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Text from PDF Page: 001ANALYTICAL SCIENCES SEPTEMBER 2020, VOL. 36 1113 2020 © The Japan Society for Analytical Chemistry Electrochemical Detection of Curcumin in Food with a Carbon Nanotube-Carboxymethylcellulose Electrode Ryotaro WADA,* Shota TAKAHASHI,* Hitoshi MUGURUMA,*† and Naomi OSAKABE** *Graduate School of Engineering and Science, Shibaura Institute of Technology, 3-7-5 Toyosu, Koto, Tokyo 135–8548, Japan **Department of Bioscience and Engineering, College of Systems Engineering and Science, Shibaura Institute of Technology, 307 Fukasaku, Minuma, Saitama 337–8570, Japan Herein, an electrochemical method is presented for the detection of curcumin in food using a carbon nanotube (CNT)- carboxymethylcellulose (CMC) electrode. The CNT-CMC electrode exhibited ideal characteristics for curcumin detection, namely, a high response current and adequate peak separation toward curcumin oxidation. Cyclic voltammetry revealed two oxidation peaks. In the first scan, only the irreversible peak (Peak I) was observed at a higher potential. In the second scan, the reversible redox peak pairs (Peaks II and II′) appeared at lower potentials, and the potential of Peak I was decreased. Peak I corresponded to oxidation of the hydroxyl groups of the benzene ring to the catechol group via a phenoxy radical, while Peaks II and II′ indicated the redox loop system of the generated catechol group. The current at Peak II was used to quantify the concentration of curcumin in the linear range of 1 – 48 μM and detection limit of 0.084 μM. The concentrations of curcumin determined by the CNT-CMC electrode in real food samples were consistent with those determined by high-performance liquid chromatography. Keywords Carbon nanotube, cyclic voltammetry, curcumin, redox reaction (Received January 22, 2020; Accepted April 24, 2020; Advance Publication Released Online by J-STAGE May 1, 2020) Introduction Curcumin, chemically called 1,7-bis(4-hydroxy-3-methoxyphenyl)- 1,6-heptadieno-3,5-dinone, is a natural polyphenol and a yellow pigment obtained from the rhizome of turmeric (Curcuma longa Linn.). Its chemical structure is shown in Fig. 1. It is often used in various cuisines as a spicing, flavoring, or coloring agent. The intake of curcumin has numerous health advantages, including anti-tumour, anti-arthritic, anti-inflammatory, anti- cancer, and anti-HIV activities, and the reduction of obesity.1,2 These effects are attributed to the antioxidant capacity or scavenging of reactive oxygen species by curcumin. Curcumin can chelate various metal ions. Several methods have been reported for the determination of curcumin, such as spectroscopy,3 resonance light scattering,4 and high-performance liquid chromatography (HPLC).5 However, these methods require bulky apparatus and are sophisticated, time-consuming, and expensive. Based on these drawbacks, an electrochemical method for the detection and quantification of curcumin is promising. However, there are only a few reports concerning electrochemical analysis of curcumin, and the electrochemistry of curcumin is still unclear.6–12 In this study, carbon nanotube (CNT)-based electrodes were chosen for the electrochemical analysis of curcumin because of their excellent electrochemical behavior. There are many reports concerning polyphenol analysis with CNT-base electrodes.13–16 † To whom correspondence should be addressed. E-mail: email@example.com In contrast, there has been only one report on curcumin sensing with CNT-based electrodes,9 likely because of the hydrophobic nature of the CNT electrode and the fact that as-synthesised CNT is an agglomeration of molecules. In a previous study, we reported on an electrode with CNT-carboxymethyl cellulose (CMC) dispersion.17,18 Herein, we have attempted to expand the applicability of the CNT-CMC electrode. In the CNT-CMC dispersion, the negatively charged CMC molecules unbundle the CNTs by electrostatic repulsion. Additionally, a large amount of the CMC surfactant blocks the electronic signal from the CNT surface. In both cases, the sheet and/or electron transfer resistance of the CNT film increase. CMC is superior to the other surfactants, namely, cellulose and sodium cholate, because the optimum mass ratio [CMC]/[CNT] is 3, which is smaller than [cellulose]/[CNT] = 5 and [sodium cholate]/[CNT] = 20.19,20 Therefore, dispersion by CMC is the most efficient method for thin-film formation while maintaining the conductivity and catalytic ability of the CNTs. The CNT-CMC thin film electrode is expected to produce a well-defined and highly reproducible electrochemical signal along with a low background current, and exhibits high stability toward curcumin. Fig. 1 Molecular structure of curcumin.
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