(Invited) Large Area Ion Sensitive Graphene Field Effect Transistors for Potassium, Sodium and Chlorine Sensing

Abstract

We review our work on large-area graphene based ion sensitive field effect transistors (ISFETs), employing metal oxide layers or ionophore based membranes. Unlike traditional silicon based ISFETs, our work is focused on macroscopic graphene devices fabricated using chemical vapour deposition methods. Large-area graphene ISFETs benefit from the combination of high mobility charge transport, reduced low-frequency noise with increasing transistor channel area, and facile integration with ion sensitive layers. Graphene ISFETs with an active area of approximately 1cm x 1cm are characterized by an rms current noise as low as 5 ~ nA in a 60 Hz bandwidth, field effect mobilities up to 5000 cm2 V-1 s-1 and quantum capacitance limited coupling between graphene channel and the solid/electrolyte interface. We have demonstrated graphene ISFETs selectively sensitive to H+, K+, Na+ and Cl-. In the case of H+ sensing, metal oxides such as Ta2O5 and Al2O3 deposited by atomic layer deposition can be used to achieve Nernstian limited sensitivity with a 0.1 mpH resolution. Ion sensitive membranes based on ionophores can be used for selective sensing of other ionic species. For example, in the specific case of the K+, real-time sensing was achieved using potassium ionophore III with a detection limit of 10-9 M [K+], equivalent to 39~ng/L, and a resolution of 1.5×10-3 log[K+]. Spiking experiments reveal good reversibility and stability. The cross-sensitivity has been measured to be: 2.5 mV/decade for Na+, 4.2 mV/decade for Ca2+, 1.5 mV/decade for Mg2+ and 9.0 mV/decade for NH4 +. Graphene ISFETs are sufficiently robust to measure the K+ content of common beverages and blood samples. We will conclude our talk with a discussion of open questions concerning graphene ISFET performance and their potential applications.