(475d) Characterization and Detection of Waterborne Pathogen Based On Dielectrophoresis

Dielectrophoresis (DEP) has been used as one of the effective way to manipulate and separate various cells and other bio-particles. The separation was achieved based on the difference of the particles dielectric properties which was an important factor on the dielectrophoresis force. This was especially proven by a lot of researchers whereby separation of viable and non-viable cells could be easily achieved due to the difference in their dielectric properties. In this project, characterization of the DEP behavior for different type of bacteria was done. Attention was paid on the bacteria from Gram-negative (Escherichia Coli) and Gram-positive (Enterococcus Faecalis) which represent two classifications of bacteria. The main difference between these two bacteria is their cell wall structure, and this may cause the effective dielectric properties to be slightly different. The DEP behavior of these two bacteria was compared and analyzed based on the theoretical ?smeared-out sphere? model developed by other researchers. Different experiment conditions and parameters were applied into the experiment in order to investigate the differences in their DEP behavior. This is important in order to obtain the optimum operating parameters whereby the two viable bacteria would exhibit different DEP force and thus yield the separation. And these could possibly replace the separation based on the antibody-antigen reaction which is costly and tedious in term of preparations even though it has better sensitivity. In this experiment, a high frequency AC current probe was used to evaluate the trapping efficiency of the bacteria. Impedance measurement on the DEP chip was performed with the current probe incorporate with an oscilloscope. This would save a lot of valuable workbench space and provide greater portability as compared with the measurement done with the impedance analyzer. Different bacteria type or concentration produced different impedance signal and these results could act as a reference signal for the DEP chip which enable the prediction of the bacteria type and concentration in a rapid manner as compared to the conventional microbiology incubation method. Preliminary Results: The figures attached show some preliminary results. When bacteria were trapped on the electrode edges as shown in Figure 2, the impedance magnitude of the DEP chip would drop. Greater amount of bacteria trapped would cause greater reduction on the impedance magnitude. Figure 3 shows that Enterococcus Faecalis has been trapped more than Escherichia Coli due to higher impedance variation produced.