Controlling Surface Oxygen Concentration of a Nanocarbon Film Electrode for Improvement of Target Analytes

Abstract

A nanocarbon film consisting of nanocrystallites with mixed sp 2 and sp 3 bonds formed by unbalanced magnetron sputtering was studied with respect to the changes in characteristics caused by surface oxygen concentration. Electrochemical pretreatment (ECP) was conducted to change the surface oxygen concentration of the nanocarbon film. X-ray photoelectron spectroscopy (XPS) measurements revealed that nanocarbon films with different amounts of surface oxygen could be prepared. In addition, we observed no significant increase of surface roughness (R a) at the angstrom level after ECP, owing to stable structure containing 40 % of sp 3 bonds. Electrode characteristics including potential window, and electrochemical properties for some redox species such as Ru(NH 3) 6 3+/2+ , Fe(CN) 6 3-/4and some biomolecules were investigated. The anodic potential limit became wider and ΔE p of Fe(CN) 6 3-/4became smaller at the treated nanocarbon film electrode than those of the as-deposited nanocarbon film electrode. Based on these results, we realized to measure uridylic acid (UMP) and inosine triphosphate (ITP) with high oxidation potential by direct oxidation, which was difficult to measure at the as-deposited nanocarbon film electrode.

Suppression of Surface Oxygen on Nanocarbon Film Electrodes for Maintaining Electrode Activity

“…In order to obtain nanocarbon film electrodes with different and lower surface oxygen concentrations, we used two treatment methods. One was an ECP that had already been reported; 13 the other was a UV/O3 treatment. 16 The ECP treatment was conducted using cyclic voltammetry (CV), 15 cycles between 0 and 2.3 V, at a scan rate of 0.1 V s -1 in a 50 mM phosphate buffer (PB) solution (pH 7.0) at room temperature.…”

“…Electrochemical measurements of Ru(NH3)6 2+/3+ , Fe(CN)6 3-/4-and Fe 2+/3+ were conducted using CV under the same conditions as in the previous report. 13 Electrochemical measurements of H2O2 (0.2 mM) were conducted using CV, measured in a deoxygenated 50 mM phosphate buffer (PB) (pH 7.0). This electrolyte solution was purged with pure Ar gas for 20 min prior to the measurements.…”

“…The ECP treatment can significantly increase the surface oxygen concentration, whereas the surface roughness also increases gradually as the number of cycles increases. 13 In contrast, the UV treatment could not significantly increase the surface oxygen concentration of the nanocarbon films, but could give a low surface oxygen concentration without losing the surface flatness. 16 This fact is attributed to the difference in the amount of energy given to the electrode surface.…”

“…As described in a later section, these differences were numerically valid and, therefore, the UV treatment could control the lower surface oxygen concentration than the ECP treatment reported in our previous study. 13 With the difference in introduced oxygen functional groups between the UV and ECP treatments, we attempted to analyze the O 1s spectra, but no large difference in the spectra shape was observed. Therefore, we consider that the types of oxygen functional groups of both of the treated nanocarbon films are almost the same.…”

“…More recently, we also reported that controlling the surface oxygen concentration (typically 0.1 of O/C) on the nanocarbon film allowed us to measure inosine triphosphate and uridylic acid with higher oxidation potentials. 13 On the other hand, we consider that not all of the analytes prefer an oxygenrich nanocarbon surface.…”