On the sensitivity of generic porous optical sensors

A porous material was considered as a platform for optical sensing. It was envisaged that the porous material was infiltrated by a fluid that contains an agent to be sensed. Changes in the optical properties of the infiltrated porous material provide the basis for detection of the agent to be sensed. Using a homogenization approach based on the Bruggeman formalism, wherein the infiltrated porous material was regarded as a homogenized composite material, the sensitivity of such a sensor was investigated. For the case of an isotropic dielectric porous material of relative permittivity ε(a) and an isotropic dielectric fluid of relative permittivity ε(b), it was found that the sensitivity was maximized when there was a large contrast between ε(a) and ε(b); the maximum sensitivity was achieved at midrange values of porosity. Especially high sensitivities may be achieved for ε(b) close to unity when ε(a)>>1, for example. Furthermore, higher sensitivities may be achieved by incorporating pores that have elongated spheroidal shapes.