The topic of this work is the family of optical biosensors based on Silicon technology. The need to develop new classes of devices able to perform in situ and real-time measurements at low cost together with the advancement in semiconductor micro fabrication technology are the main reasons for the large number of studies performed in that field. In the thesis, first of all I review the basic principles related to evanescent field sampling, together with an overview of the materials and architectures that can be exploited in this field, by extensively reviewing devices already proposed in literature, in order to better describe the theoretical concepts explored in the first part.