In this paper, we present experimental results concerning sensing of vapours and liquids in porous silicon by spontaneous Raman scattering. Raman spectra are measured in backscattering configuration using a diode laser at 404 nm. The adsorption of chemical species induces a compressive strain in the porous silicon due to the action of the molecular forces, as a consequences a reversible blue-shift of the Raman spectra of the cavity has been observed.