Novel carbon materials and microstructures for electrochemical sensors

Carbon thin films have gained a lot of attention since the discovery of carbon nanotubes in 1991, which ignited widespread research on the many forms of carbon. The most well-known form of carbon is diamond, and its synthetic version has been adopted in applications that require high wear resistance. However, carbonaceous materials have a lot more potential than just that. There is a broad spectrum of carbonaceous materials available which properties can be tailored according to need. In this thesis, three different carbon thin films were studied from the microfabrication and patterning perspective. These selected thin films were especially electrically conductive as their performance was studied as electrode material in multielectrode arrays (MEA). These three materials were nanocarbon (nC), tetrahedral amorphous carbon (ta-C), and pyrolytic carbon (PyC). In microfabrication and thin film technologies, the methods and equipment for carbon thin film patterning are limited. This thesis presents patterning methods for all three studied carbon materials. The nC film was plasma etched, the ta-C film was patterned with lift-off, and PyC was patterned while it was still photoresist before pyrolysis. Most carbon materials are naturally biocompatible without any additional surface coatings. These three materials were used in electrochemical measurements to detect the minor presence of neurotransmitters like dopamine or other biological analytes. From an electrochemistry point of view, carbon is an appealing material as it exhibits a wide potential window that allows the measurement of multiple analytes simultaneously. PyC and ta-C show promising results in dopamine detection from bulk concentrations, but there is still a need for improvement if interfering molecules and impurities are present. These three carbon materials were utilized in multielectrode arrays, which are formed of many microelectrodes close to each other. MEA devices can be used to follow the signaling between neuronal cultures, follow the activity of brain slices, or measure even the minuscule concentration of biological analytes. This thesis presents biological measurements only for nC-MEA (with brain slice). PyC and ta-C materials were successfully implemented in MEAs, but their performance was only tested in preliminary experiments.