We propose microfluidic add-ons that can be easily added onto standard assay labware such as microwells and slides to enhance the kinetics of immunoassays. We design these monolithic devices having structures that leverage the pipetting step to deliver reagents with deterministic, uniform and strong advection close to the reaction surface. This flow-driven mass transport enhances the flux of analytes to the reaction site and reduces the depletion layer. We demonstrate large gains in time-to-result (5 min instead of 1 h) and/or the sensitivity of immunoassays (approx. 1 order of magnitude), high signal homogeneity and low reagent use by recirculating μL volumes. The impact of this approach on standard immunoassay practice is minimal, preserving both assay labware and dispensing/reading equipment. The devices are compatible with mass production in plastic, offering a solution to enhance the results of conventional assays using well-established protocols and automated analyzer platforms.