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Sensors 2018, 18(7), 2178; https://doi.org/10.3390/s18072178

Role of Carboxyl and Amine Termination on a Boron-Doped Diamond Solution Gate Field Effect Transistor (SGFET) for pH Sensing

1
Faculty of Science and Engineering, Waseda University, Tokyo 169-8555, Japan
2
Institute of Materials and Systems for Sustainability, Nagoya University, Furo-Cho, Chikusa-ku, Nagoya 464-8603, Japan
3
Research and Development Department/Innovation Center, MK-Headquarters, Yokogawa Electric Corporation, Tokyo 180-8750, Japan
4
The Kagami Memorial Laboratory for Materials Science and Technology, Waseda University, 2-8-26 Nishiwaseda, Shinjuku, Tokyo 169-0051, Japan
*
Author to whom correspondence should be addressed.
Received: 18 May 2018 / Revised: 30 June 2018 / Accepted: 4 July 2018 / Published: 6 July 2018
(This article belongs to the Section Biosensors)
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Abstract

In this paper, we report on the effect of carboxyl- and amine terminations on a boron-doped diamond surface (BDD) in relation to pH sensitivity. Carboxyl termination was achieved by anodization oxidation in Carmody buffer solution (pH 7). The carboxyl-terminated diamond surface was exposed to nitrogen radicals to generate an amine-terminated surface. The pH sensitivity of the carboxyl- and amine-terminated surfaces was measured from pH 2 to pH 12. The pH sensitivities of the carboxyl-terminated surface at low and high pH are 45 and 3 mV/pH, respectively. The pH sensitivity after amine termination is significantly higher—the pH sensitivities at low and high pH are 65 and 24 mV/pH, respectively. We find that the negatively-charged surface properties of the carboxyl-terminated surface due to ionization of –COOH causes very low pH detection in the high pH region (pH 7–12). In the case of the amine-terminated surface, the surface properties are interchangeable in both acidic and basic solutions; therefore, we observed pH detection at both low and high pH regions. The results presented here may provide molecular-level understanding of surface properties with charged ions in pH solutions. The understanding of these surface terminations on BDD substrate may be useful to design diamond-based biosensors. View Full-Text
Keywords: boron-doped diamond; carboxyl termination; amine termination; pH sensitivity; polycrystalline diamond; electrolyte-solution-gate field-effect-transistor boron-doped diamond; carboxyl termination; amine termination; pH sensitivity; polycrystalline diamond; electrolyte-solution-gate field-effect-transistor
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Falina, S.; Kawai, S.; Oi, N.; Yamano, H.; Kageura, T.; Suaebah, E.; Inaba, M.; Shintani, Y.; Syamsul, M.; Kawarada, H. Role of Carboxyl and Amine Termination on a Boron-Doped Diamond Solution Gate Field Effect Transistor (SGFET) for pH Sensing. Sensors 2018, 18, 2178.

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