Electrochemistry

Biography

Biography: W Knoll

Abstract

Graphene, a two-dimensional zero band gap semiconducting material, has gained considerable interest in material science, energy storage and sensor technology, due to its remarkable electronic and mechanical properties. It’s high carrier mobility and ambipolar field effect, together with a great sensitivity towards changes in environmental conditions makes graphene perfectly suitable as transducing material for the use in various types of sensors. In this report, we first describe a novel biosensor exploiting the pH dependence of liquid gated graphene-based field-effect transistors for the enzymatic detection of urea. The channel between the interdigitated source-drain microelectrodes was non-covalently functionalized with bilayers of poly (ethylene imine) and urease using the layer-by-layer approach, providing a LoD below 1 mM urea. Next, we present a sensor based on a reduced graphene oxide field effect transistor (rGO-FET) functionalized with the cascading enzymes arginase and urease as recognition elements in a layer by layer assembly with poly (ethylene imine). The build-up of this nano-architecture was monitored by surface plasmon resonance spectroscopy. L-arginine was quantitatively detected by the change in current between source and drain electrode due to electrostatic gating effects conferred by the formation of OH^- ions upon enzymatic hydrolysis of the analyte L-arginine. And finally, we will describe first results on the coupling of calcium-responsive polymer brushes to graphene field-effect transistors. The presence of Ca⁺² ions neutralize the charge of the phosphate groups leading to a change of the Dirac point by electrostatic gating effects. A formalism using the Langmuir adsorption model and the Grahame equation is used to obtain the surface coverage from the change of the Dirac point.