Sensing organ temperature with luminescent powder

A cheap, biocompatible white powder that luminesces when heated could be used for non-invasively monitoring the temperature of specific organs within the body, according to a new study by Japanese scientists.

Thermometers measure temperature at the body’s surface, but clinicians need to be able to monitor and manage core body temperatures in some critically ill patients, such as following head injuries or heart attacks. Until now, this is most often done by inserting a tiny tube into the heart and blood vessels. But scientists are looking for less invasive means to monitor temperature from within the body.

Led by Takumi Fujiwara, an applied physicist at Tohoku University, scientists investigated the potential of a white powder called zirconia for this purpose. The results of their study were published in the journal Scientific Reports.

Zirconia is a synthetic powder that is easily accessible, chemically stable and non-toxic. When heated, its crystals become excited, releasing electrons. These electrons then recombine with ‘holes’ in the crystal molecular structure — a process that causes the crystals to emit light, or luminesce. Because of this material’s advantageous properties for use in the human body, the scientists wanted to test and see if its luminescence could be used for monitoring temperature.

The team heated zirconia under an ultraviolet lamp and found that as zirconia’s temperature rose, its luminescence intensified. The same thing happened when a near-infrared laser light was shone on the material. This demonstrated that both heat and light could be used to induce luminescence in zirconia. The scientists next showed that zirconia luminescence was visible with the naked eye when placed behind a piece of bone and illuminated using a near-infrared laser.

Together, the demonstrations suggest zirconia could potentially monitor internal body temperature by injecting it and then shining a near-infrared laser light on a targeted location, such as the brain. The intensity and longevity of the material’s luminescence will depend on the surrounding temperature.

“While this fundamental study leaves some important issues unresolved, this work is a novel and promising application of [synthetic luminescent substances] in the medical field,” the researchers wrote. Going forward, they hope to discover a method that makes the wavelength of luminescence from zirconia in the region of red to near-infrared since it makes for better transmissibility for human tissues, thus allowing for clearer information to be obtained.

Image left: Optically stimulated luminescence (OSL) from the zirconia sample observed by the irradiation of NIR-laser light without the bone sample. Image right: The OSL from the zirconia sample stimulated by the laser light through the bone sample. Dashed line indicates the contour of bone sample, which was settled in front of the NIR-laser diode. The blue emission of OSL could be observed in the zirconia sample region as well as the observation without the bone sample as indicated by dashed red circles. Image courtesy of the study authors under CC BY 4.0.

Please follow us and share on Twitter and Facebook. You can also subscribe for FREE to our weekly newsletters and bimonthly magazine.