The present manuscript describes the theoretical understanding of nanoporous alumina based fiber optic sensing structures. The Cavity Maxwell Garnett theory is used to calculate the dielectric functions of the proposed layer. The performance of the proposed sensing structure is evaluated in terms of its sensitivity towards change in the refractive index of the nearby medium. The sharpness of the resonance has also been calculated as an estimation of the performance parameters. It has been observed that the proposed structure is approximately thirteen times more sensitive than the conventional fiber optic sensors. The study has further been extended by replacing the nanolayer of Alumium with the nanolayer of the gold. A comparative study has been provided in terms of the efficiency of the fiber optic probe. The effects of change in pore radius, thickness of the adsorbed medium and shell radius have also been studied.