(Invited) Nickel Nanoparticles Modified Carbon Film Electrodes for Detection of Sugars
Authors: Niwa Osamu 
Published: February 2024

Metal nanoparticles such as Pt, Au, Ni and Cu have been employed to detect various analytes including hydrogen peroxide, alcohol and sugar. Among these metal nanoparticles, Ni and Cu nanoparticles show excellent electrocatalytic activity for oxidizing sugars in alkaline solution. We employed co-sputtering and plating technique to fabricate nanostructured electrodes for enhancing electrocatalytic activity for oxidation of sugars. First example is a metal hererodimer modified carbon film electrodes. The metal nanoparticles embedded carbon film electrodes was fabricated by unbalanced magnetron (UBM) sputtering and then plated different metal nanoparticles selectively only on the embedded metal nanoparticles by utilizing overpotential difference between carbon and metal nanoparticles surfaces. Using this technique, various combinations of metals are available to fabricate vertically oriented heterodimers embedded in the carbon films. In fact, we succeeded to fabricated Ni(upper)@Pd(lower), Pt@Pd, Au@Pd, Ni@Au, Pt@Au and Pd@Au heterodimers partially embedded in the carbon film. Among these heterodimers, Ni@Pd heterodimer embedded carbon film electrode shows much higher redox reaction of Ni(OH)2 covered on the Ni nanoparticles surface compared with that on the Ni nanoparticles without Pd. The NiOOH formed by electrochemical oxidation shows much higher electrocatalytic activity for glucose compared with that formed on Ni nanoparticles modified carbon film electrode. Also, the Ni@Pd heterodimers are mechanically very stable and most of the heterodimers remained on the surface after ultrasonication treatment because surface Ni nanoparticles attached strongly to Pd nanoparticles embedded in the carbon film. In contrast, almost all Ni nanoparticles deposited on pure carbon film were detached from carbon surface after ultrasonication.
The second example is a nitrogen terminated carbon film modified with Ni nanoparticles by plating. Carbon films were fabricated by UBM or RF sputtering methods and then introduced nitrogen containing functional groups. Then Ni nanoparticles were deposited by plating. The supporting effect of a N-doped carbon film induced superior crystallinity in plated Ni@Ni(OH)2 nanoparticles, which was confirmed by HAADF-STEM-EDS. This realized a much higher regeneration rate of catalytic sites (NiOOH) , leading to higher oxidation current for maltopentaose, which is well known oligosaccharide. Also, the overpotential of maltopentaose oxidation decreased significantly due to the effect of the electrostatic interaction between Ni nanoparticles and maltopentaose in the alkaline solution at pH 12.7. We also studied dependence of nitrogen concentration in the carbon film on regeneration rate of NiOOH and glucose oxidation. Both regeneration rate and electrocatalytic current of glucose oxidation increased with increasing nitrogen concentration from 0 to 3.1 %. With optimized nitrogen concentration, we could measure glucose from 25 µM to 400 µM. The enhanced activity of Ni nanoparticles could be advantageous to develop enzyme free biosensor or fuel cells using organic compounds such as sugars and oligosaccharides.
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