Researchers from Siemens Corporate Technology have developed a fully automatic system to test drinking water for the presence of toxic substances. The lab demonstration model can analyze water samples at a rate of one every 15 minutes and is sensitive to over 100 toxins, including insecticides and chemical weapons. At the heart of the system is a biosensor that measures the activity of special enzymes. The signal is transmitted electrically, which means that the system is fast, highly sensitive, and durable. Initial talks are now being held to discuss the possibility of developing the demonstration model into a marketable product.

At present, fish are often used to monitor the quality of drinking water. If behave in unusual ways, the water is subject to a thorough check. Around once a week, lab workers also carry out a detailed analysis for toxins. The Siemens system, by contrast, continually removes a sample from the pipe and tests it for harmful substances. No trained employees are required.

The system employs the enzyme acetylcholinesterase (AChE). Since this enzyme plays a key role in the transmission of nerve impulses, it can provide an immediate indication of whether a water sample contains substances harmful to the human metabolism.

This enzyme is fixed onto a special chip. The system measures whether the activity of the enzyme is affected by the water sample. If no toxins are present, the enzyme will continue to display maximum activity, as shown by an electrical current that is generated by a reaction chain. In the presence of toxins such as organic phosphates, carbamates, or nerve gases, the activity of the enzyme is blocked. In other words, the reaction chain cannot proceed, and the electrical current, i.e. the measuring signal, becomes weaker. To ensure high reliability, a control enzyme is also used. To the extent that its activity remain unchanged, this indicates that the system is functioning properly. At regular intervals, and following the detection of a toxin, both enzymes are automatically removed from the chip and then refixed.

In lab tests, researchers were able to show that the presence of the pesticide parathion at a concentration of less than one microgram per liter resulted in a halving of the electrical current, thus producing a clear measuring signal. This toxin is already fatal to humans at a concentration of around a tenth of a gram.