SEP 25, 2019 1:30 PM PDT

Nanolaser designed to function in brain tissue

Scientists have developed a nanolaser (miniaturized laser) that can function inside living tissues. According to researchers, the laser is about 1/1,000th the thickness of a single human hair. This means that the laser can fit inside living tissues and sense disease biomarkers or treat neurological disorders that result from dysfunctional brain structures deep inside the brain, such as epilepsy.

In a recent paper published in Nature Methods, Drs. Teri Odom and P. James Schuck from Northwestern and Colombia Universities showcased a nanolaser made mostly of glass (a biocompatible material) that can both excite at longer wavelengths of light and emit short wavelengths. The depth of tissue penetration is key.

"Longer wavelengths of light are needed for bioimaging because they can penetrate farther into tissues than visible wavelength photons," said Northwestern's Teri Odom, co-author of the paper and Charles E. and Emma H. Morrison Professor of Chemistry in Northwestern's Weinberg College of Arts and Sciences. "But shorter wavelengths of light are often desirable at those same deep areas. We have designed an optically clean system that can effectively deliver visible laser light at penetration depths accessible to longer wavelengths."

Importantly, given its small size, the nanolaser can function in tight spaces. Many biological applications, such as use in living tissues, require small lasers. The problem is that these lasers are much less efficient because they require much shorter (and ultimately more damaging) wavelengths, such as ultraviolet light, to power them. Researchers solved this issue by using a method called photom upconversion. Briefly, during upconversion, low-energy photons are absorbed and converted into one (more powerful) photon. The team started with low-energy, “bio-friendly” infrared photons and upconverted them to visible lasers.

"Our nanolaser is transparent but can generate visible photons when optically pumped with light our eyes cannot see," said Odom. "The continuous wave, low-power characteristics will open numerous new applications, especially in biological imaging."

These new nanolasers are "Excitingly, our tiny lasers operate at powers that are orders of magnitude smaller than observed in any existing lasers," Schuck said.

Source: EurekAlert!, ScienceDaily

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