An immunosensor is a type of biosensor that combines a biological recognition mechanism with a transducer, which generates a measurable signal in response to changes in the concentration of a given biomolecule. One component (ligand) of the interaction to be studied is covalently immobilized to the matrix, and other interactants (analytes) are passed over the sensor in solution. Biosensors using antibodies as ligands are called immunosensors. Immunosensor technologies are quite recent and began to be used for the analysis of food around the mid-1990s. In recent years, significant progress has been made in the miniaturization of the immunosensors. Portable immunosensors for on-site detection are now commercially available, some of them allowing the simultaneous detection of several biomolecules.