Porous silicon (PS) has a great potential in a wide range of .elds due to its tuneable e.ective refractive index, which can be tai- lored through the precise control of the formation parameters. In particular, high/low porosity layer stacks result in optical multi- layer interference .lters, such as Bragg re.ectors and optical microcavities. In addition, due to its large internal surface, the optical properties of porous silicon are highly sensitive to the environmental conditions. Hence, a change in these conditions results in a shift of the optical spectrum of the PS multilayer structures. In the present work, the optical behavior of PS mirrors is studied, revealing good performance in the visible wavelength range, and showing a great sensitivity to di.erent liquids in.ltrated in the por- ous structure. Furthermore, optical microcavities are also demonstrated to .lter the photoluminescence emission of porous silicon, narrowing its spectral width and resulting in highly chromatical light emitting devices. These devices, along with the immobilization of biomolecules on the PS surface, will allow the development of low cost, high sensitivity optical biosensors.