Bożena Sikora

Synthesis of ZnAl2O4:(Er3+,Yb3+) spinel-type nanocrystalline upconverting luminescent marker in HeLa carcinoma cells, using a combustion aerosol method route

Efficiently upconverting, spherical ZnAl2O4 nanoparticles (NPs), doped with erbium and ytterbium, were synthesized by a combustion aerosol method (CAM) and transported to cytosol of carcinoma cell line (HeLa) for the first time. Spherical, 82–140 nm spinels were obtained at various concentrations of substrates. The nanoparticles were optimized to emit in the red luminescence range (Er3+, 661 nm, 4F9/2 → 4I15/2) when excited with near infrared light. Lower absorption and scattering by aqueous biological samples, compared to the green emission (Er3+, 550 nm, 2H11/2 → 4I15/2, 2S3/2 → 4I15/2), was responsible for the preferred upconversion. In addition, the application of the near infrared light significantly reduced the cellular autofluorescence and light scattering. X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and photoluminescence spectroscopy were employed to characterize the synthesized samples. Energy dispersive X-ray microanalysis was used to confirm the composition and distribution of the nanoparticles through the spectrum and elemental mapping. The hydrophilic, spherical NPs, coated with PVP (polyvinylpyrrolidone) in the presence of a liposomal transfection factor, lipofectamine, were endocytosed into living HeLa cells and followed as luminescent markers by confocal laser scanning microscopy. We present the optimized protocols for the NPs synthesis and delivery of the spinels to cancer cells for bioimaging.

Upconverting/magnetic: Gd2O3:(Er3+,Yb3+,Zn2+) nanoparticles for biological applications: effect of Zn2+ doping

Upconverting Gd2O3 nanoparticles (NPs) doped 1% Er3+ and 18% Yb3+ permits one to perform optical imaging. Because of the presence of Gd3+ they are useful in MRI. The main challenge is to enhance the NPs upconversion efficiency. As a result of co-doping the NPs with Zn2+ ions, achieved using microwave-induced solution combustion synthesis, we obtained optimal upconversion quantum yields (UQYs). The breakdown of the local crystal field symmetry around the rare earth ions, maximal in the presence of 5% of zinc, may be responsible for the highest observed UQY. The upconversion of IR light results in emission of visible red light mainly at 660 nm and at 550 nm. Optimized red photoluminescence of the samples observed in an organic environment was examined as a function of the laser power density to explain the mechanism of the upconversion emission. Paramagnetic properties of the NPs were determined by superconducting quantum interference device measurements. The non-functionalized nanoparticles incubated with HeLa cells were endocytosed and imaged by confocal laser scanning microscopy. We investigated their localization inside HeLa cells for various incubation times and NPs concentrations. PrestoBlue toxicity assay was performed to test the NPs bio-efficacy.

The growth kinetics of colloidal ZnO nanoparticles in alcohols

We have studied the synthesis of ZnO nanostructures over a wide range of parameters to determine the kinetics of the nanocrystals growth. The initial rapid nucleation and growth is kinetically controlled, the subsequent ZnO nanocrystals growth is thermodynamically controlled through the diffusion limited Ostwald coarsening. The ZnO coarsening rates increased with number of alcohol’s alkyl group carbons and temperature increase, pointing to importance of the solvent viscosity, dielectric constants, surface energy and the bulk solubility. The results are consistent with the Lifshitz–Slyozov–Wagner model. For all alcohols, in the NaOH induced reaction, a lower activation energy was observed compared to the aqueous reaction. A lower ZnO solubility, obtained by the water synthesis could be responsible for these observations. Our results point to the importance of the reactant selection in controlling the kinetics of the nanostructure formation, their size and the nature of the surface defects responsible for their luminescence.

Novel ZnO/MgO/Fe2O3 composite optomagnetic nanoparticles.

A facile sol-gel synthesis of novel ZnO/MgO/Fe2O3 nanoparticles (NPs) is reported and their performance is compared to that of ZnO/MgO. Powder x-ray diffraction (XRD) patterns reveal the crystal structure of the prepared samples. The average particle size of the sample was found to be 4.8 nm. The optical properties were determined by UV-vis absorption and fluorescence measurements. The NPs are stable in biologically relevant solutions (phosphate buffered saline (PBS), 20 mM, pH = 7.0) contrary to ZnO/MgO NPs which degrade in the presence of inorganic phosphate. Superparamagnetic properties were determined with a superconducting quantum interference device (SQUID). Biocompatible and stable in PBS ZnO/MgO/Fe2O3 core/shell composite nanocrystals show luminescent and magnetic properties confined to a single NP at room temperature (19-24 ° C), which may render the material to be potentially useful for biomedical applications.

Fluorescence resonance energy transfer between ZnO/MgO/carboxymethyl-β-cyclodextrin and Nile Red in HeLa cells – biosensing applications

Early diagnosis remains an important problem of cancer treatment strategies. There is therefore a great need for cancer detection tests that are fast, inexpensive and do not require sophisticated laboratory equipment. For this purpose, we synthesized the ZnO/MgO core/shell nanoparticles which are relatively nontoxic, inexpensive and simple to create. We constructed biosensors based on ZnO/MgO nanoparticles which employ the fluorescence resonance energy transfer from ZnO/MgO nanoparticles (donor) to Nile Red (acceptor). Characteristic features of Nile Red luminescence are its solvatochromic and thermochromic properties. In the physiologically relevant temperature range (20–45 °C), the shift of Nile Red luminescence in the ZnO/MgO/CMCD/Nile Red complex is linear with temperature. In our experiment, thermochromic shift was 5.7 ± 1.5 cm−1 K−1. Nile Red thermochromism observed in the complex will allow us to construct a sensor capable of detecting exothermic changes and local environmental differences between normal and pathological cells. Subsequently, we studied ZnO/MgO/CMCD/Nile Red complex in vivo in biological samples. We present here, for the first time that the donor–acceptor energy transfer is affected by the intracellular or extracellular locations of the nanoparticles.

Synthesis and magnetooptic characterization of Cu-doped ZnO/MgO and ZnO/oleic acid core/shell nanoparticles

The effect of Cu ion doping on the photoluminescence (PL) and magnetic behavior of ZnO/MgO and ZnO/oleic acid core/shell nanoparticles is investigated. By means of transmission electron microscopy we determine the average size distribution of the synthesized nanoparticles, while by studying electron paramagnetic resonance we determine the oxidation state of the Cu ions to be Cu2+. The magnetic field only slightly shifts spectrally the emission of the ensemble of such quantum dots. On the other hand, the magnetic field induces a considerable strengthening of the PL intensity and a sizable circular polarization of the emission of ZnO/MgO nanocrystals.

Single-step synthesis of Er3+ and Yb3+ ions doped molybdate/Gd2O3 core–shell nanoparticles for biomedical imaging

Nanostructures as color-tunable luminescent markers have become major, promising tools for bioimaging and biosensing. In this paper separated molybdate/Gd2O3 doped rare earth ions (erbium, Er3+ and ytterbium, Yb3+) 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, Yb3+-[Formula: see text] (∣2F7/2, 3T2〉) 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 Gd2O3: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.

Upconversion fluorescence imaging of HeLa cells using ROS generating SiO2-coated lanthanide-doped NaYF4 nanoconstructs

Inorganic nanomaterials able to generate reactive oxygen species (ROS) are promising components for modern medical applications. Activated by near-infrared light, up-converting β-NaYF4 doped with Er3+–Yb3+ and Tm3+–Yb3+ pair ions nanoparticles (UCNPs), have a wide range of applications in biological imaging as compared to traditional reagents excited by ultra-violet or visible light. We analysed the green-red and the blue-red luminescence to explain the mechanism of the upconversion depended on the surface condition. The influence of SiO2 coating on the cytotoxicity of the as-produced UCNPs towards HeLa cancer cells was reported. We demonstrated a possibility of a direct UCNPs application to photodynamic therapy, without need to attach additional molecules to their surface. The presence of Tm3+–Yb3+ pair ions, thus ROS generation capability, renders the SiO2 shell coated nanoparticles to become potentially useful theranostic agent.