Bioelectronic Interfacing: Electrical and Chemical Sensing of Biological Signals
Bio-elektronische Interfacing: Elektrische en chemische sensing van biologische signalen
Braeken, Dries; M9922041
In the search for mechanisms and pathways underlying disease processes, various techniques and strategies have been developed over the last deca des. In the field of cell physiology, the recording of electrical and ch emical activities of excitable cells is addressed using advanced optical techniques such as high-speed confocal microscopy of various fluorophor es and intracellular recording of electrical activity using patch clamp techniques. However, these techniques still suffer from limited throughp ut and low sensitivity, or need specialized intervention from the user. Innovative technologies are, therefore, needed to further elucidate the working principles underlying cellular processes. Biocompatible microfab ricated chips with integrated readout circuits will help to address thes e challenges because of their ability to increase the output by miniatur ization and automatization. The aim of this work was to develop and vali date methodologies for quantifying activities of excitable cells, at che mical and electrical level, using biocompatible and non-invasive microfa bricated transducers. The first part of this work has focused on the ass esment of a bioelectronic system for detection of glutamate release by h ippocampal neurons. The detection of neurotransmitter release is of grea t interest to neurophysiologists because a large number of disorders and pathologies are caused by an impairment of the chemical communication b etween neurons and their target cells such as is the case in Alzheimer's and Parkinson's diseases. The in vitro detection of neurotransmitter release is challenging because of the small amount o f molecules released in a large volume at the synapse and the fast disap pearance. Firstly, a glutamate-sensitive surface layer was developed and characterized for different sensor materials. Then, this surface chemis try was applied to a sensor system for the detection of glutamate. Glutamate detection with t his sensor proved to show good sensitivity and selectivity. The sensitiv y of the surface chemistry was further increased by the development of a patternable bienzymatic recycling system. Finally, the surface layers s howed to be compatible with neuronal cultures. In the second part of thi s work, we evaluated a commercially available system which is used for t he recording of extracellular field potentials of excitable cells and co mpared this system with conventional techniques for electrophysiology, i .e., whole-cell patch clamp technique. In addition, we evaluated the use of calcium imaging to relate the electrical activity. Because recorded signals from conventional systems still lack a good signal-to-noise rati o and the output is rather limited, we investigated a new approach to th at uses three-dimensional nail-shaped electrodes instead of at electrode s to enhance the cell-chip coupling. Morphological investigation of the cells on electrode surfaces showed tight coupling between cell and elect rode. Finally, electrical stimulation of cardiac cells was performed usi ng a passive nail electrode array. The cell response was monitored using calcium imaging. In this work, we presented bioelectronic devices for t he monitoring of electrical and chemical activity of excitable cells. They proved to be promising tools for future biomedical research applications.