The device combines sensors made from genetically engineered bacteria with ultra-low-power electronics. The electronics convert the bacterial response into data that can then be read wirelessly by a smartphone.
“By combining engineered biological sensors together with low-power wireless electronics,” says Timothy Lu, an MIT associate professor of electrical engineering and computer science and of biological engineering, “we can detect biological signals in the body and in near real time, enabling new diagnostic capabilities for human health applications.”
Using this approach, the researchers created sensors that respond to heme – a component of blood – and demonstrated that the sensors work in pigs. They also designed sensors that can respond to a molecule that is a marker of inflammation.
While creating engineered bacteria to respond to certain stimuli is not new, such research has usually required specialized lab equipment to measure the response. The MIT researchers chose their hybrid bacteria/electronics approach to make these bacteria more useful for real-world applications.
“Our idea was to package bacterial cells inside a device,” says Phillip Nadeau, a lead author of a paper on the research. “The cells would be trapped and go along for the ride as the device passes through the stomach.”
The sensor itself is a cylinder about 1.5 inches long and requires about 13 microwatts of power. The device is equipped with a 2.7-volt battery, which is estimated to be able to power the device for about 1.5 months of continuous use. Alternatively, say the researchers, it could also be powered by a voltaic cell sustained by acidic fluids in the stomach.
The researchers’ initial demonstration of the sensor focused on bleeding in the gastrointestinal tract using an engineered probiotic strain of E. coli bacteria that emit light when they encounter heme. The bacteria were then placed into four wells – i.e., detection sites – on a custom-designed sensor, covered by a semipermeable membrane that allows small molecules from the surrounding environment to diffuse through.
A phototransistor underneath each well measures the amount of light produced by the bacterial cells and relays the information to a microprocessor, which sends a wireless signal to a nearby computer or smartphone. An Android app was also developed that can be used to analyze the data.
“Most of the work we did in the paper was related to blood, but conceivably you could engineer bacteria to sense anything and produce light in response to that,” says Mark Mimee, another lead author of the study. “Anyone who is trying to engineer bacteria to sense a molecule related to disease could slot it into one of those wells, and it would be ready to go.”
To help advance the technology toward use in actual patients, the researchers plan to reduce the size of the sensor and to study how long the bacteria cells can survive in the digestive tract, as well as develop sensors for gastrointestinal conditions other than bleeding. In addition, they say, the sensors could also be designed with additional detection sites to carry multiple strains of bacteria, allowing them to diagnose a variety of conditions, enabling more high-throughput screening.
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