University of Adelaide grad student Stefan Musolino demonstrates an optical-fiber probe that can generate and harness light to detect temperature changes in biological systems. [Image:
Stefan Musolino and Erik Schartner, University of Adelaide]
The brain is the body’s most temperature-sensitive organ, but since it’s so well protected, it’s hard for medical professionals to stick a thermometer in it. Researchers based in Australia have now developed an optical-fiber probe that can make precise temperature measurements of small regions of the brains of living, moving laboratory animals (Biomed. Opt. Express, doi:10.1364/BOE.7.003069).
To study how small changes in brain temperature, such as those caused by recreational stimulant drugs, impair or even kill neurons, researchers need something that can sense deep brain tissue’s temperature to ±0.1°C, according to the study team at the University of Adelaide and the ARC Center for Excellence in Nanoscale Biophotonics. Past temperature-probing experiments involving optical fibers inscribed with Bragg gratings required long lengths of fiber and did not resolve small temperature fluctuations.
Adelaide graduate student Stefan Musolino, research fellow Erik Schartner and their colleagues turned to another technique: rare-earth thermometry, which derives temperature measurements from changes in the emission spectra of dopant ions such as erbium or neodymium. In this case, the team manufactured thin glass fibers with trace amounts of erbium and ytterbium by dipping the tip of the optical fiber into a pool of molten tellurite glass doped with the rare earths. The ytterbium increased the efficiency of the upconversion effect, converting excitation light into shorter wavelengths.
The researchers connected the fibers, mounted in 25-gauge needles with the tips protruding and encased in standard optical fiber protective sleeves, to a 980-nm-wavelength laser source and inserted the probes into the brains of anesthetized rats. During the proof-of-concept experiments, the rats were allowed to move around their enclosures while the researchers recorded their brain and body temperatures as well as the ambient temperature.
The Adelaide group hopes that the fiber probe will help clinicians study the effects of hyperthermia induced by MDMA (the recreational drug also known as “ecstasy”) on the brain. Another potential use is monitoring brain temperatures after strokes or traumatic brain injuries.