High resolution fluorescence imaging of cancers using lanthanide ion-doped upconverting nanocrystals

During the last decade inorganic luminescent nanoparticles that emit visible light under near infrared (NIR) excitation (in the biological window) have played a relevant role for high resolution imaging of cancer. Indeed, semiconductor quantum dots (QDs) and metal nanoparticles, mostly gold nanorods (GNRs), are already commercially available for this purpose. In this work we review the role which is being played by a relatively new class of nanoparticles, based on lanthanide ion doped nanocrystals, to target and image cancer cells using upconversion fluorescence microscopy. These nanoparticles are insulating nanocrystals that are usually doped with small percentages of two different rare earth (lanthanide) ions: The excited donor ions (usually Yb3+ ion) that absorb the NIR excitation and the acceptor ions (usually Er3+, Ho3+ or Tm3+), that are responsible for the emitted visible (or also near infrared) radiation. The higher conversion efficiency of these nanoparticles in respect to those based on QDs and GNRs, as well as the almost independent excitation/emission properties from the particle size, make them particularly promising for fluorescence imaging. The different approaches of these novel nanoparticles devoted to "in vitro" and "in vivo" cancer imaging, selective targeting and treatment are examined in this reviewJ.A.C. is a Concordia University Research Chair in Nanoscience and is grateful to Concordia University for financial support of his research. J.A.C. and F.V. are grateful for financial support from the Natural Sciences and Engineering Research Council (NSERC) of Canada. R.N. is grateful for NSERC financial support through the Alexander Graham Bell Graduate Scholarship Program. B.F.Z. is grateful to les Fonds Québécois de Recherche sur la Nature et les Technologies (FQRNT) for financial support through the Graduate Scholarship Program. This work was also supported in part by the Universidad Autónoma de Madrid and Comunidad Autónoma de Madrid (Projects CCG087-UAM/MAT-4434 and S2009/MAT-1756), by the Spanish Ministerio de Educación y Ciencia (MAT 2010–16161). EMR acknowledges financial support from Fundación Alfonso Martín Escudero and Marie Curie IOF Fellowship Program (project 274404 LUNAMED