New bacteria-filled sensor for water monitoring

A small sensor filled with bacteria could be used to monitor the quality of drinking water in real time without expensive lab equipment. Developed by researchers at the University of Bath and Bristol Robotics Laboratory at the University of the West of England, the sensor is filled with bacteria that produce a small measurable current as they feed and grow. When disturbed by incoming toxins and pollutants, the electric current drops, alerting researchers to the presence of unwanted contaminants. “The sensor works through the action of specific bacteria called electrigens because they are capable of generating electricity,” Dr Mirella Di Lorenzo, a lecturer in Chemical Engineering at Bath, told Laboratory News. “The bacteria source is anaerobic sludge extracted from a wastewater treatment plant. When the bacteria are 'inoculated' inside the device, and the anode and cathode are connected to an external circuit, the generation of electricity is forced and a natural selection occurs at the anode so that only electrigens survive. When this process reaches steady-state a constant current is generated, provided that the bacteria are constantly fed with a source of organic carbon.” “In the case of a sudden presence of a pollutant in the feeding solution, the sensor sends a warning message represented by an immediate distinct change in the steady current. The current change is due to the fact that the pollutant interacts with the electrigens' metabolism and growth.” Researchers were able to monitor the level of pollutants in the water in real time without having to collect multiple samples and take them to a laboratory. The sensor was developed using rapid prototyping layer-by-layer 3D printing. It consists of the anode (carbon cloth); the anodic cell (this is the total volume of the sensor); and a membrane hot pressed to the cathode (carbon cloth). The anode and the cathode were manually inserted while printing the several solid layers. “This layer-by-layer fabrication led to a very compact device which did not need any bolts,” said Di Lorenzo. “The overall time for the fabrication was a few minutes and the materials used are really cheap. If the production would be on large scale this device would cost only few pounds.” Di Lorenzo added that only proof-of-concepts experiments have been performed to show the potential application of this technology with a model compound such as cadmium. “The sensor was surprisingly sensitive (lower detection limit in the range of micrograms per litre) compared to existing technology (order of milligrams per litre),” she said. “We have also shown that the intensity of current change was depending on the pollutant concentration. Therefore this technology is very promising.” Researchers are now testing the sensor with a range of trace pollutants, especially pharmaceuticals and pesticides to find a correlation between the type of response that the sensor to target pollutants. The work has been published in Biosensors and Bioelectronics. A small-scale air-cathode microbial fuel cell for on-line monitoring of water quality