MIT team shrinks ingestible temperature sensor for core body monitoring

MIT engineers have developed a 6-millimeter ingestible temperature sensor that can send core body readings from inside the gastrointestinal tract, a design that could help clinicians monitor infection, anesthesia risk, fertility, heat stress, and hypothermia.

The team, led by researchers at the Massachusetts Institute of Technology, reported the work June 15 in Nature Electronics. Giovanni Traverso, an associate professor of mechanical engineering at MIT and a gastroenterologist at Brigham and Women's Hospital, and Anantha Chandrakasan, MIT provost and professor of electrical engineering and computer science, served as senior authors. MIT postdoc Saransh Sharma led the study.

Clinicians often use oral, ear, or forehead thermometers because they cost little and require little training. Those tools measure surface-adjacent temperature. Core temperature gives clinicians a better read on fever, hypothermia, anesthesia response, and heat strain, yet hospitals usually need invasive probes or larger ingestible capsules to capture it.

MIT's device takes the ingestible route and reduces the scale. The capsule measures 6 millimeters across and 4 millimeters tall, close to the size of a small blueberry. That size matters in the gut. A smaller capsule gives patients a swallowable form factor and lowers the chance that the device blocks the gastrointestinal tract.

Traverso framed the clinical target as risk detection. Patients on chemotherapy or immunosuppressive drugs can deteriorate fast after an infection begins. A capsule that reports core temperature once per second could help a care team see a fever pattern before a patient feels sick enough to seek help.

The engineering challenge starts with power. Larger ingestible temperature sensors often carry circuits that consume enough energy to require a large onboard battery. That battery drives capsule size, and capsule size drives swallowability and obstruction risk.

MIT's group attacked each component: the temperature circuit, the antenna, and the battery. The researchers built a custom temperature-sensing circuit on a 1-square-millimeter silicon chip. The chip uses an oscillator based on leakage current, the small current that flows through a circuit in its off state. Temperature changes alter that current's frequency, so the circuit can infer the surrounding temperature.

The circuit draws about 10 nanowatts and measures temperature with 0.01 degrees Celsius accuracy in the team's tests. That power budget lets the capsule run from a 1.55-volt coin cell battery that measures 4.8 millimeters across and about 1.6 millimeters thick.

The team also cut radio power through backscatter communication. An external antenna, placed within about a foot or two of the body, sends an ultra-high-frequency radio wave toward the capsule. The capsule's antenna modulates the wave and reflects it back. The external reader interprets the changed signal and calculates temperature.

Backscatter shifts the energy burden from the swallowed capsule to the reader outside the body. RFID tags use the same broad idea. For an ingestible sensor, that trade-off gives engineers a path to small batteries and frequent measurements without forcing the capsule to carry a full-power transmitter.

Sharma said the team combined the silicon chip, battery, and antenna into the smallest ingestible capsule the group has seen for temperature-sensing systems. The device sends a reading once per second, which gives clinicians a continuous trace instead of an isolated measurement.

The first applications cluster around situations where temperature changes guide action. During anesthesia, patients can lose normal temperature regulation and drift toward hypothermia. Surgeons and anesthesiologists already track temperature in many procedures, but a small internal sensor could give them a direct core measurement without a tethered probe.

Home fever monitoring offers another path. Parents and caregivers often struggle to capture consistent readings from children, and skin temperature can vary with room conditions, sweat, or sensor placement. A swallowed sensor would suit only selected cases at first, but the approach points toward short-term internal monitoring for high-risk patients.

Fertility tracking gives the device a less acute use case. Core body temperature changes around ovulation, and many consumer tools try to infer that shift from surface readings. A direct internal reading could improve signal quality, though researchers would need clinical trials to show that the added precision changes outcomes for users.

The researchers also point to athletes, soldiers, and workers exposed to heat or cold. Heat illness often develops under physical stress, protective clothing, or remote conditions. A capsule sensor could help medics or trainers see dangerous core temperature trends while the person continues to move.

The MIT team tested the sensors in animals under anesthesia and in awake animals that moved during monitoring. The devices transmitted temperature data in both settings. Those tests matter because a capsule must work in a wet, moving, electrically complex environment. The gut changes orientation, surrounding tissue absorbs radio signals, and motion can alter the link between the capsule and reader.

The technology still has practical limits. The external antenna needs proximity to the capsule, so users would need a reader on the body, near a bed, or in another close-range setup. The capsule also passes through the GI tract, which means the monitoring window depends on transit time. Engineers and clinicians will need protocols for patients with strict swallowing risks, motility disorders, or known narrowing in the GI tract.

The team now plans to combine the thermometer with other sensors for vital signs such as heart rate. That step would make the capsule more useful, but it would also raise the design burden. Each added sensor needs power, calibration, packaging, and a way to send usable data through the same small body.

Clinical trials will decide whether the capsule can move from animal studies into patient care. Researchers need to test accuracy against accepted core-temperature methods, track GI passage, evaluate comfort, and study failure modes. Regulators will also scrutinize battery safety, materials, radio exposure, and retrieval or excretion expectations.

The project fits a broader push toward ingestible electronics that monitor the body from places wearables cannot reach. MIT and other groups have explored stomach-based medication adherence systems, wireless capsule control, and internal vital-sign monitors. The new temperature sensor adds a smaller building block to that field.

Funding came from the 711th Human Performance Wing, the Defense Advanced Research Projects Agency, and the Advanced Research Projects Agency for Health. The work connects MIT's Department of Mechanical Engineering and Department of Electrical Engineering and Computer Science with clinical problems that demand small, low-power devices.

A thermometer that patients swallow will not replace simple forehead checks in routine use soon. It could give clinicians and high-risk users a better tool for the cases where one missed fever or one hidden drop in core temperature changes care.