Integrated In Situ Analyzer for Manganese (IISA-Mn) for Deep Sea Environment

Many metal ions that can be found at trace or ultratrace level in ocean are coming from deep-sea hydrothermal vents. In particular, manganese (Mn²⁺) can be assimilated by phytoplankton and so can be found in all the food chain. It is then of interest to be able to detect manganese to determine its spatial distribution and/or to find new hydrothermal sources. Usually, determination of manganese concentration is done by sampling seawater in bottles, followed by analysis in lab onboard a ship or on the ground. Major drawbacks of that method are that only a few samples can be taken during each dive and that there is a risk of contamination of the sample. The use of microfabrication techniques to produce an in-situ microanalyzer that can be installed in an autonomous underwater vehicles (AUVs) or remotely operated vehicles (ROVs) can allow a higher sampling rate, with experiments over a longer time, a reduced risk of contamination. We propose here a microdevice designed for in situ detection of manganese ion in deep-sea environment. Detection is based on chemiluminescence of luminol triggered by the H₂O₂ decomposition catalyzed by manganese ion. The set-up is composed of pressure-proof micropumps for handling of the reagents, a 6-way valve for samples introduction, a PDMS (poly(dimethylsiloxane)) microchip made by soft lithography, and a photomultiplier for photon detection. The limit of detection of this system is about 10 nanomolar at the moment.