Boron δ-doped (1 1 1) diamond solution gate field effect transistors

► Solution gate-FET using a boron δ-doped channel on (1 1 1) diamond was fabricated. ► Enhancement mode operation with channel pinch-off and drain-source current saturation. ► Maximum gain and transconductance of 3 and 200 μS/mm were achieved. ► Showed a pH sensitivity of 36 mV/pH, displaying fast temporal responses. ► Demonstrated stability against anodic oxidation.