We report the first disposable fluorescent biosensor based on algae, with an organic light emitting diode and an organic photodetector (OPD) miniaturized into a microfluidic chip. A DPVBi OLED was used as the excitation source, while a blend of PTB3/PCBM was used for the organic photodetector. The fluorescence biosensor is integrated in a microfluidic chip made from polymeric materials such as (poly)dimethylsiloxane (PDMS), which is transparent, biocompatible and can easily be processed by conventional lithography. The complete detector is designed to detect Chlamydomonas reinhardtii green algae fluorescence in the microfluidic chamber. Algal chlorophyll fluorescence is a physiological parameter routinely used to measure the photochemical efficiency of PSII. This measurement is a reliable and non-invasive method to determine the toxicity of pollutants like herbicides and metals.