When Changwan Lee, then a Ph.D. student in Jim Schuck’s lab at Columbia Engineering, set off an extreme light-producing chain reaction from ultrasmall crystals developed at the Molecular Foundry at Berkeley Lab in 2021, lanthanide-doped nanoparticles made waves—or rather, an avalanche. Those equivalent precious stones are back again with a flicker that can now be purposefully and endlessly controlled.
“We’ve found the first completely photostable, completely photoswitchable nanoparticle — a sacred goal of nanoprobe configuration,” said Schuck, academic administrator of mechanical design.
The laboratories of Emory Chan and Bruce Cohen at Lawrence Berkeley National Laboratory’s Molecular Foundry and a national laboratory in South Korea were used to synthesize this one-of-a-kind substance. The Ulsan National Institute of Science and Technology (UNIST) lab of Yung Doug Suh was part of the research team as well.
The Cursed One: A straightforward, long-lasting light switch
The organic dyes and fluorescent proteins that are currently in use in applications such as optical memory, nanopatterning, and bioimaging have resulted in years of breakthroughs and were awarded the Nobel Prize in Chemistry in 2014; however, these molecules only have a limited lifespan. The majority will begin randomly blinking upon illumination, eventually going dark permanently, or “photobleaching.”
“We can use common lasers to turn these particles, which would otherwise photobleach, off with one wavelength of light and back on with another.”
Changwan Lee,
Nanoparticles doped with lanthanide, on the other hand, exhibit remarkable photostability. Schuck said that in more than 15 years of working with them in his lab, they’ve never seen one die. Until a random day in 2018, when Lee and Ph.D. student Emma Xu saw a crystal go dark and then come back to life. Lee looked into the literature and discovered that lanthanide optical fibers could be “photodarkened” and “photobrightened” for up to 30 years, implying that the blinking behavior could be regulated.
In another paper distributed today in Nature, the group does exactly that. In various ambient and aqueous environments, they used near-infrared light to darken and brighten their nanoparticles more than a thousand times without exhibiting any signs of degradation.
Lee stated, “We can simply use common lasers to turn these particles, which don’t otherwise photobleach, off with one wavelength of light and back on with another.” Specifically, near-infrared light can penetrate deeply into biological tissue and inorganic materials without causing phototoxicity or scattering.
Indefinite near-infrared photon avalanching localization microscopy (INPALM) allows for sub-Angstrom resolution imaging of three touching nanoparticles. Credit: Changhwan Lee/Columbia Engineering.
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. Changhwan Lee/Columbia Engineering Weird results brighten future applications.
“This endless, bidirectional photoswitching nanocrystal could yield an all-optical quantum memory gadget for putting away the tremendous measure of information created by quantum PCs — consider disc ROMs and album RWs, however quicker and significantly more exact,” Suh said.
Depending on the number of photons generated by a probe under a super-resolution nanoscope, the particles also offer potentially infinite resolving power. Involving gear in Suh’s lab, Lee arrived at sub-ngstrom accuracy in a couple of hours.
The team is of the opinion that the photoswitching that was observed in the current research is ultimately brought about by atomic crystal defects that are too small to be seen even with the most advanced electron microscopes. These flaws can be switched on or off by varying wavelengths of light to make the signal darker or brighter and alter the particle’s avalanche threshold.
The team is using nanoparticle synthesis robots at the Molecular Foundry, advanced computational models, and machine learning to further improve the existing crystals and investigate whether they can synthesize other kinds of nanoparticles with similar photoswitchable properties. These potential applications include optical memory, super-resolution microscopy, bioimaging, and biosensing.
Cohen stated, “The entire study surprised me.” Since our 2009 paper, we have argued that this category of nanoparticles does not switch on and off, but that is precisely what we are studying here. Something we’ve found with these nanoparticles is to embrace unusual outcomes.”
More information: Peter James Schuck, Indefinite and bidirectional near-infrared nanocrystal photoswitching, Nature (2023). DOI: 10.1038/s41586-023-06076-7. www.nature.com/articles/s41586-023-06076-7
