Analytical Sciences

An sp² and sp³ Hybrid Nanocrystalline Carbon Film Electrode for Anodic Stripping Voltammetry and Its Application for Electrochemical Immunoassay

Ryoji KURITA,* Kohei NAKAMOTO,*,** Yuko SATO,* Tomoyuki KAMATA,* Akio UEDA,* Dai KATO,* Shigeru HIRONO,*** and Osamu NIWA*,**

*National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 6, 1-1-1 Higashi, Tsukuba, Ibaraki 305–8566, Japan
**Graduate School of Pure and Applied Science, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki 305–8573, Japan
***MES Afty Corporation, 2-35-2 Hyoe, Hachioji, Tokyo 192–0918, Japan

A hybridized nanocrystalline carbon film electrode consisting of sp² and sp³ bonds was investigated to reveal the reduction properties of Cd²⁺ and for application as a highly sensitive and reliable electrochemical immunoassay. Conductive nanocrystalline carbon film consisting of about 60% sp² and 40% sp³ bonds was fabricated using electron cyclotron resonance (ECR) sputtering equipment, and then the Cd²⁺ concentrations were measured with an ECR sputtered carbon (ECR nano-carbon) electrode by employing an anodic stripping voltammetry (ASV) technique. The preconcentrated Cd was analyzed with Kelvin probe force microscopy and energy dispersive X-ray spectroscopy while observing the morphology change with an atomic force microscope and a scanning electron microscope. The preconcentrated Cd on the ECR nano-carbon electrode was revealed to be a thin sheet structure, which was significantly different from the Cd on a conventional carbon material that grows with a coralloid structure. The background current during an ASV measurement maintains a low level equivalent to that found with boron-doped diamond because the surface of the ECR nano-carbon is robust and angstrom-level flat. The carbon-electrode performance for ASV was improved by controlling its structure at a nanometer scale without any metal doping or coating. Finally, the ECR nano-carbon was used for biomolecular determination by electrochemical immunoassay with a CdSe nanoparticle label. Electrochemical immunoassay results were successfully obtained with the ECR nano-carbon, and they correlated well with fluorescence results obtained for CdSe nanoparticles.

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