A reference-less pH sensor based on an organic field effect transistor with tunable sensitivity

Despite their great potentiality, ISFET-like devices generally suffer from an intrinsic limitation in sensitivity, the so-called Nernst limit. Moreover, the high costs, the restricted range of employable materials associated to the silicon technology, and the need for a reference electrode, have reduced the applicability of such devices in the bio-sensing field. In this work, we show how a reference-less pH sensor based on an organic semiconductor device, called Organic Charge-Modulated Field-Effect Transistor (OCMFET), besides being low cost, flexible, and transparent, shows a super-nernstian sensitivity with no need of any chemical modification of the sensing area. Moreover, thanks to its peculiar transduction principle and structure, the device sensitivity can be easily tuned by acting on geometry-related parameters of the device itself, introducing an interesting alternative approach for the realization of highly sensitive, reference-less, and low-cost devices for a wide range of bio-sensing applications.