A microfluidic device is provided for conducting multiplex immunoassays to detect multiple target analytes in a liquid sample using a set of tags and anti-tags. The device comprises an array of different anti-tags immobilised on a surface of a sensor for measuring a signal. Each anti-tag is arranged to immobilise a tagged antibody or tagged antigen thereby in use separating tagged immune complexes from the liquid phase affecting the signal measured. The device comprises a sensor chamber for tagged immune complexes to form in the liquid phase and one or more detection zones each comprising the array of different anti-tags for immobilising tagged immune complexes. In use, liquid comprising the tagged immune complexes flows or is fluidically driven from the sensor chamber to the detection zone(s).