Nanocarbon Film Research Articles

Poly‐ε‐Lysine Modified Nanocarbon Film Electrodes for LPS Detection

AbstractWe developed an electrochemical system for detecting lipopolysaccharide (LPS) that uses an ultraflat nanocarbon film electrode modified with poly‐ε‐lysine with a high affinity to LPS. LPS was captured on the modified electrode, and then ferrocene labeled polymyxin B (FcPMB) was captured on the LPS adsorbed electrode via the LPS‐PMB affinity interaction. The adsorbed FcPMB provided an amplified response with Fe2+ ions, and the current response was dependent on the amount of captured LPS (LOD=2.0 ng/mL). This was due to the efficient accumulation of the obtained current for LPS and the very low noise made possible by the ultraflat surface.

バイオセンサ応用を目的としたスパッタナノカーボン薄膜電極の開発

We have developed nanocarbon film electrodes formed by an electron cyclotron resonance (ECR) sputtering method. The nanocarbon film contains a nano-crystalline sp2 and sp3 mixed bond structure with an atomically flat surface and has a wide potential window, relatively high electrochemical activity and a low background noise level similar to a boron-doped diamond electrode. Surface conditions such as hydrophilicity on the nanocarbon film electrode can be controlled by electrochemical treatments while maintaining the wide potential window and surface flatness, and, therefore, in measurements of various biomolecules including oxidatively damaged DNA and oligonucleotides, their adsorption onto the electrode surface is suppressed. For example, cytosine and methylated cytosine in oligonucleotides can be distinguished by square wave voltammetry. A carbon electrode with a thorn-like nanostructure could be fabricated by UV/ozone treatment using different etching rates depending on nanometer-order differences in the local sp3 content of the nanocarbon film. This nanostructured surface was very effective in improving efficient direct electron transfer (DET) with enzymes such as bilirubin oxidase. Carbon film electrodes doped with metal nanoparticles have been also developed by co-sputtering metal and carbon. A Pt-nanoparticle-dispersed carbon electrode shows high electrochemical activity and stability for detecting hydrogen peroxide indicating that it is suitable for use as a biosensor.

Anodic Stripping Voltammetric Determination of Cd and Pb with Nanocarbon Film Electrode Fabricated by Unbalanced Magnetron Sputtering

Anodic Stripping Voltammetric Determination of Cd and Pb with Nanocarbon Film Electrode Fabricated by Unbalanced Magnetron Sputtering

Structure and Electrochemical Performance of Nitrogen-Doped Carbon Film Formed by Electron Cyclotron Resonance Sputtering

A nitrogen-doped nanocarbon film electrode with mixed sp(2) and sp(3) bonds formed using the electron cyclotron resonance (ECR) sputtering method was studied with respect to the relationship between nitrogen concentration and electrochemical performance. The film (N-ECR) has a nanocrystalline structure, and the sp(3) content increases with increasing nitrogen concentration unlike the recently reported nitrogen-containing tetrahedral amorphous carbon film.1 The film has a very smooth surface with an average roughness of 0.1 to 0.2 nm, which is almost independent of nitrogen concentration. In contrast, the ratio of nitrogen-containing graphite-like bonding is high at low nitrogen concentrations, and then pyridine-like bonding increases as the nitrogen concentration increases. These variations in the chemical structures and the sp(2) and sp(3) content greatly change the electrochemical performance. The N-ECR electrode shows a wider potential window (∼3.8 V) than a pure nanocarbon electrode (∼3.1 V) due to its higher sp(3) content. The N-ECR electrode (N = 9.0 at. %) shows improved electrochemical activity because the lowest peak separation of Fe(CN)6(3-/4-) was observed at this nitrogen concentration. The oxygen and hydrogen peroxide (H2O2) reduction potentials at the N-ECR electrode shifted about 0.3 and 0.15 V, respectively, and the peak height of H2O2 is greatly increased. As a result, a linear relationship was obtained from 0.2 to 17 mM for the reductive current detection of H2O2. The N-ECR electrode also shows better activity for oxidizing certain biomolecules. The oxidation potentials of guanosine and adenosine decreased about 0.1 V, suggesting that the N-ECR electrode is suitable for use as a biosensing platform.

Effect of Temperature on Carbon-coated Graphene for Lithium-ion Batteries with Improved Performance

Abstract Carbon-coated graphene was synthesized through pyrolysis of a polyaniline–graphite oxide (PANI–GO) precursor by annealing in an Ar and H2 atmosphere at various temperatures. X-ray diffraction, field-emission scanning and high-resolution transmission electron microscopies, X-ray photoelectron spectroscopy, Raman spectra, and thermogravimetric analysis were used to characterize the pyrolyzed PANI–GO at different temperatures. The PANI on the graphene at temperatures above 650 °C was completely converted into a nanocarbon film. Galvanostatic charge–discharge tests revealed that PANI–GO-800 exhibited improved rate and cycle capabilities over that of graphene due to the increased conductivity in the out-of-plane direction.

Evaluation of Electrokinetic Parameters for All DNA Bases with Sputter Deposited Nanocarbon Film Electrode

The electrokinetic parameters of all the DNA bases were evaluated using a sputter-deposited nanocarbon film electrode. It is very difficult to evaluate the electrokinetic parameters of DNA bases with conventional electrodes, and particularly those of pyrimidine bases, owing to their high oxidation potentials. Nanocarbon film formed by employing an electron cyclotron resonance sputtering method consists of a nanocrystalline sp(2) and sp(3) mixed bond structure that exhibits a sufficient potential window, very low adsorption of DNA molecules, and sufficient electrochemical activity to oxidize all DNA bases. A precise evaluation of rate constants (k) between all the bases and the electrodes is achieved for the first time by obtaining rotating disc electrode measurements with our nanocarbon film electrode. We found that the k value of each DNA base was dominantly dependent on the surface oxygen-containing group of the nanocarbon film electrode, which was controlled by electrochemical pretreatment. In fact, the treated electrode exhibited optimum k values for all the mononucleotides, namely, 2.0 × 10(-2), 2.5 × 10(-1), 2.6 × 10(-3), and 5.6 × 10(-3) cm s(-1) for GMP, AMP, TMP, and CMP, respectively. The k value of AMP was sufficiently enhanced by up to 33 times with electrochemical pretreatment. We also found the k values for pyrimidine bases to be much lower than those of purine bases although there was no large difference between their diffusion coefficient constants. Moreover, the theoretical oxidation potential values for all the bases coincided with those obtained in electrochemical experiments using our nanocarbon film electrode.

Electron Cyclotron Resonance-Sputtered Nanocarbon Film Electrode Compared with Diamond-Like Carbon and Glassy Carbon Electrodes as Regards Electrochemical Properties and Biomolecule Adsorption

The electrochemical properties and biocompatible characteristics at an electron cyclotron resonance (ECR)-sputtered nanocarbon film electrode, a diamond-like carbon (DLC) electrode and a glassy carbon (GC) electrode have been studied. The three carbon electrodes show significant current reductions with increased peak separations as a result of protein fouling before oxygen plasma treatment, but the current reductions of the ECR-sputtered nanocarbon and DLC film electrodes are smaller than that of the GC electrode due to their superior surface flatness. The oxygen plasma pretreated ECR-sputtered nanocarbon film electrode exhibits a significant improvement in anti-fouling performance with an improved electron transfer. This is because the pretreated ECR-sputtered nanocarbon film enabled the surface to introduce surface oxygen functionalities that not only improve the interaction between the analytes and the electrode surface but also make the film surface more hydrophilic, which is important for the suppression of biomolecule adsorption. At the same time, the pretreated ECR-sputtered nanocarbon film also retained an ultraflat surface even after pretreatment as a result of the low background current. This excellent performance can only be achieved with our ECR-sputtered nanocarbon film, indicating that our film is promising for application to electrochemical detectors for various biomolecular analytes.

Electron Cyclotron Resonance-Sputtered Nanocarbon Film Electrode Compared with Diamond-Like Carbon and Glassy Carbon Electrodes as Regards Electrochemical Properties and Biomolecule Adsorption

The electrochemical properties and biocompatible characteristics at an electron cyclotron resonance (ECR)-sputtered nanocarbon film electrode, a diamond-like carbon (DLC) electrode and a glassy carbon (GC) electrode have been studied. The three carbon electrodes show significant current reductions with increased peak separations as a result of protein fouling before oxygen plasma treatment, but the current reductions of the ECR-sputtered nanocarbon and DLC film electrodes are smaller than that of the GC electrode due to their superior surface flatness. The oxygen plasma pretreated ECR-sputtered nanocarbon film electrode exhibits a significant improvement in anti-fouling performance with an improved electron transfer. This is because the pretreated ECR-sputtered nanocarbon film enabled the surface to introduce surface oxygen functionalities that not only improve the interaction between the analytes and the electrode surface but also make the film surface more hydrophilic, which is important for the suppression of biomolecule adsorption. At the same time, the pretreated ECR-sputtered nanocarbon film also retained an ultraflat surface even after pretreatment as a result of the low background current. This excellent performance can only be achieved with our ECR-sputtered nanocarbon film, indicating that our film is promising for application to electrochemical detectors for various biomolecular analytes.

Electrochemical DNA Methylation Detection for Enzymatically Digested CpG Oligonucleotides

We describe the electrochemical detection of DNA methylation through the direct oxidation of both 5-methylcytosine (mC) and cytosine (C) in 5'-CG-3' sequence (CpG) oligonucleotides using a sputtered nanocarbon film electrode after digesting a longer CpG oligonucleotide with endonuclease P1. Direct electrochemistry of the longer CpG oligonucleotides was insufficient for obtaining the oxidation currents of these bases because the CG rich sequence inhibited the direct oxidation of each base in the longer CpG oligonucleotides, owing to the conformational structure and its very low diffusion coefficient. To detect C methylation with better quantitativity and sensitivity in the relatively long CpG oligonucleotides, we successfully used an endonuclease P1 to digest the target CpG oligonucleotide and yield an identical mononucleotide 2'-deoxyribonucleoside 5'-monophosphate (5'-dNMP). Compared with results obtained without P1 treatment, we achieved 4.4 times higher sensitivity and a wider concentration range for mC detection with a resolution capable of detecting a subtle methylated cytosine difference in the CpG oligonucleotides (60mer).

Electrochemical Determination of Oxidative Damaged DNA with High Sensitivity and Stability Using a Nanocarbon Film

We describe the electrochemical determination of oxidative damaged DNA by using a nanocarbon film electrode combined with a high performance liquid chromatography (HPLC) system. The nanocarbon film was formed by employing the electron cyclotron resonance sputtering method, and has a nano-crystalline sp(2) and sp(3) mixed bond structure with an atomically flat surface. This film electrode provided the high electrode activity and stability needed to quantitatively detect oxidative damaged DNA, 8-hydroxy-2'-deoxyguanosine (8-OHdG), by direct electrochemical oxidation. The coefficient of variation (C.V.) value of 1 µM 8-OHdG at our film electrode was 0.75% (n = 12), which constitutes superior reproducibility to that of a conventional glassy carbon (GC) electrode (9.28%, n = 12) in flow-injection analysis. This was because the nanocarbon film suppressed fouling for the oxidized product of 8-OHdG owing to its hydrophilically ultraflat and chemically stable surface. We also investigated the performance of HPLC with an electrochemical detection (HPLC-ECD) system using our nanocarbon film electrode. The detection limit for 8-OHdG at the nanocarbon film electrode was 3 nM, which was superior to the detection limit of the GC electrode (7.2 nM). Furthermore, this electrode was more suitable for use in a urinary 8-OHdG experiment than the GC electrode. The concentration of urinary 8-OHdG in the urinary sample was 8.30 nM. These results indicate that this HPLC-ECD system with our nanocarbon film electrode enables us to realize an accurate, sensitive, reproducible and easy to use analysis technique.

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.

Development of a Sputtered Nanocarbon Film Based Microdisk Array Electrode for the Highly Stable Detection of Serotonin

AbstractWe report a nanocarbon film based microdisk array electrode with an extremely stable electrochemical response for measuring serotonin. The nanocarbon film was formed on a silicon substrate with an electron cyclotron resonance sputtering method, and the nanocarbon film based microdisk array electrode was fabricated using photolithography. The array electrode consists of 335 microdisks with a diameter of 10 µm. The center‐to‐center distance of each microdisk is 100 µm. The electrochemical properties of the nanocarbon film based microdisk array electrode are compared with those of a gold film based array electrode. Before microfabrication, both nanocarbon and gold film electrodes (both 2 mm in diameter) showed steady responses for the continuous voltammetric measurement of 1 µM of serotonin. Moreover, each microdisk array electrode exhibited a sigmoidal response. The obtained current densities were higher than those of conventional sized electrodes owing to the microelectrode effect. However, the current value at 0.45 V vs. Ag/AgCl at the gold film based microdisk array electrode decreased rapidly and fell to 30 % of its initial value after ten potential scans. In contrast, the nanocarbon film based microdisk array electrode decreased only 2 % under the same measurement condition. Despite the fact that there was more than 10 times the current density at the microelectrode, our nanocarbon film showed excellent performance in suppressing serotonin adsorption.

Made-to-order nanocarbons through deterministic plasma nanotechnology

Through a combinatorial approach involving experimental measurement and plasma modelling, it is shown that a high degree of control over diamond-like nanocarbon film sp3/sp2 ratio (and hence film properties) may be exercised, starting at the level of electrons (through modification of the plasma electron energy distribution function). Hydrogenated amorphous carbon nanoparticle films with high percentages of diamond-like bonds are grown using a middle-frequency (2 MHz) inductively coupled Ar+CH4 plasma. The sp3 fractions measured by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy in the thin films are explained qualitatively using sp3/sp2 ratios 1) derived from calculated sp3 and sp2 hybridized precursor species densities in a global plasma discharge model and 2) measured experimentally. It is shown that at high discharge power and lower CH4 concentrations, the sp3/sp2 fraction is higher. Our results suggest that a combination of predictive modeling and experimental studies is instrumental to achieve deterministically grown made-to-order diamond-like nanocarbons suitable for a variety of applications spanning from nano-magnetic resonance imaging to spin-flip quantum information devices. This deterministic approach can be extended to graphene, carbon nanotips, nanodiamond and other nanocarbon materials for a variety of applications.

Fabrication of carbon nanoneedle and carbon nanowall mixture film with two-step growth method

A novel nano-carbon electron emitter film has been developed on a stainless steel substrate by a direct current plasma chemical vapor deposition system. Samples grown at temperatures of 900 °C and 1100 °C showed different surface morphologies. It is found that a two-step growth process established by combining these two temperature growths together is suitable for deposition of a high density emitter array film. The as-grown nano-carbon film indicates a carbon nanoneedle and carbon nanowall mixture film, where the needle array density is about 3 × 10 7/cm 2. The I–V characteristic shows an emission current density of 228 mA/cm 2 at 2.5 V/μm, and the field emission current is stable, making it possibly suitable for developing field emission devices.

Direct electrochemical detection of DNA methylation for retinoblastoma and CpG fragments using a nanocarbon film

We describe the direct electrochemical detection of DNA methylation in relatively long sequences by using a nanocarbon film electrode. The film was formed by employing the electron cyclotron resonance sputtering method and had a nanocrystalline sp 2 and sp 3 mixed bond structure. Our methylation detection technique measures the differences between the oxidation currents of both 5-methylcytosine and cytosine without a bisulfite reaction or labeling. This was possible because this film electrode has a wide potential window while maintaining the high electrode activity needed to quantitatively detect both bases by direct oxidation. By optimizing the electrode surface conditions using electrochemical pretreatment, we used this film to quantitatively detect single cytosine methylation regardless of the methylation position in the sequence including retinoblastoma gene fragments (∼24mers). This was probably due to the high stability of this film electrode, which we achieved by controlling the surface hydrophilicity to suppress the fouling, and by maintaining electrode activity against all the bases. The pH optimization of the oligonucleotide measurements was also useful for distinguishing both bases separately. Under the optimized conditions, this film electrode allowed us to realize the quantitative detection of DNA methylation ratios solely by measuring methylated 5′-cytosine-phosphoguanosine (CpG) repetition oligonucleotides (60mers) with different methylation ratios.

Fabrication of electrochemically stable fluorinated nano-carbon film compared with other fluorinated carbon materials

We fabricated electrochemically stable fluorinated nano-carbon film that had an sp 2 and sp 3 hybrid nanocrystalline structure formed using the electron cyclotron resonance (ECR) sputtering method. This fluorinated ECR (F-ECR) nano-carbon film prepared with a short CF 4 plasma treatment has a high fluorine content (F/C:0.20) and a low oxygen content (O/C:0.02) on its surface and retains its original morphology. This F-ECR nano-carbon is capable of a lower capacitance current, and a wider potential window than untreated ECR nano-carbon. The electron transfer rates at an F-ECR electrode are as high as those of untreated carbons for Ru ( NH 3 ) 6 2 + / 3 + , whereas they are much slower than those of untreated ECR nano-carbon for Fe 2+/3+ and Fe ( CN ) 6 3 - / 4 - owing to its selective sp 2 fluorination. These slow electron transfer rates for Fe 2+/3+ and Fe ( CN ) 6 3 - / 4 - are maintained during potential cycles due to its robust nanocrystalline structure. In contrast, these slow electron transfer rates were easily recovered for fluorinated glassy carbon under same condition. Furthermore, a smaller fluorination effect was observed for polycrystalline boron-doped diamond owing to the low reactivity of its sp 3 bonds. Our ECR nano-carbon film is suitable for the effective fabrication of a fluorinated surface while maintaining a relatively active electrochemical interface and excellent stability.

Electrochemical Properties of Fluorinated Nano-carbon Film Compared with Other Carbon Materials

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Control of a Nano-carbon Film Electrode Surface for Highly Sensitive Detection of the Biomolecules

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Controllable electrode activities of nano-carbon films while maintaining surface flatness by electrochemical pretreatment

A carbon film consisting nanocrystallites with mixed sp 2 and sp 3 bonds formed by using the electron cyclotron resonance (ECR) sputtering method was studied with respect to the changes in characteristics caused by electrochemical pretreatment (ECP). Unlike glassy carbon, our sputtered nanocrystalline carbon film deposited at an acceleration voltage of 75 V (ECR-75 nano-carbon film) largely retained its surface flatness after the ECP. This robust surface could be caused by an increase of 42% in the sp 3 carbon realized by increasing the acceleration voltage during sputtering. The electrode activity of ECR-75 nano-carbon film was improved for surface sensitive species including Fe 3+/2+ unlike the boron doped diamond (BDD) electrode. This is because a sufficient quantity of surface sp 2 bonds remained and because the introduction of surface oxygen-containing groups is more efficient than with the BDD electrode. With pretreated ECR-75 nano-carbon film, the peak potential of glutathione was reduced solely due to the increase in the surface hydrophilicity with a sufficient quantity of surface sp 2 bonds, thus achieving the lowest detection limit (0.4 μM) ever obtained with carbon electrodes. We also achieved the stable measurement of 30 μM of serotonin (20 times) without the electrode surface fouling found with other electrodes.

Nanocarbon Film as a Percolation Network for Nanocarbon/Polymer Composites

Starting with a nanocarbon film, which has some special characteristics, the present study uses this film as a cluster of connected particles that induces the percolation of electrical carrier in composites. The composite is formed through the free infiltration of the polymer through the filler’s aggregates. This method forms nanocarbon/polymer composites which have an electrical conductivity more than three orders of magnitude greater than those prepared by mixing.