The mighty snouts on dogs are famously known for their abilities to sniff out everything from disease to explosives, but science is quickly catching up with its own range of artificial noses. Now, in the most recent breakthrough in this exciting field, researchers have used genetically modified E. coli bacteria to spin electrically conductive nanowires capable of detecting the odor molecules created by kidney disease. What's more, they say their microbial manufacturing plant can be tuned to create other wires to pick up even more medical conditions.
When it comes to sensing the world around us through our noses, humans fall well short of our canine companions. In an effort to catch up though, scientists have been hard at work over the years, creating a dizzying array of artificial odor sensors. We've seen man-made "noses" that can find cancer in blood or urine samples, detect Parkinson's disease from skin odor, pick up on bacteria in water, find people buried beneath rubble from a natural disaster, and sniff out dangerous toxins in the air.
The problem with many of the nanowires used in these sensors, say researchers at the University of Massachusetts Amherst (UMA), is that they are made from toxic and non-biodegradable materials such as silicon or carbon fiber. To tackle this issue, the research team turned to a bacterial solution.
Last year, UMA microbiologist Derek Lovley and electrical and computer engineer Jun Yao used a bacteria called Geobacter sulfurreducens to create a wearable biofilm that generates electricity from sweat. The success of that experiment centered on the bacteria's ability to grow extremely small wires that can actually conduct electricity. The team decided to put those nanowires to work in their new artificial nose.
However, G. sulfurreducens is hard to culture, as it requires very particular conditions in which to thrive. So, the team enlisted the help of a much more hardy bacteria.
“What we’ve done,” says Lovley, “is to take the ‘nanowire gene’ – called pilin – out of G. sulfurreducens and splice it into the DNA of Escherichia coli, one of the most widespread bacteria in the world.”
In addition to getting E. coli to start producing nanowires, Lovely and Yao also performed an additional genetic modification that caused those wires to become coated with a peptide known as DLESFL. This made the wires 100 times more sensitive than they were before to ammonia, a byproduct found in the breath of those with kidney disease. The bio wires were then implanted onto a sensor which was more effective at spotting the ammonia than previous sensors made from traditional materials.
“One of the most exciting things about this line of research is that we’re taking electrical engineering in a fundamentally new direction,” said Yao. "Instead of wires made from scarce raw resources that won’t biodegrade, the beauty of these protein nanowires is that you can use life’s genetic design to build a stable, versatile, low impact and cost-effective platform.”
The researchers say the tiny bacterial factories could be made to produce wires coated in different peptides that could sense for the chemical makers of other diseases.
"It’s possible to design unique peptides, each of which specifically binds a molecule of interest," said study co-author Toshiyuki Ueki. "So, as more tracer molecules emitted by the body and which are specific to a particular disease are identified, we can make sensors that incorporate hundreds of different chemical-sniffing nanowires to monitor all sorts of health conditions.”
The research has been published in the journal Biosensors and Bioelectronics.