In this paper, we present our work on an optical biosensor for the detection of the interaction between a DNA single strand and its complementary oligonucleotide, based on the porous silicon (PSi) microtechnology. The crucial point in this sensing device is how to make a stable and repeatable link between the DNA probe and the PSi surface. We have experimentally compared some functionalization processes which modify the PSi surface in order to covalently fix the DNA probe on it: a pure chemical passivation procedure, a photochemical functionalization process, and a chemical modification during the electrochemical etching of the PSi. We have quantitatively measured the efficiency of the chemical bond between the DNA and the porous silicon surface using Fourier transform infrared spectroscopy (FT-IR) and light induced photoluminescence emission. From the results and for its intrinsic simplicity …