Abstract: The present invention relates to a microfluidic electrochemical sensor apparatus and a method for conducting analytical tests with said apparatus for multi-reactant assays. The apparatus of this invention is a multi-layer body made of at least three layers, the first one being a polymer layer (1) comprising a microstructure (5) with at least one integrated microelectrode (4) and conductive tracks (13) for connection to an external electrochemical unit, the second one being a non-porous material serving to cover said microstructure so as to enable microfluidic manipulations and the third one being a porous layer (2) such as a membrane or a glass frit, said porous layer comprising at least one reagent (3) to be solubilized upon contact with a test solution (7) and reacting with an analyte (6) present in said solution to form a product that is transported along said microstructure so as to enable electrochemical detection of said analyte.