The invention relates to a microelectronic sensor device for manipulating a sample in an exchangeable carrier (111), for example for optically detecting target particles (1) in a sample liquid that is provided in a sample chamber (2) of the carrier (111). The microelectronic sensor device comprises a number of n>1 magnetic field generators (141-143), e.g. electromagnetic coils, with which magnetic fields can be generated in a target region (110). A control unit (150) is provided that can determine and evaluate the mutual coupling or the self-inductance of the magnetic field generators and/or signals from magnetic field sensors attached to the carrier with respect to the presence and/or state of a carrier (111) in the target region (110). In this way, the control unit (150) can for example detect if the carrier (111) is correctly positioned in the sensor device and/or where a magnetically interactive substance (1, 120) is located.