Interestingly, chemical binding on a plate in lab (think: LAL assay for endotoxins) is not the only way to determine substance concentration by fluorescence. A new assay has been developed using the largest plate well (and dilution!) in the world–the ocean. Scientists have been using bioluminescent marine bacteria to quantify aquatic toxicity. Under normal conditions, these bacteria fluoresce, making pretty lights when you paddle in the ocean at night (shameless plug: join Outing Club!). However, at high toxin concentration, the bacteria’s health of metabolic processes shut down so that the (usually dead) bacteria no longer emit light. The dangerousness of each toxin is recorded by their EC50 value, or the concentration at which the bacterial fluorescence level decreases to half the initial output.
I thought this mechanism was a kind of neat application of biochemistry found in nature as well as in the lab!
See here for more information (though it’s not really an article, per se): http://www.ineos.com/Global/Oligomers/SHE/Durasyn%20Environmental%20Summary%20202009.pdf