Remarkably enhanced upconversion luminescence in Na+ codoped spinel nanoparticles for photothermal cancer therapy and SPECT imaging

Glioblastoma multiforme (GBM) is the most fatal brain tumor and chemo/radiotherapeutic options and other palliative care have not fetched much success in its management due to the highly heterogeneous nature of GBM tissue and the presence of the blood–brain barrier. Impressively, Na+ co-doped ZnAl2O4:Ho3+, Yb3+ upconversion nanoparticles (UCNPs) with remarkably enhanced upconversion luminescence (UCL) have demonstrated good cellular uptake, bio/cyto compatibility and anticancer efficacy in C6 glioma cells. The % cell viability of C6 cells treated with UCNPs decreased to 46% under 980 nm near infrared (NIR) laser exposure exhibiting an excellent potential in photothermal therapy (PTT). Laser power dependence studies explain the UC mechanism and the role of Na+ ions in the UC luminescence enhancement is also investigated using density functional theory (DFT) calculations and positron annihilation lifetime spectroscopy (PALS). The Na+ ion codoping resulted in a significant lowering of zinc vacancies in ZnAl2O4:Ho3+, Yb3+, indicating its effective role in eliminating defect-induced non-radiative channels. Intrinsically (166-Holmium) radiolabeled ZnAl2O4:Yb3+, 166Ho3+, Na+ has also shown great potential towards in vivo single-photon emission computed tomography (SPECT) imaging. The results presented herein highlight the potential of this highly upconvertible molecule for dual modality SPECT/optical imaging for therapeutic and theranostic applications as well as for photothermal cancer therapy.