[eng] The present thesis work titled “Analysis and characterisation of biological samples in nano and microfluidic devices using AC and DC electric fields” has as main objective study the effects that electric fields have biologic samples to develop microfluidic tools (lab-on-a-chip) that allow to manipulate and sensing these samples. This work is divided in three main issues oriented to develop different modules for a diagnostic device.In the first block, we studied the movement of DNA molecules confined in a nanochannel of 20 nm height under the effect of DC and AC electric fields. The objective is to determine the mechanism behind the size separation of DNA molecules, in gel-free environments.The second block presents the development of a new dielectrophoretic system for size sorting of cells. It is based in the competence between dielectrophoretic forces and the dragging forces generated by the fluid motion. The system is able to separate red blood cells form monocytes in physiological conditions (high conductivity) in continuously flow.And finally, in the third block it is developed a new instrumentation for microcytometry applications based on impedance detection. The electronic device is validated by using a synchronised optical detection system that allow us relate the obtained signal with the position of the cell on the sensing area. The system demonstrated good sensing and sizing capabilities. We also used hydrodynamic focusing, to increase the sensing capabilities of a sensing geometry base don coplanar electrodes.
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