Taking your temperature from the inside

MIT engineers have developed an ingestible temperature sensor measuring just six by four millimeters — small enough to swallow comfortably — that transmits continuous core body temperature readings wirelessly, according to MIT Technology Review.

The sensor is built around a circuit that fits on a one-square-millimeter silicon chip. The team designed an oscillator based on leakage current — the small residual current that flows through a circuit even when it is off — whose frequency shifts with the surrounding temperature. That design allows the sensor to detect temperature within 0.01 °C. Power comes from a 1.55-volt coin cell battery, and a technique called backscattering reduces energy consumption further: an external antenna emits an ultra-high-frequency radio wave, which the sensor's internal antenna modulates and reflects back. The external antenna then reads the changes in that wave to calculate temperature, effectively outsourcing most of the power load to hardware outside the body.

The device is described as "the smallest ingestible capsule that we have seen for temperature-sensing paradigms" by Saransh Sharma, a former MIT postdoc now at the University of Cambridge and lead author of the research paper, per MIT Technology Review. Existing ingestible temperature sensors on the market have been large enough to be difficult to swallow and carry a risk of obstructing the gastrointestinal tract, while oral and forehead thermometers often fail to accurately reflect core body temperature.

The researchers list a range of potential applications: monitoring infections, observing patients under or recovering from anesthesia, tracking fevers in children, helping identify ovulation, and tracking core temperature in athletes or soldiers exposed to extreme heat or cold. "A sensor like this gives us the ability to monitor infections and identify them early," co-senior author Giovanni Traverso, an associate professor of mechanical engineering at MIT, told MIT Technology Review. "That's very relevant, particularly for at-risk populations like people who are immunosuppressed." The paper's other senior author is MIT provost Anantha Chandrakasan.

Traverso said he ultimately hopes the sensor could replace conventional thermometers for broad consumer use, though the article does not specify a timeline for commercialization, clinical trials, or regulatory filings.