Gas Ion Implanted Electrode Prepared By the Electron Cyclotron Resonance Ion Source and Catalytic Effects
Authors: Won Mi-Sook , Lee Dong-Wook , Yoon Jang-Hee , Park Jin Yong , Shim Yoon-Bo 
Published: February 2020

Although diverse catalytic materials have been reported, there are still demands for specific and highly catalytic materials. One of the ways to get catalytic property is surface modification of materials by ion implantation that can be used for various applications. A few studies have been reported using ions or organic group implantation to get specific functionalized surfaces, to date [1,2]. In the present study, the electrochemical properties of the gas ions implanted glassy carbon electrode (GCE) were studied for the application to sensors. Two parameters of ion energy and ion flux are mainly considered in the implantation process. The current density of the ion mainly depends on the plasma density, which in turn is directly proportional to the number of energetic ions implanted on the substrate. The electrocatalytic activities of the modified electrode are preferentially driven by the chemical defects or the morphological affect on the surface, which not only improve the interaction between the analytes and the electrode surface, but also make the surface more hydrophilic resulting the suppression of biomolecular adsorption. Thus, an ion implanted electrode can be potentially applied as a selective electrochemical sensor for various biomolecules.
Various gas ions were examined and compared for the catalytic property in the present experiment. Of these ions, the catalytic performance for the oxidation of organic molecules by O+ ion was the best and it was studied for the sensor application. Where, the substrate was implanted at beam energy of 2 keV using the 28 GHz electron cyclotron resonance ion source (ECRIS). The ion beam current density was kept below 330 μA to prevent ion irradiation heating of the specimen. The pressure in the target chamber during ion implantation was kept at about 1 × 10-4 Pa. Optimizations of experimental conditions for the analysis of dopamine were carried out in terms of pH (7.4), temperature (60 oC), implantation beam energy (2 keV), and detection potential (+0.25 V) in amperometry.
Analytical performance of the O+ ion implanted GC electrode was examined under the optimized conditions. The CVs were recorded for bare and implanted electrodes in a 0.1 M phosphate buffer solution (PBS, pH 7.4) containing 0.1 mM dopamine between 0.0 and +1.0 V (vs. Ag/AgCl). Very clear redox peaks were observed at +0.195/+144.6 mV by the catalytic redox of dopamine at the ion implanted GCE, while small redox peaks at +250.7/+138.2 mV were appeared at bare GCEs. The calibration plot for the ion implanted GC electrode was obtained in different concentrations of dopamine using chronoamperometry. After the addition of dopamine in the measuring buffer solution, 95% of steady state current was achieved after about 3s. A calibration plot shows the linear dynamic range between 50.0 nM and 0.3 mM. The linear regression equation is expressed as follows: Ip (μA) = 0.0017 (± 0.0021) + 0.0107 (± 0.0001) [dopamine, μM], with a correlation coefficient of 0.999. The detection limit for dopamine was determined to be 10.0 ± 2.5 nM (RSD <5%) based on measurements performed five times for the standard deviation of the blank solution (95% confidence level, k = 3, n = 5). This detection limit is lower than that previously reported for dopamine using the other modified electrode [3]. The strategy described here has many attractive features such as simplicity, rapidity, no requirement for a specific label (i.e., a fluorescent or reactive moiety), and low cost. In addition, no interference from common metabolites present in the real matrix. Thus, the present method could be effectively useful in clinical diagnoses, drug toxicity analyses, and pharmacological examinations.
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