Peter Lobotka

Carboxybetaine Modified Interface for Electrochemical Glycoprofiling of Antibodies Isolated from Human Serum

Impedimetric lectin biosensors capable of recognizing two different carbohydrates (galactose and sialic acid) in glycans attached to antibodies isolated from human serum were prepared. The first step entailed the modification of a gold surface by a self-assembled monolayer (SAM) deposited from a solution containing a carboxybetaine-terminated thiol applied to the subsequent covalent immobilization of lectins and to resist nonspecific protein adsorption. In the next step, Sambucus nigra agglutinin (SNA) or Ricinus communis agglutinin (RCA) was covalently attached to the SAM, and the whole process of building a bioreceptive layer was optimized and characterized using a diverse range of techniques including electrochemical impedance spectroscopy, cyclic voltammetry, quartz crystal microbalance, contact angle measurements, zeta-potential assays, X-ray photoelectron spectroscopy, and atomic force microscopy. In addition, the application of the SNA-based lectin biosensor in the glycoprofiling of antibodies isolated from the human sera of healthy individuals and of patients suffering from rheumatoid arthritis (RA) was successfully validated using an SNA-based lectin microarray. The results showed that the SNA lectin, in particular, is capable of discriminating between the antibodies isolated from healthy individuals and those from RA patients based on changes in the amount of sialic acid present in the antibodies. In addition, the results obtained by the application of RCA and SNA biosensors indicate that the abundance of galactose and sialic acid in antibodies isolated from healthy individuals is age-related.

Electron scattering mechanisms in Cu-Mn films for interconnect applications

Electrical properties and corresponding structural features of Cu-Mn alloy films with potential application as barrier and interconnect layers were studied. Cu-Mn films were deposited by DC magnetron sputtering at room temperature on SiO2 substrates. Electrical resistivity measurements were made as a function of film composition and temperature. The specific resistivity varies linearly with the Mn content showing a maximum of 205 μΩcm at 80 at. % Mn. The temperature coefficient of resistance (TCR) of all alloy films is low, showing non-metallic conductivity for most compositions. Also a minimum TCR has been observed in the 40–80 at. % Mn range which was attributed to a magnetic transformation around 200–300 K. Electrical resistivity measurements are correlated with the film structure revealed by transmission electron microscopy to clarify the phase regions throughout the composition range. In the 20–40 at. % and 70–80 at. % Mn ranges, two-phase structures were identified, where Cu- or Mn-rich solid solution grains were surrounded by a thin amorphous covering layer. Based on the revealed phase regions and morphologies electron scattering mechanisms in the system were evaluated by combining the Matthiessens rule and the Mayadas-Schatzkes theory. Grain boundary reflectivity coefficients (r = 0.6–0.8) were calculated from fitting the model to the measurements. The proposed model indicates that, in a binary system, the special arrangement of the two phases results in new scattering mechanisms. The results are of value in optimizing the various parameters needed to produce a suitable barrier layer.

Preparation of Nanostructured Magnetic Films by the Plasma Jet Technique

Magnetic films were prepared by the plasma jet technique from Fe, mumetal, and Fe/Hf or Fe/Ta nozzles. Two different plasma jet systems with different vacuum pumps were used to compare the quality of the produced films. The films prepared from a Fe nozzle in the two different equipments shows that oxygen in the residual atmosphere of the low vacuum reactor leads mainly to the formation of iron oxides. The Fe and mumetal films prepared in the high vacuum system contain only a very small amount of oxygen, as proved by chemical analysis and ferromagnetic resonance. The mumetal film, moreover, shows good soft magnetic properties and low magnetic damping. For the reactive plasma jet deposition of nanogranular Fe-Hf-O and Fe-Ta-O films, the low vacuum system was used. The films with higher oxygen content exhibit tunneling-type conductivity. In some films, superparamagnetic behaviour and spin-dependent tunneling magnetoresistance were observed.

Ferromagnetic resonance study of exchange and dipolar interactions in discontinuous multilayers

We studied interlayer and intergranular exchange and dipolar coupling in (Fe97Si3∕SiO2)5 discontinuous multilayer (DM) by means of ferromagnetic resonance (FMR). Due to a strong ferromagnetic exchange coupling (J∼−3ergs∕cm2), the precessional motions of magnetic moments of the granules are coupled, which results in acoustic and optical modes. Moreover, there is a notable FMR line splitting in the optical mode under the external field normal to the DM, which is explained by an interlayer dipolar coupling, only possible for the DMs. The detailed structural analysis and electrical measurements confirmed that the metal nanoparticles were separated by an insulating matrix, and the single-electron transport phenomena (Coulomb blockade and tunneling magnetoresistivity) were observed at low temperatures (77–100K).

Electronic transport properties of amorphous W/Si multilayers

Abstract The temperature dependence of the sheet resistance of e-beam evaporated W/Si multilayers was investigated. A positive temperature coefficient of resistivity (TCR) 190–600 ppm/K was obtained for multilayers with crystalline tungsten layers (dw > 4 nm). Multilayers with amorphous tungsten layers 1–4 nm thick revealed nom-metallic resistivity behaviour with a negative TCR, -(100–300) ppm/K in the temperature range 1.8–300 K, and were superconducting with the superconducting transition temperature Tc up to 4.21 K. The resistivity behaviour of the amorphous W/Si multilayers with Si layer thicknesses 1–10 nm can be described within the framework of 3D weak localization and interaction models. At temperatures close to Tc superconducting fluctuations decrease the resistance of these samples. At temperatures above Tc both effects can be comparable, resulting in a maximum in the temperature dependence of the resistance. A relatively strong coupling between metallic layers was observed. This coupling could originate from mixing at the W/Si interfaces and interdiffusion during the deposition and subsequent annealing. The different resistivity behaviour of amorphous tungsten monolayers strongly supports this assumption.

Vertically stacked (Nb/Si)*10 Josephson junction

We report on “Josephson superlattice”—a stack of junctions consisting of a multilayer [Nb(7nm)/Si(2nm)]*10 deposited by dc sputtering. The silicon barriers are amorphous and Nb sublayers are polycrystalline. The stacked junctions exhibit both ac and dc Josephson effects. In the IC(B) diffraction pattern there is an extra periodicity of about 2–3 G in addition to larger period of about 21 G. The shape of IC(B) curve resembles the characteristics obtained on two JJs placed close to each other and connected in parallel. The possible explanation of this fine structure of the interference pattern is shortly discussed.

Modification of Polyaniline-Based Gas Sensor by Electrophoretic Deposition of Metal Nanoparticles in Ionic Liquids

Nanoparticles synthesized in various ionic liquids (ILs) were immobilized by electrophoretic deposition (EPD) at the surface of a gas sensor made of thin polyaniline (PAni) film. We used pulsed DC voltage to overcome electrochemical treatment in IL-based electrolytes. In spite that EPD is commonly used for synthesis of nanoparticle films or coatings, here we just functionalized the surface of PAni by scattered nanoparticles. Immobilized nanoparticles were observed by SEM imaging and dynamic responses of gas sensors functionalized by different nanoparticles (Ni, Ni-Fe and Ag-Cu) were compared. Using the EPD technique, sensitivity or selectivity of a gas sensor based on PAni can be improved easily.

Polymer/Carbon Composites for Sensing

It is indisputable that sensors are indispensable in our daily life. In parallel to the research in the field of organic electronics, there is a serious effort to develop technologically compatible sensors based on polymers. Due to the widespread usage of microelectronics, it is quite natural that the main effort is focused on the development of sensors providing electrical output. But until the discovery of conducting polymers, it was necessary to find a way how to increase the basic electrical conductivity of the polymers, which had been considered to be perfect insulators. The easiest way to do it is to add and disperse in a polymer a small amount of conducting or semiconducting material with particles on the micro- or sub-micrometer scale, for example, carbon fibers or carbon black. A proper concentration of the “filler” is around the percolation threshold, at which the sensor’s sensitivity reaches the maximum. The details are described in Sect. 2.