In this work we discussed feasibility studies and examples of biological molecules integration in Si-based miniaturized devices. We investigated three main issues:(i) device surface functionalization,(ii) biological molecule functionality after immobilization and (iii) biosensor working principle using both electrical and optical transduction mechanisms. In the first case the idea is to fabricate electrolyte-insulator-semiconductor (EIS) and, in the near future, ion-sensitive field effect transistor (ISFET) biosensors. The electrical characterization of MOS-like capacitors with ssDNA anchored on the SiO2 dielectric, allowed us to conclude that the structures tested are sensitive to DNA immobilization and hybridization, as demonstrated by a positive shift in the flat band voltage after ssDNA immobilization and by a further shift after prefect match hybridization. The optical transduction mechanism, using an approach closer to commercial devices (eg DNA-chip) is based on the use of pixelated solid state photon-detectors (Silicon Photomultipliers, SiPM). We showed this new device can be used to replace traditional optical detector in DNA-chip applications and allows designing new optical detection systems based on photon counting operation.