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
Who is interested?