Lanthanide-doped nanocrystals as bio-probes for ion beam induced fluorescence imaging

(1) Centre for Ion Beam Applications, Department of Physics, National University of Singapore, Singapore 117542.
(2) Department of Chemistry, National University of Singapore, Singapore 117543.

Fluorescent probes play an important role in biological labeling and targeting for applications such as bioimaging, biodetection and therapeutics. We report a fluorescent material, lanthanide ions Yb3+/Tm3+ co-doped NaYF4 nanocrystal, which can generate intense emission under the excitation of mega-electron-volt (MeV) helium ions. A systematic spectroscopic study of NaYF4:Yb/Tm nanocrystals shows that both downconversion and energy transfer upconversion contribute to the fluorescence emission. More importantly, these lanthanide-doped nanocrystals exhibit enhanced resistance to iono-bleaching rather than those conventional fluorescent probes, such as quantum dots and organic dyes, allowing for long-term scanning for super-resolution imaging purpose. As a demonstration, sufficient brightness and inconspicuous iono-bleaching of the as-fabricated 100 nm nanoparticles under 1.6 MeV helium ions’ excitation makes them singly resolved inside a whole Hela cell, which is significant for biological and biomedical analysis at a single whole cell level.