The theoretical design, fabrication and characterisation of an evanescent field integrated optical (IO) sensor based on a rib anti-resonant reflecting optical waveguide (ARROW) structure are presented. The optical waveguides are designed to verify two conditions: mono-mode behaviour and high surface sensitivity. The sensor system is fabricated with ‘silicon microelectronics technology’ and it has been tested as a refractometer with glucose solutions of different refractive indices. The feasibility of applying the sensor for immunosensing is shown with antibody/antigen binding experiments.