This image showcases microscale optical rewritable patterning using stable, photoswitchable, avalanching nanoparticles. The pattern is erased and rewritten using only infrared light, changing between all bright, all off, the Columbia Crown, all off and a smiley face. Image: Changhwan Lee/Columbia Engineering.In 2021, lanthanide-doped nanoparticles made waves – or rather, an avalanche – when Changwan Lee, then a PhD student in Jim Schuck’s lab at Columbia Engineering, set off an extreme light-producing chain reaction from ultrasmall crystals developed at Lawrence Berkeley National Laboratory’s Molecular Foundry. Now, those same crystals are back with a blink that can be deliberately and indefinitely controlled.
“We’ve found the first fully photostable, fully photoswitchable nanoparticle – a holy grail of nanoprobe design,” said Schuck, associate professor of mechanical engineering.
This unique material was synthesized in the laboratories of Emory Chan and Bruce Cohen at the Molecular Foundry, as well as in 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) in South Korea.
Existing organic dyes and fluorescent proteins used in applications like optical memory, nanopatterning and bioimaging have yielded years of breakthroughs (and garnered a Nobel Prize in Chemistry in 2014), but these molecules have limited lifespans. Upon illumination, most will eventually begin blinking randomly and ultimately go dark permanently, or ‘photobleach’.
In contrast, lanthanide-doped nanoparticles show remarkable photostability. Schuck noted that, in over 15 years of working with them in his lab, he and his team had never seen one die. Until one random day in 2018 when Lee and PhD student Emma Xu observed a crystal go dark, and then turn back on again. Lee dug into the literature and found 30-year-old mentions of lanthanide optical fibers that could be ‘photodarkened’ and ‘photobrightened’ – suggesting the blinking behavior could be controlled.
In a paper in Nature, the team reports doing just that. Using near-infrared light, they darkened and brightened their nanoparticles over 1000 times in different ambient and aqueous environments with no signs of degradation.
“We can turn these particles – which don’t otherwise photobleach – off with one wavelength of light and back on with another, simply using common lasers,” Lee said. Notably, near-infrared light can penetrate deeply into both inorganic materials and biological tissue with minimal scattering or phototoxicity.
Looking towards potential applications, the team demonstrated how the particles can be used to write – and rewrite – patterns onto 3D substrates, which could one day improve high-density optical data storage and computer memory.
"This indefinite, bidirectional photoswitching nanocrystal could yield an all-optical quantum memory device for storing the vast amount of data produced by quantum computers—think of CD-ROMs and CD-RWs, but faster and much more precise,” 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 in Suh’s lab, Lee reached sub-Àngstrom precision in only a few 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 particle’s avalanche threshold up or down and can be toggled by different wavelengths of light to make the signal dimmer or brighter.
Schuck and his team are pursuing potential applications in optical memory, super-resolution microscopy, and bioimaging and biosensing. They are also using nanoparticle synthesis robots at the Molecular Foundry with advanced computational models and machine learning to improve the current crystals further and explore whether they can synthesize other kinds of nanoparticles with similar photoswitchable properties.
This entire study was a surprise, said Cohen. “We had been saying since our 2009 paper that this class of nanoparticles doesn't switch on and off, and yet that's exactly what we're studying here. One of the things we've found with these nanoparticles is to embrace weird results.”
This story is adapted from material from Columbia Engineering, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.