This thesis documents research on microfabricated sensors and actuators for single particles and cells. While the on-chip characterization of single biological cells is the ultimate goal, the devices presented here were always evaluated using particles of defined physical properties, in order to obtain reliable references before cell measurements were conducted.In microfluidic setups, optical and impedance based sensor implementations were investigated for label-free detection of particles and cells. For mechanical on-chip manipulation of flowing particles and cells, a method based on electric fields (dielectrophoresis) was examined that proved to be useful for separation purposes. In the following, the motivation and historical context of this research is highlighted. Additionally, in section 1.2 some remarks on the theory of microfluidics is given.