Fast-acting bio-sensor warns of hazardous substances in water supply

Although drinking water is monitored more strictly than almost anything, water supply networks are not immune to accidents, wear and tear or targeted attacks. A one-minute warning system for toxins and other substances in water hazardous to health could set off alarms in future if there is a danger.

It is supposed to be cool, colourless, tasteless and odourless. It may not have any pathogens or impair your health.

This is the reason why drinking water is put to a whole series of screenings at regular intervals. In Germany, the AquaBioTox project will be added to create a system for constant real-time drinking water monitoring.

At present, the tests required by the German Drinking Water Ordinance are limited to random samples that often only provide findings after hours and are always attuned to specific substances. In contrast, the heart of the AquaBioTox system is a bio-sensor that reacts to a wide range of potentially hazardous substances after just a couple of minutes. It works on the taster principle.

Some drinking water is diverted from the main line through the sensor in a branching descending line and it contains two different strains of bacteria and mammalian cells. These microscopically small bacteria have a large surface that guarantees quick material turnover and reacts to toxic substances within minutes.

The mammalian cells are favoured because of their close relationship to the human organism.
The Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB in Stuttgart, Germany tested various classes of substances that might occur in water – even though they shouldn’t – and to date their sensor has reacted to each of these substances.

The micro-organisms in the sensor were modified so that they produce a protein that has a red fluorescence. The fluorescence changes if it comes into contact with toxic substances. A highly sensitive camera system developed by the Fraunhofer Institute of Optronics, System Technologies and Image Exploitation IOSB has an analysis unit that registers even the most minute changes in fluorescence and then analyses them automatically.

The monitoring unit has a machine-learning process for learning from historical data which fluctuations in the physical, chemical and biological parameters are normal. It sets off an alarm if an unusual pattern shows up in the signals.

The bio-sensor reacts to the smallest quantities of hazardous substances. This sensor can document even very slight concentrations. Classical poisons such as cyanide or ricin as well as plant protectives or toxic metabolic products from bacteria can be fatal even in concentrations of nanograms per litre.

They have to guarantee optimum life conditions for the microorganisms to operate the bio-sensor on a permanent basis. Hence, the researchers at the IOSB have come up with a system that automatically monitors and regulates important parameters such as temperature and inflow of nutrients.

Another component of the Aqua-BioTox system is a daphnia toximeter of their Kiel, Germany-based project partner bbe Moldaenke, who noticed that water fleas react particularly sensitively to nerve poisons. They are testing this monitoring system in a closed setup on the grounds of Berlin’s water company, another partner in this project.

The idea behind it is making the system as small and cost-effective as possible so that a network of sensor units communicating with one another could be installed at sensitive points in the drinking water network.

(Image courtesy Fraunhofer IGB.)

[Dr Iris Trick is with the Fraunhofer Institute for Interfacial Engineering and Biotechnology. Dr Thomas Bernard is group manager with the Fraunhofer-Institute of Optronics, System Technologies and Image Exploitation. Fraunhofer is the largest organisation for applied research in Europe.]