We present a microfluidic device for multiplexed immunoassays based on DNA-directed immobilization. Because of the versatile building blocks used for this technique, it is possible to build up user configurable protein microarrays within the microfluidic system by means of DNA-directed self-assembly, which can be used for immunoassay applications. We demonstrate the performance of our system by parallel detection of cytokines in a multiplex immunoassay, employing silver deposition labeling and optical read-out.