A micro flow injection electrochemical biosensor for organophosphorus pesticides.

We describe a disposable, amperometric micro flow injection electrochemical biosensor that can be applied to the identification and quantification of highly toxic organophosphorus (OP) compounds in the environment, on the spot and in a short time. The system traces very small quantities of OP by monitoring the enzymatic reaction of acetylcholine esterase (AChE) and its inhibition. The sensor is sensitive, rapid, small, inexpensive, disposable and can be operated by non-professional technicians. The electrochemical cell consists of screen-printed electrodes covered with an enzymatic membrane and placed in a home-made flow cell. The electrodes are connected to a computer-controlled potentiostat. We quantitatively detected the OP compound, dimethyl 2,2-dichlorovinyl phosphate (DDVP), by monitoring the OP induced decrease in enzymatic degradation of the substrate, acetylthiocholine chloride (ATCh), to thiocholine and acetic acid. Thiocholine reacts with hexacyanoferrate ion in the working solution and the reduction of Fe(CN)6 to Fe(CN)6 and its subsequent reoxidization by the electrode generates very sharp, rapid and reproducible electric signals. The ability to detect low quantities is extremely important when dealing with hazardous environmental pollutants.