A microfluidic device and its use for the production of micro-arrays, in particular for the detection of protein interactions, is described. Said microfluidic device comprises a flow cell part (1) and a chip part (2) together forming at least two crossing, preferably perpendicular, closed channels (3, 4), said flow cell part forming open channels providing the bottom wall and at least part of the side walls, in particular three walls of said closed channels (3, 4), said closed channels (3, 4) being connected to at least three fluid providing means for generating at least three fluid flows (7) and said closed channels (3, 4) being designed and dimensioned such that the flow of at least three aqueous fluids streaming through each of said channels (3, 4) is laminar at least until after said crossing of said channels (6), said chip part (2) forming the top wall and optionally part of said side walls, in particular the fourth wall, of said closed channels (3, 4) and having a surface that is activatable by reaction with an activating molecule.