Electrochemical detection of glucose was achieved at a glucose oxidase (GOx)-cobalt phthalocyanine (CoPc)-modified boron-doped diamond (BDD) electrode without any additional electron mediator in the electrolyte solution. The surface of the hydrogen-terminated BDD thin film prepared by microwave plasma-assisted CVD was modified with 4-vinylpyridine (4VP) via photochemical modification. The 4VP-BDD was then immersed in a CoPc solution to obtain CoPc-BDD. A poly(p-phenylenediamine) (PPD) thin film containing GOx was coated on the CoPc-BDD electrode surface via electropolymerization. At the GOx/PPD-CoPc-BDD electrode, anodic current for glucose oxidation was observed with a sigmoidal voltammetric curve, indicating successful electron mediation of H2O2 generated as the result of glucose oxidation at GOx. The signal-to-background ratio for voltammetric current of glucose detection was larger at the GOx/PPD-CoPc-BDD electrode than at the GOx/PPD-modified platinum electrode due to the smaller background current of the modified BDD electrode. 1. Introduction Highly boron-doped diamond (BDD) electrodes have been known to be a promising electrode material for sensitive electroanalysis based on the wide potential window and low background current as well as physical and chemical stability and biocompatibility . Glucose is a compound, whose concentration is one of the most desired to be determined via electrochemical methods in relation to increasing demands for diabetes care . In order to use BDD electrode for glucose detection, one should modify the surface with catalysts or enzymes due to the large overpotential for direct glucose oxidation at unmodified BDD electrodes. For glucose detection at BDD electrodes using electrocatalysts, Cu [3–5] and Ni [6–9] have been used for modification of the surfaces. Immobilization of particles or line patterns of these metals with micrometer or nanometer scale onto BDD surface enables sensitive glucose detection with low background current. On the other hand, BDD electrodes modified with glucose oxidase (GOx) [10–13] are advantageous because of their selectivity and sensitivity of the glucose molecule. In some cases, additional mediators, such as ferrocene carboxylic acid , were employed for glucose detection at GOx-modified BDD electrodes. Glucose detection without any additional reagents to samples is possible for simple analysis systems, and especially for monitoring concentration. Hydrogen peroxide is a product of glucose oxidation at GOx and thus can act as an electroactive mediator for electrochemical detection
T. Watanabe, T. A. Ivandini, Y. Makide, A. Fujishima, and Y. Einaga, “Selective detection method derived from a controlled diffusion process at metal-modified diamond electrodes,” Analytical Chemistry, vol. 78, no. 22, pp. 7857–7860, 2006.
M. Chiku, T. Watanabe, and Y. Einaga, “Fabrication of Cu-modified boron-doped diamond microband electrodes and their application for selective detection of glucose,” Diamond and Related Materials, vol. 19, no. 7–9, pp. 673–679, 2010.
K. Ohnishi, Y. Einaga, H. Notsu et al., “Electrochemical glucose detection using nickel-implanted boron-doped diamond electrodes,” Electrochemical and Solid-State Letters, vol. 5, no. 3, pp. D1–D3, 2002.
T. Watanabe and Y. Einaga, “Design and fabrication of nickel microdisk-arrayed diamond electrodes for a non-enzymatic glucose sensor based on control of diffusion profiles,” Biosensors and Bioelectronics, vol. 24, no. 8, pp. 2684–2689, 2009.
K. E. Toghill, L. Xiao, M. A. Phillips, and R. G. Compton, “The non-enzymatic determination of glucose using an electrolytically fabricated nickel microparticle modified boron-doped diamond electrode or nickel foil electrode,” Sensors and Actuators, B, vol. 147, no. 2, pp. 642–652, 2010.
L. Su, X. Qiu, L. Guo, F. Zhang, and C. Tung, “Amperometric glucose sensor based on enzyme-modified boron-doped diamond electrode by cross-linking method,” Sensors and Actuators, B, vol. 99, no. 2-3, pp. 499–504, 2004.
K. B. Male, S. Hrapovic, and J. H. T. Luong, “Electrochemically-assisted deposition of oxidases on platinum nanoparticle/multi-walled carbon nanotube-modified electrodes,” Analyst, vol. 132, no. 12, pp. 1254–1261, 2007.
M. J. Song, J. H. Kim, S. K. Lee et al., “Pt-polyaniline nanocomposite on boron-doped diamond electrode for amperometic biosensor with low detection limit,” Microchimica Acta, vol. 171, no. 3-4, pp. 249–255, 2010.
T. Kondo, A. Tamura, and T. Kawai, “Cobalt phthalocyanine-modified boron-doped diamond electrode for highly sensitive detection of hydrogen peroxide,” Journal of the Electrochemical Society, vol. 156, no. 11, pp. F145–F150, 2009.
T. A. Ivandini, R. Sato, Y. Makide, A. Fujishima, and Y. Einaga, “Pt-implanted boron-doped diamond electrodes and the application for electrochemical detection of hydrogen peroxide,” Diamond and Related Materials, vol. 14, no. 11-12, pp. 2133–2138, 2005.
T. Kondo, S. Aoshima, K. Honda, Y. Einaga, A. Fujishima, and T. Kawai, “Fabrication of covalent SAM/Au nanoparticle/boron-doped diamond configurations with a sequential self-assembly method,” Journal of Physical Chemistry C, vol. 111, no. 34, pp. 12650–12657, 2007.
P. N. Mashazi, K. I. Ozoemena, and T. Nyokong, “Tetracarboxylic acid cobalt phthalocyanine SAM on gold: potential applications as amperometric sensor for H2O2 and fabrication of glucose biosensor,” Electrochimica Acta, vol. 52, no. 1, pp. 177–186, 2006.
H. H. Weetall, D. W. Hatchett, and K. R. Rogers, “Electrochemically deposited polymer-coated gold electrodes selective for 2,4-dichlorophenoxyacetic acid,” Electroanalysis, vol. 17, no. 19, pp. 1789–1794, 2005.
S. J. Killoran and R. D. O'Neill, “Characterization of permselective coatings electrosynthesized on Pt-Ir from the three phenylenediamine isomers for biosensor applications,” Electrochimica Acta, vol. 53, no. 24, pp. 7303–7312, 2008.