Intentionally Created Localized Bridges for Electron Transport Through Graphene Monolayer Between Two Metals.

Monolayer graphene (1LG) is frequently unpredictably modified by supporting material so that it limits development of devices. Van der Waals interaction is dominant in the models describing the in-plane processes, including the electrical charge transport. However, the current flow perpendicular to the plane of the graphene is still less understood. This report analysed specific aspect of the perpendicular current and disclosed an original way to create transport bridges perpendicular to the plane across the 1LG. The most extraordinary finding is that the electron transport between two parallel metal surfaces can be shut down and opened if the metals are separated by the 1LG. The electron transmission can be intentionally varied in this metal - 1LG - metal (M-G-M) system by pressure. In the experimental study the AFM force curve and tunnelling current measurements were combined when the external load force (0 - 1200 nN) and electrical potential (-1.5 V - +1.5 V) were used. It is proved that for low voltages (< ±9 mV) a bridge is opened perpendicular to the graphene across the M-G-M systems by the external force, if the compression dependent Fermi level crosses electronic states in the interfaces and graphene. The localised bridges with diameter about 10 - 40 nm can be opened and kept continuously by the stabilised force in separated points of the system. However, the predictable changes can be produced in the system if the voltage and the force exceeded critical magnitudes. A combined model was proposed acceptable to explain the bridging and predictably modify the characteristics.

Single variable defined technology control of the optical properties in MoS2 films with controlled number of 2D-layers.

Fabrication of practical devices based on the transient metal dichalcogenides (TMDs) can be successively extended to various areas of the applications if the large area growth technology can be intentionally controlled and the characteristics of the layers can be easily predicted. In present work we presented the principles of the technology control based on the single key variable that can be directly related to the sequence of the technological processes. The atomically thin MoS2 layers were used as a model material and the layers were obtained by the CVD synthesis of the molybdenum precursor. Our thorough study demonstrated that the method allowed to deliberately choose the number of the MoS2 two-dimensional (2D)-layers between 1 and 10 by simply choosing the precursor deposition time. The optical properties of the layers were characterised by the optical transitions that corresponded to the known band structure of the MoS2 layers. Fused calibration diagram was proposed as the practical tool for the technology control and it was proved to be highly successive in relating the 2D-properties of the films with the initial stage of the fabrication technology. The method can be adapted to the wafer size TMDs growth on the diverse substrates.

Synthesis of Reduced Graphene Oxide with Adjustable Microstructure Using Regioselective Reduction in the Melt of Boric Acid: Relationship Between Structural Properties and Electrochemical Performance.

The melt of H3BO3 was used to reach a controllable reduced graphene oxide (rGO) synthesis protocol using a graphene oxide (GO) precursor. Thermogravimetric analysis and differential scanning calorimetry (TG/DSC) investigation and scanning electron microscopy (SEM) images have shown that different from GO powder, reduction of GO in the melt of H3BO3 leads to the formation of less disordered structure of basal graphene planes. Threefold coordinated boron atom acts as a scavenger of oxygen atoms during the process of GO reduction. Fourier-transform infrared (FTIR) spectra of synthesized products have shown that the complex of glycerol and H3BO3 acts as a regioselective catalyst in epoxide ring-opening reaction and suppress the formation of ketone C=O functional groups at vacancy sites. Thermal treatment at 800 °C leads to the increased concentration of point defects in the backbone structure of rGO. Synthesized materials were tested electrochemically. The electrochemical performance of these materials essentially differs depending on the preparation protocol. The highest charge/discharge rate and double-layer capacitance were found for a sample synthesized in the melt of H3BO3 in the presence of glycerol and treated at 800 °C. The effect of optimal porosity and high electrical conductivity on the electrochemical performance of prepared materials also were studied.

Functionalization of α-synuclein fibrils.

The propensity of peptides and proteins to form self-assembled structures has very promising applications in the development of novel nanomaterials. Under certain conditions, amyloid protein α-synuclein forms well-ordered structures - fibrils, which have proven to be valuable building blocks for bionanotechnological approaches. Herein we demonstrate the functionalization of fibrils formed by a mutant α-synuclein that contains an additional cysteine residue. The fibrils have been biotinylated via thiol groups and subsequently joined with neutravidin-conjugated gold nanoparticles. Atomic force microscopy and transmission electron microscopy confirmed the expected structure - nanoladders. The ability of fibrils (and of the additional components) to assemble into such complex structures offers new opportunities for fabricating novel hybrid materials or devices.

Fine structure and related properties of the assembleable carbon nanotubes based electrode for new family of biosensors with chooseable selectivity.

Surfaces of constituent parts of biosensors based on single wall carbon nanotube layer were investigated and compare for properly functioning and faulty biosensors. Though the original technology is acceptable for changing of the selectivity, only glucose sensitive biosensors are investigated. Based on the results of the study, a correlation between the features of the nanoscale structures and parameters of amperiometric biosensors for assemblage of which an innovative approach is described. Original template of the electrodes has been prepared on a base of single wall carbon nanotube layer deposited on the supporting polycarbonate membrane. Original immobilisation of enzymes within special membrane allows functional modification of biosensors being accomplished by simple replacement of the enzymatic membrane. The original technology leads to a novel family of biosensors acceptable for detection of wide range of carbohydrates. The morphology and the local electric properties of the constituent parts of the biosensors are characterized by scanning probe microscopy. The sensitivity, selectivity and stability are described for typical types of the biosensors.

Expression and purification of active recombinant equine lysozyme in Escherichia coli.

Equine lysozyme (EL) is a calcium (Ca)-binding lysozyme and is an intermediary link between non-Ca-binding C-type lysozyme and alpha-lactalbumin. The feature of lysozymes to assemble into the fibrils has recently gained considerable attention for the investigation of the functional properties of these proteins. To study the structural and functional properties of EL, a synthetic gene was cloned and EL was overexpressed in Escherichia coli as a fused protein. The His-tagged recombinant EL was accumulated as inclusion bodies. Up to 50 mg/l of the recombinant EL could be achieved after purification by Ni(2+) affinity chromatography, refolding in the presence of arginine, CM-Sepharose column purification following TEV protease cleavage. The purified protein was functionally active, as determined by the lysozyme activity, proving the proper folding of protein. The purified lysozyme was used for the oligomerisation studies. The protein formed amyloid fibrils during incubation in acidic pH and elevated temperature. The recombinant EL forms two types of fibrils: ring shaped and linear, similar to the native EL.