2.5.2025
Doctoral thesis on the stability of electrolyte-gated organic field-effect transistors
M.Sc. Axel Luukkonen’s doctoral thesis in Physics will be put forth for public defence at The Faculty of Science and Engineering at Åbo Akademi University.
The thesis is entitled Operational Stability of Electrolyte-Gated Organic Field-Effect Transistors.
The public defence of the doctoral thesis takes place on Friday 9 May 2025 at 1PM in auditorium XXII, Agora, Vesilinnantie 3, Turku. Professor Thomas D. Anthopoulos, University of Manchester, United Kingdom, will serve as opponent and Professor Ronald Österbacka, Åbo Akademi University, as custos.
Summary
The thesis examines the stability of electrolyte-gated organic field-effect transistors (EGOFETs) during use, considering their application in biosensors. Like other field-effect transistors, the current between two of the EGOFET’s electrodes, source and drain, is controlled by a voltage applied to the third electrode, gate. Source and drain are connected through a layer of organic semiconductor, which changes conductivity when charges accumulate in it. This semiconductor is in contact with an ionic liquid – in this case pure water – where the gate electrode is submerged. When a voltage is applied to the gate electrode, ions gather at its surface, causing charges to accumulate in the semiconductor and allowing current to flow between source and drain. The current thus depends on the voltage applied to the gate.
EGOFETs can be used in biosensors to convert biological reactions into measurable electrical signals. A biosensor has two parts: a detector element that senses when a specific biomolecule is present, and a transducer that converts this into a signal. In an EGOFET-based biosensor, the EGOFET itself is the transducer, while the detector element consists of receptors attached to the gate electrode. When a biomolecule binds to a receptor, the gate electrode’s electrical properties change, affecting the charges in the semiconductor and causing a measurable change in current. Such biosensors are highly sensitive but face stability issues, limiting their practical use.
The thesis aims to provide new insights into these stability problems to pave the way for better EGOFET-based biosensors. By building EGOFETs with different materials and using various electrical measurement methods, the results show that both material choice and measurement approach affect stability. A new method for studying key EGOFET properties is also presented.
Axel Luukkonen was born in 1994 in Jakobstad, Finland. He can be reached by email axel.luukkonen@abo.fi.
The doctoral thesis can be read online through the Doria publication archive.