The subject of the invention is a device comprising a fibre-optic sensor for the detection of biologically active molecules, characterised in that the fibre-optic sensor is placed in a capillary closed on one side (1) whose one-sided closure is a light-permeable material (2), the outer face (3) of which is coated with an analyte-sensitive material (8) and the inner face (4) of the light-permeable material (2) is separated from the face of the optical fibre (5) from 0 µm to 30 mm.
