Josef Hormes

Microfluidic Synthesis of Nanomaterials

An overview of the current information and analyses on the microfluidic synthesis of different types of nanomaterial, including metallic and silica nanoparticles and quantum dots, is presented. Control of particle size, size distribution, and crystal structure of nanomaterials are examined in terms of the special features of microfluidic reactors.

Displacement Synthesis of Cu Shells Surrounding Co Nanoparticles

Copper shells were fabricated by a displacement method around Co nanoparticles (3.2 ′ 0.6 nm) at room temperature in a copper-citrate aqueous electrolyte. The nanoparticles were synthesized by a wet chemical approach using the surfactant sulfobetaine, dodecyldimethyl (3-sulfopropyl) ammonium hydroxide (98%) in tetrahydrofuran. X-ray absorption near-edge structure analysis confirmed that cobalt oxide was not present in the nanoparticles upon exposure to air, consistent with a shell formation. Additionally, the presence of the shell resulted in an increase of the blocking temperature of the core-shell nanoparticles, stabilizing the ferromagnetic behavior up to 235 K.

Facility Update: The Center for Advanced Microstructures and Devices: A Status Report

The J. Bennett Johnston, Sr., Center for Advanced Microstructures and Devices (CAMD) is a second-generation synchrotron-radiation facility owned and operated by the state of Louisiana through Louisiana State University (LSU). It was built by special-appropriation funding from the US Senate through the US Department of Energy (DoE). The funding came in the spring of 1988 and the ring first produced user radiation in September 1992. The storage ring was constructed by the Brobeck Division of Maxwell Technologies of San Diego, CA. The storage ring is the heart of the facility in that it supplies radiation to 15 beamlines that are used for spectroscopy, spectro-microscopy and microtomography, molecular and crystal-structure determinations and microfabrication. In addition to this equipment directly involved with synchrotron-radiation utilization, other components of the CAMD infrastructure include 230 m2 of class-100 clean room housing state-ofthe-art equipment and instruments supporting fabrication and metrology of micro-mechanical and MEMS devices, a laboratory for chemistry associated with synthesis of nano-scale materials (including a micro flow reactor system), a modest bio lab for support of the protein-crystallography work (lab is under construction as of late 2005), an extensive electroplating facility and hot-embossing unit to support researchers’ efforts, and applied technologies in microfabrication and stand-alone atomic-force and scanning-electron microscopes. The CAMD organizational structure consists of six groups: Administration, Safety, Accelerator, Vacuum and Mechanical, Microfabrication, and Basic Sciences (Spectroscopy). Staffing these groups are a total of over 50 research faculty, research associates and technicians, mechanical, electrical, computer and IT engineers and technicians, facility managers and administrative personnel. Though a second-generation facility, CAMD has developed over the last years into a strong regional center for the use of synchrotron radiation. In 2004/2005, CAMD had users from 56 institutes/departments from 43 different institutions, not only from the Southeast but also from the “rest” of the US together with some international users. To optimize techniques and processes and to train new users, CAMD also has an “in house” research program and scientists and engineers on the CAMD staff are actively involved in basic and applied research projects.

The influence of various coatings on the electronic, magnetic, and geometric properties of cobalt nanoparticles (invited)

From the results reported here for Co nanoparticles coated with 3-(N,N-dimethyl-dodecylammonium)- propanesulfonate (SB12), Cu, or Au, and from experimental and theoretical results published by several other groups there is strong evidence that the various coatings (organic as well as inorganic) not just influence but even determine the properties of small metallic nanoparticles. In an empirical manner, the core-coating interaction is already used to influence the size and the shape of nanoparticles. Based on previously published results and some experiments, in this paper the influence is described that various coatings have on the geometric, electronic, and magnetic properties of cobalt nanoparticles with diameters smaller than 10nm. The results indicate that there is an interdependence of various properties (e.g., size and electronic properties of a particle with the same coating) so that is seems to be difficult to vary one property in a systematic way without changing others.

Unexpected extracellular and intracellular sulfur species during growth of Allochromatium vinosum with reduced sulfur compounds.

Before its uptake and oxidation by purple sulfur bacteria, elemental sulfur probably first has to be mobilized. To obtain more insight into this mobilization process in the phototrophic purple sulfur bacterium Allochromatium vinosum, we used HPLC analysis and X-ray absorption near-edge structure (XANES) spectroscopy for the detection and identification of sulfur compounds in culture supernatants and bacterial cells. We intended to identify soluble sulfur compounds that specifically occur during growth on elemental sulfur, and therefore compared spectra of cultures grown on sulfur with those of cultures grown on sulfide or thiosulfate. While various unexpected oxidized organic sulfur species (sulfones, C-SO(2)-C, and sulfonates, C-SO(3)(-)) were observed via XANES spectroscopy in the supernatants, we obtained evidence for the presence of monosulfane sulfonic acids inside the bacterial cells by HPLC analysis. The concentrations of the latter compounds showed a tight correlation with the content of intracellular sulfur, reaching their maximum when sulfur began to be oxidized. None of the detected sulfur compounds appeared to be a specific soluble intermediate or product of elemental sulfur mobilization. It therefore seems unlikely that mobilization of elemental sulfur by purple sulfur bacteria involves excretion of soluble sulfur-containing substances that would be able to act on substrate distant from the cells.

X-Ray Absorption Near-Edge Structure (XANES) Spectroscopy Study of the Interaction of Silver Ions with Staphylococcus aureus, Listeria monocytogenes, and Escherichia coli

ABSTRACT Silver ions are widely used as antibacterial agents, but the basic molecular mechanism of this effect is still poorly understood. X-ray absorption near-edge structure (XANES) spectroscopy at the Ag LIII, S K, and P K edges reveals the chemical forms of silver in Staphylococcus aureus and Escherichia coli (Ag+ treated). The Ag LIII-edge XANES spectra of the bacteria are all slightly different and very different from the spectra of silver ions (silver nitrate and silver acetate), which confirms that a reaction occurs. Death or inactivation of bacteria was observed by plate counting and light microscopy. Silver bonding to sulfhydryl groups (Ag-S) in cysteine and Ag-N or Ag-O bonding in histidine, alanine, and dl-aspartic acid was detected by using synthesized silver-amino acids. Significantly lower silver-cysteine content, coupled with higher silver-histidine content, in Gram-positive S. aureus and Listeria monocytogenes cells indicates that the peptidoglycan multilayer could be buffering the biocidal effect of silver on Gram-positive bacteria, at least in part. Bonding of silver to phosphate groups was not detected. Interaction with DNA or proteins can occur through Ag-N bonding. The formation of silver-cysteine can be confirmed for both bacterial cell types, which supports the hypothesis that enzyme-catalyzed reactions and the electron transport chain within the cell are disrupted.

Functionalization of Gold and Glass Surfaces with Magnetic Nanoparticles Using Biomolecular Interactions

Advances in nanotechnology have enabled the production and characterization of magnetic particles with nanometer‐sized features that can be functionalized with biological recognition elements for numerous applications in biotechnology. In the present study, the synthesis of and interactions between self‐assembled monolayers (SAMs) on gold and glass surfaces and functionalized magnetic nanoparticles have been characterized. Immobilization of 10–15 nm streptavidin‐functionalized nanoparticles to biotinylated gold and glass surfaces was achieved by the strong interactions between biotin and streptavidin. Fluorescent streptavidin‐functionalized nanoparticles, biotinylated surfaces, and combinations of the two were characterized by Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, and electron and fluorescent microscopy to confirm that little or no functionalization occurred in nonbiotinylated regions of the gold and glass surfaces compared to the biotinylated sites. Together these techniques have potential use in studying the modification and behavior of functionalized nanoparticles on surfaces in biosensing and other applications.

X-Ray Absorption Near Edge Structure Spectra as a Basis for the Speciation of Lead

For this study several inorganic lead (II) compounds were measured at the Pb-L3-(13035 eV), L1- (15860 eV) and M5- (2484 eV) edge using X-Ray Absorption Near Edge Structure Spectroscopy (XANES) to determine experimentally which edge is most sensitive to the coordination environment. Each edge probes a different electronic configuration because of the selection rules and has a different resolution because of life-time broadening. Pb-L1-XANES spectra are only sensitive to the first coordination shell. Pb-M5-XANES spectra show a better energy resolution which is due to decreased lifetime broadening, but the pure lead spectra are also sensitive only to the first coordination shell. Spectra at the Pb-L3-edge show the highest sensitivity: differences in coordination out to the third shell could be distinguished. Therefore, even though Pb-L1- and M5-edges have some advantages, because of physical conditions compared to the L3-edge, these advantages do not result in increased sensitivity.

The speciation of soluble sulphur compounds in bacterial culture fluids by X‐ray absorption near edge structure spectroscopy

Over the last decade X‐ray absorption near edge structure (XANES) spectroscopy has been used in an increasing number of microbiological studies. In addition to other applications it has served as a valuable tool for the investigation of the sulphur globules deposited intra‐ or extracellularly by certain photo‐ and chemotrophic sulphur‐oxidizing (Sox) bacteria. For XANES measurements, these deposits can easily be concentrated by filtration or sedimentation through centrifugation. However, during oxidative metabolism of reduced sulphur compounds, such as sulphide or thiosulphate, sulphur deposits are not the only intermediates formed. Soluble intermediates such as sulphite may also be produced and released into the medium. In this study, we explored the potential of XANES spectroscopy for the detection and speciation of sulphur compounds in culture supernatants of the phototrophic purple sulphur bacterium Allochromatium vinosum. More specifically, we investigated A. vinosum ΔsoxY, a strain with an in frame deletion of the soxY gene. This gene encodes an essential component of the thiosulphate‐oxidizing Sox enzyme complex. Improved sample preparation techniques developed for the ΔsoxY strain allowed for the first time not only the qualitative but also the quantitative analysis of bacterial culture supernatants by XANES spectroscopy. The results thus obtained verified and supplemented conventional HPLC analysis of soluble sulphur compounds. Sulphite and also oxidized organic sulphur compounds were shown by XANES spectroscopy to be present, some of which were not seen when standard HPLC protocols were used.

Interconnected multilevel microfluidic channels fabricated using low-temperature bonding of SU-8 and multilayer lithography

This paper describes a novel fabrication method for the manufacture of multi-level microfluidic structures using SU-8. The fabrication method is based on wafer bonding of SU-8 layers and multilayer lithography in SU-8 to form microchannels and other structures at different levels. In our method, non-UV-exposed SU-8 layers are transferred to SU-8 structured wafers at desirably low temperatures. This technique is particularly useful for building multi-level fluidic structures, because non-UV-exposed SU-8 can be used as cover for microchannels and the cover can then be lithographically structured, i.e., to form interconnects, after which subsequent transferring of non-UV-exposed SU-8 onto the wafer allows for the fabrication of interconnected multi-level channels and other structures. Examples of interconnected multi-level microchannels were realized using this newly developed method. Liquid has been introduced into the microchannels at different levels to reveal the desirable functionality of the interconnected multi-level channels. The method described here is easily implementable using standard photolithography and requires no expensive bonding equipment. More importantly, the fabrication procedure is CMOS compatible, offering the potential to integrate electronic devices and MEMS sensors into microfluidic systems.