Super Nernstian pH sensing using ionic liquid gated 2D transition metal dichalcogenide transistors

Dual-gated field-effect transistor pH sensors (dualFETs) with asymmetric gates were developed that surpassed the Nernst sensitivity of 59 mV/pH by orders of magnitude. We also demonstrated an improved signal-to-noise ratio (SNR) and thereby a lower limit of detection relative to previously reported dualFETs [1]. We present an experimental pH sensing study by using 2D transition metal dichalcogenide transistors, fabricated on oxide substrates, with ionic liquid top gates. Our devices operate at low voltages and feature asymmetric front-gate (ionic liquid) and back-gate (substrate oxide) capacitances which allow a signal amplification ranging from 35 to 200 depending on the substrate oxide thickness (70 nm and 300 nm). We demonstrate that in the dual-gate configuration, the dualFETs response to a change in pH increases proportionally to the ratio of the asymmetric gate capacitances, and exceeds the Nernst limit. This higher sensitivity, combined with lower limit of detection makes dualFETs a powerful tool for field monitoring of pH with wide ranging applications in healthcare, environmental monitoring and agriculture.
[1] T. Wu, et al., ACS Nano 2017, 11, 7142–7147.