Michael Mertig

Construction of highly conductive nanowires on a DNA template

We present measurements of the electrical conductivity of metallic nanowires which have been fabricated by chemical deposition of a thin continuous palladium film onto single DNA molecules to install electrical functionality. The DNA molecules have been positioned between macroscopic Au electrodes and are metallized afterwards. Low-resistance electrical interfacing was obtained by pinning the nanowires at the electrodes with electron-beam-induced carbon lines. The investigated nanowires exhibit ohmic transport behavior at room temperature. Their specific conductivity is only one order of magnitude below that of bulk palladium, confirming that DNA is an ideal template for the production of electric wires, which can be utilized for the bottom-up construction of miniaturized electrical circuits.

Mechanical and structural properties of YOYO-1 complexed DNA

YOYO-1 is a fluorescent dye widely used for probing the statistical–mechanical properties of DNA. However, currently contradicting data exist how YOYO-1 binding alters the DNA structure and rigidity. Here, we systematically address this problem using magnetic tweezers. Remarkably, we find that the persistence length of DNA remains constant independent of the amount of bound YOYO-1, which contrasts previous assumptions. While the ionic conditions can considerably alter the stability of YOYO-1 binding, the DNA bending rigidity seems not to be affected. We furthermore determine important structural parameters such as the binding site size, the elongation, as well as the untwisting angle per bound YOYO-1 molecule. We expect that our assay, in which all the parameters are determined within a single experiment, will be beneficial for a large range of other DNA binding drugs.

Biocers: ceramics with incorporated microorganisms for biocatalytic, biosorptive and functional materials development

Biologically modified ceramics (biocers) are understood as a class of nanocomposites which combine biocomponents with ceramic-like matrices. Biocers containing biocomponents can be prepared as a bulk material or as coatings by sol–gel and freeze-cast techniques from inorganic nanosols or by special CVD methods. By avoiding critical preparation conditions (high temperature, organic solvents) which would lead to denaturation, even bacteria, fungi, and yeast cells can be incorporated while maintaining their viability (‘living ceramics’). In this article the preparation and structure of such biocers and their applicative potential for biocatalytic, biosorptive and structure-forming processes will be discussed.

Mineralization of the metre-long biosilica structures of glass sponges is templated on hydroxylated collagen

The minerals involved in the formation of metazoan skeletons principally comprise glassy silica, calcium phosphate or carbonate. Because of their ancient heritage, glass sponges (Hexactinellida) may shed light on fundamental questions such as molecular evolution, the unique chemistry and formation of the first skeletal silica-based structures, and the origin of multicellular animals. We have studied anchoring spicules from the metre-long stalk of the glass rope sponge (Hyalonema sieboldi; Porifera, Class Hexactinellida), which are remarkable for their size, durability, flexibility and optical properties. Using slow-alkali etching of biosilica, we isolated the organic fraction, which was revealed to be dominated by a hydroxylated fibrillar collagen that contains an unusual [Gly-3Hyp-4Hyp] motif. We speculate that this motif is predisposed for silica precipitation, and provides a novel template for biosilicification in nature.

Three-dimensional metallization of microtubules

Abstract Microtubules (MTs), components of the cytoskeletons of eukaryotic cells, are protein filaments with outer diameters of 25 nm and lengths of several micrometers. Due to their large geometrical aspect ratios, they are well suited for use as biomolecular templates for the fabrication of magnetic and electrically conductive nanowires. Three-dimensional metallization of these MTs is demonstrated by an electroless deposition technique of nickel initiated by molecular palladium catalysts. In this study of the deposition conditions, it is shown that in the use of electroless plating for the metallization of tubulin assemblies the process parameters, such as temperature and pH, need to be adjusted to the chemical conditions of the in-vitro self-assembly process of MTs. The activated and metallized MTs have been characterized by scanning electron microscopy and transmission electron microscopy. Depending on the distribution of the Pd catalyst particles after MT activation, we found that a minimum nickel thickness of about 10 nm is required to produce a continuous film.

Nanostructural organization of naturally occurring composites-part II: silica-chitin-based biocomposites

Investigations of the micro-and nanostructures and chemical composition of the sponge skeletons as examples for natural structural biocomposites are of fundamental scientific relevance. Recently, we show that some demosponges (Verongula gigantea, Aplysina sp.) and glass sponges (Farrea occa, Euplectella aspergillum) possess chitin as a component of their skeletons. The main practical approach we used for chitin isolation was based on alkali treatment of corresponding external layers of spicules sponge material with the aim of obtaining alkali-resistant compounds for detailed analysis. Here, we present a detailed study of the structural and physicochemical properties of spicules of the glass sponge Rossella fibulata. The structural similarity of chitin derived from this sponge to invertebrate alpha chitin has been confirmed by us unambiguously using physicochemical and biochemical methods. This is the first report of a silica-chitin composite biomaterial found in Rossella species. Finally, the present work includes a discussion related to strategies for the practical application of silica-chitin-based composites as biomaterials.

Self-assembly of DNA nanotubes with controllable diameters

The synthesis of DNA nanotubes is an important area in nanobiotechnology. Different methods to assemble DNA nanotubes have been reported, and control over the width of the nanotubes has been achieved by programmed subunits of DNA tiles. Here we report the self-assembly of DNA nanotubes with controllable diameters. The DNA nanotubes are formed by the self-organization of single-stranded DNAs, exhibiting appropriate complementarities that yield hexagon (small or large) and tetragon geometries. In the presence of rolling circle amplification strands, that exhibit partial complementarities to the edges of the hexagon- or tetragon-building units, non-bundled DNA nanotubes of controlled diameters can be formed. The formation of the DNA tubes, and the control over the diameters of the generated nanotubes, are attributed to the thermodynamically favoured unidirectional growth of the sheets of the respective subunits, followed subjected to the folding of sheets by elastic-energy penalties that are compensated by favoured binding energies.

Surface plasmon resonance platform technology for multi-parameter analyses on polymer chips

The development of a surface plasmon resonance (SPR) spectrometer comprising angular‐resolved analysis for quasi‐monochromatic illumination is reported. The optical system utilizes disposable, injection‐molded chips combined with a lateral imaging optical system for parallel analysis of one‐dimensional spot arrays. Further parallelization is achieved by introducing a segmented light source. This source sequentially illuminates three neighbored one‐dimensional arrays in order to keep angular‐resolved analysis without introducing any mechanically moving parts. This system is applied to detect genetic variations among different DNA samples obtained from polymerase chain reaction (PCR). For this purpose, 135 spots on the chip surface have been prepared by spotting and analyzed separately.

Scanning Force Microscopy and Geometric Analysis of Two‐Dimensional Collagen Network Formation

Monomeric collagen ‐lms were prepared by spin-coating of acidic collagen solutions on di†erent atomically Nat surfaces. The thin biomolecular coatings have been investigated by scanning force microscopy. Depending on both the wetting behaviour and the microtopology of the substrates used, di†erent ‐lm morphologies have been observed. Collagen monomers cover the surface of hydrophilic substrates homogeneously, whereas pore formation due to dewetting processes takes place at non-structured hydrophobic surfaces. The size of pores depends on the evaporation velocity of the solvent during spin-coating. Topological and metric properties of the resulting networks have been analysed and compared to soap foam network structures. 1997 by John Wiley & Sons, Ltd.

DNA microarrays for hybridization detection by surface plasmon resonance spectroscopy

We report on the development of a new platform technology for the detection of genetic variations by means of surface plasmon resonance (SPR) spectroscopy. TOPAS chips with integrated optics were exploited in combination with microfluidics. Within minutes, the detection of hybridization kinetics was achieved simultaneously at all spots of the DNA microarray. A nanoliter dispenser is used to deposit thiol-modified single-stranded probe DNA on the gold surface of the chips. We investigated the influence of different parameters on hybridization using model polymerase chain reaction (PCR) products. These PCR products comprised a single-stranded tag sequence being complementary to an anti-tag sequence of probes immobilized on the gold surface. The signals increased with increasing length of PCR products (60, 100 or 300 base pairs) as well as with their concentration. We investigated hybridizations on DNA microarrays comprising 90 spots of probe DNA with three different sequences. Furthermore, we demonstrate that sequences with possible hairpin structures significantly lower the binding rate, and thus, the SPR signals during hybridization.