Abstract: A device for diagnosis by DNA comprises: a porous substrate comprising at least: an area for depositing a sample, the sample comprising at least one target compound; a plurality of channels positioned in the thickness of the porous substrate; an area, referred to as the “diagnostic area”, comprising at least one reactive compound suitable for reacting with a so-called target compound; an area for depositing a carrier vector suitable for being transported by capillarity into all of areas and channels: each of the areas being linked to the others by at least one element chosen from a channel and an area, a means for locally conditioning the temperature of the diagnostic area.