Anthropogenic activities generate a large number of contaminants (heavy metals, polychlorinated biphenyls (PCBs), pesticides, drugs ...) that endanger both the sustainability of ecosystems and human health. The measurement of surface water contaminants is traditionally carried out in an analytical laboratory using conventional techniques allowing the detection of a large panel of molecules. The representatively and reliability of the final results depend on the handling from water source to the laboratory. Because of water quality monitoring technologies are numerous but are not totally integrated, human and time consuming as well as expensive, the improvement of this surveillance involves the development and the optimization of tools accounting for all (eco-)toxic risks. In this way, monitoring the effects of chemical contamination using biological tools associated with networks of suitable integrated fluidic systems represents a very promising approach. Lab-On-a-Disc (LOD) format based on a multi-measures/multi-responses represents a versatile micro-fluidic platform to offer a sample-to-answer demonstrator. Water pollutants such as pesticides can inhibit cell growth, fluorescence and photosynthesis depending on their molecular structure and site of action. Since water quality is defined according to its chemical, biological and physical characteristics, the LOD system will integrate a network of complementary sensors and algal cell biosensors of which the transduction system will be adapted to the parameters to be assessed. One of sensors are based on organic photodetectors (OPDs) which will have to convert a biochemical phenomenon i.e. fluorescence into a detectable and measurable signal.

As a promising candidate for next-generation photodetectors, solution-processed organic-based photodetectors (OPDs) provide the opportunity to develop innovative, low cost, and large-area imaging technologies for industrial applications. Thanks to their advantages as a large range of available materials, a tunable spectral response range, compatibility with lightweight flexible substrates, they have gained a continuous increasing interest. However, compared to inorganic-based photodetectors, OPD devices have shown noticeably higher dark current and relatively lower sensitivity which is critical when the sensor needs to detect specific signals (the fluorescence wavelength of algae) under low illumination intensities. Thus, we present here different designed OPDs as function of structure, contacts, and material layer properties to optimize the opto-electrical response of the devices.