%0 Generic
%A Mehlhose, Sven
%D 2019
%F heidok:26523
%R 10.11588/heidok.00026523
%T Biofunctionalization of GaN/AlGaN/GaN High Electron Mobility Transistors
%U https://archiv.ub.uni-heidelberg.de/volltextserver/26523/
%X 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.