title: Electrochemical sensing of membrane potential and enzyme function using gallium arsenide electrodes functionalized with supported membranes.
abstract: We deposit phospholipid monolayers on highly doped p-GaAs electrodes that are precoated with methyl-mercaptobiphenyl monolayers and operate such a biofunctional electrolyte-insulator-semiconductor (EIS) setup as an analogue of a metal-oxide-semiconductor setup. Electrochemical impedance spectra measured over a wide frequency range demonstrate that the presence of a lipid monolayer remarkably slows down the diffusion of ions so that the membrane-functionalized GaAs can be subjected to electrochemical investigations for more than 3 days with no sign of degradation. The biofunctional EIS setup enables us to translate changes in the surface charge density Q and bias potentials Ubias into the change in the interface capacitance Cp. Since Cp is governed by the capacitance of semiconductor space charge region CSC, the linear relationships obtained for 1/Cp2 vs Q and 1/Cp2 vs Ubias suggests that Cp can be used to detect the surface charges with a high sensitivity (1 charge per 18 nm2). Furthermore, the kinetics of phospholipids degradation by phospholipase A2 can also be monitored by a significant decrease in diffusion coefficients through the membrane by a factor of 104. Thus, the operation of GaAs membrane composites established here allows for electrochemical sensing of surface potential and barrier capability of biological membranes in a quantitative manner.
authors.affiliation: Biophysical Chemistry II, Institute of Physical Chemistry and BIOQUANT, University of Heidelberg, D69120 Heidelberg, Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Gassull
authors.forename: Abraham
authors.initials: A
authors.lastname: Ulman
authors.forename: Michael
authors.initials: M
authors.lastname: Grunze
authors.forename: Motomu
authors.initials: M
authors.lastname: Tanaka
mesh_terms: D001152:Arsenicals / Q000737:chemistry*; D004563:Electrochemistry; D004566:Electrodes; D005708:Gallium / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008564:Membrane Potentials; D008954:Models, Biological; D054467:Phospholipases A2 / Q000737:chemistry* / Q000378:metabolism*; D010743:Phospholipids / Q000737:chemistry; D013499:Surface Properties
chemical_list: D001152:Arsenicals; D010743:Phospholipids; C043055:gallium arsenide; D005708:Gallium; D054467:Phospholipases A2