High-stability pH sensing with a few-layer MoS field-effect transistor.

Recently, molybdenum disulfide (MoS), an emerging 2D material, has become an alternative candidate for ultra-sensitive biosensors due to its semiconducting behavior and the unique layer-by-layer atomic structure. Here, we report on highly stable and repeatable real-time pH sensing with few-layer MoS field-effect transistor (FET) biosensors, fabricated with both HfO and AlO/HfO gate dielectrics on top of MoS flakes exfoliated from natural crystals onto SiO/Si samples. Both types of sensors demonstrate a highly linear, stable and repeatable response over a wide pH range with near-ideal pH sensitivity close to the theoretical limit of 59.6 mV pH. Ascribing from a different device operation regime in the pH sensing test-subthreshold regime for a sensor with an AlO/HfO dielectric and linear regime for a sensor with HfO-a sensor with AlO/HfO shows significantly higher current sensitivity (∼105-fold) and relatively better linearity than a sensor with HfO, while the latter shows relatively higher stability and higher repeatability. An AlO/HfO-coated MoS FET reveals a high sensitivity or low detection limit of 0.01 pH.