Gold Nanoparticles Monolayer Based Field-Effect Sensors for Fast and Sensitive Molecular Detection

Abstract

This thesis presents the development of a novel field-effect-based molecular sensor for sensitive and rapid molecular detection. This involves the design, fabrication, characterization, and validation of the developed sensor with a variety of chemical and biological molecules. This work addresses the critical need for early diagnosis in clinical applications, as well as in industrial settings. The sensor is based on a new physical concept that exploits field-effect modulation at the interface of gold nanoparticles (Au-NPs) and SiO2/Si substrate. The active medium of the field-effect nanosensor comprises a monolayer of citrate-capped Au-NPs rigorously and uniformly assembled between two metal electrodes (Ti/Au), separated by a gap of 100 m on the SiO2/Si substrate. These nanoparticles possess a significant negative surface potential, and hence, due to their extremely small size, they exhibit a high surface charge density. This, in turn, leads to an enhanced local electric field at the interface of AuNPs and SiO2 film, which depresses the conduction band of the underlying silicon substrate, resulting in the formation of an electron channel beneath the oxide layer. This electron channel is highly sensitive to changes in the net surface charge of the NPs monolayer, which can be modulated by the adsorption of polar or electrostatically charged molecules, thereby enabling detection through changes in electron transport between the electrodes. This thesis is structured into four major contributions to the field of sensor technology. First, a novel physical model is presented for the molecular field-effect sensor, which includes the electron transport and sensing mechanisms. Second, an innovative method for the formation of a monolayer of Au-NPs is developed based on a field-driven self-assembly of NPs during solvent evaporation, resulting in a well-ordered monolayer on the silicon substrate. Third, the design, fabrication process, and testing of the sensor device are detailed. Finally, the sensor’s performance is demonstrated across a wide range of molecules, including water molecules (humidity), charged and polar chemical molecules, synthetic DNA oligonucleotides of different base sequences, and DNA extracted from Burkitt’s lymphoma cell lines (BL30) and their Epstein-Barr virus-infected counterparts (BL30-B95.8). Collectively, this work establishes a new platform for field-effect based molecular sensing with promising applications in clinical diagnostics, point-of-care technologies, and industrial settings.

Date of Award	2025
Original language	American English
Supervisor	Moh'D Rezeq (Supervisor)