A nanocrystal turns on and off indefinitely — ScienceDaily

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In 2021, lanthanide-doped nanoparticles made waves — or rather, an avalanche — when Changwan Lee, then a doctoral student in Jim Schuck’s lab at Columbia Engineering, set off a chain reaction that produces extreme light from ultra-small crystals developed at the Molecular Foundry at Berkeley Lab. Those same crystals have returned again with the blink of an eye that can now be controlled deliberately and indefinitely.

“We have found the first fully photostable, fully photoswitchable nanoparticle, a holy grail of nanoprobe design,” said Schuck, an associate professor of mechanical engineering.

This unique material was synthesized in the labs of Emory Chan and Bruce Cohen at the Molecular Foundry, Lawrence Berkeley National Laboratory, and a national lab in South Korea. The research team also included Yung Doug Suh’s lab at Ulsan National Institute of Science and Technology (UNIST).

The holy grail: a simple and stable light switch

Existing organic dyes and fluorescent proteins used in applications such as optical memory, nanopatterning and bioimaging have yielded years of breakthroughs (and earned a 2014 Nobel Prize in Chemistry), but these molecules have limited lifespans. Upon illumination, most will start to flash randomly and eventually go dark permanently, or “photobleach.”

In contrast, lanthanide-doped nanoparticles exhibit remarkable photostability. In over 15 years of working with them in his lab, Schuck noted that they’ve never seen one die. Until one random day in 2018, when Lee and PhD student Emma Xu watched a crystal darken and then rekindle. Lee dug into the literature and found 30-year-old mentions of lanthanide optical fibers that could be “photo-obscured” and “photo-illuminated,” suggesting that the blinking behavior could be controlled.

In a new paper published today in Nature, the team does just that. Using near-infrared light, they darkened and brightened their nanoparticles more than a thousand times in different environmental and aqueous environments with no signs of degradation.

“We can turn off these particles, which otherwise don’t photobleach, with one wavelength of light and turn them back on with another, just using ordinary lasers,” Lee said. In particular, near-infrared light can penetrate deeply into both inorganic materials and biological tissues with minimal scattering or phototoxicity.

Strange results illuminate future applications

Looking at potential applications, the team demonstrated how particles can be used to write and rewrite patterns on 3D substrates, which could one day improve high-density optical data storage and computer memory.

“This undefined, bidirectional photoswitching nanocrystal could produce an all-optical quantum memory device for storing the vast amount of data produced by quantum computers — think CD-ROM and CD-RW, but faster and much more accurate,” Suh said. .

The particles also offer potentially infinite resolving power, which depends on the number of photons produced by a probe under a super-resolution nanoscope. Using equipment from Suh’s laboratory, Lee achieved sub-Angstrom accuracy within hours.

The team believes that the photoswitching observed in the current work ultimately results from atomic crystal defects too small to be visualized even with the most advanced electron microscopes. These defects shift the avalanche threshold of the particle up or down and can be triggered by different wavelengths of light to make the signal dimmer or brighter.

In addition to pursuing potential applications in optical memory, super-resolution microscopy, bioimaging and biosensing, the team is using nanoparticle synthesis robots at the Molecular Foundry, advanced computational models and machine learning to further improve current crystals and explore whether they can synthesize other types of nanoparticles with similar photo-switchable properties.

The whole study came as a surprise, Cohen said. “We were saying from our 2009 paper that this class of nanoparticles don’t turn on and off, yet that’s exactly what we’re studying here. One of the things we’ve found with these nanoparticles is that they embrace strange results.”

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