title: Controlled synthesis and single-particle imaging of bright, sub-10 nm lanthanide-doped upconverting nanocrystals.
abstract: Phosphorescent nanocrystals that upconvert near-infrared light to emit at higher energies in the visible have shown promise as photostable, nonblinking, and background-free probes for biological imaging. However, synthetic control over upconverting nanocrystal size has been difficult, particularly for the brightest system, Yb(3+)- and Er(3+)-doped β-phase NaYF(4), for which there have been no reports of methods capable of producing sub-10 nm nanocrystals. Here we describe conditions for the controlled synthesis of protein-sized β-phase NaYF(4): 20% Yb(3+), 2% Er(3+) nanocrystals, from 4.5 to 15 nm in diameter. The size of the nanocrystals was modulated by varying the concentration of basic surfactants, Y(3+):F(-) ratio, and reaction temperature, variables that also affected their crystalline phase. Increased reaction times favor formation of the desired β-phase nanocrystals while having only a modest effect on nanocrystal size. Core/shell β-phase NaYF(4): 20% Yb(3+), 2% Er(3+)/NaYF(4) nanoparticles less than 10 nm in total diameter exhibit higher luminescence quantum yields than comparable >25 nm diameter core nanoparticles. Single-particle imaging of 9 nm core/shell nanoparticles also demonstrates that they exhibit no measurable photobleaching or blinking. These results establish that small lanthanide-doped upconverting nanoparticles can be synthesized without sacrificing brightness or stability, and these sub-10 nm nanoparticles are ideally suited for single-particle imaging.
authors.affiliation: The Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720, USA.
authors.forename: Alexis D
authors.initials: AD
authors.lastname: Ostrowski
authors.forename: Emory M
authors.initials: EM
authors.lastname: Chan
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Gargas
authors.forename: Elan M
authors.initials: EM
authors.lastname: Katz
authors.forename: Gang
authors.initials: G
authors.lastname: Han
authors.forename: P James
authors.initials: PJ
authors.lastname: Schuck
authors.forename: Delia J
authors.initials: DJ
authors.lastname: Milliron
authors.forename: Bruce E
authors.initials: BE
authors.lastname: Cohen
mesh_terms: D028581:Lanthanoid Series Elements / Q000737:chemistry*; D008163:Luminescent Measurements; D057054:Molecular Imaging / Q000379:methods*; D053758:Nanoparticles / Q000737:chemistry*; D036103:Nanotechnology / Q000379:methods*; D010316:Particle Size; D013997:Time Factors
chemical_list: D028581:Lanthanoid Series Elements