Péter Berki

Real-Time Sensing of Hydrogen Peroxide by ITO/MWCNT/Horseradish Peroxidase Enzyme Electrode

The accurate and sensitive determination of H2O2 is very important in many cases because it is a product of reactions catalysed by several oxidase enzymes in living cells and it is essential in environmental and pharmaceutical analyses. The fabrication of enzyme protein activity based biosensors is a very promising way for this purpose because the function of biological molecules is very specific, sensitive, and selective. Horseradish peroxidase HRP is the most commonly used enzyme for H2O2 detection because it can oxidize hydrogen atoms and, for example, xenobiotics in the presence of H2O2. In order to define the limit of detection LOD of H2O2 we made calibrations with guaiacol and amplex red AR, which are hydrogen donors of HRP. The accumulation of the reaction products, tetraguaiacol, and resorufin, respectively, then can be easily detected by absorption or emission fluorescence spectroscopy. In our experiments an enzyme electrode was fabricated from ITO indium tin oxide, functionalized multiwalled carbon nanotubes f-MWCNTs, and HRP. Although the enzyme activity was smaller by about two orders of magnitude when the enzyme was bound to the f-MWCNTs ca. 10−2 M H2O2/M HRP·sec compared to ca. 2 M H2O2/M HRP·sec and 5 M H2O2/M HRP·sec with AR and guaiacol in buffer solution, LOD of the H2O2 decomposition was about 6 pM H2O2/sec and 10 pM H2O2/sec in the case of AR and guaiacol, respectively.

Preparing SnO2/MWCNT Nanocomposite Catalysts via High Energy Ball Milling

Ball milling method was used to fabricate successfully tin dioxide (SnO₂)/multi-walled carbon nanotubes nanocomposite materials using SnCl₂ ×2H₂O as precursor together with soda and salt as admixture. The as-prepared materials were characterized by transmission electron microscopy, scanning electron microscopy with energy-dispersive X-ray spectroscopy, Raman microscopy, and X-ray diffraction techniques. Observations revealed that applying both soda and salt are advantageous for increasing dispersity of tin dioxide nanoparticles on the surface of carbon nanotubes. These multi-walled carbon nanotube-based composites are promising candidates as thick film gas sensors or catalysts. Results indicate that SnO₂/MWCNT composites can be achieved under solvent free dry conditions, too.

CCVD preparation of highly uniform carbon micro- and nanocoil fibers

Micro- and nanosized carbon fibers with special helical structure have many promising applications. These structures can be used as reinforcing materials in polymer composites, wave absorption or tactile sensor elements. In this fiber preparation method the applied catalyst precursor were nickel (II) oxide nanoparticles. Sulfuric modification of nickel containing catalyst grain yields carbon fibers with special coiled structures in acetylene decomposition. The preparation of carbon fiber coils by the CCVD method was carried out between 700- 800 C using thiophene impurity. The catalyst particles and the observed structures were studied by X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The lengths of fibers can even reach millimeter size and the average fiber diameter is 1 μm. The diameter of coils is 1-20 μm, the coil pitch is 0.5-1.5 μm. Carbon microcoils might have interesting applications in the near future.