Surface-Tuned Organic Thin-Film Transistors for High-Performance Mercury Detection

This research pioneers the development of portable, rapid response chemical sensors for on-site mercury (Hg) detection, addressing a critical need for environmental monitoring. A suite of donor–acceptor systems composed of triphenylamine (TPA) and 3-(1H-pyrazol-4-yl)acrylonitrile (PzAN), including DPPDA, DFPPA, DPMPPA, DPPPA, and DMPPPA, was meticulously synthesized and characterized by leveraging single-crystal X-ray diffraction and photophysical analyses to elucidate their structural and optical properties. These molecules were engineered for selective mercury ion binding, forming an active sensing layer within organic thin-film transistors (OTFTs). By precisely depositing these molecules onto OTFT devices, we achieved nondestructive integration, enabling real-time Hg (II) ion detection through modulation of the OTFT’s electrical characteristics. Notably, the sensor molecules’ ability to permeate the OTFT’s active layer boundaries induced significant electrical property alterations, a key mechanism for sensitive detection. Optimized deposition protocols ensured uniform sensor layers, maximizing the device sensitivity. Surface morphology, quantified via atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM), revealed a direct correlation between surface roughness and sensor performance. X-ray photoelectron spectroscopy (XPS) confirmed the sensing mechanism, demonstrating the direct binding of Hg (II) ions to the donor–acceptor molecules. Among the synthesized molecules, DFPPA exhibited superior performance, characterized by high electrical mobility, a substantial on/off ratio, and rapid Hg (II) ion detection kinetics. This study delivers critical insights into the design and fabrication of high-performance mercury sensors utilizing tailored organic molecules and OTFT platforms, highlighting the paramount importance of controlled growth and surface engineering for achieving optimal sensing capabilities.