UBC Theses and Dissertations
Development of an electrokinetic based microfluidic device for capturing particles in different water conditions Rahman, Tasrif
Scarcity of safe drinking water is a critical issue in developing countries. Every year millions of people die due to waterborne diseases. Despite the development of different quality monitoring and detection devices, the presence of microorganisms in drinking water which is a threat to human health cannot still be detected with a great reliability. In essence, the conventional detection methods are not efficient enough to produce fast and reliable results required for decision making. Moreover, these analyses are costly and require special facilities. In this research, a microfluidic device was developed for the capture of bioparticles. Two electrokinetic mechanisms, i.e., electrophoresis (EP) and dielectrophoresis (DEP), were studied to find the best capturing mechanism for trapping particles. For EP, a microfluidic flow cell consisting of two electrodes, gold and steel, was developed. Positive DC electric field was applied to the gold electrode, and the steel was electrically grounded. For the DEP analysis, different electrode geometries were considered to identify the most effective trapping arrangement. AC voltage was applied to one of the electrodes while the other electrode was grounded. A vertical microscope was used to monitor the motion of the particles inside the microchannel for both electrokinetic mechanisms. Charged polystyrene beads were used as surrogate particles. Preliminary results revealed that electrophoresis is not effective in trapping particles. DEP, on the other hand, could capture the particles in the traps. However, the dimension of the trap, frequency of the applied field, and the gap between the two electrodes were needed to be optimized for the water flowing condition during which water containing bioparticles are pumped through the device for continuous sampling required for water quality monitoring. The device with the optimum parameters was then used to study the effect of turbidity and chlorine on the efficiency of the device in capturing the particles. The results show that the maximum flow rate reduces for water samples with turbidity of 1 NTU (maximum turbidity of drinking water); while it increases with the addition of chlorine, which increases the conductivity of the sample and hence the DEP force applied on the particles.
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