Preparation of Colloidal Sols: A magnetite colloid was prepared in alkaline solution according to the procedure published by Massart [11]. An aqueous solution containing 2.3 g (8.5 mmol) FeCl 3 ×6H 2 O in 4 mL H 2 O and 1.69 g (4.3 mmol) Fe(NH 4 ) 2 (SO 4 ) 2 in 1 mL of 2 M HCl, was added to 50 mL of 1 M (CH 3 ) 4 NOH×5H 2 O. The resulting black suspension was stirred for 1 h at room temperature and then sonicated in an ultrasonic bath for 1 h. The colloid was then centrifuged at 20 000 g for 1 h. The supernatant was decanted and the slurry resuspended in 20 mL water by sonication before being passed through a 0.2 mm pore cellulose nitrate membrane.A titanium dioxide sol was prepared by hydrolysis of titanium tetraisopropoxide under a nitrogen atmosphere following the procedure described by O'Regan et al. [12]. 25 mL of titanium tetraisopropoxide was mixed with 4 mL of isopropanol in a dropping-funnel under a nitrogen atmosphere. This mixture was added slowly over a period of 5 min to 150 mL of vigorously stirred double-distilled, deionized water in a 250 mL three-neck flask equipped with heater, thermometer and stirrer. Ten minutes after the final alkoxide addition, 1 mL of 69 % HNO 3 was added. The white hydrolysis mixture was then stirred for 8 h at 80 C to remove the isopropanol, filtered through a 0.2 mm pore cellulose nitrate membrane, and sonicated for 1 h to produce a stable colloidal solution with a bluish-white coloration.Preparation of the Composites and Method of Calcination: Typically, a sample of the sliced copolymer gel (ca. 5 mm thick) was added to the colloidal sol and left for the desired period of time. The colloid-loaded gels were removed, washed with water and allowed to dry in air. Thermogravimetric analysis (TGA) measurements were made using a NETZSCH STA 409EP machine. Samples were heated under air in an alumina crucible to a final temperature of 800 C at a rate of 5 K/min. Large samples of the mineralized gels were calcined by heating to a temperature of 450 or 500 C in a Carbolite furnace (type ELF11/6) at a heating rate of 1 C min ±1 .

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.

The microscopic mechanism of platinum cluster nucleation on DNA templates is studied by first-principle molecular dynamics simulations. We find that Pt(II) complexes bound to DNA can form strong Pt−Pt bonds with free Pt complexes after a single reduction step, and may thus act as preferential nucleation sites. This is confirmed by a series of reduction experiments, in which we achieve purely heterogeneous platinum growth on DNA, and use it to fabricate metal cluster necklaces of unprecedented thinness and regularity.

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.

To find new ways for the synthesis of improved bone implant materials, we studied the mineralization of collagen in vitro. Collagen was mineralized by combining the collagen fibril assembly and the formation of calcium phosphate in one process step. Both reactions were initiated simultaneously by mixing an acid, calcium-containing collagen solution with a phosphate-containing neutralization buffer. Under suitable conditions first fibril assembly occurred along with the precipitation of an amorphous calcium phosphate phase. Subsequently, the amorphous calcium phosphate transformed into a crystalline, apatite-like phase, as revealed by IR spectroscopy and X-ray diffraction. In this way, a homogeneously mineralized collagen gel was obtained, consisting of a three-dimensional network of collagen fibrils covered with calcium phosphate. The attachment between the collagen fibrils and the calcium phosphate crystals could be further improved by the addition of polyaspartate to the reaction mixture. In the absence of polyaspartate the calcium phosphate crystals formed clusters loosely bound to the fibrils, while in its presence separate crystals were located on or inside the collagen fibrils. The applied method is useful for studying the mineralization of collagen and offers a promising approach for the development of new bone implant materials.

Film rupture as the initial stage of dewetting is investigated for a volatile, spin-coated nonwetting film. During structure formation in the liquid film the film thickness is continuously reduced via evaporation. The dynamical character of the experiment allows the study of hole formation caused by distinct rupture mechanisms occurring at different film thicknesses. Both heterogeneous nucleation for thick films as well as spinodal dewetting for film thickness below 10 nm have been observed. The balance between both processes can be shifted by controlling the ambient humidity. The structures resulting from film rupture are quantified with respect to their different geometrical properties. For the first time we find that spinodal dewetting is caused by destabilizing polar interactions. [S0031-9007(98)05676-2]

We report on the first micro-scale observation of the velocity field imposed by a non-uniform heat content along the solid/liquid boundary. We determine both radial and vertical velocity components of this thermo-osmotic flow field by tracking single tracer nanoparticles. The measured flow profiles are compared to an approximate analytical theory and to numerical calculations. From the measured slip velocity we deduce the thermo-osmotic coefficient for both bare glass and Pluronic F-127 covered surfaces. The value for Pluronic F-127 agrees well with Soret data for polyethylene glycol, whereas that for glass differs from literature values and indicates the complex boundary layer thermodynamics of glass-water interfaces.

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