A $2000 piece of equipment to measure the amount of chlorophyll in a sample using the fact that it fluoreses under light. Be great to DIY, usefull for tracking algae blooms. Bit of discussion here http://forum.arduino.cc/index.php?topic=194982.0 using arduino.
Related paper: In situ Measurements of Phytoplankton Fluorescence Using Low Cost Electronics Thomas Leeuw * , Emmanuel S. Boss and Dana L. Wright openaccess paper
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