Christina Graf

Christina Graf
Darmstadt University of Applied Sciences

PhD

About

104
Publications
21,155
Reads
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6,514
Citations
Additional affiliations
March 2003 - September 2006
University of Wuerzburg
Position
  • Professor (Assistant)
March 2000 - March 2003
Utrecht University
Position
  • PostDoc Position
October 1996 - February 2000
Johannes Gutenberg University Mainz
Position
  • PhD Student

Publications

Publications (104)
Article
Full-text available
We report on photoelectron spectra of SiO2 nanoparticles (d = 157 ± 6 nm) above the Si 2p threshold in the photon energy range 118-248 eV with electron kinetic energy 10-140 eV and analyze the photoelectron yield as a function of photon energy. Comparison of the experimental results with Monte-Carlo simulations on electron transport allows us to qu...
Article
Full-text available
Amorphous, non-doped, and copper- and selenium-doped Sb2S3 nanoparticles were synthesized by a hot-injection method. Zinc-doped Sb2S3 nanoparticles were prepared for the first time using the same approach. Electron microscopy revealed that spherical nanoparticles of 1–4 nanometers aggregated into larger spherical clusters. Introducing dopants into...
Article
Full-text available
Amorphous, non-doped, and copper- andselenium-doped Sb2S3 nanoparticles were synthesized bya hot-injection method. Zinc-doped Sb2S3 nanoparticleswere prepared for the first time using the same approach.Electron microscopy revealed that spherical nanoparti-cles of 1–4 nanometers aggregated into larger sphericalclusters. Introducing dopants into the...
Preprint
Full-text available
The modified hot-injection method was applied for the synthesis of amorphous non-doped and copper (Cu) and selenium (Se) doped antimony (III) sulfide (Sb2S3) nanoparticles with reduced sizes. Moreover, zinc (Zn) doped Sb2S3 nanoparticles were synthesized for the first time by the same approach. High-resolution transmission electron microscopy (HRTE...
Article
Full-text available
Here, the controlled formation of platinum nanoparticles (PtNPs) and silver nanoparticles (AgNPs) using amine-functionalized multivalent ligands are reported. The effects of reaction temperature and ligand multivalency on the growth kinetics, size, and shape of PtNPs and AgNPs were systematically studied by performing a stepwise and a one-step proc...
Article
Full-text available
The free expansion of a planar plasma surface is a fundamental non-equilibrium process relevant for various fields but as-yet experimentally still difficult to capture. The significance of the associated spatiotemporal plasma motion ranges from astrophysics and controlled fusion to laser machining, surface high-harmonic generation, plasma mirrors,...
Article
Amorphous non-doped, iodine- and tin-doped Sb2S3 nanoparticles were prepared via the hot-injection method. HRTEM of amorphous undoped and doped samples revealed the formation of spherical nanoparticles of 20–50 nm diameter aggregated into clusters in the size of 100–200 nm. EDX analysis indicated the presence of desired elements in all observed sam...
Preprint
Full-text available
The free expansion of a planar plasma surface is a fundamental non-equilibrium process relevant for various fields but as-yet experimentally still difficult to capture. The significance of the associated spatiotemporal plasma motion ranges from astrophysics and controlled fusion to laser machining, surface high-harmonic generation, plasma mirrors,...
Article
Full-text available
Sb 2 S 3 is a promising nanomaterial for application in solar cells and in the fields of electronics and optoelectronics. Herein, Sb 2 S 3 nanoparticles were prepared via the hot-injection approach. In contrast to earlier work, the reaction temperature was decreased to 150 °C so that the reaction was slowed down and could be stopped at defined reac...
Preprint
Full-text available
Sb 2 S 3 is a promising nanomaterial for application in solar cells and other fields of electronics and optoelectronics. Sb 2 S 3 nanoparticles were prepared via the hot-injection approach. In contrast to earlier work, the reaction temperature was decreased to 150°C, so that the reaction was slowed down and could be stopped at defined reaction stag...
Article
Full-text available
Upconversion nanoparticles (UCNPs), consisting of NaYF 4 doped with 18% Yb and 2% Er, were coated with microporous silica shells with thickness values of 7 ± 2 and 21 ± 3 nm. Subsequently, the negatively charged particles were functionalized with N -(6-aminohexyl)-3-aminopropyltrimethoxysilane (AHAPS), which provide a positive charge to the nanopar...
Preprint
Full-text available
Upconversion nanoparticles (UCNP) consisting of NaYF₄ doped with 18% Yb and 2% Er were coated with microporous silica shells of 7±2 nm and 21±3 nm thickness. Subsequently, the initially negatively charged particles were optionally functionalized with N-(6-aminohexyl)-aminopropyltrimethoxysilane (AHAPS), providing a positive charge onto the nanopart...
Article
Wide-angle soft X-ray scattering on free silica particles of different porosity prepared in a beam is reported. The explored q-region is mostly dominated by features due to surface roughness and bulk porosity. A comprehensive experimental and theoretical analysis of silica particles of different porosity is presented for various incident photon ene...
Article
A versatile method for the preparation extended, well-ordered, non-close-packed monolayers of silica nanoparticles (137 ± 4 nm diameter ) with adjustable interparticle distances is presented, which is based on a simple self-assembly procedure using aqueous dispersion with different ionic strengths. It is shown that these structures can be successfu...
Article
Full-text available
A concept for the growth of silica shells with a thickness of 5–250 nm onto oleate-coated NaYF4:Yb3+/Er3+ upconversion nanoparticles (UCNP) is presented. The concept enables the precise adjustment of shell thicknesses for the preparation of thick-shelled nanoparticles for applications in plasmonics and sensing. First, an initial 5–11 nm thick shell...
Preprint
Full-text available
A concept for the growth of silica shells with a thickness of 5-250 nm onto oleate-coated NaYF 4 :Yb ³⁺ /Er ³⁺ upconversion nanoparticles (UCNP) is presented that enables precise adjustment of shell thicknesses for the preparation of thick-shelled nanoparticles for applications in plasmonics and sensing. This concept comprises the growth of an init...
Article
The adsorption thermodynamics of 4-(dimethylamino)pyridine (DMAP) and its five divalent derivatives di-DMAP-n (2 ≤ n ≤ 6) with gradually increasing methylene-spacer lengths n binding to planar gold surfaces has been studied by surface-enhanced Raman spectroscopy (SERS) and density functional theory (DFT). SERS intensities of the totally symmetrical...
Chapter
Imaging techniques for probing the interactions of nanoparticles with cells and skin are essential for a qualitative and quantitative understanding of uptake and penetration processes. A variety of important visualization techniques is reviewed for providing an overview on established and recently developed techniques. This includes optical microsc...
Article
For the application of iron oxide nanoparticles from thermal decomposition approaches as contrast agents in magnetic resonance imaging (MRI), their initial hydrophobic ligands have to be replaced by hydrophilic ones. This exchange can influence the surface oxidation state and the magnetic properties of the particles. Here, the effect of the anchor...
Article
Cellular uptake and dissolution of trigonal silver nanoprisms (edge length: 42±15 nm, thickness: 8±1 nm) and mostly spherical silver nanoparticles (diameter: 70±25 nm) in human mesenchymal stem cells (hMSC) and human keratinocytes (HaCaT cells) were investigated. Both particles are stabilized by polyvinylpyrrolidone (PVP), the prisms additionally b...
Article
Nanostructured surfaces play an important role in modern science and technology. In particular, ordered arrangements of nonclose-packed nanoparticles created by self-assembly offer a versatile route to prepare systems, which can be used in various applications such as sensing, plasmonic devices or antireflection coatings. Self-assembly based system...
Article
Full-text available
All over the world, different types of nanomaterials with a diversified spectrum of applications are designed and developed, especially in the field of nanomedicine. The great variety of nanoparticles (NPs), in vitro test systems and cell lines led to a vast amount of publications with conflicting data. To identify the decisive principles of these...
Article
The scattering of electrons in dielectric materials is central to laser nanomachining, light-driven electronics and radiation damage. Here, we demonstrate real-time access to electron scattering by implementing attosecond streaking spectroscopy on dielectric nanoparticles: photoelectrons are generated inside the nanoparticles and both their transpo...
Article
The excitation of nanoscale near-fields with ultrashort and intense laser pulses of welldefined waveform enables strongly spatially and temporally localized electron emission, opening up the possibility for the generation of attosecond electron pulses. Here, we investigate the electron photoemission from isolated nanoparticles of different material...
Article
Full-text available
When plasmonic nanoparticles are incorporated into nanostructures and they are exposed to external optical fields, plasmonic coupling causes electric near-field enhancement which is significantly larger than that of isolated nanoparticles. We report on the plasmonic coupling in arrays of gold nanospheres (20 ± 3 and 50 ± 4 nm) prepared by colloidal...
Article
Full-text available
Nanoparticles (NPs) are widely used as components of drugs or cosmetics and hold great promise for biomedicine, yet, their effects on cell physiology remain poorly understood. Here we demonstrate that clathrin-independent dynamin 2-mediated caveolar uptake of surface-functionalized silica nanoparticles (SiNPs) impairs cell viability due to lysosoma...
Article
Nanogels are water soluble cross-linked polymer networks with nanometer size dimensions that can be designed to incorporate different types of compounds and are promising carrier systems for drugs and biological molecules. In this study, the interactions of thermoresponsive nanogels (tNGs) with the human skin barrier and underlying epidermis cells...
Article
In light of the importance of nanostructured surfaces for a variety of technological applications, the quest for simple and reliable preparation methods of ordered, nanometer ranged structures is ongoing. Herein a versatile method to prepare ordered, non-close-packed arrangements of nanoparticles on centimeter sized surfaces by self-assembly is des...
Article
Elastic small-angle X-ray scattering (SAXS) of free silica (SiO2) nanoparticles is reported (d = 100–180 nm). The particles were prepared by a modified Stöber synthesis in narrow size distributions with controlled surface roughness and functionalization. Angle-resolved small-angle X-ray scattering patterns are shown to be sensitive to these changes...
Conference Paper
We investigated the attosecond electronic collisional dynamics in a dielectric nanomaterial, which are of primary importance to fully understand the transport properties in future dielectric-electronic devices with up to petahertz switching speeds.
Article
Quartz crystal microbalance (QCM) is frequently used to investigate adsorption of nanometer-sized objects such as proteins, viruses or organic as well as inorganic nanoparticles from solution. The interpretation of the data obtained for heterogeneous adsorbate layers is not straightforward in particular if the systems exhibit sizable amounts of dis...
Article
Full-text available
Near-fields of non-resonantly laser-excited nanostructures enable strong localization of ultrashort light fields and have opened novel routes to fundamentally modify and control electronic strong-field processes. Harnessing spatiotemporally tunable near-fields for the steering of sub-cycle electron dynamics may enable ultrafast optoelectronic devic...
Article
Full-text available
Iron oxide nanoparticles (FeOx-NP) are applied in medicine as contrast agents in magnetic resonance imaging (MRI) where they reduce the spin-spin relaxation time (T2-time) of absorbing tissue. Hence, control of their magnetic properties is essential for these applications. Magnetic properties strongly depend on the particle size and shape as well a...
Conference Paper
The penetration of spherical and rod-like gold nanoparticles into human skin is reported. Several skin preparation techniques are applied, including cryo techniques, such as plunge freezing and freeze drying, and the use of wet cells. Their advantages and drawbacks for observing nanoparticle uptake are discussed. Independent of the particle shape n...
Article
Full-text available
5-6 nm gold nanoparticles were prepared by hydrolytic decomposition of [NMe4][Au(CF3)2] and in situ functionalized with mono- and multivalent thio-lated PEG ligands. Time-dependent changes of the nanoparticles were moni-tored in aqueous NaCl, NaBr, and NaI solutions by UV-Vis spectroscopy, TEM, and HRTEM. The purely sterically protected particles a...
Article
Full-text available
The increasing interest and recent developments in nanotechnology pose previously unparalleled challenges in understanding the effects of nanoparticles on living tissues. Despite significant progress in in vitro cell and tissue culture technologies, observations on particle distribution and tissue responses in whole organisms are still indispensabl...
Article
Full-text available
The investigation of nanoparticle interactions with tissues is complex. High levels of standardization, ideally testing of different material types in the same biological model, and combinations of sensitive imaging and detection methods are required. Here, we present our studies on nanoparticle interactions with skin, skin cells, and biological me...
Article
Full-text available
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 th...
Article
Full-text available
Allergic contact dermatitis (ACD) is a common skin disease in people and may become a potential site of exposure to nanoparticles (NP). Silica nanoparticles (SiO2-NP) possess a promising potential for various medical and non-medical applications, including normal and diseased skin as target organs. However, it has been shown that negatively charged...
Article
Full-text available
Monodisperse small iron oxide nanoparticles functionalized with dendritic polyglycerol (dPG) or dendritic polyglycerol sulfate (dPGS) are prepared. They are highly stable in aqueous solutions as well as physiological media. In particular, oleic acid capped iron oxide particles (core diameter = 11 ± 1 nm) were modified by a ligand exchange process i...
Article
The skin is a potential site of entry for nanoparticles (NP) but the role of disease-associated barrier disturbances on the path and extent of skin penetration of NP remains to be characterized. Silica nanoparticles (SiO2-NP) possess promising potential for various medical applications. Here, effects of different skin barrier disruptions on the pen...
Article
Several nanoparticle-based formulations used in cosmetics and dermatology are exposed to sunlight once applied to the skin. Therefore, it is important to study possible synergistic effects of nanoparticles and ultraviolet radiation. Electron paramagnetic resonance spectroscopy (EPR) was used to detect intracellular free radicals induced by ultravio...
Article
Unprotected ("naked") gold nanoparticles with high monodispersity (( , 5.5+/- 0.5 nm) were obtained in a facile and single-step microwave-assisted hydrolytic decomposition of the molecular precursor [NMe4][Au(CF3)2]. Given their chloride-free surface chemistry, the as-obtained gold nanoparticles were in situ functionalized with mono-, di-, and triv...
Article
The use of nanoparticle beams for the preparation and characterization of isolated nanoscopic matter is reviewed. It is a general preparation scheme which is shown to be of broad use, whenever the intrinsic properties of nanoscopic matter without any interactions with other particles or substrates are of interest. The size regime spans a few nanome...
Article
Multivalent interactions can be applied universally for a targeted strengthening of an interaction between different interfaces or molecules. The binding partners form cooperative, multiple receptor-ligand interactions that are based on individually weak, noncovalent bonds and are thus generally reversible. Hence, multi- and polyvalent interactions...
Article
Multivalentes Binden von dendritischem Polyglycerolsulfat (dPGS) an den Adhäsionsrezeptor L‐Selectin auf der Oberfläche von Leukozyten verhindert deren Adhäsion an aktivierte Gefäßendothelzellen. Bei einer überschießenden Entzündungsreaktion reduziert die dPGS‐Behandlung die Leukozytenwanderung erheblich und ist so eine hocheffektive entzündungshem...
Article
Multivalent binding of dendritic polyglycerolsulfate (dPGS) to the surface‐exposed adhesion receptor L‐selectin shields white blood cells from contacting activated vascular endothelium. In the case of overwhelming inflammation, dPGS treatment strongly inhibits leukocyte emigration and thus acts as a highly effective anti‐inflammatory compound. Furt...
Article
Multivalente Wechselwirkungen können universell zur gezielten Bindungsverstärkung zwischen verschiedenen Grenzflächen oder Molekülen genutzt werden. Die Bindungspartner bilden dabei kooperativ multiple Rezeptor‐Ligand‐Wechselwirkungen, die auf einzelnen schwachen, nichtkovalenten Bindungen basieren und daher prinzipiell reversibel sind. Daher spiel...
Article
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 aggregat...
Article
Full-text available
Waveform-controlled light fields offer the possibility of manipulating ultrafast electronic processes on sub-cycle timescales. The optical lightwave control of the collective electron motion in nanostructured materials is key to the design of electronic devices operating at up to petahertz frequencies. We have studied the directional control of the...
Article
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 potentia...
Article
In this study the kinetics of plasma protein adsorption onto ultrasmall superparamagnetic iron oxide (USPIO) particles have been analyzed and compared to previously published kinetic studies on polystyrene particles (PS particles), oil-in-water nanoemulsions and solid lipid nanoparticles (SLNs). SPIO and USPIO nanoparticles are commonly used as mag...
Article
Approaches for the controlled formation of gold nanoparticle dimers are investigated. These are based on a locally confined surface modification of gold nanoparticles followed by bridging two particles with an organic linker. A key factor in these approaches is the use of multivalent ligands. Citrate-stabilized gold nanoparticles are immobilized on...
Article
A high number of treatments in dermatology are based on the penetration of topically applied drugs through the skin barrier. This process is predominantly inefficient, on account of the strong protection properties of the upper skin layer – the stratum corneum. If the skin barrier is damaged, the penetration efficiency of topically applied drugs in...
Article
Particle-based drug delivery systems allow the controlled and targeted release of incorporated active compounds to the skin and are promising tools to improve the efficacy of topical therapies. In this study we investigated the stability and release properties of biodegradable polylactic acid (PLA) particles upon topical application on human skin e...
Article
Full-text available
High-speed, single-shot velocity-map imaging (VMI) is combined with carrier-envelope phase (CEP) tagging by a single-shot stereographic above-threshold ionization (ATI) phase-meter. The experimental setup provides a versatile tool for angle-resolved studies of the attosecond control of electrons in atoms, molecules, and nanostructures. Single-shot...
Article
Full-text available
Collective electron motion in condensed matter typically unfolds on a sub-femtosecond timescale. The well-defined electric field evolution of intense, phase-stable few-cycle laser pulses provides an ideal tool for controlling this motion. The resulting manipulation of local electric fields at nanometre spatial and attosecond temporal scales offers...
Article
The effect of ligand multivalency and nanoparticle size on the binding kinetics of thiol ligands on gold nanoparticles is investigated by exchanging monovalently bound pyrene on gold nanoparticles against flexible mono- and multivalent thiol ligands. Variable-sized gold nanoparticles of 2.2 ± 0.4, 3.2 ± 0.7, and 4.4 ± 0.9 nm diameter are used as su...
Article
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 particu...
Article
A general method for synthesizing bifunctional hydroxamic acids containing carboxylic acid or amino functionalities is reported. Various products from simple alkyl to complex dendrimer-like structures are described. Such molecules have recently been used in ligand-exchange reactions for the hydrophilic stabilization of originally oleic acid protect...
Article
X-Ray magnetic circular dichroism (XMCD) experiments on diluted magnetic semiconductor nanocrystals (2–7 nm) are reported in order to study their local electronic structure and magnetic properties. ZnSe nanoparticles containing either single manganese ions (Mn2+) distributed in the lattice of the entire particle or a MnSe core in the center are pre...
Article
Recent progress from experiments on clusters and free nanoparticles is reported, where emphasis is put on studies in the soft X-ray regime. We review selected examples on the characterization of free molecular clusters and nanoparticles. Specifically, we discuss recent progress in changes of the local structure in free clusters. Photoemission and p...
Article
First results on single particle detection in human skin samples by x-ray microscopy are reported. 94+/-6 and 161+/-13 nm gold core particles with silica shells and 298+/-11 nm silica particles coated with a gold shell on ultramicrotome sections of human skin were determined. The particles were applied on fresh intact skin samples, which were secti...