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.