Nanocarbon Film Electrodes Can Expand the Possibility of Electroanalysis

Electroanalysis is a way to detect analytes by measuring the current or potential on an electrode interface during a redox reaction. However, analytes that can be detected by the methods at conventional electrode materials have been limited due to a narrow measurable potential range and insufficient sensitivity for trace analytes. This article reviews our recently developed nanocarbon film electrodes for detecting trace amounts of various analytes. We have been studying nanocarbon film electrodes formed by electron cyclotron resonance sputtering or an unbalanced magnetron sputtering method. The film provides a nanocrystalline sp(2) and sp(3) mixed bond structure with an atomically flat surface (surface roughness of 0.05 - 0.1 nm) and high conductivity without doping. The film electrode has excellent properties, including a low background current, a wide electrochemical potential window, and little surface fouling, while maintaining relatively high electrode activity. These characteristics allow the detection of various analytes, especially ultratrace amounts of biomolecules. The nanocarbon film surface can be also easily modified with other atoms (oxygen or fluorine) without losing its ultraflatness that provides various nanocarbon film electrodes with hydrophilic and/or hydrophobic surfaces. For example, the hydrophilic nanocarbon film electrode can quantitatively measure various biomolecules (e.g., all DNA bases and cerebral gliotransmitter), which are difficult to measure at conventional carbon electrodes. In contrast, a fluorinated nanocarbon film is successfully used for the selective detection of lipophilic antioxidants (vitamin E) in combination with bicontinuous microemulsion. Moreover, we developed a new carbon film electrode material with surface nanostructures to realize efficient direct electron transfer (DET) with enzymes that can construct DET-type biosensors. Our study has expanded the possibility using electrochemical methods, and is expected to be applied to many practical measurement devices. These could find applications in various fields, such as drinks, foods, environmental and biochemical substances.