and viruses. DEP can be used to separate particles with different sign polarizabilities as they move in different directions at a given frequency of the AC field applied. DEP has been applied for the separation of live and dead cells, with the remaining live cells still viable after separation or to force contact between selected single cells to study cell-cell interaction. Strains of bacteria and viruses red and white blood and cells. DEP can also be used to detect apoptosis soon after drug induction measuring the changes in electrophysiological properties. DEP as a cell characterisation tool DEP is mainly used for characterising cells measuring the changes in their electrical properties. To do this, many techniques are available to quantify the dielectrophoretic response, as it is not possible to directly measure the DEP force. These techniques rely on indirect measures, obtaining a proportional response of the strength and direction of the force that needs to be scaled to the model spectrum. So most models only consider the Clausius-Mossotti factor of a particle. The most used techniques are collection rate measurements: this is the simplest and most used technique – electrodes are submerged in a suspension with a known concentration of particles and the particles that collect at the electrode are counted; crossover measurements: the crossover frequency between positive and negative DEP is measured to characterise particles – this technique is used for smaller particles (e.g. viruses), that are difficult to count with the previous technique; particle velocity measurements: this technique measures the velocity and direction of the particles in an electric field gradient; measurement of the levitation height: the levitation height of a particle is proportional to the negative DEP force that is applied. Thus, this technique is good for characterising single particles and is mainly used for larger particles such as cells; impedance sensing: particles collecting at the electrode edge have an influence on the impedance of the electrodes – this change can be monitored to quantify DEP. In order to study larger populations of cells, the properties can be obtained by analysing the dielectrophoretic spectra. Implementing dielectrophoresis Electrode geometries At the start, electrodes were made mainly from wires or metal sheets. Nowadays, the electric field in DEP is created by means of electrodes which minimize the magnitude of the voltage needed. This has been possible using fabrication techniques such as photolithography, laser ablation and electron beam patterning. These small