Gerhard E. Nauer

Miniaturized thin-film biosensors using covalently immobilized glucose oxidase☆

Abstract The production of a miniaturized glucose sensor by means of thin-film technology is reported. Two main problems related to miniaturization and device integration were solved: (1) the microminiaturization of a suitable electrochemical cell; (2) localized enzyme immobilization with a technology well suited for device integration. The well-known glucose oxidase/H 2 O 2 system was used to determine the glucose concentration. A miniaturized four-electrode arrangement was introduced to measure H 2 O 2 produced by the enzyme. A double working electrode array for reproducibility tests or differential measurements to suppress interferences is easily produced and can be placed on glass or flexible polymer substrates by means of thin-film technology. The enzyme was covalently coupled to a derivatized platinum thin-film working electrode by means of 1,2-arenequinones, which yield highly reproducible, fast and stable sensors. Measurement of a drop (5 μl) of physiological glucose solution is easily performed, giving a stable response after 40 s.

Thin-film Clark-type oxygen sensor based on novel polymer membrane systems for in vivo and biosensor applications

Abstract A planar miniaturized Clark-type oxygen sensor based on the Ross principle has been produced by means of thin-film technology. The use of a polarizable counter electrode in a three-electrode configuration allows the regeneration of the cathodically consumed oxygen, resulting in a zero-flux amperometric oxygen sensor. The platinum working and counter electrodes and the Ag/AgCl reference electrode were covered with a photostructured hydrogel layer, forming the electrolyte compartment, and a photostructured hydrophobic gas-permeable membrane. This arrangement exhibits no oxygen consumption and therefore the signal of the sensor shows almost no flow dependence. Additionally, this electrochemical feature leads to a dynamic equilibrium of the reaction products in the hydrogel layer, overcoming the lifetime limitations caused by buffer degradation in the classical Clark principle. The sensor was tested in buffer solutions and bovine serum, showing excellent performance and no effects of fouling on sensor response. This device can be scaled down and is best suited for integration with other sensors and as a basic transducer for biosensors.

Molecular dynamics simulations of the adsorption of industrial relevant silane molecules at a zinc oxide surface

The physical behavior of different adsorbed silane molecules (octyltrihydroxysilane, aminopropyltrihydroxysilane, and thiolpropyltrihydroxysilane) at a ZnO surface (0001) dissolved in isopropanol are studied via constant temperature (298 K) molecular dynamics simulations. The adsorbed silane molecules exhibit a different behavior depending on the chemical nature of their tail. Octyltrihydroxysilane molecules with their rather unpolar tail show two distinct, energetic different orientations at the polar metal oxide surface. Mostly the three polar hydroxy groups of the head are in contact with ZnO the unpolar tail remaining in the isopropanol phase. Occasionally only two hydroxy groups interact with the surface the whole tail simultaneously being attached. On the contrary, due to their highly polar tail aminopropyltrihydroxysilane molecules have only one favorite orientation at the surface: Apart from some minor fluctuations two hydroxy groups as well as the amino group of the tail are in contact with the ...

Structural stability of hair over three thousand years

Abstract Ten hair samples of Copts from the 8th–10th century AD obtained during the 1963–1964 excavation campaign in the district of Sayala, and 11 hair samples of Egyptian mummies dated to the 18th–25th dynasty were examined for their structural properties compared with recent hair samples. Structural comparison was performed using X-ray diffraction and infra-red spectroscopy. Using the attenuated total reflection technique, which allows multiple reflection infra-red spectroscopy on native hair, we were able to reveal the structural integrity of the ancient hair samples. X-ray diffraction studies using Cr-alpha radiation confirmed the infra-red results. Signs of dehydration could be observed but no conformational changes, indicating the structural stability of hair protein over thousands of years.

In situ Fourier transform infrared attenuated total reflection (FTIR-ATR) spectroscopic investigations on the base-acid transitions of leucoemeraldine

Leucoemeraldine, the reduced form of the polyaniline, was obtained by electrochemical polymerization. Extensive infrared spectroscopic studies are discussed in this work. Ex situ FTIR spectra measured in NaReO4HReO4 electrolytes with different pH-values are presented and the absorption bands are assigned to different vibrational modes. Additionally, a distinct picture of the base-acid transition is evaluated using in situ FTIR-ATR measurements in electrolytes containing the supporting salts KPF6HPF6, NaClO4HClO4 and NaReO4HReO4 The results demonstrate that in strong acidic media leucoemeraldine nitrogen atoms can be partly protonated. The protonation process starts in the pH-range 2.5 and 3 in the intercalation of anions from the electrolyte into the polymer structure is determined semi-quantitatively.

Study of the Dendritic Growth of Ni–Co Alloys Electrodeposited on Cu Substrates

Ni–Co alloy deposits and their parent metals were formed on Cu substrates by electrolysis under different current densities applied in the galvanostatic regime. A quantitative scanning electron microscopy technique was employed to study the morphology and surface roughness of the obtained deposits. The structure of the deposits is governed by the nature of depositing ions and quantity of evolved hydrogen. The cauliflower morphology and the highest mean surface roughness values are the results of electrodeposition from the Ni containing bath. The structure of the Co deposits formed under the same conditions and determined by the formation of the hexagonal close-packed phase results in a more uniform grain size distribution and formation of smoother platelet deposits. The mean surface values of the parent metals are independent of the current density. The dendritic growth is a special case of a structure formed only in the Ni–Co alloy deposition at selected, high current densities of 220 and 400 mA cm �2 . The dendrites obtained at a higher current density of 400 mA cm �2 have shown more developed structures with smaller dendrites that

N,N'-Di(alkyloxy)imidazolium Salts: New Patent-free Ionic Liquids and NHC Precatalysts

1-Hydroxyimidazole-3-oxides (2-H, 2-Me) were alkylated with (RO)2SO2 (R =Me, Et) to give the new 1,3-di(alkyloxy)imidazolium cations which were isolated as hexafluorophosphates. Ion metathesis yielded new hydrophobic ionic liquids (bis(trifluoromethanesulfonyl)imides, tris(pentafluoroethyl) trifluorophosphates). Bromination afforded 2-bromo derivatives which were converted to Ni and Pd N-heterocyclic carbene complexes by oxidative insertion. Fifteen crystal structures were determined by X-ray diffraction. The N-alkyloxy groups are twisted out of the imidazole ring plane and adopt either syn or anti conformations in the solid state.

In-situ grazing incidence X-ray diffractometry of polycrystalline copper in alkaline chloride and sulphate electrolytes

Abstract In-situ grazing incidence X-ray diffractometry (GIXD) was used to study the electrochemical oxidation and reduction of copper in solutions at pH 9, 12 and 14. Crystalline Cu 2 O and CuO films down to thicknesses of tens of nanometers were detected under such conditions, whereas a crystalline Cu(OH) 2 phase did not occur. The formation rate of crystalline Cu 2 O films increases with pH and formation time. In the Cu(II) potential region, Cu 2 O can coexist with amorphous Cu(OH) 2 phases. Crystalline CuO is not formed directly. At pH 14, it occurs by slow conversion of Na 2 CuO 2 precipitates. Crystalline CuCl formation takes place only in the Cu(II) potential region at pH 9.

Syntheses, crystal structures, and polymorphism of quaternary pyrrolidinium chlorides

The syntheses, properties, and X-ray crystal structures of 1-methyl-1-propylpyrrolidinium chloride1, 1-allyl-1-methylpyrrolidinium chloride2, and 1-methyl-1-propargylpyrrolidinium chloride3 are described. Colorless plates of 1 (C8H18ClN) crystallize in the orthorhombic space groupPnab with Z = 8 and unit cell parameters a = 10.0354(11) A, b = 13.254(2) A, c = 14.6231(16) A. Colorless prisms of 2 (C8H16ClN) crystallize in the monoclinic space groupP21/c with Z = 4 and unit cell parameters a = 6.4857(10) A, b = 12.005(3) A, c = 12.526(2) A, and β=102.746(13)°. Colorless needles of 3 (C8H14ClN) crystallize in the monoclinic space groupP21/n with Z = 4 and unit cell parameters a = 8.4849(14) A, b = 8.1271(16) A, c = 13.501(2) A, and β=100.408(13)°. The five-membered ring adopts a twisted conformation in 1 but an N-envelope in 2 and 3. The salts form networks of weak C–H…Cl−hydrogen bonds. Hot stage microscopy, differential scanning calorimetry and temperature-controlled X-ray powder diffractometry revealed that each of the three compounds exists in at least two different crystal forms.

In situ external reflection absorption FTIR spectroscopy on lead electrodes in sulfuric acid

The oxidation and reduction reactions of lead electrodes in 5 molar sulfuric acid were investigated in situ using the technique of external reflection absorption infrared spectroscopy in combination with standard electrochemical techniques. The generation and consumption of lead sulphate were measured during galvanostatic experiments at different current densities. The amount of lead sulphate on the electrode surface was quantitatively determined by integrating the area of characteristic vibrational bands. Different anodic current densities lead only to a little different oxidation behaviour of the lead electrodes, the thickness of the passive lead sulphate layer depends mainly on the consumed charge. An increase for the amount of lead sulphate on the electrode surface was found during the cathodic processes also in the region of the lead oxide reduction. This behaviour depends on the current densities applied and can be explained by the chemical reaction of lead oxide with sulfuric acid or of freshly produced lead, forming lead sulphate.