The development of whole cell biosensors for on‐line screening of herbicide pollution of surface waters

Abstract

Abstract The use of mediator assisted amperometric whole‐cell biosensors, monitoring microbial photosynthetic electron transfer, to screen for herbicides in intake protection by the water industry is described. Cells harvested from axenic cultures are loaded onto bacteriological filters and held against a working carbon electrode polarised against the silver chloride reference. Redox mediators are reduced by the microorganisms and then reoxidised at the working electrode resulting in a flow of current. For on‐line applications the sensors are controlled by a programmable electrochemical analyser (Artek) and housed in specially designed perspex flow cells which incorporate light emitting diodes (LEDs) for photosynthetic stimulation. A range of cyanobacteria and algae have been tested, but biosensors incorporating unicellular cyanobacteria have proven the most successful. Results obtained using the cyanobacterium Synechococcus show detection levels of less than 200 ppb with response times of less than ten minutes for selected herbicides. Sensor stability in the absence of pollutant poisoning has been found to be greatly influenced by the choice of mediator. Membrane penetrating mediators such as ‐benzoquinone reduce sensor life to about 24 hours, while a sensor life of up to six days has been achieved with ferricyanide.