Carbon Nanostructures for Enzymatic Electrochemical Biosensors

Neurological diseases are a significant burden not only to patients suffering from them but also to the society from economic point of view. The reason behind various neurological conditions is suggested to be disrupted neurotransmitter homeostasis. By monitoring the neurotransmitter concentrations in vivo it could be possible to find new means to treat and study these diseases. However, there are no current methods to measure the neurotransmitter release and uptake in vivo in real time. The aim of this work was to develop electrochemical sensors for the detection of neurotransmitter glutamate. The main materials studied were Pt-alloyed amorphous carbon and carbon nanofibers grown either from Ni or Pt catalyst. Carbon is an attractive material for sensor applications with its versatile forms and good electrochemical properties. Pt, on the other hand, is a critical material and its use should be minimized. This was achieved here by utilizing nanomaterials. It was shown in this study that the addition of Pt changed the physical structure of carbon thin films and carbon nanofibers. The electrochemical response was dominated by Pt despite its significantly lower concentration (less than 10 at-%) in the material. This could be utilized to enhance the detection of H2O2, which could not be achieved with only carbon. Glutamate is not innately electroactive and there is no current method to directly measure it electrochemically in neutral pH. Thus, glutamate oxidase enzyme was immobilized on the sensors surface and the electrochemical detection was based on measuring enzymatically produced H2O2. The studied nanostructures exhibited good properties for enzyme immobilization as well as electrochemical detection of both H2O2 and glutamate. The best sensitivity for H2O2 reduction was obtained with carbon nanofibers grown from Pt catalyst (0.43 µA µM-1 cm-2). This sample type had also the best sensitivity for the detection of glutamate (0.27 µA µM-1 cm-2). However, these results were proposed to have some additional contribution from oxygen reduction reaction. In addition, the results indicated that presence of chlorides affect the detection of H2O2. Moreover, glutamate itself was found to foul Pt surfaces which should be considered when designing sensors for its detection. In addition to showing their suitability for fabrication of electrochemical sensors, cell culture experiments were utilized to evaluate the biocompatibility of the materials. The initial results showed good cell viability on all the studied materials. It was demonstrated that it is possible to affect the host response by different surface structures. However, further investigations are still needed to make more profound conclusions. As a summary, the novel carbon materials studied here were found to be suitable candidates for electrochemical biosensors for the detection of glutamate.