Defect-engineered liquid-gated MoS2 field-effect transistor for pH sensing

Defects in nanomaterials are always considered as instability factors for device performance. However, we have discovered a positive role for the defects in monolayer molybdenum disulfide (MoS 2 ) lattice in the registration and transformation of useful bio and chemical signals. In this study, we developed a liquid-gated MoS 2 field-effect transistor (FET) employing a chemically synthesized MoS 2 film that serves dual functions as both the active channel and pH-sensitive layer. Through defect engineering, we activated the inert basal plane of MoS 2 , significantly enhancing the chemisorption of hydrogen ions (H⁺) at defect sites and improving specific responses to pH variations. The optimized defect-engineered, liquid-gated MoS 2 FET demonstrates a low subthreshold swing ( SS ) of 70 mV/dec in electrolyte solution, approaching the theoretical limit, with a record-high current sensitivity of 534.8%/pH in the subthreshold region due to the smaller SS . Remarkably, the device demonstrates a minimal hysteresis width of 5 nA after two cycling tests. Combined with theoretical calculations, this study reveals the crucial role of defect sites in MoS 2 for the adsorption of H + ions. The findings provide key insights for achieving high-performance pH sensors and offer important guidelines for maintaining the operational stability of FET biosensors in complex systems.