Assessment of core body temperature is important for diagnosing infections and monitoring gastrointestinal disorders and circulatory abnormalities. Traditionally, taking these measurements has relied on oral or rectal probes, which can be uncomfortable and restrict patient mobility.
Recent advancements in ingestible electronics have enabled a more autonomous approach to internal biotelemetry. Technologies developed for aerospace health monitoring were later adapted for clinical and sports medicine applications, including heat-stress assessment and gastrointestinal tracking.
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However, most early monitoring capsules measured between 15 and 27 millimeters in length, creating a risk of gastrointestinal retention, particularly in pediatric patients and individuals with structural abnormalities or impaired motility.
A major limitation of these devices has been their dependence on large batteries and power-intensive wireless systems. Thus, developing smaller ingestible sensors requires ultra-low-power electronic architectures and communication strategies that reduce energy demands.
Design Features of the Miniaturized Sensor
To mitigate gastrointestinal retention risks, researchers developed a miniaturized ingestible temperature sensor measuring just 6 mm in diameter and 4 mm in height. This matches the established safety dimensions for orally controlled-release systems.
The device is built around a custom 1 mm × 1 mm complementary metal-oxide semiconductor (CMOS) application-specific integrated circuit that operates in the subthreshold leakage regime. Using a three-delay-unit ring oscillator, the circuit converts temperature-dependent variations in leakage current into measurable frequency shifts while consuming only 10 nW of power.
The system is powered by a 4.8 mm silver-oxide coin-cell battery and regulated through an on-chip low-dropout regulator that provides a stable 1 V supply with minimal current consumption.
Wireless communication is achieved through passive backscatter transmission using a custom 5 mm × 5 mm antenna tuned to 433 MHz. Instead of generating an active radio signal, the device modulates antenna impedance to encode temperature information onto an externally supplied carrier wave, substantially reducing power requirements.
For assembly, the electronics were integrated onto a flexible printed circuit board and housed within a biocompatible casing. The system was encapsulated with ultraviolet-cured protective materials to shield the electronics from the acidic gastrointestinal environment.
Validation of Performance Through Rigorous Testing
Extensive laboratory testing demonstrated that the ingestible sensor maintains high thermal accuracy across the physiological range of 34 °C to 40 °C, with a measurement error below 0.1 °C following calibration. Long-term in vitro evaluations in simulated gastric and intestinal fluids for 30 days confirmed resistance to moisture ingress and chemical degradation while supporting battery operation well beyond typical gastrointestinal transit times.
In vivo studies in large animal models further validated the device's performance. The capsule accurately tracked internal temperatures across multiple organs and maintained agreement with established clinical reference probes, with an error margin below 0.1 °C.
During monitoring, the sensor captured subtle physiological changes, including a 0.4 °C decline in core temperature over 15 minutes following anesthesia and a 2.3 °C decrease within one hour after euthanasia.
The device showed reliable operation during multi-day gastrointestinal transit, remaining functional throughout a five-day passage before natural excretion. In occlusive mesenteric ischemia experiments, the sensor detected a localized temperature reduction of approximately 0.3 °C associated with reduced tissue perfusion.
Applications Beyond Ingestible Sensors
The compact size of the circuit has implications beyond ingestible capsules. Researchers integrated the sensor into the tip of a catheter with a 1 mm diameter using ultra-thin wiring for power and data transmission. When incorporated into an endotracheal tube, the system continuously monitors internal temperature without needing additional invasive probes.
The wired sensor was also evaluated as a tool for vascular access guidance. By exploiting the natural temperature difference between blood vessels and surrounding tissues, the device recorded a gradual increase in temperature during catheter insertion.
It also stabilized near core body temperature upon entry into the femoral vein. These results demonstrate that high-resolution thermal sensing can support real-time verification of vascular placement.
Future Directions for Physiological Monitoring Technology
This study demonstrates that millimeter-scale ingestible sensors can provide accurate, continuous internal temperature monitoring while maintaining a form factor compatible with established gastrointestinal safety requirements.
The platform combines sensor miniaturization, low power consumption, and long operational lifetime, offering a promising practical solution for clinical monitoring and remote physiological surveillance.
Future work should focus on further reducing system size and dependence on conventional power sources through wireless or battery-free operating strategies. Additionally, integrating wearable receiver systems will support continuous ambulatory monitoring outside laboratory environments.
Expanding the platform into a multimodal sensing system capable of simultaneously measuring pH, pressure, and other physiological biomarkers could significantly enhance its diagnostic capabilities, broadening the utility of the technology across critical care and long-term health monitoring applications.
Journal References
Sharma, S., et al. (2026). A miniaturized ingestible temperature sensor for continuous internal monitoring. Nature Electronics. https://www.nature.com/articles/s41928-026-01643-y
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