In the present work we propose a new optical immunosensor based on capillary geometry and capable of multianalyte determinations. The device is made of a polystyrene capillary tube. The inner walls of the capillary are segmented into distinct bands which are coated with appropriate binding molecules. Following excitation, some of the fluorescent photons emitted by the label are trapped and waveguided into the capillary walls provided they are launched towards the walls and within the critical angle. Here, Europium-labeled streptavidin reacted with different amounts of biotinylated bovine serum albumin immobilized onto each one of the bands. Due to the small inner volume of the capillary and the multianalyte feature we expect that the proposed device can be used for fast and inexpensive assays.