Photosystem II is the enzimatic complex supporting photosynthetic electron transport, splitting water and producing ATP and NADPH in photosynthetic organisms. For its inherent feature Photosystem II (PSII) is extremely suitable for the realization of biosensors. Upon illumination PSII runs electrons and fluorescens, reactions that are inhibited in the presence of photosynthetic herbicide. One of the advantages is the simplicity of the biological transduction which can be monitored directly without requiring other markers or transducer molecules. Another advantage is that PSII is extremely susceptible and selective to some agents; these agents are widely used in agriculture as herbicides. Phenylurea, triazine, diazine and phenolic derivatives represent economically very important compounds since they are used in chemical, pharmaceutical and agricultural industry. They still represent about 50% of all herbicides used at the present in agriculture, with a world use of many thousands of tons. Recent work showed the possibility to isolate quite stable PSII particles and building a flow cell provided of Clark’s electrode a very high sensitivity (in the nanomolar range for the herbicide) of the developed biosensor was obtained (1).

In the present work we tried to test the practical application of the biosensor for monitoring under real operational conditions.

In the first step we analyzed the modification of PSII activities in various waters. We observed that PS II activity is stimulated by 10-15% in normal water and the nature of stimulation was partially attributed to the presence of bivalent ions. The bivalent ions cause a different staking in the membrane with consequent change of electron transfer capacity. A comparison of the biosensor analytical response with capillary electrophoresis and HPLC techniques was performed.