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Biofunctionalization of GaN/AlGaN/GaN High Electron Mobility Transistors

Mehlhose, Sven

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Abstract

The primary aim of this thesis is the creation of new electrochemical biosensor systems on solution-gated GaN/AlGaN/GaN high electron mobility transistors (HEMT) for the transduction of biological functions into electrical readouts. For this purpose, the surface of transistors was functionalized with various biomimetic and bioorganic molecular systems, such as helical peptides, lipid monalayers and membranes. The full characterization of thickness, roughness, and density of such biomimetic molecular assemblies enables to quantitatively translate the change in surface monopoles and dipoles into the carrier mobility. In Chapter 4, monolayers of bio-inspired, non-biological helical peptides were deposited on GaN semiconductor surfaces in order to modulate the electronic band structures of GaN by macromolecular dipole moments. By covalently coupling the peptides via N- or C-terminus to the GaN surfaces, the sign (direction) of exerted dipole moments could precisely be controlled, realizing the modulation of the carrier mobility. Moreover, the chronoamperometry measurements have demonstrated the additional ferrocene terminal group enables the directed electron transfer through peptide chains via an inelastic hopping mechanism. In Chapter 5.3, cell membrane models were deposited on the GaN surfaces pre-coated with hydrophobic, organic silane monolayers. By incorporating lipids with nitrilotriacetic acid (NTA) head groups into lipid membranes, changes in the surface potentials induced by the binding of charged recombinant proteins to the surface lipid membranes could be detected at a high sensitivity. The systematic variation of surface density of NTA lipids and the comparison with impedance spectroscopy data of bulk GaN electrodes, it has been demonstrated that the sensitivity of this system to changes in the surface charge density is as high as ΔQ < 0.1 μC/cm2. In Chapter 5.2, to accommodate the incorporation of transmembrane proteins under nondenaturing conditions, a more realistic cell membrane model, bilayer lipid membranes, was deposited on GaN by using regenerated cellulose films as the polymer support. The current-voltage characteristics clearly indicated the high electric resistance of lipid membranes, which seems promising for the detection of molecular recognition and selective material transport. Last but not least, such molecular constructs were transferred onto the surface of molecularly thin, organic semiconductors that have shown a high charge mobility under dry conditions (Chapter 6). The preliminary attempts already demonstrated the formation of uniform lipid monolayers on organic semiconductor surfaces exposing hydrocarbon chains. Moreover, the reversible binding and unbinding of recombinant proteins has been confirmed. Although further optimization of the device geometry and Ohmic contacts are necessary, the data suggest a large potential of all organic electronic sensors operating under water. The obtained results highlighted the potential of the combination of biomimetic molecular constructs and inorganic and organic semiconductor devices for the highly sensitive and quantitative determination of properties and functions under physiological conditions.

Item Type: Dissertation
Supervisor: Tanaka, Prof. Dr. Motomu
Date of thesis defense: 20 May 2019
Date Deposited: 07 Jun 2019 08:53
Date: 2019
Faculties / Institutes: Fakultät für Chemie und Geowissenschaften > Institute of Physical Chemistry
Subjects: 530 Physics
540 Chemistry and allied sciences
Controlled Keywords: HEMT, Biomembran, Biosensor
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