Here we present an analysis of a fully planar optical sensor based on ARROW waveguides. We consider a device geometry that consists of two intersecting ARROW waveguides, one with solid and one with liquid core. The pump wavelength is input from the solid core waveguide and penetrates through the wall into the liquid core of the other waveguide where the fluorescence is excited in the sample material. Then it is captured by the ARROW waveguide and guided to a detector at the end. Pump and signal wavelength can be guided with low loss through the solid and hollow core respectively. At the same time, high loss discrimination inside the core can be obtained by tailoring the thickness of ARROW layers, leading to efficient filtering. The pump wave can be transmitted efficiently in and out of the core, allowing for multiple intersections. In the following experimental part, we investigate the waveguide loss of the liquid core as a function of core width, we measure values as low as 1.7cm-1 that can be further reduced by improving the thickness control of ARROW layers in the fabrication process. Finally, we report fluorescence experiments on Alexa dye molecules. We demonstrate fluorescence detection at concentrations as low as 10-8 mol/l from a detection volume of 21pl. Photo-bleaching is observed and discussed as a function of input power intensity.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.