Structure and Electroanalytical Application of Nitrogen-doped Carbon Thin Film Electrode with Lower Nitrogen Concentration.

We studied a nitrogen-doped nanocarbon film electrode with a nitrogen concentration of lower than 10.9 at% formed by the unbalanced magnetron (UBM) sputtering method. The sp(3) content in the nitrogen-doped UBM sputtering nanocarbon film (N-UBM film) slightly increases with increasing nitrogen concentration. The nitrogen-containing graphite-like bonding decreases and pyridine-like bonding increases with increasing nitrogen concentration. The N-UBM film has a very smooth surface with an average roughness of 0.1 to 0.3 nm, which is almost independent of nitrogen concentration. The N-UBM film electrode shows a wider potential window (4.1 V) than a pure-UBM film electrode (3.9 V) due to its slight increase in the sp(3) content. The electrocatalytic activity increased with increasing nitrogen concentration, suggesting that the electroactivity is maximum when the nitrogen concentration is around 10.9 at%, which is confirmed by the peak separation of Fe(CN)6(4-). The hydrogen peroxide (H2O2) reduction potentials at the N-UBM film electrode shifted about 0.1 V, and the peak current of H2O2 increased about 4 times.

Efficient direct electron transfer with enzyme on a nanostructured carbon film fabricated with a maskless top-down UV/ozone process.

We have developed a new carbon film electrode material with thornlike surface nanostructures to realize efficient direct electron transfer (DET) with enzymes, which is very important for various enzyme biosensors and for anodes or cathodes used in biofuel cells. The nanostructures were fabricated using UV/ozone treatment without a mask, and the obtained nanostructures were typically 2-3.5 nm high as confirmed by atomic force microscopy measurements. X-ray photoelectron spectroscopy and transmission electron microscopy revealed that these nanostructures could be formed by employing significantly different etching rates depending on nanometer-order differences in the local sp(3) content of the nanocarbon film, which we fabricated with the electron cyclotron resonance sputtering method. These structures could not be realized using other carbon films such as boron-doped diamond, glassy carbon, pyrolyzed polymers based on spin-coated polyimide or vacuum-deposited phthalocyanine films, or diamond-like carbon films because those carbon films have relatively homogeneous structures or micrometer-order crystalline structures. With physically adsorbed bilirubin oxidase on the nanostructured carbon surface, the DET catalytic current amplification was 30 times greater than that obtained with the original carbon film with a flat surface. This efficient DET of an enzyme could not be achieved by changing the hydrophilicity of the flat carbon surface, suggesting that DET was accelerated by the formation of nanostructures with a hydrophilic surface. Efficient DET was also observed using cytochrome c.