In Vitro Targeting of Avidin-Expressing Glioma Cells with Biotinylated Persistent Luminescence Nanoparticles

Far red emitting persistent luminescence nanoparticles (PLNP) were synthesized and functionalized with biotin to study their targeting ability toward biotin-binding proteins. First, the interaction of biotin-decorated PLNP with streptavidin, immobilized on a plate, was shown to be highly dependent on the presence of a PEG spacer between the surface of the nanoparticles and the biotin ligand. Second, interaction between biotin-PEG-PLNP and free neutravidin in solution was confirmed by fluorescence microscopy. Finally, in vitro binding study on BT4C cells expressing lodavin fusion protein, bearing the extracellular avidin moiety, showed that such biotin-covered PLNP could successfully be targeted to malignant glioma cells through a specific biotin–avidin interaction. The influence of nanoparticle core diameter, incubation time, and PLNP concentration on the efficiency of targeting is discussed

Storage of Visible Light for Long-Lasting Phosphorescence in Chromium-Doped Zinc Gallate

ZnGa₂O₄:Cr³⁺ presents near-infrared long-lasting phosphorescence (LLP) suitable for in vivo bioimaging. It is a bright LLP material showing a main thermally stimulated luminescence (TSL) peak around 318 K. The TSL peak can be excited virtually by all visible wavelengths from 1.8 eV (680 nm) via d–d excitation of Cr³⁺ to above ZnGa₂O₄ band gap (4.5 eV–275 nm). The mechanism of LLP induced by visible light excitation is entirely localized around Cr_N2 ion that is a Cr³⁺ ion with an antisite defect as first cationic neighbor. The charging process involves trapping of an electron–hole pair at antisite defects of opposite charges, one of them being first cationic neighbor to Cr_N2. We propose that the driving force for charge separation in the excited states of chromium is the local electric field created by the neighboring pair of antisite defects. The cluster of defects formed by Cr_N2 ion and the complementary antisite defects is therefore able to store visible light. This unique property enables repeated excitation of LLP through living tissues in ZnGa₂O₄:Cr³⁺ biomarkers used for in vivo imaging. Upon excitation of ZnGa₂O₄:Cr³⁺ above 3.1 eV, LLP efficiency is amplified by band-assistance because of the position of Cr³⁺⁴T₁ (⁴F) state inside ZnGa₂O₄ conduction band. Additional TSL peaks emitted by all types of Cr³⁺ including defect-free Cr_R then appear at low temperature, showing that shallower trapping at defects located far away from Cr³⁺ occurs through band excitation