Two simple optical fibre structures that do not require the inscription of a grating, a cladding removed multimode optical fibre (CRMOF) and a single-mode multimode single-mode structure (SMS), are compared in terms of their adequateness for sensing once they are coated with thin-films. The thin-film deposited (TiO 2 /PSS) permits increasing the sensitivity to surrounding medium refractive index. The results obtained can be extrapolated to other fields such as biological or chemical sensing just by replacing the thin-film by a specific material.