E. Rühl

Skin Penetration and Cellular Uptake of Amorphous Silica Nanoparticles with Variable Size, Surface Functionalization, and Colloidal Stability

In this study, the skin penetration and cellular uptake of amorphous silica particles with positive and negative surface charge and sizes ranging from 291 ± 9 to 42 ± 3 nm were investigated. Dynamic light scattering measurements and statistical analyses of transmission electron microscopy images were used to estimate the degree of particle aggregation, which was a key aspect to understanding the results of the in vitro cellular uptake experiments. Despite partial particle aggregation occurring after transfer in physiological media, particles were taken up by skin cells in a size-dependent manner. Functionalization of the particle surface with positively charged groups enhanced the in vitro cellular uptake. However, this positive effect was contrasted by the tendency of particles to form aggregates, leading to lower internalization ratios especially by primary skin cells. After topical application of nanoparticles on human skin explants with partially disrupted stratum corneum, only the 42 ± 3 nm particles were found to be associated with epidermal cells and especially dendritic cells, independent of their surface functionalization. Considering the wide use of nanomaterials in industries and the increasing interest for applications in pharmaceutics and cosmetics versus the large number of individuals with local or spread impairment of the skin barrier, e.g., patients with atopic dermatitis and chronic eczema, a careful dissection of nanoparticle-skin surface interactions is of high relevance to assess possible risks and potentials of intended and unintended particle exposure.

Homogeneous nucleation rates of supercooled water measured in single levitated microdroplets

Homogeneous nucleation rates are determined for micrometer sized water droplets levitated inside an electrodynamic Paul-trap. The size of a single droplet is continuously measured by analyzing the angle-resolved light scattering pattern of the droplets with classical Mie theory. The freezing process is detected by a pronounced increase in the depolarization of the scattered light. By statistical analysis of the freezing process of some thousand individual droplets, we obtained the homogeneous nucleation rate of water between 236 and 237 K. The values are in agreement with former expansion cloud chamber measurements but could be determined with considerably higher precision. The measurements are discussed in the light of classical nucleation theory in order to obtain the size and the formation energy of the critical nucleus.

Surface Functionalization of Silica Nanoparticles Supports Colloidal Stability in Physiological Media and Facilitates Internalization in Cells

The influence of the surface functionalization of silica particles on their colloidal stability in physiological media is studied and correlated with their uptake in cells. The surface of 55 ± 2 nm diameter silica particles is functionalized by amino acids or amino- or poly(ethylene glycol) (PEG)-terminated alkoxysilanes to adjust the zeta potential from highly negative to positive values in ethanol. A transfer of the particles into water, physiological buffers, and cell culture media reduces the absolute value of the zeta potential and changes the colloidal stability. Particles stabilized by L-arginine, L-lysine, and amino silanes with short alkyl chains are only moderately stable in water and partially in PBS or TRIS buffer, but aggregate in cell culture media. Nonfunctionalized, N-(6-aminohexyl)-3-aminopropyltrimethoxy silane (AHAPS), and PEG-functionalized particles are stable in all media under study. The high colloidal stability of positively charged AHAPS-functionalized particles scales with the ionic strength of the media, indicating a mainly electrostatical stabilization. PEG-functionalized particles show, independently from the ionic strength, no or only minor aggregation due to additional steric stabilization. AHAPS stabilized particles are readily taken up by HeLa cells, likely as the positive zeta potential enhances the association with the negatively charged cell membrane. Positively charged particles stabilized by short alkyl chain aminosilanes adsorb on the cell membrane, but are weakly taken up, since aggregation inhibits their transport. Nonfunctionalized particles are barely taken up and PEG-stabilized particles are not taken up at all into HeLa cells, despite their high colloidal stability. The results indicate that a high colloidal stability of nanoparticles combined with an initial charge-driven adsorption on the cell membrane is essential for efficient cellular uptake.

Highly monodisperse water-dispersable iron oxide nanoparticles for biomedical applications

We demonstrate a unique approach for preparing high quality iron oxide (Fe3O4) nanoparticles functionalized by newly developed multifunctional dendron ligands for biomedical applications. These particles are suitable for magnetic resonance imaging (MRI), highly stable in aqueous solutions as well as physiological media and not cytotoxic. In particular, oleic acid capped Fe3O4 particles (d = 12 ± 0.8 nm) were modified in a ligand exchange process by investigating several dendron ligands of variable size and an adjustable number of polar end groups. The dendron based ligands lead only to a slight increase in hydrodynamic diameter of the nanoparticles after the ligand exchange process (∼6 nm). They also allow an adjustment of the particle polarity as well as a gradually variable surface functionalization. Light scattering, transmission electron microscopy, and visible spectroscopy studies show consistently that the dendron-capped iron oxide nanoparticles exhibit excellent stability in various physiological media as well as aqueous solutions in a broad pH range. It is also demonstrated by magnetic resonance studies that the magnetic relaxivity is almost not affected by the ligand exchange. Therefore, such small particles might be of specific interest for cardiovascular MRI and MRI of extravascular targets. In addition, the present approach opens new possibilities for the specific linking of biomolecules to the particle surface, which can be beneficial for various biological sensing and therapeutic applications. The cytotoxicity of the Fe3O4 nanoparticles was evaluated using the WST-8 assay. In the examined concentration range up to 100 μg Fe/mL no significant decrease in cell viability was detected.

Ar 2p spectroscopy of free argon clusters

Total electron and total and partial ion yield spectra of Ar clusters (with average size up to 600±200) in the region of Ar 2p excitation have been measured using synchrotron radiation and time‐of‐flight mass spectrometry. As the average cluster size increases, the x‐ray absorption spectrum changes systematically from that of atomic Ar to that of solid Ar. The shape of the Ar 2p3/2→4s region is found to be a sensitive monitor of the cluster sizes present in a molecular beam of Ar clusters. Extended x‐ray absorption fine structure (EXAFS) is detected in the spectra of the larger clusters. There is a strong correlation between the intensity of the components of the Ar 2p3/2→4s signal associated with clusters and the intensity of the Fourier filtered first shell Ar 2p EXAFS signal. A low amplitude, high frequency fine structure is observed in the Ar 2p continuum of the heaviest clusters which corresponds closely to that observed in solid Ar. This signal develops with cluster size more slowly than the Ar 2p E...

Penetration of normal, damaged and diseased skin — An in vitro study on dendritic core–multishell nanotransporters

A growing intended or accidental exposure to nanoparticles asks for the elucidation of potential toxicity linked to the penetration of normal and lesional skin. We studied the skin penetration of dye-tagged dendritic core-multishell (CMS) nanotransporters and of Nile red loaded CMS nanotransporters using fluorescence microscopy. Normal and stripped human skin ex vivo as well as normal reconstructed human skin and in vitro skin disease models served as test platforms. Nile red was delivered rapidly into the viable epidermis and dermis of normal skin, whereas the highly flexible CMS nanotransporters remained solely in the stratum corneum after 6h but penetrated into deeper skin layers after 24h exposure. Fluorescence lifetime imaging microscopy proved a stable dye-tag and revealed striking nanotransporter-skin interactions. The viable layers of stripped skin were penetrated more efficiently by dye-tagged CMS nanotransporters and the cargo compared to normal skin. Normal reconstructed human skin reflected the penetration of Nile red and CMS nanotransporters in human skin and both, the non-hyperkeratotic non-melanoma skin cancer and hyperkeratotic peeling skin disease models come along with altered absorption in the skin diseases.

Photoactivation of CdSe/ZnS Quantum Dots Embedded in Silica Colloids

A study of the influence of the local environment on the light-induced luminescence enhancement of CdSe/ZnS quantum dots (QD) embedded in silica colloids that are dispersed in various solvents is presented. The photoluminescence of the embedded QD is enhanced up to a factor of ten upon photoactivation by ultraviolet or visible light. This enhancement is strongly dependent on the local environment. The thickness-dependent permeability of the silica shell covering the QD controls the influence of the solvent on the QD. If foreign ions are present the activation state is stabilized after termination of the activation, whereas in their absence the process is partially reversible. A new qualitative model for the photoactivation of QD in various environments is developed. It comprises light-induced passivation and subsequent oxidation processes. The embedded QD also retain their fluorescence quantum yield inside living cells. Moreover, they can be activated for many hours in living cells by laser radiation in the visible regime.

PVP-coated, negatively charged silver nanoparticles: A multi-center study of their physicochemical characteristics, cell culture and in vivo experiments

Summary PVP-capped silver nanoparticles with a diameter of the metallic core of 70 nm, a hydrodynamic diameter of 120 nm and a zeta potential of −20 mV were prepared and investigated with regard to their biological activity. This review summarizes the physicochemical properties (dissolution, protein adsorption, dispersability) of these nanoparticles and the cellular consequences of the exposure of a broad range of biological test systems to this defined type of silver nanoparticles. Silver nanoparticles dissolve in water in the presence of oxygen. In addition, in biological media (i.e., in the presence of proteins) the surface of silver nanoparticles is rapidly coated by a protein corona that influences their physicochemical and biological properties including cellular uptake. Silver nanoparticles are taken up by cell-type specific endocytosis pathways as demonstrated for hMSC, primary T-cells, primary monocytes, and astrocytes. A visualization of particles inside cells is possible by X-ray microscopy, fluorescence microscopy, and combined FIB/SEM analysis. By staining organelles, their localization inside the cell can be additionally determined. While primary brain astrocytes are shown to be fairly tolerant toward silver nanoparticles, silver nanoparticles induce the formation of DNA double-strand-breaks (DSB) and lead to chromosomal aberrations and sister-chromatid exchanges in Chinese hamster fibroblast cell lines (CHO9, K1, V79B). An exposure of rats to silver nanoparticles in vivo induced a moderate pulmonary toxicity, however, only at rather high concentrations. The same was found in precision-cut lung slices of rats in which silver nanoparticles remained mainly at the tissue surface. In a human 3D triple-cell culture model consisting of three cell types (alveolar epithelial cells, macrophages, and dendritic cells), adverse effects were also only found at high silver concentrations. The silver ions that are released from silver nanoparticles may be harmful to skin with disrupted barrier (e.g., wounds) and induce oxidative stress in skin cells (HaCaT). In conclusion, the data obtained on the effects of this well-defined type of silver nanoparticles on various biological systems clearly demonstrate that cell-type specific properties as well as experimental conditions determine the biocompatibility of and the cellular responses to an exposure with silver nanoparticles.

Charge separation in core excited argon clusters

Charge separation in core excited argon clusters is reported. Neutral argon clusters have been prepared in a supersonic molecular beam. Photoionization with monochromatized synchrotron radiation in the L3/L2 regime (240–260 eV) initiates various single and double ionization processes. The photoion–photoion‐coincidence (PIPICO) technique is applied to measure dissociative double ionization processes in core excited argon clusters. Three series of charge separation channels are observed: (i) Ar+/Ar+n, (ii) Ar+2/Ar+n, and (iii) Ar+3/Ar+n. Kinetic energy releases from charge separation reactions as well as the relative intensities of the PIPICO signals are discussed in relation to fragmentation mechanisms, resonant Auger spectra, and properties of cluster dications, such as cluster dication fragmentation energies and charge separation distances.

Transition metal 2p excitaton of organometallic compounds studied by electron energy loss spectroscopy

Abstract Oscillator strengths for Mn, Fe, and Co 2p excitation of dicyclopentadienyl, carbonyl and mixed ligand complexes have been derived from inner shell electron energy loss spectra (ISEELS) recorded under electric dipole scattering conditions. The spectra are found to be surprisingly sensitive to the identity of the ligands and/or the character of the metal-ligand bonding and apparently insensitive to the molecular symmetry or even the d count of the metal atoms. A simple model in terms of the relative energies of unoccupied orbitals of large 3d character involving in-line (“dσ*”) and off-axis (“dπ*”) interactions with ligand orbitals is proposed. Extended Huckel (EHT) calculations have been used to aid assignment of the observed spectral features. The EHT results suggest that the metal 2p spectra should be more sensitive to the molecular symmetry than is actually observed. The 2p spectra are compared to the metal 3p spectra of the same species and to the metal 2p spectra of the pure metals and various halide and oxide compounds.