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Open Access Publications from the University of California

Low irradiance multiphoton imaging with alloyed lanthanide nanocrystals

  • Author(s): Tian, B
  • Fernandez-Bravo, A
  • Najafiaghdam, H
  • Torquato, NA
  • Altoe, MVP
  • Teitelboim, A
  • Tajon, CA
  • Tian, Y
  • Borys, NJ
  • Barnard, ES
  • Anwar, M
  • Chan, EM
  • Schuck, PJ
  • Cohen, BE
  • et al.

© 2018, The Author(s). Multiphoton imaging techniques that convert low-energy excitation to higher energy emission are widely used to improve signal over background, reduce scatter, and limit photodamage. Lanthanide-doped upconverting nanoparticles (UCNPs) are among the most efficient multiphoton probes, but even UCNPs with optimized lanthanide dopant levels require laser intensities that may be problematic. Here, we develop protein-sized, alloyed UCNPs (aUCNPs) that can be imaged individually at laser intensities >300-fold lower than needed for comparably sized doped UCNPs. Using single UCNP characterization and kinetic modeling, we find that addition of inert shells changes optimal lanthanide content from Yb3+, Er3+-doped NaYF4nanocrystals to fully alloyed compositions. At high levels, emitter Er3+ions can adopt a second role to enhance aUCNP absorption cross-section by desaturating sensitizer Yb3+or by absorbing photons directly. Core/shell aUCNPs 12 nm in total diameter can be imaged through deep tissue in live mice using a laser intensity of 0.1 W cm−2.

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