Development of electrochemical sensors for sensing of Dopamine

Abstract

In this thesis the development of an electrochemical sensor for sensing of Dopamine on the basis of redox cycling was pursued. A 3-dimensional, plane-parallel electrode array was designed, consisting of bottom and top electrodes, where pores provide a spatial confinement and electrode interface to the measurement solution. In a micromechanical bottom-up process, a multi-layered formation of electrically conducting gold structures and insulating silicon nitride passivation was created by optical lithography, vapor deposition and plasma-enhanced chemical vapor deposition. Pore-channels of 5 μm diameter were opened by reactive ion etching. The produced sensors were evaluated by redox-cycling measurements on potassium hexacyanoferrate via cyclic voltammetry and amperometry. Stable sensors could be produced with an inter-electrode distance of 300 and 400 nm and were further evaluated by amperometric measurements in a fluidic setup, investigating the temporal and spatial resolution on concentration-changes of dopamine in solution. The electrode fouling process of dopamine on gold electrodes could be shown for a concentration of 1 mmol/l dopamine. Repetitive potential switches between oxidative and reductive potential could not initiate a reversal of the process. For an in-vitro evaluation of the produced sensors dopaminergic PC12 cells were cultivated on the sensor surface and the release of physiological dopamine by the cells was induced by potassium chloride and dopamine. The designed sensor could be evaluated to a sensitivity for dopamine of 10 μmol/l, a fast response time and a cycling efficiency larger than 84 %. To further enhance the sensitivity, a modification towards smaller pores was done by nanosphere lithography. Polystyrene nanospheres of 500 nm diameter were deposited on the sensor by spin-coating and air-water-interface self-assembly and served as a shadow mask for the pore etching. Pore structures in the range of 202 nm and 141 nm mean pore diameters could be created. For the modification towards a flexible sensor array, the existing design was transferred to a polymer-based insulation and substrate material by exchanging silicon nitride with polyimide, resulting in a functioning flexible electrode array embedded in polyimide.