Examination Committee

Prof Ross MURCH, ECE/HKUST (Chairperson)
Prof George YUAN, ECE/HKUST (Thesis Supervisor)
Prof Mansun CHAN, ECE/HKUST 

Abstract

E. coli bacteria are major causes of intestinal infections. Detection of E. coli using clinical methods take 1-2 days. New methods are required to detect the bacteria quickly with high sensitivity.  In this work, we designed microfabricated immuno-electrodes, which are of the size of antigen cells, to accomplish single cell detection. We report the fabrication process of this electrochemical immunosensor. A microelectrode array was fabricated and was immobilized with antibody. Various methods were used to characterize the fabrication process. Electrochemical impedance spectroscopy was used as the sensing method. A distributed electrode impedance model was established for the microelectrode-cell interface. With the small microelectrode and the new impedance model, the number of cells attached to the electrode can be digitized.

Although electrochemical impedance spectroscopy was used to analyze the antigen-antibody interaction, it was never used to quantize the number of cells immobilized on a microelectrode mathematically. We propose a new equivalent circuit model to quantify the number of cells present on a single microelectrode using Electrochemical Impedance Spectroscopy (EIS) and to analyze immobilization process. Using the impedance of cell covered electrode and the impedance of bare electrode, we determine the number of cells present on an electrode using the proposed model. The number of cells determined by the model was verified using the Scanning Electron Microscope (SEM) images.

At last we have incorporated a microfluidic channel in this immunosensor. It was designed and fabricated using SU-8 and PDMS and fitted over this immune-sensing microelectrode array.