Apparatus for determining the quantity of a target protein, biomarker or analyte present in a sample, comprising a top plate and a bottom plate, each comprising a plurality of recesses arranged to form a plurality of rows extending parallel to one another, and a plurality of channels extending perpendicularly to the plurality of rows of the bottom plate; wherein the top plate and the bottom plate are assembled together so that the top plate is on top of the bottom plate and the recesses of the top plate communicate with the recesses of the bottom plate so as to form a plurality of rows; and wherein at least one of the top and bottom plate is configured to slide relative to the other of the top and bottom plate in order to form a plurality of columns, with each of the columns in communication with each of the channels.