Novel Gate Electrode Design for Flexible Planar Electrolyte-Gated Field-Effect Transistor-Based Sensors for Real-Time Ammonium Detection

In this work, the comparison between two different gate electrode layouts (square-shaped and U-shaped, designed with the same area) for flexible and planar electrolyte-gated field-effect transistor-based sensors for ammonium detection is reported. Spray-deposited semiconducting carbon nanotubes were employed as active material, while the functionalization was achieved by means of an ion-selective membrane, based on the nonactin ionophore. The devices fabricated with the two designs were compared in terms of the response towards different concentrations of ammonium. Both showed excellent linear detection for ammonium in the physiological range of interest from 0.1 to 10 mM. The devices with the square-shaped gate achieved average sensitivity of 1.270 µA/decade (relative standard deviation 70.55%), while the devices with the novel U-shaped gate showed an improved sensitivity of 2.669 µA/decade (relative standard deviation 31.46%).