The invention provides a multiplexed assay device comprising a reaction chamber and several sets of encoded microcarriers 2 wherein the reaction chamber is a microchannel 1 and wherein the longitudinal movement of the microcarriers 2 is restricted and wherein the microcarriers 2 have a shape in relation to the geometry of the microchannel 1 such that at least two can stand side by side in the microchannel 1 without touching each other and without touching the perimeter of the microchannel 1 and are preferably observable in the reaction chamber. Moreover, the invention provides a method for performing multiplexed assay based on microcarriers 2 that improves mass transfer, simplifies the preparation and the execution of the assay and facilitates readout of biological reactions and identity of microcarriers 2.