MIT researchers have built an ingestible sensor equipped with genetically engineered bacteria that can diagnose bleeding in the stomach or other gastrointestinal problems.
This “bacteria-on-a-chip” approach combines sensors made from living cells with ultra-low-power electronics that convert the bacterial response into a wireless signal that can be read by a smartphone.
“By combining engineered biological sensors together with low-power wireless electronics, we can detect biological signals in the body and in near real-time, enabling new diagnostic capabilities for human health applications,” says Timothy Lu, an MIT associate professor of electrical engineering and computer science and of biological engineering.
In the new study, appearing in the May 24 online edition of Science, the researchers created sensors that respond to heme, a component of blood, and showed that they work in pigs. They also designed sensors that can respond to a molecule that is a marker of inflammation.
Lu and Anantha Chandrakasan, dean of MIT’s School of Engineering and the Vannevar Bush Professor of Electrical Engineering and Computer Science, are the senior authors of the study. The lead authors are graduate student Mark Mimee and former MIT postdoc Phillip Nadeau.
In the past decade, synthetic biologists have made great strides in engineering bacteria to respond to stimuli such as environmental pollutants or markers of disease. These bacteria can be designed to produce outputs such as light when they detect the target stimulus, but specialized lab equipment is usually required to measure this response.
To make these bacteria more useful for real-world applications, the MIT team decided to combine them with an electronic chip that could translate the bacterial response into a wireless signal.
“Our idea was to package bacterial cells inside a device,” Nadeau says. “The cells would be trapped and go along for the ride as the device passes through the stomach.”
For their initial demonstration, the researchers focused on bleeding in the GI tract. They engineered a probiotic strain of E. coli to express a genetic circuit that causes the bacteria to emit light when they encounter heme.
They placed the bacteria into four wells on their custom-designed sensor, covered by a semipermeable membrane that allows small molecules from the surrounding environment to diffuse through. Underneath each well is a phototransistor that can measure the amount of light produced by the bacterial cells and relay the information to a microprocessor that sends a wireless signal to a nearby computer or smartphone. The researchers also built an Android app that can be used to analyze the data.
The sensor, which is a cylinder about 1.5 inches long, requires about 13 microwatts of power. The researchers equipped the sensor with a 2.7-volt battery, which they estimate could power the device for about 1.5 months of continuous use. They say it could also be powered by a voltaic cell sustained by acidic fluids in the stomach, using technology that Nadeau and Chandrakasan have previously developed.
“The focus of this work is on system design and integration to combine the power of bacterial sensing with ultra-low-power circuits to realize important health sensing applications,” Chandrakasan says.