Abstract: The device comprises at least one element for immobilizing certain molecules contained in the medium to be tested. According to the invention, the immobilizing element is in the form of a hydrophilic material fixed on the surface of a plane hydrophobic material, such as for example viscose fibers (2) implanted by flocking into a sheet (3) of polyvinyl chloride. The device (4) further comprises:(a) a bottom plate (5) supporting the plane hydrophobic material,(b) at least one cavity (6) for the liquid medium to be tested, said cavity having an outlet orifice (9) situated above the plane hydrophobic material, and(c) scraping means (8) acting on the hydrophilic material (1) and capable of moving the liquid contained therein over the surface of the plane hydrophobic material (3).