Technical Papers and Presentations

In regular biosensors, the detected bacteria have to be in drawn towards the sensing area. To increase the sensitivity of the biosensors, bacteria should be drawn towards the sensing area, which can be achieved by dielectrophoresis (DEP). DEP is a mechanism which is used to move dielectric particles inside a liquid by applying an alternating electric field. The force which is affects to the bacteria is called dielectrophoretic force and induced due to an inhomogeneous electric field. For a successful movement, the particles have to be in very close proximity to the electrodes which induce the inhomogeneous electric field. In areas with a high force, partials can be locked in position. To bring new bacteria in the effective radius of the dielectrophoretic force, turbulences inside the liquid can be utilized. In order to induce these turbulences, a droplet of a bacteria solution is located on top of two electrodes. By applying a pulsed voltage to one of these electrodes, while the other one is constantly grounded, the surface tension of the droplet partially changes, resulting in an oscillation of the droplet. To recreate this setup in the COMSOL Multiphysics® software, a geometry which is mainly constructed as a block is implemented. It illustrates the physical, most interesting portion of the real setup. The geometry consists of a DEP-structure with several electrodes on the top and two electrodes for the droplet oscillation at the bottom. Using the AC/DC Module, a voltage with the DEP-frequency is applied to the top structure. At the bottom, one electrode is grounded, and the other one has an applied voltage of 6 V, which is alternating to 0 V with the frequency used for the droplet oscillation. Via the CFD Module, a creeping flow is applied to simulate the turbulences. By defining the inlet, outlet and surface conditions, an illustration of the liquid flow inside of the droplet is achieved. The Particle Tracing Module is being used to simulate the response of the bacteria to the electric field and creeping flow applied. The particles are defined by parameters which incorporate the dielectric and inertia properties of the bacteria. At the starting point of the simulation, these particles are distributed evenly in the volume and then influenced by the dielectrophoretic force and the forces generated by the creeping flow. The simulation indicates that an optimal amount of fluid flow exists, where new bacteria is brought in at a consistent pace while the already bounded bacteria is not removed. Hence, the efficiency of DEP can be enhanced by utilizing droplet oscillation.