Fluorescence detection is a widely spread tool for diagnostic or monitoring in various biomedical and environment applications. Its integration in lab-on-a-chip systems opens up the possibility of using it in the field, as close as possible to the sampling site. In this paper, we present the development and characterization of a transparent organic LED (OLED) emitting in the blue range, and integrating an optical cavity to shape the transmitted spectral range. First fluorescence level measurements in a microfluidic chip are reported.