The present invention provides a method for detecting the presence or amount of an analyte in a sample, said method comprising: a porous surface to which particles having attached thereto a binding substance, analyte and binding substance coated label particles are added. If said analyte is present in the sample an immuno- or chemical reaction occurs in the liquid phase. The separation of bound complex from unbound material is achieved by using said surface where the separation occurs mainly two dimensionally on the surface of the porous surface (e.g. grid). Interestingly, the disclosed surface enables a separation where said complexes are distributed two dimensionally on the porous surface (e.g. grid), whereas unbound materials are distributed three dimensionally. Accordingly, said surface enables both a two and a three dimensional separation.