Abstract— The integration of optical source with microfluidics leads to promising low-cost, rapid and sensitive lab-on-a-chip analytical systems. This work deals with the optimization of the electrochemical sensors and the dedicated organic light-emitting diode (OLED) for the monitoring of herbicides though algal photosynthetic activities disturbances. . Various blue OLED are considered in order to achieve highest sensitivity in O 2 electrochemical detection during micro-algae photosynthesis. I. INTRODUCTION Aquatic ecosystems are very sensitive to global climatic changes and other human impacts [1]. In the last decades, agricultural and urbanization expansion have induced increasing quantities of pollutant contaminations. It is therefore challenging to develop disposable systems for rapid and in situ analysis to assay toxicants traces in water. Our lab-on-chip structure consists in electrochemical sensors fully integrated on a microfluidic platform, fabricated on a glass substrate. Pollution level is estimated by electrochemical monitoring of oxygen during algae (Chlamydomonas Reinhardtii) photosynthesis in presence of different herbicide concentrations. In previous studies, we demonstrated that blue OLED based integrated system shows higher detection characteristics than those using external white light source [2]. The appeal of OLED as excitation sources in such a detection platform consists in their integration capacity and low fabrication costs. In this paper we propose to analyze algae photosynthesis using various wavelengths and power selective blue organic light-emitting diodes as stimulation light sources. II. LAB-ON-CHIP DESCRIPTION A. Electrochemical sensor The integrated three electrode electrochemical microcells (working, reference, and counter electrodes) are developed through photolithography patterning, followed by physical vapor deposition (PVD) process of titanium/platinum (Ti/Pt) films. A Si 3 N 4 layer deposited by inductively coupled plasma chemical vapor deposition ICP-CVD is used as long-term passivation. Microfluidic platform is structured by patterning SU8 photoresist. Platinum electrodes are directly used as counter electrodes, while working electrodes are functionalized by platinum black deposition to enhance the *Research supported by ABC Foundation. (1) CNRS, LAAS, 7 avenue du colonel Roche, F-31400 Toulouse, France (2) Université de Toulouse, UPS, LAAS, F-31400 Toulouse, France. E.mail : fsekli@laas.fr (3) Université du Québec à Montréal, 201 Président Kennedy, Montréal, Canada. electrochemical detection of O 2 . To create the integrated reference electrodes, silver layers are electroplated directly on platinum surface and then oxidized to obtain Ag/AgCl. This method gives stable and durable integrated reference electrodes. B. Excitation source In order to demonstrate the versatility of OLED technology and its impact on algae oxygen production, we plan to (i) place OLED on the top of the detection chamber to validate this device as excitation source and (ii) fabricate three different OLEDs to test their efficiency. Key technical issue for developing the suitable exciting source is to obtain the appropriate light intensity and spectral overlap between OLED emission and algal absorption displayed in Fig.1. Table 1 summarizes the configuration of different blue OLED (devices A-C) fabricated by thermal evaporation on indium thin oxide (ITO) coated glass under high vacuum conditions. TABLE I. STRUCTURE OF BLUE OLEDS Device Organic thin film stack A NPB (20 nm)/ PCAN (40 nm)/ Alq3 (20 nm) B NPB (80 nm)/ Bphen (30 nm) C HAT-CN (10 nm)/ NPB (35 nm)/ TAPC (5 nm)/ MADN (20 nm)/ Bphen (35 nm) Figure 1. Chlamydomonas reinhardtii absorption spectra in High Salt Medium with the adjusted pH 6.8. and O2 production during photosynthesis at different excitation wavelengths. Lab-on-chip with microalgal based biosensor for water assessment F. Sekli Belaidi 1,2 , A. Tsopela 1,2 , L. Salvagnac 1,2 , V. Ventalon 1,2 , E. Bedel-Pereira 1,2 , V. Bardinal 1,2 , I. Séguy 1,2 , P. Temple-Boyer 1,2 , P. Juneau 3 , R. Izquierdo 3 , J. Launay 1,2