In vitro assays and nanothermometry studies of infrared-to-visible upconversion of nanocrystalline Er3+,Yb3+ co-doped Y2O3 nanoparticles for theranostic applications

Luminescent spherical, redispersable, and monodisperse Er3+,Yb3+ co-doped Y2O3 nanoparticles were synthesized by homogenous precipitation followed by thermal annealing. Cubic Y2O3 nanoparticles exhibited high colloidal stability in water and biological medium and 90% cell viability toward glioblastoma multiforme cell lines. Confocal microscopy revealed cellular internalization of Y2O3 nanoparticles. Upon excitation at 980 nm, efficient near-infrared to visible upconversion luminescence from Y2O3:Er3+,Yb3+ nanoparticles occurred. The upconversion dynamics was determined by the number of photons, which evidenced that energy transfer by the upconversion mechanism is predominated. On the basis of luminescence nanothermometry studies, the nano particles exhibited features of a primary thermometer with high thermal sensitivity (1.27 +/- 0.05% K-1 (303 K) and large repeatability (>97%), attesting that it can be used as a contactless optical thermal sensor. This primary thermometer is also successfully applied in a cell culture medium showing that the nanoparticles can operate on biological media. This opens the possibility of the use of Y2O3:Er3+,Yb3+ nanoparticles in the design of a theranostic platform, able to simultaneously monitor temperature and, coupled to photosensitizers, produce reactive oxygen species for cancer therapy. (AU)