and ion channels, this platform will also lead to the engineering of new sensors and biomedical instrumentation, with a host of applications in medical diagnostics, food/water safety, homeland security and environmental protection.