A Field-Portable Toxicity Tester using Bacterial Bioluminescence

This paper describes a simple, inexpensive and easily constructed toxicity biosensor that uses freeze-dried bioluminescent bacteria, photobacterium phosphoreum IFO 13896. To compensate for bacterial activity, we apply a differential photometer circuit to measure bioluminescence. Instead of a photomultiplier tube, dual photodiodes were used to reduce the cost of the sensor system. The concentrations of toxic compounds causing 50% light loss (50% effective concentrations, EC50) were determined immediately and 30 min after rehydration of the bacteria from a freeze-dried state. The EC50 values at dual mode operation with differential amplification are nearly constant for the temperature range between 10 and 25degC, whereas the EC50 values at single mode operation increase with temperature, resulting in low sensitivity. The performance of the portable biosensor as a tool for determining p-nitrophenol, mercury, cadmium, and lead toxicity is demonstrated.