The lab-on-chip (LOC) nitrate sensor is a miniaturised wet chemical analyser capable of in situ nitrate plus nitrite measurements in almost any aquatic environment. The system uses the Griess assay with cadmium reduction to perform measurements comparable in quality to standard laboratory analysis methods, and of superior quality to UV absorbance measurements. The system carries an on-board standard to correct against drift, and is capable of performing hourly measurements for three months with a typical reagent payload. Range is 0.025 to 1000 µM; LOD is 0.025 µM.
LOC nitrate sensors have been successfully deployed in a range of marine and freshwater aquatic environments. These include rivers (both pristine and polluted), estuaries, glacial meltwater (proglacial streams), shelf seas, the surface ocean (buoys and moorings in the Arctic), the seafloor (on benthic landers) and profiling in the deep ocean (deepest deployment 4800m). We have recently completed a number of deployments on board autonomous and remote-operated vehicles. The sensor and reagents have been deployed inside the payload bay of a Kongsberg Seaglider, on an AutoSub, and on an ROV.