Institute of Fundamental Technological Research
Polish Academy of Sciences

Staff

Prof. Michał Giersig, PhD, DSc

Department of Theory of Continuous Media and Nanostructures (ZTOCiN)
ZeBNZEiB (ZeBNZEiB)
position: professor
direct telephone: (+48) 22 826 98 01
telephone: (+48) 22 826 12 81 ext.: 410
room: 420
e-mail:
ORCID: 0000-0002-5394-0413

Education
1999 Dr. rer. nat habil. (Venia Legendi) Faculty of Physical Chemistry; University of Potsdam
1988 Dr. rer. nat.; Department of Chemistry; Freie University Berlin, Germany
1984 Master Dipl. Phys. Department of Physics; Freie University Berlin, Germany
Other
2013 Foreign member of Polish Academy of Sciences

Recent publications
1.  Gabriele V.R., Mazhabi R.M., Alexander N., Mukherjee P., Seyfried T.N., Nwaji N., Akinoglu E.M., Mackiewicz A., Zhou G., Giersig M., Naughton M.J., Kempa K., Light- and melanin nanoparticle-induced cytotoxicity in metastatic cancer cells, Pharmaceutics, ISSN: 1999-4923, DOI: 10.3390/pharmaceutics13070965, Vol.13, No.7, pp.965-1-14, 2021

Abstract:
Melanin nanoparticles are known to be biologically benign to human cells for a wide range of concentrations in a high glucose culture nutrition. Here, we show cytotoxic behavior at high nanoparticle and low glucose concentrations, as well as at low nanoparticle concentration under exposure to (nonionizing) visible radiation. To study these effects in detail, we developed highly monodispersed melanin nanoparticles (both uncoated and glucose-coated). In order to study the effect of significant cellular uptake of these nanoparticles, we employed three cancer cell lines: VM-M3, A375 (derived from melanoma), and HeLa, all known to exhibit strong macrophagic character, i.e., strong nanoparticle uptake through phagocytic ingestion. Our main observations are: (i) metastatic VM-M3 cancer cells massively ingest melanin nanoparticles (mNPs); (ii) the observed ingestion is enhanced by coating mNPs with glucose; (iii) after a certain level of mNP ingestion, the metastatic cancer cells studied here are observed to die—glucose coating appears to slow that process; (iv) cells that accumulate mNPs are much more susceptible to killing by laser illumination than cells that do not accumulate mNPs; and (v) non-metastatic VM-NM1 cancer cells also studied in this work do not ingest the mNPs, and remain unaffected after receiving identical optical energy levels and doses. Results of this study could lead to the development of a therapy for control of metastatic stages of cancer.

Keywords:
melanoma, melanin nanoparticles, cytotoxicity, laser medical applications, hyperthermia

Affiliations:
Gabriele V.R. - other affiliation
Mazhabi R.M. - South China Normal Universit (CN)
Alexander N. - other affiliation
Mukherjee P. - other affiliation
Seyfried T.N. - other affiliation
Nwaji N. - other affiliation
Akinoglu E.M. - University of Melbourne (AU)
Mackiewicz A. - other affiliation
Zhou G. - South China Normal Universit (CN)
Giersig M. - IPPT PAN
Naughton M.J. - other affiliation
Kempa K. - other affiliation
2.  Nwaji N., Akinoglu E.M., Giersig M., Gold nanoparticle-decorated Bi2S3 nanorods and nanoflowers for photocatalytic wastewater treatment, Catalysts, ISSN: 2073-4344, DOI: 10.3390/catal11030355, Vol.11, No.3, pp.355-1-12, 2021

Abstract:
Colloidal synthesis of photocatalysts with potential to overcome the drawback of low photocatalytic efficiency brought by charge recombination and narrow photo-response has been a challenge. Herein, a general and facile colloidal approach to synthesize orthorhombic phase Bi2S3 particles with rod and flower-like morphology is reported. We elucidate the formation and growth process mechanisms of these synthesized nanocrystals in detail and cooperate these Bi2S3 particles with metallic gold nanoparticles (AuNPs) to construct heterostructured photocatalysts. The unique properties of AuNPs featuring tunable surface plasmon resonance and large field enhancement are used to sensitize the photocatalytic activity of the Bi2S3 semiconductor particles. The morphology, structure, elemental composition, and light absorption ability of the prepared catalysts are characterized by (high-resolution) transmission electron microscopy, scanning electron microscopy, X-ray diffraction spectroscopy, X-ray photoelectron spectroscopy, and UV–vis absorption spectroscopy. The catalysts exhibit high and stable photocatalytic activity for the degradation of organic pollutants demonstrated using rhodamine B and methyl orange dyes under solar light irradiation. We show that the incorporation of the AuNPs with the Bi2S3 particles increases the photocatalytic activity 1.2 to 3-fold. Radical trapping analysis indicates that the production of hydroxyl and superoxide radicals are the dominant active species responsible for the photodegradation activity. The photocatalysts exhibit good stability and recyclability.

Keywords:
Bi2S3, nanoflower, nanorod, photocatalysis, heterostructures, AuNPs

Affiliations:
Nwaji N. - other affiliation
Akinoglu E.M. - University of Melbourne (AU)
Giersig M. - IPPT PAN
3.  Yang H., Akinoglu E.M., Guo L., Jin M., Zhou G., Giersig M., Shui L., Mulvaney P., A PTFE helical capillary microreactor for the high throughput synthesis of monodisperse silica particles, Chemical Engineering Journal, ISSN: 1385-8947, DOI: 10.1016/j.cej.2020.126063, Vol.401, pp.126063-1-29, 2020

Abstract:
We propose a simple and inexpensive SiO2 submicron particle synthesis method based on a PTFE helical capillary microreactor. The device is based on Dean flow mediated, ultrafast mixing of two liquid phases in a microfluidic spiral pipe. Excellent control of particle size between 100 nm and 600 nm and narrow polydispersity can be achieved by controlling the device and process parameters. Numerical simulations are performed to determine the optimal device dimensions. In the mother liquor the silica particles exhibit zeta potentials < -60 mV, rendering them very stable even at high particle volume fractions. The current device typically produces around 0.234 g/h of the silica particles.

Keywords:
SiO2 particle synthesis, continuous flow synthesis, helical capillary microreactor

Affiliations:
Yang H. - South China Normal Universit (CN)
Akinoglu E.M. - University of Melbourne (AU)
Guo L. - South China Normal Universit (CN)
Jin M. - South China Normal Universit (CN)
Zhou G. - South China Normal Universit (CN)
Giersig M. - IPPT PAN
Shui L. - South China Normal Universit (CN)
Mulvaney P. - University of Melbourne (AU)
4.  Bozheyev F., Akinoglu E.M., Wu L., Lou S., Giersig M., Effect of Mo-doping in SnO2 thin film photoanodes for water oxidation, International Journal of Hydrogen Energy , ISSN: 0360-3199, DOI: 10.1016/j.ijhydene.2020.09.050, Vol.45, No.58, pp.33448-33456, 2020

Abstract:
New semiconducting metal oxides of various compositions are of great interest for efficient solar water oxidation. In this report, Mo-doped SnO2 (Mo:SnO2) thin films deposited by reactive magnetron co-sputtering in the Ar and O2 gas environment are studied. The Sn to Mo ratio in the films can be controlled by changing the O2 partial pressure and the deposition power of the Sn and Mo targets. Increasing the Mo concentration in the film leads to the increase in the oxygen vacancy density, which limits the maximum achievable photocurrent density. The thin films exhibit a direct band gap of 2.7 eV, the maximum achievable photocurrent density of 0.6 mA cm^−2 at 0 VRHE and the onset potential of 0.14 VRHE. The incident photon to current transfer (IPCE) efficiency of 22% is shown at a 450 nm wavelength. The initial performance of the Mo:SnO2 thin films is evaluated for solar water oxidation.

Keywords:
Mo:SnO2, thin films, photoanode, photocurrent density, Sn/mo ratio, band gap

Affiliations:
Bozheyev F. - other affiliation
Akinoglu E.M. - University of Melbourne (AU)
Wu L. - other affiliation
Lou S. - other affiliation
Giersig M. - IPPT PAN
5.  Akinoglu E.M., Luo L., Dodge T., Guo L., Akinoglu G.E., Wang X., Shui L., Zhou G., Naughton M.J., Kempa K., Giersig M., Extraordinary optical transmission in nano-bridged plasmonic arrays mimicking a stable weakly-connected percolation threshold, OPTICS EXPRESS, ISSN: 1094-4087, DOI: 10.1364/OE.403034, Vol.28, No.21, pp.31425-31435, 2020

Abstract:
Ultrasensitive sensors of various physical properties can be based on percolation systems, e.g., insulating media filled with nearly touching conducting particles. Such a system at its percolation threshold featuring the critical particle concentration, changes drastically its response (electrical conduction, light transmission, etc.) when subjected to an external stimulus. Due to the critical nature of this threshold, a given state at the threshold is typically very unstable. However, stability can be restored without significantly sacrificing the structure sensitivity by forming weak connections between the conducting particles. In this work, we employed nano-bridged nanosphere lithography to produce such a weakly connected percolation system. It consists of two coupled quasi-Babinet complementary arrays, one with weakly connected, and the other with disconnected metallic islands. We demonstrate via experiment and simulation that the physics of this plasmonic system is non-trivial, and leads to the extraordinary optical transmission at narrowly defined peaks sensitive to system parameters, with surface plasmons mediating this process. Thus, our system is a potential candidate for percolation effect based sensor applications. Promising detection schemes could be based on these effects.

Affiliations:
Akinoglu E.M. - University of Melbourne (AU)
Luo L. - other affiliation
Dodge T. - other affiliation
Guo L. - South China Normal Universit (CN)
Akinoglu G.E. - other affiliation
Wang X. - other affiliation
Shui L. - South China Normal Universit (CN)
Zhou G. - South China Normal Universit (CN)
Naughton M.J. - other affiliation
Kempa K. - other affiliation
Giersig M. - IPPT PAN
6.  Mieloch A.A., Żurawek M., Giersig M., Rozwadowska N., Rybka J.D., Bioevaluation of superparamagnetic iron oxide nanoparticles (SPIONs) functionalized with dihexadecyl phosphate (DHP), Scientific Reports, ISSN: 2045-2322, DOI: 10.1038/s41598-020-59478-2, Vol.10, pp.2725-1-11, 2020

Abstract:
Superparamagnetic iron oxide nanoparticles (SPIONs) have been investigated for wide variety of applications. Their unique properties render them highly applicable as MRI contrast agents, in magnetic hyperthermia or targeted drug delivery. SPIONs surface properties affect a whole array of parameters such as: solubility, toxicity, stability, biodistribution etc. Therefore, progress in the field of SPIONs surface functionalization is crucial for further development of therapeutic or diagnostic agents. In this study, SPIONs were synthesized by thermal decomposition of iron (III) acetylacetonate Fe(acac)3 and functionalized with dihexadecyl phosphate (DHP) via phase transfer. Bioactivity of the SPION-DHP was assessed on SW1353 and TCam-2 cancer derived cell lines. The following test were conducted: cytotoxicity and proliferation assay, reactive oxygen species (ROS) assay, SPIONs uptake (via Iron Staining and ICP-MS), expression analysis of the following genes: alkaline phosphatase (ALPL); ferritin light chain (FTL); serine/threonine protein phosphatase 2A (PP2A); protein tyrosine phosphatase non-receptor type 11 (PTPN11); transferrin receptor 1 (TFRC) via RT-qPCR. SPION-DHP nanoparticles were successfully obtained and did not reveal significant cytotoxicity in the range of tested concentrations. ROS generation was elevated, however not correlated with the concentrations. Gene expression profile was slightly altered only in SW1353 cells.

Affiliations:
Mieloch A.A. - other affiliation
Żurawek M. - other affiliation
Giersig M. - IPPT PAN
Rozwadowska N. - other affiliation
Rybka J.D. - other affiliation
7.  Gabriele V.R., Shvonski A., Hoffman C.S., Giersig M., Herczynski A., Naughton M.J., Kempa K., Towards spectrally selective catastrophic response, PHYSICAL REVIEW E, ISSN: 2470-0045, DOI: 10.1103/PhysRevE.101.062415, Vol.101, pp.062415-1-6, 2020

Abstract:
We study the large-amplitude response of classical molecules to electromagnetic radiation, showing the universality of the transition from linear to nonlinear response and breakup at sufficiently large amplitudes. We demonstrate that a range of models, from the simple harmonic oscillator to the successful Peyrard-Bishop-Dauxois type models of DNA, which include realistic effects of the environment (including damping and dephasing due to thermal fluctuations), lead to characteristic universal behavior: formation of domains of dissociation in driving force amplitude-frequency space, characterized by the presence of local boundary minima. We demonstrate that by simply following the progression of the resonance maxima in this space, while gradually increasing intensity of the radiation, one must necessarily arrive at one of these minima, i.e., a point where the ultrahigh spectral selectivity is retained. We show that this universal property, applicable to other oscillatory systems, is a consequence of the fact that these models belong to the fold catastrophe universality class of Thom's catastrophe theory. This in turn implies that for most biostructures, including DNA, high spectral sensitivity near the onset of the denaturation processes can be expected. Such spectrally selective molecular denaturation could find important applications in biology and medicine.

Affiliations:
Gabriele V.R. - other affiliation
Shvonski A. - other affiliation
Hoffman C.S. - other affiliation
Giersig M. - IPPT PAN
Herczynski A. - other affiliation
Naughton M.J. - other affiliation
Kempa K. - other affiliation
8.  Luo L., Akinoglu E.M., Wu W., Dodge T., Wang X., Zhou G., Naughton M.J., Kempa K., Giersig M., Nano-bridged nanosphere lithography, NANOTECHNOLOGY, ISSN: 0957-4484, DOI: 10.1088/1361-6528/ab7c4c, Vol.31, pp.245302-1-6, 2020

Abstract:
We develop nano-bridged nanosphere lithography (NB-NSL), a modification to the widely used conventional nanosphere lithography (NSL). Nano-bridges between polystyrene (PS) spheres of a pristine NSL template are controllably formed in a two-step process: (i) spin-coating of a dilute styrene solution on top of the template, followed by (ii) oxygen plasma etching of the template. We show that the nanobridge dimensions can be precisely tuned by controlling the pre-processing conditions and the plasma etching time. The resulting lithography templates feature control over the shape and size of the apertures, which determine the morphology of the final nano-island arrays after material deposition and template removal. The unique advantage of NB-NSL is that PS particle templates based on a single PS particle diameter can be utilized for the fabrication of a variation of nano-island shapes and sizes, whereas conventional NSL yields only bowtie-shaped nano-islands, with their size being predetermined by the PS particle diameter of the template.

Keywords:
nanofabrication, nanosphere lithography, colloid lithography

Affiliations:
Luo L. - other affiliation
Akinoglu E.M. - University of Melbourne (AU)
Wu W. - other affiliation
Dodge T. - other affiliation
Wang X. - other affiliation
Zhou G. - South China Normal Universit (CN)
Naughton M.J. - other affiliation
Kempa K. - other affiliation
Giersig M. - IPPT PAN
9.  Feng K., Akinoglu E.M., Bozheyev F., Guo L., Jin M., Wang X., Zhou G., Naughton M.J., Giersig M., Magnetron sputtered copper bismuth oxide photocathodes for solar water reduction, JOURNAL OF PHYSICS D-APPLIED PHYSICS, ISSN: 0022-3727, DOI: 10.1088/1361-6463/abaf25, Vol.53, pp.495501-1-11, 2020

Abstract:
There is an urgent need for new materials that can catalyze or drive the photoelectrochemical (PEC) conversion of solar energy into chemical energy, i.e. solar fuels. Copper bismuth oxide (CBO) is a promising photocathode material for the photochemical reduction of water. Here, we systematically control the stoichiometry of CBO thin films prepared by reactive, direct-current magnetron co-sputtering from metallic Bi and Cu targets. The intrinsic photophysical and PEC material properties are investigated and evaluated in order to determine the optimum composition for hydrogen formation. Changing the stoichiometry of the films reveals a dramatic change in the optical band gap and crystal structure of CBO. The largest photocurrent density was achieved for a copper-to-bismuth ion ratio of 0.53, close to the CuBi2O4 stoichiometry, which yielded Jph = − 0.48 mA cm^−2 at 0 VRHE (RHE = reversible hydrogen electrode). This is the highest value to date for the photochemical reduction of water with CuBi2O4 without an externally applied bias. The absorbed photon-to-current efficiency and the photostability of the films in neutral and alkaline electrolytes were also investigated.

Keywords:
CuBi2O4, copper bismuth oxide, water reduction, water splitting, photocathode, magnetron sputtering

Affiliations:
Feng K. - other affiliation
Akinoglu E.M. - University of Melbourne (AU)
Bozheyev F. - other affiliation
Guo L. - South China Normal Universit (CN)
Jin M. - South China Normal Universit (CN)
Wang X. - other affiliation
Zhou G. - South China Normal Universit (CN)
Naughton M.J. - other affiliation
Giersig M. - IPPT PAN
10.  Kucharczyk K., Rybka J.D., Hilgendorff M., Krupinski M., Slachcinski M., Mackiewicz A., Giersig M., Dams-Kozlowska H., Composite spheres made of bioengineered spider silk and iron oxide nanoparticles for theranostics applications, PLOS ONE, ISSN: 1932-6203, DOI: 10.1371/journal.pone.0219790, Vol.14, No.7, pp. e0219790-1-20, 2019

Abstract:
Bioengineered spider silk is a biomaterial that has exquisite mechanical properties, biocompatibility, and biodegradability. Iron oxide nanoparticles can be applied for the detection and analysis of biomolecules, target drug delivery, as MRI contrast agents and as therapeutic agents for hyperthermia-based cancer treatments. In this study, we investigated three bioengineered silks, MS1, MS2 and EMS2, and their potential to form a composite material with magnetic iron oxide nanoparticles (IONPs). The presence of IONPs did not impede the self-assembly properties of MS1, MS2, and EMS2 silks, and spheres formed. The EMS2 spheres had the highest content of IONPs, and the presence of magnetite IONPs in these carriers was confirmed by several methods such as SEM, EDXS, SQUID, MIP-OES and zeta potential measurement. The interaction of EMS2 and IONPs did not modify the superparamagnetic properties of the IONPs, but it influenced the secondary structure of the spheres. The composite particles exhibited a more than two-fold higher loading efficiency for doxorubicin than the plain EMS2 spheres. For both the EMS2 and EMS2/IONP spheres, the drug revealed a pH-dependent release profile with advantageous kinetics for carriers made of the composite material. The composite spheres can be potentially applied for a combined cancer treatment via hyperthermia and drug delivery.

Affiliations:
Kucharczyk K. - other affiliation
Rybka J.D. - other affiliation
Hilgendorff M. - other affiliation
Krupinski M. - other affiliation
Slachcinski M. - other affiliation
Mackiewicz A. - other affiliation
Giersig M. - other affiliation
Dams-Kozlowska H. - other affiliation
11.  Rybka J.D., Mieloch A.A., Plis A., Pyrski M., Pniewski T., Giersig M., Assembly and characterization of HBc derived virus-like particles with magnetic core, Nanomaterials, ISSN: 2079-4991, DOI: 10.3390/nano9020155, Vol.9, No.2, pp.155-1-11, 2019

Abstract:
Core-virus like particles (VLPs) assembly is a kinetically complex cascade of interactions between viral proteins, nanoparticle's surface and an ionic environment. Despite many in silico simulations regarding this process, there is still a lack of experimental data. The main goal of this study was to investigate the capsid protein of hepatitis B virus (HBc) assembly into virus-like particles with superparamagnetic iron oxide nanoparticles (SPIONs) as a magnetic core in relation to their characteristics. The native form of HBc was obtained via agroinfection of Nicotiana benthamiana with pEAQ-HBc plasmid. SPIONs of diameter of 15 nm were synthesized and functionalized with two ligands, providing variety in ζ-potential and hydrodynamic diameter. The antigenic potential of the assembled core-VLPs was assessed with enzyme-linked immunosorbent assay (ELISA). Morphology of SPIONs and core-VLPs was evaluated via transmission electron microscopy (TEM). The most successful core-VLPs assembly was obtained for SPIONs functionalized with dihexadecyl phosphate (DHP) at SPIONs/HBc ratio of 0.2/0.05 mg/mL. ELISA results indicate significant decrease of antigenicity concomitant with core-VLPs assembly. In summary, this study provides an experimental assessment of the crucial parameters guiding SPION-HBc VLPs assembly and evaluates the antigenicity of the obtained structures.

Keywords:
virus-like particles, VLPs, hepatitis B virus capsid protein, HBc, viral self-assembly, magnetic core, HBcAg

Affiliations:
Rybka J.D. - other affiliation
Mieloch A.A. - other affiliation
Plis A. - other affiliation
Pyrski M. - other affiliation
Pniewski T. - other affiliation
Giersig M. - other affiliation
12.  Akinoglu G.E., Akinoglu E.M., Kempa K., Giersig M., Plasmon resonances in coupled Babinet complementary arrays in the mid-infrared range, OPTICS EXPRESS, ISSN: 1094-4087, DOI: 10.1364/OE.27.022939, Vol.27, No.16, pp.22939-22950, 2019

Abstract:
A plasmonic structure with transmission highly tunable in the mid-infrared spectra range is developed. This structure consists of a hexagonal array of metallic discs located on top of silicon pillars protruding through holes in a metallic Babinet complementary film. We reveal with FDTD simulations that changing the hole diameter tunes the main plasmonic resonance frequency of this structure throughout the infrared range. Due to the underlying Babinet physics of these coupled arrays, the spectral width of these plasmonic resonances is strongly reduced, and the higher harmonics are suppressed. Furthermore, we demonstrate that this structure can be easily produced by a combination of the nanosphere lithography and the metal-assisted chemical etching technique.

Affiliations:
Akinoglu G.E. - other affiliation
Akinoglu E.M. - University of Melbourne (AU)
Kempa K. - other affiliation
Giersig M. - other affiliation
13.  Brinkert K., Akay Ö., Richter M.H., Liedtke J., Fountaine K.T., Lewerenz H-J., Giersig M., Experimental methods for efficient solar hydrogen production in microgravity environment, Journal of Visualized Experiments, ISSN: 1940-087X, DOI: 10.3791/59122, Vol.154, pp.e59122-1-9, 2019

Abstract:
Long-term space flights and cis-lunar research platforms require a sustainable and light life-support hardware which can be reliably employed outside the Earth's atmosphere. So-called 'solar fuel' devices, currently developed for terrestrial applications in the quest for realizing a sustainable energy economy on Earth, provide promising alternative systems to existing air-revitalization units employed on the International Space Station (ISS) through photoelectrochemical water-splitting and hydrogen production. One obstacle for water (photo-) electrolysis in reduced gravity environments is the absence of buoyancy and the consequential, hindered gas bubble release from the electrode surface. This causes the formation of gas bubble froth layers in proximity to the electrode surface, leading to an increase in ohmic resistance and cell-efficiency loss due to reduced mass transfer of substrates and products to and from the electrode. Recently, we have demonstrated efficient solar hydrogen production in microgravity environment, using an integrated semiconductor-electrocatalyst system with p-type indium phosphide as the light-absorber and a rhodium electrocatalyst. By nanostructuring the electrocatalyst using shadow nanosphere lithography and thereby creating catalytic 'hot spots' on the photoelectrode surface, we could overcome gas bubble coalescence and mass transfer limitations and demonstrated efficient hydrogen production at high current densities in reduced gravitation. Here, the experimental details are described for the preparations of these nanostructured devices and further on, the procedure for their testing in microgravity environment, realized at the Bremen Drop Tower during 9.3 s of free fall.

Keywords:
chemistry, issue 154, solar fuels, hydrogen, microgravity, photoelectrocatalysis, drop tower, shadow nanosphere lithography, semiconductor-electrocatalyst systems

Affiliations:
Brinkert K. - other affiliation
Akay Ö. - other affiliation
Richter M.H. - other affiliation
Liedtke J. - other affiliation
Fountaine K.T. - other affiliation
Lewerenz H-J. - other affiliation
Giersig M. - other affiliation
14.  Henglein A., Giersig M., Formation of colloidal silver nanoparticles: capping action of citrate, JOURNAL OF PHYSICAL CHEMISTRY B, ISSN: 1520-6106, DOI: 10.1021/jp9925334, Vol.103, pp.9533-9539, 1999

Abstract:
Colloidal silver sols of long-time stability are formed in the γ-irradiation of 1.0 x 10^-4 M AgClO4 solutions, which also contain 0.3 M 2-propanol, 2.5 x 10^-2 M N2O, and sodium citrate in various concentrations. The reduction of Ag+ in these solutions is brought about by the 1-hydroxyalkyl radical generated in the radiolysis of 2-propanol; citrate does not act as a reductant but solely as a stabilizer of the colloidal particles formed. Its concentration is varied in the range from 5.0 x 10^-5 to 1.5 x 10^-3 M, and the size and size distribution of the silver particles are studied by electron microscopy. At low citrate concentration, partly agglomerated large particles are formed that have many imperfections. In an intermediate range (a few 10^-4 M), wellseparated particles with a rather narrow size distribution and little imperfections are formed, the size slightly decreasing with increasing citrate concentration. At high citrate concentrations, large lumps of coalesced silver particles are present, due to destabilization by the high ionic strength of the solution. These findings are explained by two growth mechanisms: condensation of small silver clusters (type-I growth), and reduction of Ag+ on silver particles via radical-to-particle electron transfer (type-II growth). The particles formed in the intermediate range of citrate concentration were studied by high-resolution electron microscopy and computer simulations. They constitute icosahedra and cuboctahedra.

Affiliations:
Henglein A. - other affiliation
Giersig M. - other affiliation
15.  Liz-Marzán L.M., Giersig M., Mulvaney P., Synthesis of nanosized gold-silica core-shell particles, LANGMUIR, ISSN: 0743-7463, DOI: 10.1021/la9601871, Vol.12, No.18, pp.4329-4335, 1996

Abstract:
Gold colloids have been homogeneously coated with silica using the silane coupling agent (3-aminopropyl)- trimethoxysilane as a primer to render the gold surface vitreophilic. After the formation of a thin silica layer in aqueous solution, the particles can be transferred into ethanol for further growth using the Stöber method. The thickness of the silica layer can be completely controlled, and (after surface modification) the particles can be transferred into practically any solvent. Varying the silica shell thickness and the refractive index of the solvent allows control over the optical properties of the dispersions. The optical spectra of the coated particles are in good agreement with calculations using Mie's theory for core-shell particles.

Affiliations:
Liz-Marzán L.M. - other affiliation
Giersig M. - other affiliation
Mulvaney P. - University of Melbourne (AU)
16.  Vossmeyer T., Katsikas L., Giersig M., Popovic G., Diesner K., Chemseddine A., Eychmüller A., Weller H., CdS nanoclusters: synthesis, characterization, size dependent oscillator strength, temperature shift of the excitonic transition energy, and reversible absorbance shift, JOURNAL OF PHYSICAL CHEMISTRY B, ISSN: 1520-6106, DOI: 10.1021/j100082a044, Vol.98, No.31, pp.7665-7673, 1994

Abstract:
Improved synthetic routes and size-selective precipitation have enabled the preparation of almost monodisperse CdS clusters. Six samples of 1-thioglycerol stabilized clusters with diameters of approximately 13,14,16,19, 23, and 39 A have been prepared as fully redispersible powders and were characterized by elemental analysis, powder X-ray diffraction, electron microscopy, thermogravimetric analysis, and UV-vis spectroscopy. Smallangle X-ray scattering was used to determine the mean cluster size. The well-structured UV-vis spectra reveal that the size-dependent shift of the 1s-1s excitonic transition is in agreement with the tight-binding theory and the pseudopotential theory. Moreover, as expected by quantum mechanical calculations the oscillator strength of the transition increases proportional to 1/r^3. UV-vis spectra taken at various temperatures between 4 and 295 K have shown that the temperature shift of the excitonic transition energy becomes stronger with decreasing particle size. Strong, reversible absorbance shifts were observed, upon transferring the clusters from their solutions onto quartz plates and vice versa.

Affiliations:
Vossmeyer T. - other affiliation
Katsikas L. - other affiliation
Giersig M. - other affiliation
Popovic G. - other affiliation
Diesner K. - other affiliation
Chemseddine A. - other affiliation
Eychmüller A. - other affiliation
Weller H. - other affiliation
17.  Giersig M., Mulvaney P., Preparation of ordered colloid monolayers by electrophoretic deposition, LANGMUIR, ISSN: 0743-7463, DOI: 10.1021/la00036a014, Vol.9, No.12, pp.3408-3413, 1993

Abstract:
Citrate- and alkanethiol-stabilized gold colloids have been electrophoretically deposited onto carboncoated copper grids. The colloid particles form ordered monolayers, and the core-to-core interparticle spacing is determined by the size of the alkane chains on the stabilizers used in the preparation of the sols. In the case of longer alkane chains, some interpenetration of the chains occurs when the gold particles form monolayers. When the gold sols are stabilized by sodium 3-thiopropionate, they can be reversibly coagulated and peptized by cycling the pH between 3 and 7. The method has also been used to form ordered monolayers and bilayers of latex particles.

Affiliations:
Giersig M. - other affiliation
Mulvaney P. - University of Melbourne (AU)

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