The invention relates to an integrated optical waveguide evanescent field sensor (1) for sensing of chemical and/or physical quantities, comprising a substrate (2) carrying a waveguide layer structure provided with—a waveguide core layer (10) sandwiched between two cladding layers (11, 12) formed by a lower (11) and a upper (12) cladding layer, of a lower refractive index than the waveguide core layer (10), —a sensing section (14A, 14B) comprising a sensing layer (13) included in the upper cladding layer (12), wherein a longitudinal section of said substrate including said waveguide layer structure and said sensing section (14A, 14B) is exchangeable as a separate element (20).