12-07-2018 | | By Rob Coppinger
Genetically engineered bacteria that can detect bleeding in the stomach and potentially other gastrointestinal problems have been combined with electronics that convert the bacterial response into a wireless signal that can be read by a smartphone. “At the moment, we’ve only done testing on pigs and we need further clinical trials especially safety trials to show it would be safe for humans,” MIT researcher Phillip Nadeau explained. “Right now, it is this three centimetre by one centimetre capsule. We’d like to make it about one third of the volume and that is about making it safer for ingestion.”
A strain of E. coli was engineered to emit light when it encounters a key component of blood, heme. The bacteria was placed in four wells in the capsule and covered by a membrane that allows small molecules to pass through. A phototransistor was placed in the capsule in a position to detect the bacteria’s light the phototransistor’s microprocessor sends a signal to a nearby computer or smartphone. The researchers also built an Android app to receive the data. Nadeau’s team tested the capsule with pigs and that work showed that it could identify when there was blood in the stomach.
Electronics on one side of the transparent case. Image credit: Lillie Paquette/MIT School of Engineering.
The next step is to have longer experiments with the capsule operate inside a body for a greater duration. For use by humans, Nadeau wants to put all the functions that in the capsule were on a few chips, like photo detection, data processing and signal transmission, on to one chip and make the battery smaller. The capsule design now needs about 13 microwatts of power and uses a 2.7-volt button battery – like a watch battery. This battery is oversized as it could power the capsule for 1.5 months.
Six weeks of use of the sensor could be diagnostically valuable when the device remains in the digestive tract sending continuous signals. Bowel cancer is another ailment it could detect and monitor. One constraint that must be overcome for a capsule or other version of the sensor to last such a long time in the body is extending the bacteria’s lifespan. “We only have needed them to last a single ingestion, but if we want to enable long term monitoring strategies, the key challenge is the longevity of the bacteria,” said Nadeau.
For long term use another option is to make the sensor device bio-compatible. “The metal in the capsule and the acid in the stomach, the hydrochloric acid, acting as the electrolyte activates this little mini biocompatible battery,” Nadeau explained. He also described how other researchers have developed a capsule that dissolves in the stomach, releasing a drug delivering material with an origami-like design, folding outwards so it is too large to enter the small intestine. It sits in the stomach releasing the drug until it has shrunk enough to enter the intestine.
Nadeau also envisions a completely bio-compatible, dissolving sensor where the electronics are organic and can also be broken down to pass safely through the human body when not needed. Today, organic electronics are not powerful enough for the computation needed, but Nadeau recognised that one day they would be.
The research was funded by Texas Instruments, the Hong Kong Innovation and Technology Fund, the United States government’s Office of Naval Research and National Science Foundation, the Center for Microbiome Informatics and Therapeutics, Brigham and Women’s Hospital, a Qualcomm Innovation Fellowship, and the Natural Sciences and Engineering Council of Canada.