Implantable medical monitoring devices could change how we define wearable technology if engineers can make it past hurdles like eliminating bulk and the need for batteries. We recently covered a miniaturized sensor developed by researchers at the University of California that’s smaller than your average ladybug. Now, engineers at Columbia University have created an even smaller sensor that can only be seen under a microscope.

Both sensors rely on ultrasound waves transmitted from outside the body for power and communication. At just 0.1 mm (roughly the size of a dust mite), the Columbia University Engineering team believes their design is the smallest-ever single-chip system. The engineers began with a tiny, integrated circuit temperature sensor upon which they layered conductive film, a microscale piezoelectric transducer, and layers of gold and copper to enhance connectivity.

After testing the sensor in chicken muscle tissue, the team implanted the sensor in live mice. The researchers successfully measured local heating in different internal areas within the mice. Finally, they implanted the sensor at the base of the sciatic nerve to monitor local temperature while the animals received neurostimulation. One day, the sensor could help track nerve temperature in humans receiving a similar procedure for sciatica and other nerve pain conditions. 

The engineers plan further development of sensor chips, hoping to produce microscopic devices that could be implanted in humans using a hypodermic needle. Such devices could monitor temperature, blood pressure, glucose, and other metrics internally without the need for an internal power supply that would need recharging. Because the sensors can record data locally from organs and other tissue structures, they have a broad range of clinical applications. Implantable sensors might even replace smartwatches and other external health tracking devices someday.

The research team recently published their findings in the journal Science Advances.