Porous silicon (PS) has a great potential in a wide range of fields due to its tuneable effective refractive index, which can be tailored through the precise control of the formation parameters. In particular, high/low porosity layer stacks result in optical multilayer interference filters, such as Bragg reflectors 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 different liquids infiltrated into the porous structure. Furthermore, optical microcavities are also demonstrated to filter 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.