Tiny, Biocompatible Laser Could Function Inside Living Tissues

Nanolaser has potential to treat neurological disorders or sense disease biomarkers

Oct 01 2019 | Images courtesy of P. James Schuck

About the Study

The study, “Ultralow-threshold, continuous-wave upconverting lasing from subwavelength plasmons,” was supported by the National Science Foundation (award number DMR-1608258), the Vannevar Bush Faculty Fellowship from the U.S. Department of Defense (award number N00014-17-1-3023) and the U.S. Department of Energy (DE-AC02-05CH11231).

Columbia engineers collaborating with researchers at Northwestern University have developed a tiny nanolaser that can function inside of living tissues without harming them.

Just 50-150 nanometers thick, the laser is about 1/1,000th of the thickness of a single human hair. At this size, the laser can fit and function inside living cells and tissues, with the potential to sense disease biomarkers or perhaps treat deep-brain neurological disorders, such as epilepsy.

The nanolaser also can operate in extremely confined spaces, including quantum circuits and microprocessors for ultra-fast and powerful electronics.

The research was co-led by P. James Schuck, an expert in nano-optics at Columbia Engineering, and Teri Odom, an expert in designing structured nanoscale materials at Northwestern University. Their paper was published in the journal Nature Materials.

While many applications require increasingly small lasers, researchers continually run into the same roadblock: Nanolasers tend to be much less efficient than their macroscopic counterparts. And these lasers are typically powered by high-energy photons, such as ultraviolet light.

“This is bad because the unconventional environments in which people want to use small lasers are highly susceptible to damage from UV light and the excess heat generated by inefficient operation,” said Schuck, an associate professor of mechanical engineering.

The two teams were able to achieve a nanolaser platform that solves these issues by using photon upconversion. In upconversion, low-energy photons are absorbed and converted into one photon with higher energy. To do this, the researchers started with low-energy, “bio-friendly” infrared photons and upconverted them to visible laser beams. The result is a powerful laser that is thinner than the wavelength of light.

“Our nanolaser is transparent but can generate visible photons when optically pumped with light our eyes cannot see,” said Odom, Northwestern’s Charles E. and Emma H. Morrison Professor of Chemistry. “The continuous wave, low-power characteristics will open numerous new applications.”

In particular, their nanolaser shows specific promise for imaging in living tissues. Not only is it made mostly of glass, which is intrinsically biocompatible, the laser can also be excited with longer wavelengths of light and emit at shorter wavelengths.

“Longer wavelengths of light are needed for bioimaging because they can penetrate farther into tissues than visible wavelength photons,” said Odom. “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.”

Their device makes use of plasmonic arrays of tailored silver nanoparticles coated with designer upconverting particles, created in collaboration with the groups of Bruce Cohen and Emory Chan, upconverting nanoparticle experts located at the Molecular Foundry, a Nanoscale Science Research Center at Lawrence Berkeley National Laboratory.

“Excitingly, our tiny lasers operate at powers that are orders of magnitude smaller than observed in any existing multiphoton lasers,” Schuck said.

“Through an elegant combination of physics and materials science, this study achieves one of the holy grails in laser science,” said Giulio Cerullo, a physics professor at Politecnico di Milano (Italy) who was not involved in the study. “After nearly 60 years of research, the laser concept still proves its versatility, lending itself to many embodiments and enabling disruptive applications.”

Excitingly, our tiny lasers operate at powers that are orders of magnitude smaller than observed in any existing multiphoton lasers.

P. James Schuck
Associate Professor of Mechanical Engineering
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