A study of the principles, fabrication and behaviour of a range of optical sensor platforms based on evanescent wave interactions is presented. The platforms utilise a range of sensing techniques including absorption, fluorescence quenching and surface plasmon resonance. The absorbance-based platforms employ sol-gel-derived planar waveguides and grating couplers to launch light into guided modes, the evanescent fields of which can interrogate a sensing layer. A detailed characterisation of these integrated optic devices is presented. Two platforms employing few-mode and multimode waveguides, respectively, are described and applied to the detection of gaseous ammonia and carbon dioxide. A fluorescence-based sensor platform which utilises the anisotropy of fluorescence emitted near an interface is also presented. The platform consists of a planar waveguide coated with a sol-gel-derived fluorescent layer. A substantial amount of the analytesensitive fluorescence is captured by guided modes in the planar waveguide. This configuration is described in detail and is applied to the detection of gaseous oxygen as a proof of principle. Finally, work leading to the development of a fibre optic probe biosensor based on surface plasmon resonance is presented together with its application to the detection of red blood cells. In summary, this work highlights the feasibility of combining evanescent wave interactions and sol-gel technology to fabricate miniature sensor platforms which may be applied to the detection of a wide range of target analytes in a reliable and cost effective manner.