Abstract
In this research, nickel films with different thicknesses were deposited by electron-beam evaporation on nitrogen-doped nanodiamond (NND) substrates and then reacted to nickel hydroxide, Ni(OH)2 by cyclic voltammetry (CV) in alkaline solution. The morphology of Ni(OH)2 modified NDD electrodes was composed of sponge-like micro-structure and a large number of nano-spheres. The Ni(OH)2-NND exhibited high electrocatalysis ability to electroinactive amino acids such as D-serine (Ser), L-glycine (Gly), L-aspartic acid (Asp) and 讪-aminobutyric acid (GABA), which are key neurotransmitters in central nervous system of mankind. In addition, glucose could be also electrocatalyzed with great ease on Ni(OH)2-NND electrodes. The reaction mechanisms of above molecules on Ni(OH)2-NND were all determined to be the diffusion-controlled reaction by CV and chronoamperometry (CA). This outstanding electrocatalysis behavior could be ascribed to promoted heterogeneous diffusion by the feature structure and large active surface area of Ni(OH)2-NND. Besides, the Ni(OH)2-NND could be applied to instant measurements without any complex pre-treatment for Ni(OH)2 enrichment. The dependence of Ni thickness on the electrocatalysis of Ni(OH)2-NND was investigated, and the result showed that the 150 nm Ni was superior to other thicknesses for detection to above molecules. The measurements conducted by CV in alkaline solution were used to define the sensitivities and linear dynamic ranges of those amino acids. The sensitivity to Ser response was up to 2.5 贡AmΜ-1cm-2 within the range from 20 to 350 贡M, and the limit of detection (LOD) was estimated to be 3.8 贡M at a signal-to-noise ratio of 3. As for glucose sensing, the sensitivity was around 3200 贡AmΜ-1cm-2 within the range from 20 to 1000 贡M and 1406 贡AmΜ-1cm-2 from 1 to 9 mM, with LOD of 1.5 贡Μ. The electrode also exhibited stable responses to glucose while interfered by species including ascorbic acid (AA), uric acid (UA) and acetaminophen (AC) which are common compounds in blood samples. Besides, the electrodes were stored in air for more than two months to examine the long-term stability of electrodes. The Ni(OH)2-NND electrodes were characterized by scanning electron microscopy and Raman spectroscopy.