Mycotoxins are chemical compounds produced by various families of fungi and belong to a class of substances whose concentration must be determined in several categories of food due to their negative effects on human health as these compounds present, each to varying degrees, hepatotoxic, immunosuppressive, mutagenic and/or carcinogenic effects. In order to ensure the good quality of food, continuous control is required at all stages of their production and processing to verify absence of mycotoxins. However, due to the large volume of samples, it is practically impossible to analyze them in a short period. Therefore, there is a need for methods and devices capable of accurately identifying groups of harmful substances outside the laboratory. Biosensors are detection devices that can meet these needs as they enable the simultaneous identification of multiple analytes in a sample and at the same time, they can be integrated into small size devices. In this context, the aim of the project is to develop an optical biosensor for the simultaneous identification of three mycotoxins, namely Aflatoxin B1, Fumonisin B1 and Deoxynivalenol in cereal samples. The choice of the three mycotoxins was due to the fact that they are one most commonly encountered in cereals as well as due to their high toxicity. Simultaneous determination of the targeted mycotoxins is pursued through the development of an immunosensor based on White Light Reflectance Spectroscopy using silicon chips with multiple reactive areas made of silicon dioxide layer with different thickness. Each of these regions is activated by a protein conjugate of a different mycotoxin. The reflection spectrum received from all regions during the immune responses is analyzed by appropriate processing into the individual spectra allowing the reactions that take place in each region to be monitored separately without the need for moving optical components. The experimental part of the thesis is performed in the Immunoassays/Immunosensors Lab of INRASTES in collaboration with the Chemistry Department of the University of Athens (Prof. A. Economou).