Multicolor upconversion of SiO₂-coated nanoparticles using for cells imaging and reactive oxygen species generation.

Abstract

Nanostructures as color-tunable luminescent markers have become major, promising tools for bioimaging and biosensing. In this paper separated molybdate/Gd ₂ O ₃ doped rare earth ions (erbium, Er ³⁺ and ytterbium, Yb ³⁺ ) core–shell nanoparticles (NPs), were fabricated by a one-step homogeneous precipitation process. Emission properties were studied by cathodo- and photoluminescence. Scanning electron and transmission electron microscopes were used to visualize and determine the size and shape of the NPs. Spherical NPs were obtained. Their core–shell structures were confirmed by x-ray diffraction and energy-dispersive x-ray spectroscopy measurements. We postulated that the molybdate rich core is formed due to high segregation coefficient of the Mo ion during the precipitation. The calcination process resulted in crystallization of δ / ξ (core/shell) NP doped Er and Yb ions, where δ —gadolinium molybdates and ξ —molybdates or gadolinium oxide. We confirmed two different upconversion mechanisms. In the presence of molybdenum ions, in the core of the NPs, Yb ³⁺ – MoO 4 2 − (∣ ² F _7/2 , ³ T ₂ 〉) dimers were formed. As a result of a two 980 nm photon absorption by the dimer, we observed enhanced green luminescence in the upconversion process. However, for the shell formed by the Gd ₂ O ₃ :Er, Yb NPs (without the Mo ions), the typical energy transfer upconversion takes place, which results in red luminescence. We demonstrated that the NPs were transported into cytosol of the HeLa and astrocytes cells by endocytosis. The core–shell NPs are sensitive sensors for the environment prevailing inside (shorter luminescence decay) and outside (longer luminescence decay) of the tested cells. The toxicity of the NPs was examined using MTT assay.

Hollow multimetallic PtNiSn nanoparticles (NPs) were formed from solid Ni-core/Pt-frame NPs by the galvanic replacement reaction (GRR) of Ni by Sn. The GRR was performed by adding SnCl₄·5H₂O dissolved in ethylene glycol into the PtNi₃ NPs containing suspension. The reaction yielded nanoframes with a hollow interior, having Pt-rich edges covered with a thin, incomplete Sn layer. They were investigated using transmission electron microscopy (TEM), energy dispersion X-ray spectroscopy (EDS) and X-ray diffraction (XRD). EDS analysis showed that the GRR rate could be modified by changing the solvent and the concentration of tin ions. Indeed, compared to water, ethylene glycol was found to facilitate the reduction of tin chloride and to affect nickel dissolution. TEM analysis revealed that the galvanic replacement of nickel and tin involves two different mechanisms. The first one consists of nickel oxidation followed by reduction of tin ions. In the second mechanism, oxidation of nickel and reduction of tin ions occur simultaneously.