Authors: J.H. Yoo, M.S. Cha, J. Lee
Affilation: Seoul National University, Korea
Pages: 611 - 614
Keywords: dielectrophoresis (DEP), capacitance, electrowetting, bacteria, detection
The concentration of Escherichia coli (E.coli) cells in water was detected by depositing them on an array of electrodes using dielectrophoresis (DEP). Electrowetting was used to effectively concentrate the E.coli in a droplet of water which dried out during the DEP deposition, enabling a simple but powerful system without complicated microfluidic components. By measuring the capacitance after the deposition, it was possible to quantitatively evaluate the cell population correlated with concentration. The E.coli media in six different concentration (1~10^5 cfu/µl) were prepared by diluting from the highest concentration. A viable counting (VC) at the lowest concentration with 100µl solution was used to estimated the higher concentrations. After drying up the liquid, the capacitance was measured and correlated with the E.coli concentration. It was discovered that large capacitance variation occurred at high humidity condition (89% RH @RT vs. 24% RH @RT). We believe that the electrolytic water around the E.coli created the capacitive bridge which substantially increased the measurable signal. A new type E.coli sensor will be developed based on the result of this work.