All-Solid, Ultra-Micro, and Ultrasensitive pH Sensor by Monolayer MoS₂‑Based Array Field-Effect Transistors

The hydrogen ion is a fundamental marker in various production activities, including environmental evaluation, microorganism growth, enzyme activity, and fine chemicals. Especially in some extreme conditions, the pH sensor requires high-pressure resistance, ultralow detectable amount, and ultralow limit of detection, which are also very important in the wearable devices of life analysis. However, the traditional glass-based pH sensor is always easily broken under high pressure. Herein, an all-solid and ultra-micro pH sensor is demonstrated by integrating the monolayer MoS₂-based array field-effect transistors (FETs) on a printed circuit board (PCB), which can test with the artificial external circuit directly. Due to the high mobility and large surface area of monolayer MoS₂, the minimum volume of the detectable sample could reduce to 0.10 μL and the working area to 100 μm². A large pH range of different acid solutions has shown an excellent concentration-dependent relationship with the sensing current, including the HCl, H₂SO₄, H₃PO₄, CH₃COOH, and NH₃·H₂O solutions. Moreover, this sensor exhibited long-term stability and high repeatability for acidic solutions of different pH values. This work provides an approach to industrialize the production and large-scale application of all-solid pH sensors by monolayer MoS₂-based FETs.