SIEMENS

People in the German state of Baden-Württemberg still shudder when they think about the poison attack. In 2005 an unknown person submerged three canisters of herbicide in Lake Constance, very close to a drinking water pumping station. An anonymous letter claiming responsibility for the attack led divers to the poison in 70 m of water. Fortunately, only small amounts of the pesticide were released into the lake, and thresholds weren’t exceeded. But similar scenarios - for instance if terrorists poured poison into water lines - continue to give water companies nightmares. Fish or water fleas are often used as natural alarm systems, but this is hardly optimal. Drinking water undergoes extensive laboratory testing at extended intervals. “But these tests only find things that are specifically being looked for,” says Dr. Heike Barlag, Head of the Biosensors team at Siemens Corporate Technology (CT) in Erlangen, Germany. Neurotoxins or pesticides that are no longer registered are not on the analysis list.

This is why Siemens biosensor chemists and a group headed by Prof. Maximilian Fleischer at Siemens CT in Munich are exploring new approaches to pollutant detection. The researchers have developed three sensor systems that can be used for effective monitoring of air and water. All three systems use biological components for detection and are mutually complementary.

For example, a system called SiequaSAFE, which was developed by Barlag’s team in collaboration with several water utilities, functions as a warning system in the event of a terrorist attack. At the heart of the system is a sensor that duplicates the crucial metabolic process performed by acetylcholinesterase (AChE), an enzyme that functions as an extremely fast catalyst. AChE breaks down the messenger substance that, in animals, transmits signals from nerve cells to muscles. Substances that inhibit the enzyme, such as the chemical weapons Sarin and Tabun or the banned insecticide E605, are highly toxic. “If a substance such as Sarin interferes with this enzyme, then it is a good indication that something very dangerous is in the water,” says Barlag. However, the initial concern is not so much the identification of the substance, as the ability to instantaneously sound a warning.

The challenge for Siemens chemists was to convert the enzyme inhibition test - an established laboratory procedure - into a fully automated system. The prototype is roughly the size of a printer and has multiple connections for thin tubes through which water samples and solutions are conveyed to a sensor chip. “We found a form of AChE whose cleavage product can be detected electrochemically,” explains Barlag. SiequaSAFE begins by pumping the water sample across the chip. It then provides the AChE with a substance to which it can cleave. As long as the AChE is intact, it breaks down this substance. But if it has been exposed to a poison, it stops working and no decomposition products are formed. The sensor uses the flow at an electrode to determine the amount of these products.

The activity of a control enzyme is also monitored. SiequaSAFE sounds an alarm only if this enzyme is working properly and AChE is not. “But even if SiequaSAFE does encounter a dangerous substance, it is not disabled,” stresses Barlag. The system regenerates automatically by flushing the chip and replacing the enzyme. SiequaSAFE is extremely sensitive, detecting the toxin E605 in amounts of less than one millionth of a gram per liter. A tenth of a gram is deadly to humans. Many more applications will be possible in the future, however. “Heavy metals, phenols, and bluegreen algae toxins are suitable candidates for enzyme inhibition tests,” says Barlag.

Mobile Laboratory Barlag’s team is working not only on SiequaSAFE, which can continuously monitor the safety of a drinking water system, but also on a portable laboratory system that can identify a large number of pollutants and roughly determine their amounts - within half an hour.