In this work enzyme-modified solution-gated AlGaN/GaN field-effect transistors (EnFETs) were prepared using the enzymes penicillinase (PenFETs) and acetylcholinesterase (AcFETs). Covalent immobilization of the enzymes on the gate surface was carried out via silanization with (3-aminopropyl)triethoxysilane followed by crosslinking with glutaraldehyde. The successful silanization was proven by X-ray photoelectron spectroscopy.Quantitative analysis of the PenFET response curves at varied measurement conditions demonstrated the applicability of the used kinetic model for pH-sensitive solution-gated EnFETs. The quantitative analysis allowed the determination of the respective Michaelis constant as well as three normalized rate constants which describe the transport of protons, buffer molecules and substrate molecules through the EnFET/enzyme/electrolyte interface.By evaluation of those four model parameters the influence of buffer concentration and pH-value on the PenFET response curves could be assessed. Furthermore, the extracted model parameters made an investigation of the stability of PenFETs and AcFETs possible. Here, PenFETs could be analyzed with the kinetic model over the course of 252 days while analysis of AcFETs was only feasible over the course of 77 days. In addition, analysis with the kinetic model allowed the quantitative comparison of the response curves of PenFETs and AcFETs, as well as the conclusion that the method used for the enzyme immobilization is highly reproducible.Based on those results, AcFETs were successfully used for the detection of the neurotransmitter acetylcholine which was released by stimulated neuronal tissue cultivated on the gate surface. In the context of this work three types of neuronal tissue were investigated: isolated myenteric neurons from (4 - 12) days old Wistar rats as well as myenteric neurons still embedded in the muscularis propria and coeliac ganglia from adult Wistar rats. In all casees, the response of an AcFET towards the release of acetylcholine could be linked to the activity of the covalently immobilized acetylcholinesterase by utilizing the reversible acetylcholinesterase blocker donepezil. These results demonstrate the realization of a functional neuron/AcFET hybrid.
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