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The detection of smallest mechanical loads plays an increasingly important role in many areas of advancing automation and manufacturing technology, but also in everyday life. In this doctoral thesis, various microparticle systems were developed that are able to indicate mechanical shear stress via simple mechanisms. Using a toolbox approach, these systems can be spray-dried from various nanoscale primary particles (silica and iron oxide) to micrometer-sized units, so-called supraparticles. By varying the different building blocks and in combination with different dyes, a new class of mechanochromic shear stress indicators was developed by constructing hierarchically structured core-shell supraparticles that can indicate mechanical stress via an easily detectable color change. Three different mechanisms can be distinguished. If a signal becomes visible only by a mechanical load, it is a turn-on indicator. In the opposite case, the turn-off indicator, the signal is switched off by a mechanical load. In the third mechanism, the color-change indicator, the color changes as a result of a mechanical load. In principle, these indicators can be used in two different ways. First, they can be incorporated into a coating as an additive. These coatings can be applied to a wide range of products, including food packaging, medical devices, and generally any sensitive surface where mechanical stress, such as scratches, is difficult to detect but can have serious consequences. Second, these shear stress indicators can also be used directly in powder form and for example then applied in 3D-printing or in ball mills. A total of six different shear stress indicators were developed, three of which were used as additives in coatings and three were applied in powder form. Depending on their composition, these indicators were readout by fluorescence, UV-Vis or Magnetic Particle Spectroscopy. The development of these novel shear stress indicator supraparticles were successfully combined molecular chemistry with the world of nano-objects to develop macroscopic systems that can enable smart and communicating materials to indicate mechanical stress in a variety of applications.
Based on previous results showing that thioether modification of gold nanoparticles (AuNPs), especially coating with a multivalent system, yielded in excellent colloidal stability, the first aim of this thesis was to prove whether functionalization of silver nanoparticles (AgNPs) with thioether also has a comparable or even enhanced stabilization efficacy compared with the gold standard of coating with thiols and, particularly, whether the multivalency of polymers leads to stable AgNPs conjugates. Herein, AgNPs coated with mono- and multivalent thiol- and thioether polymers were prepared to systematically investigate the adsorption kinetics onto the silver surface as well as the colloidal stability after exposure to different conditions relevant for biomedical application. Although the thioether-polymers showed a slower immobilization onto AgNPs, same or mostly even better stabilization was exhibited than for the thiol analogs.
As multivalent thioether-poly(glycidol) (PG) is already proven as a promising candidate for AuNP modification and stabilization, the second aim of this thesis was to examine the stealth behavior of thioether-PG, side-chain functionalized with various hydrophobic (alkyl and cholesteryl) units, to gain a deeper understanding of AuNP surface functionalization in terms of protein adsorption and their subsequent cellular uptake by human monocyte-derived macrophages. For this purpose, citrate-stabilized AuNPs were modified with the amphiphilic polymers by ligand exchange reaction, followed by incubation in human serum. The various surface amphiphilicities affected protein adsorption to a certain extent, with less hydrophobic particle layers leading to a more inhibited protein binding. Especially AuNPs functionalized with PG carrying the longest alkyl chain showed differences in the protein corona composition compared to the other polymer-coated NPs. In addition, PGylation, and especially prior serum incubation, of the NPs exhibited reduced macrophage internalization.
As the use of mammals for in vivo experiments faces various challenges including increasing regulatory hurdles and costs, the third aim of this thesis was to validate larvae of the domestic silkworm Bombyx mori as an alternative invertebrate model for preliminary in vivo research, using AuNPs with various surface chemistry (one PEG-based modification and three PG-coatings with slightly hydrophobic functionalization, as well as positively and negatively charges) for studying their biodistribution and elimination. 6 h and 24 h after intra-hemolymph injection the Au content in different organ compartments was measured with ICP-MS, showing that positively charged particles appeared to be eliminated most rapidly through the midgut, while AuNPs modified with PEG, alkyl-functionalized PG and negatively charged PG exhibited long-term bioavailability in the silkworm body.
Gold nanoparticles of diameter ca. 60 nm have been synthesized based on Turkevich and Frens protocols. We have demonstrated that the carboxyl-modified gold nanoparticles can be coupled covalently with antibodies (Ab) of interest using the EDC/NHS coupling procedure. Binding studies with Ab-grafted AuNPs and GpL fusion proteins proved that conjugation of AuNPs with antibodies enables immobilization of antibodies with preservation of a significant antigen binding capacity. More importantly, our findings showed that the conjugation of types of anti-TNF receptors antibodies such as anti-Fn14 antibodies (PDL192 and 5B6) (Aido et al., 2021), anti-CD40, anti-4-1BB and anti-TNFR2 with gold nanoparticles confers them with potent agonism. Thus, our results suggest that AuNPs can be utilized as a platform to immobilize anti-TNFR antibodies which, on the one hand, helps to enhance their agonistic activity in comparison to “free” inactive antibodies by mimicking the effect of cell-anchored antibodies or membrane-bound TNF ligands and, on the other hand, allows to develop new generations of drug delivery systems. These constructs are characterized with their biocompatibility and their tunable synthesis process.
In a further work part, we combined the benefits of the established system of Ab-AuNPs with materials used widely in the modern biofabrication approaches such as the photo-crosslinked hydrogels, methacrylate-modified gelatin (GelMA), combined with embedded variants of human cell lines. The acquired results demonstrated clearly that the attaching of proteins like antibodies to gold nanoparticles might reduce their release rate from the crosslinked hydrogels upon the very low diffusion of gold nanoparticles from the solid constructs to the surrounding medium yielding long-term local functioning proteins-attached particles. Moreover, our finding suggests that hydrogel-embedded AuNP-immobilized antibodies, e.g. anti-TNFα-AuNPs or anti-IL1-AuNPs enable local inhibitory functions,
To sum up, our results demonstrate that AuNPs can act as a platform to attach anti-TNFR antibodies to enhance their agonistic activity by resembling the output of cell-anchoring or membrane bounding. Gold nanoparticles are considered, thus, as promising tool to develop the next generation of drug delivery systems, which may contribute to cancer therapy. On top of that, the embedding of anti-inflammatory-AuNPs in the biofabricated hydrogel presents new innovative strategy of the treatment of autoinflammatory diseases.
This thesis aimed to evaluate the possibility to use nanoparticles as antifungal drug carriers as well as their potential application in screening and diagnostics of invasive aspergillosis. The interaction of nanogels, superparamagnetic iron oxide nanoparticles (SPIOs) and gold nanoparticles (GNP) with fungal-specific polysaccharides, cells and biofilms was investigated.
Firstly, it was evaluated how the charge of nanogels influence their interaction with fungal cells. Linear poly(glycidol)s (pG) and poly(2-methyl-2-oxazoline) (pMOx) polymers were synthesized and further functionalized with thiol groups for preparation of redox responsive nanogels. Results showed that negatively charged nanogels were internalized by the fungi to a much greater extent than positively charged ones.
Furthermore, it was investigated how amphiphilicity of polymers used for preparation of nanogels influences nanogel-fungi interaction. It was concluded that nanogels prepared from polymers with degree of functionalization of 10% had the strongest interaction, regardless the length of the alkyl chain. Moreover, amphotericin B-loaded nanogels had a higher antifungal effect and lower toxicity towards mammalian cells than the free drug. In addition, inverse nanoprecipitation of thiol functionalized pGs was shown to be successful for preparation of nanogels with narrow size distribution.
It was also demonstrated that crosslinking of the polymeric coating in hydrogel-like network with thiol functionalized pGs improved the SPIOs imaging performance.
Finally, it was investigated whether GNPs could be used as model particles for the assessment of targeting to fungi. Fc dectin-1 was conjugated covalently to GNPs decorated with pGs, and binding affinity towards β-glucans was tested by surface plasmon resonance.
In summary, this thesis demonstrated evidence for the potential of pG nanogels and pG coated nanoparticles for antifungal therapy and diagnostics of fungal infections caused by A. fumigatus.
The aim of this thesis was the development of a multifunctional coating system for AuNPs based on thioether polymers, providing both excellent colloidal stability and a variable possibility to introduce functionalities for biological applications.
First, two thioether-polymer systems were synthesised as a systematic investigation into colloidal stabilisation efficacy. Besides commonly used monovalent poly(ethylene glycol) (PEG-SR), its structural analogue linear poly(glycidol) (PG-SR) bearing multiple statistically distributed thioether moieties along the backbone was synthesised. Additionally, respective thiol analogues (PEG-SH and PG-SH) were produced and applied as reference.
Successive modification of varyingly large AuNPs with aforementioned thiol- and thioether-polymers was performed via ligand exchange reaction on citrate stabilised AuNPs. An increased stabilisation efficacy of both thioether-polymers against biological and physiological conditions, as well as against freeze-drying compared to thiol analogues was determined.
Based on the excellent colloidal stabilisation efficacy and multi-functionalisability of thioether-PG, a plethora of functional groups, such as charged groups, hydrophilic/hydrophobic chains, as well as bio-active moieties namely diazirine and biotin was introduced to the AuNP surface. Moreover, the generic and covalent binding of diazirine-modified PG-SR with biomolecules including peptides and proteins was thoroughly demonstrated.
Lastly, diverse applicability and bioactivity of aforementioned modified particles in various studies was displayed, once more verifying the introduction of functionalities. On the one hand the electrostatic interaction of charged AuNPs with hydrogels based on hyaluronic acid was applied to tune the release kinetics of particles from three-dimensional scaffolds. On the other hand the strong complexation of siRNA onto two positively charged AuNPs was proven. The amount of siRNA payload was tuneable by varying the surface charge, ionic strength of the surrounding medium and the N/P ratio. Moreover, the biological activity and selectivity of the biotin-streptavidin conjugation was verified with respectively functionalised particles in controlled agglomeration test and in laser-triggered cell elimination experiments. In the latter, streptavidin-functionalised AuNPs resulted in excellent depletion of biotinylated cells whereas unfunctionalised control particles failed, excluding unspecific binding of these particles to the cell surface.
The aim of this work was to synthesize and functionalize different bio-relevant nanomaterials like silica-coated superparamagnetic iron oxide nanoparticles (SPIONs) as contrast agents for T2 magnetic resonance imaging (MRI) and detonation nanodiamond (DND) with the neurohormone peptide allatostatin 1 (ALST1) and a fluorescent dye. Analytical techniques for the determination and quantification of surface functional groups like amines, azides, and peptides were also developed and established.
Thus, in the first part of the work, a TGF-1 binding peptide and allatostatin 1 (ALST1), both supposed to act as active tumour targeting vectors, were synthesized by solid-phase peptide synthesis (SPPS) and characterized by high pressure liquid chromatography (HPLC) and mass spectrometry. Then, azide-functionalized silica nanoparticles were synthesized by the Stöber process and characterized by transmission electron microscopy (TEM) and infrared spectroscopy (IR). The surface loading of amine and azide groups was determined by a new protocol. The azide groups were reduced with sodium boronhydride to amine and then functionalized with Fmoc-Rink Amide linker according to a standard SPPS protocol. Upon cleavage of Fmoc by piperidine, the resulting dibenzofulvene and its piperidine adduct were quantified by UV/Vis spectroscopy and used to determine the amount of amine groups on the nanoparticle surface. Then, ALST1 and related tyrosine- and phenylalanine substituted model peptides were conjugated to the azide-functionalized silica nanoparticles by copper(I)-catalyzed azide-alkyne dipolar cycloaddition (CuAAC). The successful peptide conjugation was demonstrated by the Pauly reaction, which however is only sensitive to histidine- and tyrosine-containing peptides. As a more general alternative, the acid hydrolysis of the peptides to their individual amino acid building blocks followed by derivatization with phenyl isothiocyanate (PITC) allowed the separation, determination, and quantification of the constituent amino acids by HPLC.
In the second part of the work, amine- and azide-functionalized silica-coated superparamagnetic iron oxide nanoparticles (SPIONs) were synthesized by co-precipitation and subsequent silica-coated based on the Stöber process and characterized by TEM and IR. The amine surface loading was determined by the method already established for the pure silica systems. The azide surface loading could also be quantified by reduction with sodium boronhydride to amine groups and then conjugation to Fmoc-Rink amide linker. Upon cleavage of Fmoc with piperidine, the total amine surface loading was obtained. The amount of azide surface groups was then determined from the difference of the total amine surface loading and the amine surface loading. Thus, it was possible to quantify both amine and azide surface groups on a single nanoparticle system. Superparamagnetic iron oxide nanoparticles (SPIONs) are potent T2 contrast agents for magnetic resonance imaging (MRI). Due to their natural metabolism after injection into the blood stream, SPIONs mostly end up inside macrophages, liver, spleen or kidneys. To generate a potential target-specific SPION-based T2 contrast agent for MRI, the neurohormone peptide ALST1 was conjugated by CuAAC to the azide- and amine functionalized superparamagnetic iron oxide nanoparticles, since ALST1 is supposed to target difficult-to-treat neuroendocrinic tumours due to its analogy to galanin and somastatin receptor ligands. The organic fluorescent dye cyanine 5 (Cy5) was also conjugated to the silica-coated superparamagnetic iron oxide nanoparticles (SPIONs) via a NHS-ester to the amines to enable cell uptake studies by fluorescence microscopy. These constructs were characterized by TEM, dynamic light scattering (DLS), and IR. The amino acids of the conjugated ALST1 were determined by the HPLC method as described before for peptide-modified silica nanoparticle surfaces. Then, the relaxivity r2 was measured at 7 T. However, a r2 value of 27 L/mmolFe·s for the dual ALST1-/Cy5-functionalized silica-coated SPIONs was not comparable to T2 contrast agents in clinical use, since their relaxivity is commonly determined at 1.5 T, and no such instrument was available. However, it can be assumed that the synthesized dual
ALST1-/Cy5-functionalized silica-coated SPION would show a lower r2 at 1.5 T than at 7T. Commercial T2 MRI contrast agents like VSOP-C184 from Ferropharm show at r2 values of about 30 L/mmolFe·s at 1.5 T. Still, the relaxivity of the new material has some potential for application as a T2 contrast agent. Then, the material was used in cell uptake studies by fluorescence microscopy with the conjugated Cy5 dye as a probe. The dual
ALST1-/Cy5-functionalized silica-coated SPION showed a high degree of agglomeration with no cellular uptake unlike described for ALST1-functionalized nanoparticles in literature. It is assumed that upon agglomeration of the particles, constructs form which are unable to be internalized by the cellular endocytotic pathways anymore. As a future perspective, the tendency of the particle to agglomerate should be reduced by changing the coating material to polyethylene glycol (PEG) or chitosan, which are known to be bio-compatible, bio-degradable and prevent agglomeration.
In the third part of the work, the rhenium compound [ReBr(CO)3(L)] with L = 2-phenyl-1H-imidazo[4,5-f][1,10]phenanthroline and its manganese analogue were synthesized by heating the ligand and rhenium pentacarbonyl bromide or and manganese pentacarbonyl bromide respectively, in toluene. However, [MnBr(CO)3(L)] was unstable upon illumination by UV light at 365 nm. Thus, it was dismissed for further application. The photophysical properties of [ReBr(CO)3(L)] were explored, by determination of the excited-state life time by the time-correlated single-photon counting (TCSPC) method and the quantum yield by a fluorescence spectrometer equipped with an integration sphere. A value of = 455 ns, a Stokes shift of 197 nm and a rather low quantum yield =were found. Metal complexes are supposed to have superior properties compared to organic dyes due to their large Stokes shifts, long excited-state life times, and high quantum yields. Thus, amine- and azide-functionalized detonation nanodiamond (DND) as an alternative biological inert carrier system was functionalized with ALST1 to enhance its cell uptake properties. A luminescent probe for cell uptake studies using fluorescence microscopy was also attached, either based on the new rhenium complex or the commercially available organic dye Cy5, respectively. The aldehyde-functionalized rhenium complex was conjugated to the DND via oxime ligation, which is known to be a mild and catalyst-free conjugation method. The amount of peptide ALST1 on the DND was analyzed and quantified after acid hydrolysis and PITC derivatization by HPLC as described before. Then, the ALST1-/luminescent probe-functionalized DND was investigated for its photophysical properties by fluorescence spectroscopy. The Cy5-functionalized material showed a slightly lower fluorescence performance in aqueous solution than reported in literature and commercial suppliers with a life time < 0.4 ns and quantum yields not determinable by integration sphere due to the week signal intensity. The rhenium complex-functionalized material had a very low signal intensity in only aqueous medium, and thus determination of life times and quantum yield by fluorescence spectroscopy was not possible. After incubation with MDA-MB 231 cells, the Cy5-functionalized DND could easily be detected due to its red fluorescence. However, it was not possible to visualize the rhenium complex-functionalized DND with fluorescence microscopy due to the low fluorescence intensity of the complex in aqueous medium and the lack of proper filters for the fluorescence microscope. Cy5-functionalized DND did not show any cellular uptake in fluorescence microscopy after conjugation with ALST1. Since the nanodiamond surface is known to strongly adsorb peptides and proteins, it is assumed that the peptide chain is oriented perpendicular to the nanoparticle surface and thus not able to interact with cell membrane receptors to promote cell uptake of the particles. As a future perspective, the ALST1-promoted cellular uptake of the DND should be improved by using different linker systems for peptide conjugation to prevent adsorption of the peptide chain on the particle surface.
The new analytical methods for amino-, azide-, and peptide-functionalized nanoparticles have great potential to assist in the quantification of nanoparticle surface modifications by UV/Vis spectroscopy and HPLC. The determination of surface amine and azide groups based on the cleavage of conjugated Fmoc-Rink amide linker and detected by UV/Vis spectroscopy is applicable to all amine-/azide-functionalized nanomaterials. However, particles which form very stable suspension with the cleavage mixture can cause quantification problems due to scattering, making an accurate quantification of dibenzofulvene and its piperidine adduct impossible. The detection of tyrosine- and histidine-containing peptides based on the Pauly reaction is well-suited as a fast and easy-to-perform qualitative demonstration of successful peptide surface conjugation. However, its major drawback as a colourimetric approach is that coloured particles cannot be evaluated by this method. The amino acid analysis based on HPLC after acid hydrolysis of peptides conjugated to nanoparticle surfaces to its individual building blocks and subsequent derivatization with PITC, can be used on all nanomaterials with peptide or protein surface modification. It allows detection of amino acids down to picomolar concentrations and even enables analysis of very small peptide surface loadings. However, the resulting HPLC traces are difficult to analyze.
Three new analytical methods based on UV/Vis and HPLC techniques have been developed and established. They assisted in the characterization of the synthesized DND and SPIONs with dual functionalization by ALST1 and Cy5 or [ReBr(CO)3(L)], respectively. However, the nanomaterials showed no cellular uptake due to a high tendency to agglomerate. The cellular uptake should be improved and the tendency to agglomerate of the SPIONs should be reduced by changing the surface coating from silica to either PEG or chitosan. Furthermore, different linker systems for connecting peptides to DND surfaces should be synthesized and evaluated to reduce potential peptide chain adsorption.
n this work the synthesis and analysis of chromophore functionalized spherical gold nanoparticles is presented. The optical, electrochemical and spectroelectrochemical properties of these hybrid materials are furthermore studied. The work therefore is divided into two parts. The first part deals with triarylamine and PCTM-radical functionalized gold nanoparticles. The focus thereby was on the synthesis and on the investigations of chromophore-chromophore interactions and gold core-chromophore interactions. The chromopores, especially triarylamines, were attached to the gold core via different bridging units and were studied with optical and electrochemical methods. The purity and dimensions of the nanoparticles was determined by 1H-NMR spectroscopy, diffusion ordered NMR spectroscopy (DOSY), TGA, XPS and STEM. Furthermore a cyclic voltammetry technique was used to determine the composition of the particles via the Randles-Sevcik equation. An analysis of these parameters led to a model of a sea urchin-shaped nanoparticle. Optical measurements of the particles revealed an anisotropic absorption behavior of the triarylamine units due to gold core-chromophore interaction. However this behavior depends strongly on the relative orientation of the transition dipole moment of the chromophore to the gold surface and the distance of the chromophore to the surface. Hence, the anisotropic behavior was exclusively detected in the spectra of the Au-Tara1 particles. The short and rigid pi-conjugated bridging unit thereby facilitates this gold core-chromophore interaction. It was shown from electrochemical investigations that the triarylamine units can be chemically reversibly oxidized to the triarylamine monoradical cation. Furthermore, the measurements revealed a strong interligand triarylamine-triarylamine interaction which was only seen for the Au-Tara1 particles. The long pi-conjugated bridging units of the Au-Tara2 and Au-Tara3 particles as well as the aliphatic bridging unit of Au-Tara4 prevent any detectable interligand interactions. One may conclude that both the gold core-chromophore and the interligand triarylamine-triarylamine interaction depend on the length and the rigidity of the bridging unit. The electron transfer behavior of the triarylamine units adsorbed onto the gold core was additionally studied via spectroelectrochemical (SEC) measurements which are able to reveal weaker interactions. The investigations of Au-Tara1 and Au-Tara2 revealed a significant strong coupling between neighboring triarylamine units which is due to through-space intervalence interactions. This behavior was not detected for Au-Tara3 or for Au-Tara4. The SEC analysis also revealed that these observed interligand interactions depend on the length and the rigidity of the bridging unit. Thus, the systematic variation of the bridging unit gave a basic insight in the optical and electrochemical properties of triarylamines, located in the vicinity of a gold nanoparticle. The second part of this work aimed at the synthesis of new molecules, denoted as SERS-markers, for immuno SERS applications. For this purpose, the SERS-markers were designed to have a Raman-active unit and a thiol group for chemisorptions to Au/Ag nanoshells. In cooperation with the group of Schlücker (University of Osnabrück) the SERS-markers were absorbed onto Au/Ag nanoshells, denoted as SERS-labels, and characterized. The SERS spectra of the SERS-labels exhibited intense and characteristic SERS-signals for each marker. For immuno SERS investigations SEMA3 was functionalized with a hydrophilic end unit. This marker was adsorbed onto an Au/Ag nanoshell and encapsulated with silica. An anti-p63 antibody was bound to the silica surface in order to generate a SERS-labeled antibody for the detection of the tumor suppressor p63 in benign prostate. Immuno-SERS imaging of prostate tissue incubated with SERS-labeled anti-p63 antibodies demonstrated the selective detection of p63 in the basal epithelium. The results show the potential of the method for the detection of several biomolecules in a multiplexing SERS experiment.
Very small, thioglycerol (TG)-capped CdS nanoparticles were synthesized by a wet chemical technique and investigated in the framework of this thesis. Also glutathione-capped particles were investigated for a comparison of the capping agents. High-resolution photoelectron spectroscopy using high-brilliance synchrotron radiation was applied as the major tool for the characterization of these particles. Additionally, the particles were investigated with UV-VIS absorption spectroscopy, XPS using a laboratory source, valence band photoemission spectroscopy (VBPES), near-edge x-ray absorption spectroscopy (NEXAFS), and micro-Raman spectroscopy to address various aspects of the particles. In the beginning, an overview on size quantization effects is given to create a theoretical background behind the work presented in this thesis. Furthermore, an overview of various conventional techniques for size determination is presented. Exact information about size, shape and size distribution of nanoparticles is not yet achievable because of experimental limitations of the various size determination methods. Nanoparticles, with a range of sizes from 1.1 to 4. 2 nm, were synthesized using non-aqueous preparation and a TG capping. It is demonstrated that the use of the non-aqueous wet chemical synthesis method enables the production of very small particles and prohibits the aging of the particles. Furthermore, TG capping leads to a significant improvement for a narrow size distribution. Moreover, the results are very reproducible with TG capping and non-aqueous synthesis. Monodispersed particles can be produced by a size selective precipitation method, however, the reproducibility is questionable due to the aqueous medium of the synthesis in this case. High-resolution photoemission measurements on the small particles, i.e., 1.1 nm (CdS-A), 1.4 nm (CdS-B), 1.7 nm (CdS-C), and 1.8 nm (CdS-D, glutathione-capped), revealed five components as constituents of the S 2p signal after a careful data evaluation. Furthermore, it was observed that the particles with different sizes and capping show differences in the photoemission spectra and also in the beam damage behaviour. The different components of CdS-B were assigned as S atoms with different Cd neighbors, S atoms from thiol and S atoms in a partially oxidized state, based on the observed intensity changes of these components as a function of photon energy and beam damage, and on previous photoemission work on CdS nanoparticles [23, 45]. Furthermore, it was found that this assignment cannot be directly transferred to other particles. A new approach of structural model-based photoemission intensity calculations in comparison with the experimental data is presented. This enables us to understand subtle features in the photoemission spectra, in particular the intensity changes of the different components as a function of photon energy and beam exposure. This approach is especially applied to CdS-B (as some structural information for this particle is avialable from XRD), using three different structural models. It is found that a structural model with 33 S atoms can explain the experimental intensity changes of CdS-B. Furthermore, it is found that the photoemission spectra can be used to determine the particle size indirectly, as other plausible models show significant deviation from the experimental data. To study the various aspects by calculations, such as the influence of the particle shape and of the value of the mean free path, a program developed with L. Weinhardt and O. Fuchs is used for the intensity calculations. In order to determine a reasonable value of the mean free path for the used photon energies, two different equations from previous reports (Seah et al. and Powell et al.) are applied. As average mean free path values for the two photon energies we chose 5.5 ± 2 Å (254 eV) and 14 ± 2 Å (720 eV). The program calculation confirms the result of simple “manual” calculations of the different models. Moreover, it is tested that the value of , used in the calculations does not produce any significant influence on the calculation results. Another interesting feature is derived from the calculations that a model with a rather round shape produces similar intensity ratios for the different components to those of the data. Thus this new approach of analysis of photoemission spectra offers a way to determine particle sizes and to some extent to give an impression of the approximate particle shape. Furthermore, it is observed that the electronic band gap is larger compared to the optical band gap, which was attributed to an enhanced electron-hole correlation for optical absorption in small particles. The XPS experiments performed in the laboratory using an x-ray tube, show that the thin films produced from a freshly synthesized nanoparticle solution are fairly homogeneous and non-charging. Moreover, annealing experiments indicated that TG-capped particles posses less thermal stability as compared to MPA-capped particles. It was demonstrated that beam-induced effects play a major role. However, the knowledge of the time scale for such effects gives the possibility to record photoemission spectra with fairly good signal quality and to extrapolate to zero radiation damage. Further, particles with different sizes and capping show different beam damage behaviour. The thin film preparation by electrophoresis results in significant changes in the spectrum indicating agglomeration, while the drop-deposition technique points towards spectral changes on the rim of the sample, which can be avoided by focusing the radiation to the centre of the deposited dried drop. Micro-Raman experiments carried out in collaboration with C. Dem, Dr. M. Schmitt and Prof. W. Kiefer exhibited major differences in the spectra of nanoparticles as compared to those of the capping molecule thioglycerol. For instance, the absence of the S-H vibrational modes indicates the consumption or removal of all unreacted capping molecules. There is definitely a need for further detailed investigations concerning various interesting aspects of this work. For instance, it would be of significance to extend the program calculations to more models. Also more information about the band gap opening has to be gathered in order to find out the reason for the larger electronic band gap as compared to the optical band gap. The photoemission analysis approach using a model calculation has to be extended to differently prepared nanoparticles, in particular, to address the differences in the location of the various species in the particle as a function of preparation. The efforts of XRD simulations by C. Kumpf et al. [50] may reveal significant new information about the particle size and the size distribution. It can be expected that the program calculations, if extended to more models, can prove the potential of photoelectron spectroscopy to serve as a tool for size and shape determination of nanoparticles, which is a new contribution to the investigation of nanoparticles.