Precision pH Sensing beyond the Nernst Limit with MoS ₂ /WSe ₂ Van der Waals Heterostructure Ion Sensitive Field Effect Transistors

Field-effect transistor (FET)-based sensors are widely investigated for label-free, real-time ion detection; however, their sensitivity is commonly limited by the Nernstian response (∼59 mV/pH). In this work, real-time pH sensing is demonstrated using a MoS₂ (top)/WSe₂ (bottom) van der Waals heterostructure ion-sensitive FET (ISFET), achieving a pH sensitivity of ∼441.3 mV/pH. The device incorporates a screening layer formed by interfacial and channel charges, along with engineered trap states, which leads to enhanced sensitivity while maintaining device scalability. The ultrascaled ISFET employs ∼15 nm Al₂O₃ as the top dielectric, ∼30 nm HfO₂ as the back dielectric, and a few layers of MoS₂/WSe₂ as the channel. The sensor shows a linear, stable, and repeatable response over a wide pH range, as verified through cycling measurements. Low-frequency noise analysis indicates a pH sensing resolution of 1.36 × 10^-3 pH. These results highlight the applicability of van der Waals heterostructure-based ISFETs for scalable and high-resolution biosensing applications.