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

Abstract

SynopsisThe 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 a t 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.

Microalgal motility measurement microfluidic chip for toxicity assessment of heavy metals

“…However, cell entrapment was shown to decrease the sensitivity of microalgal biosensors by an order of magnitude compared with nonentrapped cells [14,15]. Limited previous studies on algal sensor chips demonstrated that the photosynthesis inhibition was the physiological end point most often chosen as the response signal to toxicants [16][17][18][19]. The detectors in these devices use the principles of flow cytometry or chlorophyll fluorometry and have optical alignment systems with high power lasers or LEDs, which make the devices relatively complicated and expensive.…”

Novel Cyanobacterial Biosensor for Detection of Herbicides

“…About one-half of the herbicides presently used in agriculture act by inhibiting the light reactions in photosynthesis, mostly by targeting the photosystem II (PSII) complex (10). A series of algal and cyanobacterial PSII-based whole-cell (5,6,11,14,27,28,34,37,43) and tissue (3,15,17,18,19,30,31,32) biosensors have therefore been developed for detection of a class of herbicides which inhibit photosynthetic electron transport. In these systems, herbicides are detected by testing inhibition of the Hill reaction (6,17,31,32), inhibition of 2,6-dichlorophenol indophenol photoreduction (4,5,15), or change in chlorophyll fluorescence (8,11,19,30), which can be correlated with the pollutant concentration.…”

Biocapteurs pour le contrôle de la toxicité des eaux : application des bioélectrodes algales

“…Ces conclusions rejoignent les travaux de RAWSON et al (1987) qui ont montré que l'utilisation de tels médiateurs réduisait la vie d'un biocapteur à cyanobactéries à 24 heures, alors qu'elle est de 6 jours avec un médiateur comme le Fe(CN) 6 .…”