The sensor uses electric-charge-conducting protein nanowires derived from the bacterium Geobacter to provide biomaterials for electrical devices. The microbes, say the researchers, grow hair-like protein filaments that work as nanoscale "wires" to transfer charges for their nourishment and to communicate with other bacteria.
The researchers chose to design their first sensor to measure ammonia because that gas is important to agriculture, the environment, and biomedicine. For example, in humans, ammonia on the breath may signal disease, while in poultry farming the gas must be closely monitored and controlled for bird health and comfort and to avoid feed imbalances and production losses.
"This sensor allows you to do high-precision sensing," says Assistant Professor in Electrical and Computer Engineering Jun Yao. "It's much better than previous electronic sensors."
"We didn’t expect them to work as well as they have," adds biomedical engineering doctoral student Alexander Smith, first author of a paper on the research. "I really think they could have a real positive impact on the world."
Existing electronic gas sensors, says the researchers, often have either limited or low sensitivity, and are prone to interference from other gases. Their sensor, however, says Smith, in addition to having superior function and low cost, is biodegradable so does not produce electronic waste. And it is produced sustainably by bacteria using renewable feedstocks without the need for toxic chemicals.
The research followed on earlier studies that showed that the protein nanowires' conductivity changed in response to pH – the acid or base level – of solution around the protein nanowires. This prompted the researchers to test the idea that they could be highly responsive to molecule binding for biosensing.
"If you expose them to a chemical," says Smith, "the properties change and you can measure the response."
When the nanowires were exposed to ammonia, the response, say the researchers, was "really noticeable and significant."
"Early on, we found we could tune the sensors in