The National Academy of Engineering has identified “provide access to clean water” as one of the fourteen grand challenges for engineering in the coming decades. Monitoring water quality is essential for delivering safe and clean drinking water to the public. Conventional approaches are commonly based on physicochemical analyses, which enable accurate and sensitive detection of a wide range of chemical compounds. However, these methods are often time-consuming, cumbersome, and dependent on extensive instrumentation. They also cannot readily capture synergistic and antagonistic toxic effects that may arise from complex biological and chemical mixtures. Other approaches use living organisms such as fish, protozoans, algae, bivalves, and daphnids to monitor water quality by tracking changes in behavior, survival, growth, or physiological condition. Even so, these methods still suffer from the challenge of evaluating the large amount of information generated from continuously monitored organisms. For that reason, simple, fast, sensitive, and generic biosensors are needed for real-time applications.
Microbial fuel cells (MFCs) can potentially serve as biosensors for water-toxicity detection because a broad range of toxic components can inhibit bacterial metabolic activity. MFCs are bioelectrochemical systems that generate current through bacterial metabolism. As a result, the current produced by the MFC can be used as a measure of water quality, since changes in electrical current depend on environmental factors such as pH, dissolved oxygen, biochemical oxygen demand, and other organic compounds. In particular, the presence of toxic substances in water, including formaldehyde, benzene, hexane, toluene, and heavy metals, can significantly affect bacterial metabolism and growth. Therefore, when a current drop is monitored from the MFC biosensor, an alarm can be triggered and appropriate action can be taken to help protect waterways from pollution.