Fluid-solid interfacial phenomena are a subject of much interest. In the adsorption phenomena, the adsorbent experiences the action of the molecular forces inducing strains. In this paper, we experimentally investigate adsorption phenomena in porous silicon microcavities by spontaneous Raman scattering. Polarised Raman spectra are measured in a backscattering configuration using a diode laser at 404 nm. We observe a reversible blue shift of the Raman spectra exposing a porous silicon multilayer to air saturated with vapor of pentane or iso-propanol. We ascribe the shift of the Raman spectra to the strain in porous silicon due to the adsorption in the pore walls.