Combination of Droplet Oscillation and Dielectrophoresis to Increase the Sensitivity of Biosensors

Biosensors have become a research field of high interest over the last few years. Especially the detection of bacteria is one of the main issues for biosensors. To prevent human health risks and detect even a small quantity of bacteria e.g. in water sources, reliable and accurate detection of bacteria must be guaranteed even for small concentration of bacteria. To increase the sensitivity of such biosensors it is of high importance to increase the number of bacteria on the sensing area. In this work dielectrophoresis (DEP) is utilized to improve bacteria collection at the sensing area.<br/><br/>DEP accelerates dielectric particles suspended in a liquid towards regions of either high or low electric field gradient by applying an alternating inhomogeneous electric field. The force associated with DEP is called dielectrophoretic force (DEP force). This force operates in a radius of micrometers. The transport of particles to the operating area of the DEP force is improved by droplet oscillation. This method provides liquid turbulences inside the particle solution. Thereby, more bacterial cells are collected on the sensing area.<br/><br/>The droplet oscillations are generated by two oscillation electrodes. Those electrodes are implemented beneath the DEP setup with a distance of micrometers. Between the DEP and oscillation electrodes a droplet of a polar liquid is located. By applying a voltage to one of the droplet oscillation electrodes the polar molecules of the liquid align with the electric field. The alignment of the molecules leads to a decrease of surface tension in the area of the electric field. As a response the liquid starts to flow towards the region of low surface tension. To get a consistent flow inside the droplet the applied voltage switches between the two oscillation electrodes.<br/><br/>This research focuses on optimizing the reciprocal influence of the DEP field and the electric field for the droplet oscillation. In order to enhance the experimental setup, the simulation software COMSOL Multiphysics® was used. In this simulation parameters like the frequencies of the electric fields or electrode geometries were taken into account. The results of the simulations should allow us to construct a setup combining droplet oscillation and DEP, that is capable of improving the sensitivity of biosensors.<br/><br/>Key words: droplet oscillation, dielectrophoresis, liquid turbulences, biosensors, bacteria