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This paper describes the characterization, electrochemical properties, and applications of carbon films prepared by the electron cyclotron resonance (ECR) sputtering method. The ECR-sputtered carbon film was deposited within several minutes at room temperature. The optimized sputtering conditions significantly change the film structure, which includes many more [sp.sup.3] bonds ([sp.sup.3]/[sp.sup.2] = 0.702) than previously reported film [([sp.sup.3]/[sp.sup.2] = 0.274).sup.1] with an extremely fiat surface (0.7 [Angstrom]). The ECR-sputtered carbon films exhibit excellent electrochemical properties. For example, they have nearly the same potential window in the positive direction as that of high-quality, boron-doped diamond ((moderately doped, [10.sup.19]-[10.sup.20] boron atoms/[cm.sup.3]).sup.2] and an even wider potential window in the negative direction with a low background current, high stability, and suppression of fouling by electroactive species without pretreatment. The electron-transfer rates at ECR-sputtered carbon films are similar to those of glassy carbon (GC) for [Ru(N[H.sub.3]).sub.6.sup.2+/3-] and [Fe(CN).sub.6.sup.3-/4-], whereas they are much slower than those of GC for [Fe.sup.2-/3+], dopamine oxidation, and [O.sub.2] reduction due to weak interactions between electroactive species and the ECR-sputtered carbon film surface. Such a response can be attributed to the ultraflat surface and low surface O/C ratios of ECR-sputtered carbon films. ECR-sputtered carbon film is advantageous for measuring biochemicals with high oxidation potentials because of its wide potential window and high stability. Highly reproducible and well-defined cyclic voltammograms were obtained for histamine and azide ions with a peak potential at 1.25 and 1.12 V vs Ag/AgCl, respectively. The film is very stable for continuous voltammetry measurements in 10 [micro]M bisphenol A, which usually fouls the electrode surface with oxidation products.

We have already reported a method for fabricating ultra-microelectrodes (Suzuki, K. JP Patent, 2004-45394, 2004). This method is based on the selective chemical etching of optical fibers. In this work, we undertake a detailed investigation involving a combination of etched optical fibers with various types of tapered tip (protruding-shape, double- (or pencil-) shape and triple-tapered electrode) and insulation with electrophoretic paint. Our goal is to establish a method for fabricating nanometersized optical fiber electrodes with high reproducibility. As a result, we realized pencil-shaped and triple-tapered electrodes that had radii in the nanometer range with high reproducibility. These nanometer-sized electrodes showed well-defined sigmoidal curves and stable diffusion-limited responses with cyclic voltammetry. The pencil-shaped optical fiber, which has a conical tip with a cone angle of 20[degrees], was effective for controlling the electrode radius. The pencil-shaped electrodes had higher reproducibility and smaller electrode radii ([r.sub.app] < 1.0 nm) than those of other etched optical fiber electrodes. By using a pencil-shaped electrode with a 105-nm radius as a probe, we obtained simultaneous electrochemical and optical images of an implantable interdigitated array electrode. We achieved nanometer-scale resolution with a combination of scanning electrochemical microscopy SECM and optical microscopy. The resolution of the electrochemical and optical images indicated sizes of 300 and 930 nm, respectively. The neurites of living PC12 cells were also successfully imaged on a 1.6-[micro]m scale by using the negative feedback mode of an SECM.

A novel, smart, chemical taste sensor that realistically mimics the behavior of the human gustatory system is described. The taste sensor consists of an array of electrochemical sensors that represent the gustatory receptors on the human tongue, and a two-phase optimized radial basis function network (RBFN) to represent the human brain, which comprehensively analyzes the gustatory stimulation and judges the overall taste. In the illustrated model, eight electrodes were fabricated to determine the eight major taste-causing substances, [Na.sup.+], [K.sup.+], [Cl.sup.-], [H.sup.+], sucrose, glucose, glutamate, and caffeine. The detected signals were fed to a two-phase RBFN optimized by the implementation of a basis optimization algorithm and weight decay term for appropriate data processing. The first phase of the two-phase RBFN quantifies the amount of taste-causing substances in food samples from the responses of the electrodes. These results are then fed to the second phase, which correlates the amount of substances with the overall taste. The final output is scored on a scale of 1-5 for each of the five basic tastes sensed by the human gustatory system, which are saltiness, sourness, sweetness, bitterness, and umami. The constructed network estimated the intensity of the basic tastes of 30 drink varieties with an average relative error of 7.0% compared to the human scores. The network could also estimate the variance in the human sensory perception. Moreover, the sensor successfully predicted the interactions of tastes such as suppression of bitterness by sweetness and enhancement of umami by saltiness, which are illusions sensed by the human gustatory system. With these abilities, the novel taste sensor can be considered as a quantitative yet humanlike sensor with a great potential for practical applications.

Application of a dipyrido[3,2-a:2',3'-c]phenazine (DPPZ)-type metal complex as an DNA electrochemical probe was studied. The introduction of electron-donating groups (N[H.sub.2]) was effective for controlling the redox potential and binding affinities of the DPPZ-type osmium complex. The [[Os[(DA-bpy).sub.2]DPPZ].sup.2+] complex (DA-bpy; 4,4'-diamino-2,2'-bipyridine) had a lower half-wave potential ([E.sub.1/2]) of 147 mV (vs Ag|AgCl) and higher binding affinity with DNA (binding constant, K = 3.1 x [10.sup.7] [M.sup.-1]) than those of other complexes. With a single-stranded DNA immobilized gold electrode, the hybridization signal ([DELTA]I) of the [[Os[(DAbpy).sup.2]DPPZ].sup.2+] complex was linear in the concentration range of 1.0 pg [mL.sup.-1] - 0.12 [micro] g [mL.sup.-1] for the targeted DNA with a regression coefficient of 0.999. The detection limit was 0.1 pg [mL.sup.1]. The 400-bp yA[L.sub.3] gene was also detected with good sensitivity and selectivity using the [[Os[(DAbpy).sub.2]DPPZ].sup.2+] complex.