Micro electrical impedance tomography on a single CMOS chi

This dissertation is a detailed description of the design and demonstration of a 'System-on-Chip' device for performing micro-impedance imaging on biological cells. The structure of this thesis is constructed around three major topics, namely: the design of the system electronics in CMOS technology; the fabrication of a CMOS integrated microelectrode array; and the implementation of a tomography algorithm for the construction of an impedance map corresponding to the impedance measurements made on biological cells. This device has the potential to become a platform technology for monitoring the physiological state of tissue cells in vitro (Latin: (with) in the glass). The system electronics for the microchip were implemented on a standard CMOS technology. They were designed modularly where each module was thoroughly simulated and verified. The microelectrodes that were integrated with the system were constructed using the top metal layer (aluminium) of the CMOS process. Unfortunately, the native surface of the aluminium electrode was unsuitable for purpose of cell culture as it would become toxic. Therefore, they were plated with gold (a suitable metal) using an electroless gold jolating process. The electroless gold plating process is compatible with conventional CMOS microfabrication process which providers a feasible solution for constructing biocompatible microelectrodes on CMOS microchip. The gold plated microelectrodes using the electroless method have an amorphous surface which implied that the toxic aluminium electrode would be properly sealed for cell culture experiments The construction of the impedance map was achieved with an electrical impedance tomography method. This technician uses the impedance measurements that are made on the surface of a body to construct the internal conductivity distribution of the body. The algorithm for this method was adapted from a large scale system that was meant for studying human organs. However, the planar electrode arrangement from the large scale system provided the opportunity for the adaptation required to observe at microscale. In this thesis, the adaptation was realized with the integrated microelectrodes on the CMOS microchip. The gold plated microelectrodes were tested for cell culture. The results from fluorescence microscopy showed that the cells were able to survive and adhere over the surface of the microelectrodes. The results from the impedance measurements also verified that the cells have adhered on the microelectrodes. The reconstructed impedance image with the electrical impedance tomography showed that the algorithm was able to detect the presence of cells as well as the location of the cells.