Nutrients such as phosphate, ammonia, nitrite and nitrate are central in many environmental processes within the marine environment, including several microbial, plant and animal metabolic processes. This work is carried out as part of the COMMON SENSE FP7 project. The COMMON SENSE project aims to provide a cost effective reliable sensing platform for in-situ measurements of key parameters relating to eutrophication, contaminants, marine litter and underwater noise. The project will design and develop new generation sensors focused on the detection of: Nutrient analytes by utilising established colorimetric chemistries for phosphate, ammonia, nitrate and nitrite, low concentrations of heavy metals (Pb, Hg, Cd, Zn and Cu), surface concentration of micro plastics, and underwater noise. The COMMON SENSE nutrient sensor will be based on a similar approach to the systems previously developed at DCU for autonomous detection of phosphate1 and other parameters based on a combination of microfluidic analytical systems, colorimetric reagent chemistry, low-cost LED-based optical detection and wireless communications. Here we focus on the development of an autonomous sensor for the in-situ detection of nutrients by utilising colorimetric chemistries nitrite and nitrate.