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ozone modification
Talanta 192 (2019) 40–45
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Improvement of electrochemical performance of screen-printed carbon electrodes by UV/ozone modification
T
⁎
Jing Wanga, Zheng Xua, , Mengqi Zhanga, Junshan Liua, Hongqun Zoub, Liding Wangb a b
Dalian University of Technology, Key Laboratory for Micro/Nano Technology and System of Liaoning Province, Dalian 116085, China Dalian University of Technology, Key Laboratory for Precision and Non-traditional Machining Technology of Ministry of Education, Dalian 116085, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Screen-printed carbon electrode UV/ozone Electron transfer
Screen-printed carbon electrode (SPCE) has been widely used in electrochemical (EC) field. Nevertheless, compared with some metal electrodes, SPCE is not sensitive to small amounts of reagent owing to its relatively low electron transfer rate. In this paper, the UV/ozone modification was proposed to treat SPCE to improve its electron transfer rate and EC performance. The changes of SPCE morphology and composition induced by UV/ ozone modification were investigated in detail. The results show that the improved electron transfer rate can be mainly attributed to the increase of oxygen functional groups. To clarify the essential EC characterization, potentiodynamic polarization and electrochemical impedance spectroscopy of K3[Fe(CN)6] was studied. Furthermore, to demonstrate the improved EC effect, two typical samples: small-molecule K3[Fe(CN)6] and macro-molecule nicotinamide adenine dinucleotide (NADH), were measured by cyclic voltammetry. After UV/ ozone modification, the oxidation potential and peak current responses to K3[Fe(CN)6] and NADH were obviously improved in both original and CNT-modified SPCEs. Whereas, the original SPCE is more suitable to measure macromolecule NADH rather than CNT-modified one as the oxidative products of NADH are more likely to adsorb on rough surface.
1. Introduction Screen-printed carbon electrode (SPCE) has been widely used in electrochemical (EC) field, owing to its excellent properties, such as low background current, wide potential window, high chemical stability etc [1–5]. Furthermore, SPCE is inexpensive as disposable unit [6]. However, compared with platinum electrode etc, SPCE is not sensitive to small amounts of reagent due to its relatively low electron transfer rate which limits its application [7,8]. In order to improve the EC performance of SPCE, several methods had been employed, including chemical treatment [9–11], EC activation [12,13], plasma treatment [14,15], surface modification with various catalysts [16,17] and nanomaterials [18–21]. For example, Wei et al. [9] modified SPCE by chemical treatment. SPCE was soaked into 3 M NaOH solution for 1 h, and then was anodized at 1.2 V in 0.5 M NaOH solution for 20 s. The peak to peak separation of modified SPCE for Fe(CN)63-/4- couple was reduced from 480 to 84 mV. Cui et al. [12] activated SPCE in saturated Na2CO3 solution at 1.2 V for 5 min, the peak to peak separation of activated SPCE for Fe(CN)63-/4- couple was reduced from 122 to 72 mV. Generally, chemical or EC activation of
SPCE utilizes anodization to increase the EC activity of SPCE through the increase of surface functionalities and roughness. However, these chemical methods are not fully suitable for SPCEs that are composed of counter/reference electrode made of silver or copper since these metals are more likely to be corroded by alkaline solution. On the other hand, the oxygen plasma treatment of SPCE can etch SPCE, and both vacuum pump and gas resource are indispensable to produce plasma too [22,23]. Herein, the method of UV/ozone modification is presented to improve electron transfer rate and EC performance of SPCE. Both original and carbon nanotubes (CNT) modified SPCEs were treated with UV/ ozone. The changes of SPCE morphology and composition induced by UV/ozone modification were investigated. The improved EC responses of modified SPCEs were evaluated by the measurement of two typical electroactive samples: small-molecule K3[Fe(CN)6] and macro-molecule nicotinamide adenine dinucleotide (NADH). The results show that UV/ ozone modification is helpful to improve the EC performance of SPCEs. Compared with other methods, UV/ozone modification is cost-effective since it doesn’t require both extra reagents and external gas source. In addition, the price of UV/ozone cleaner is acceptable.
⁎ Correspondence to: Dalian University of Technology, School of Mechanical Engineering, Key Laboratory for Micro/Nano Technology, No.2 Linggong Road, Dalian City, Liaoning Province, China. E-mail address: [email protected] (Z. Xu).
https://doi.org/10.1016/j.talanta.2018.08.065 Received 18 May 2018; Received in revised form 19 August 2018; Accepted 27 August 2018 0039-9140/ © 2018 Elsevier B.V. All rights reserved.
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Fig. 1. Scanning electron micrographs of original SPCE (a) before and (b) after UV/ozone modification. Scanning electron micrographs of CNT-modified SPCE (c) before and (d) after UV/ozone modification. The red circles are for step-like carbon sheets.
2. Experimental section
3. Results and discussion
2.1. Materials
3.1. Investigation on the surface characteristics of SPCEs
Two kinds of SPCE strips: SPCE modified with CNT and original SPCE without CNT, were purchased from Dropsens. Both SPCE strips consist of a carbon electrode as working electrode, silver electrode as reference electrode, and another carbon electrode as counter electrode. NADH was purchased from Roche. NAD+ was purchased from SigmaAldrich. K3[Fe(CN)6] was purchased from Dalian Meilun. NADH and K3[Fe(CN)6] samples were freshly prepared in PBS (0.1 M, pH 7.4) and KCL (0.1 M) solutions respectively.
Surface morphology of original and CNT-modified SPCEs was investigated by SEM. A series of images were analyzed for each surface morphology (40 images). One image selected for each type of surface morphology is shown in Fig. 1. It can be seen that the step-like carbon sheets increase after UV/ozone modification of both original and CNTmodified SPCEs. This is because ozone or single oxygen molecules could slowly etch the carbon surface to form oxygen-containing groups which would let the carbon surface become rough [24]. Besides, some organic binders existed on the electrode surface can be removed via UV/ozone modification [25]. Therefore, the morphology of both original and CNT-modified SPCEs becomes rougher after modification. The change of chemical composition of original and CNT-modified SPCEs was investigated by XPS. As shown in Fig. 2, O1 s peak intensity obviously increases for both original and CNT-modified SPCEs after UV/ ozone modification. The ratio of O1 s increases from 0.04 to 0.13 for original SPCE and from 0.06 to 0.12 for CNT-modified one. The reason is that oxygen-containing functional groups were generated on SPCE surface [24]. Since the oxygen-containing groups on the SPCE surface can improve the wettability which could promote the diffusion-controlled process and thus enhance the electron transfer rate of SPCE [26]. The detailed change of oxygen atoms was further studied through Gaussian decompositions of O1 s spectra as follows. For original SPCE, there is only one C-O bond peak before UV/ozone modification. It becomes the mixture of C-O and C˭O bonds via UV/ozone modification, and the ratio of C-O and C˭O bonds are 37.8% and 62.2% respectively. For CNTmodified SPCE, the ratio of C-O and C˭O bonds are 45.9% and 54.1% before UV/ozone modification, and the ratio of C-O and C˭O bonds become to 53.7% and 46.3% via UV/ozone modification.
2.2. Apparatus A UV/ozone cleaner (144AX-220, JELIGHT Co., Ltd., USA) was used to modify SPCEs, in which a 10 mW/cm2 Hg lamp provided 185 and 254 nm UV light. The lamp was warmed for 15 min, and then SPCE strips were placed in chamber and modified at 6 cm distance from the Hg lamp for 5 min. In the process, oxygen molecules (O2) absorbed 185 nm UV light and formed ozone, then ozone molecules (O3) absorbed 254 nm UV light and broke into atomic oxygen (O). The electrochemical impedance spectroscopy (EIS) of SPCE was determinated with an impedance analyzer (E4990A, Keysight Co., USA). The surface morphology of SPCE was characterized by a scanning electron microscope (SEM, JSM-6360, LV JEOL Co., Japan). Chemical compositions of SPCE were analyzed by an X-ray photoelectron spectroscope (ESCALAB 250Xi, ThermoFisher Co., USA). All EC experiments were carried out with an electrochemical workstation (Reference 600 +, Gamry Co., USA).
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Fig. 2. O1s spectra and Gaussian decompositions of O1s spectra before and after UV/ozone modification for (a) original SPCE and (b) CNT-modified SPCE.
Therefore, the interfacial impedance was measured from 20 to 500 Hz. From Fig. 3, it can be seen that the impedances are decreased for both original and CNT-modified SPCEs by UV/ozone modification, and the interfacial impedance of CNT-modified SPCE is lower than that of original SPCE. The decrease of interfacial impedance is primarily contributed to the incremental C-O and C˭O bonds that can anchor H2O molecules via intermolecular bonding and then the interfacial reaction between SPCE and electrolyte was enhanced [27,28]. 3.3. Electrochemical tests 3.3.1. Measurement of essential EC characterizations To clarify the EC characterization of modified SPCEs, two EC methods: potentiodynamic polarization and EC impedance spectroscopy, were used. Both original and CNT-modified SPCEs were measured with 1 mM K3[Fe(CN)6] solution. Test of potentiodynamic polarization was performed after stabilization of open-circuit potential (OCP). And the test was carried out from −500–500 mV/OCP at a scanning rate of 0.1 mV s−1 [29]. Fig. 4(a) and (b) present the results for original and CNT-modified SPCEs respectively. It can be seen that the potential negative shift and the current density increase slightly after UV/ozone modification for both original and CNT-modified SPCEs. Higher current density or more negative potential means the UV/ozone modified SPCEs is of less EC resistance compared with the unmodified SPCEs [30]. EIS is a powerful technique to characterize the charge transfer
Fig. 3. Interfacial impedance of SPCEs before and after UV/ozone modification.
3.2. Measurement of interfacial impedance Since the interfacial impedance plays an important role in electron transfer process, it was measured with 10 mM NaCl solution. When the scanning rate is too high, the mass transfer rate can't keep up with the change of external potential, resulting in the saturation of EC reaction. Thus, limited by mass transfer, most EC detections are carried out in the relatively low frequency region. For example, the scan rate of cyclic voltammetry (CV) is often limited in the range of 10–100 mV s−1. 42
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Fig. 4. Potentiodynamic polarization curves of (a) original SPCE and (b) CNT-modified SPCE before and after UV/ozone modification.
Fig. 5. Nyquist plots of (a) original SPCE and (b) CNT-modified SPCE in a 1.0 mM K3Fe(CN)6 solution containing 0.1 KCl in the frequency range of 20 Hz to 100 kHz.
Fig. 6. Cyclic voltammograms of (a) 1 mM K3[Fe(CN)6] and (b) 1 mM NADH with original and CNT-modified SPCEs before and after UV/ozone modification.
Cyclic voltammograms (CVs) of 1 mM K3[Fe(CN)6] are shown in Fig. 6(a). For K3[Fe(CN)6], the scanning range is −0.3–0.5 V and the scanning rate is 50 mV s−1. From Fig. 6(a), the anodic potential peak (original SPCE: 200 mV, CNT-modified SPCE: 178 mV) is lower and the anodic current peak (original SPCE: 11.01 µA. CNT-modified SPCE: 12.62 µA) is higher for CNT-modified SPCE than that of original SPCE. After UV/ozone modification, the peak-to-peak potential separation (ΔEp) between oxidative (Epa) and reductive peak potentials (Epc) becomes narrower (original SPCE: from 170 to 112 mV, CNT-modified SPCE: from 108 to 90 mV), and anodic current becomes higher (original SPCE: from 11.01 to 12.97 µA, CNT-modified SPCE: from 12.62 to 14.58 µA). Compared with other methods, the peak-to-peak potential separation of K3[Fe(CN)6] on UV/ozone modified SPCE is narrower than that of oxygen plasma treated SPCE (from 440 to 156 mV) [14], and is comparable with that of chemical modified SPCEs [9,12]. CVs of 1 mM NADH are shown in Fig. 6(b). For NADH, the scanning
process at various electrode surfaces [25,31,32]. Here the EIS experiment was performed in a solution of 1 mM K3[Fe(CN)6] containing 0.1 M KCl with the frequency range from 20 Hz to 100 kHz. As shown in Fig. 5(a) and (b), there are two approximately linear curves in EIS Nyquist plots for both original and CNT-modified SPCEs. And the slopes of lines become lower via UV/ozone modification, indicating that the electron transfer becomes easier [33]. In addition, the linear relationship for both original and CNT-modified SPCEs shows that the EC process is mainly mass-diffusion controlled [34]. In summary, the electron transfer rate was obviously improved in both original and CNT-modified SPCEs via UV/ozone modification.
3.3.2. Test of the effect of UV/ozone modification on EC performance To evaluate the effect of UV/ozone modification on EC performance, the cyclic voltammetric behavior was investigated with two samples: small molecule K3[Fe(CN)6] and macromolecule NADH. 43
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Fig. 7. Amperometric response to K3[Fe(CN)6] concentration for (a) original SPCE and (b) CNT-modified SPCE before and after UV/ozone modification. (c) Amperometric response to NADH concentration for SPCEs before and after UV/ozone modification.
range is −0.2–0.7 V and the scanning rate is 50 mV s−1. The anodic peak current increases from 18.83 to 21.75 µA and the oxidation potential reduces from 320 to 292 mV for original SPCE via UV/ozone modification. Similarly, the anodic peak current increases from 16.85 to 17.68 µA and the oxidation potential reduces from 310 to 260 mV for CNT-modified SPCE. In the above measurement of K3[Fe(CN)6] and NADH, the improved amplitudes of anodic peak current are 17.81% and 15.53% respectively in original SPCE, 15.51% and 4.93% in CNT-modified SPCE. In terms of NADH, the improved amplitude of CNT-modified SPCE is relatively lower than that of original SPCE. It is due to NAD+ (EC oxidative product of NADH [35]), which has stronger adsorption for CNT-modified SPCE than original one since the CNT-modified SPCE has larger surface area [36]. The interfacial impedance can be used to demonstrate the difference of NAD+ adsorption on the original and CNT-modified SPCEs surface too. After SPCEs were immersed into 5 mM NAD+ solution for 30 min, the interfacial impedances increased by 12.53% and 30.33% in 20 Hz for original and CNT-modified SPCEs, respectively (original SPCE: from 1.34 to 1.51 KΩ mm−2, CNT-modified SPCE: from 0.54 to 0.71 KΩ mm−2). Because the improved amplitude of interfacial impedance is higher for CNT-modified SPCE than original one, more quantity of NAD+ is absorbed on the CNT-modified SPCE surface. And NAD+ might hinder the EC activity of SPCE and increase the resistance which will slow the total kinetic of reaction.
The cathodic peak currents is in the range of 2.63–74.07 µA before UV/ ozone modification and in the range of 2.97–80.44 µA after modification. Correspondingly, the sensitivity of cathodic peak current increases from 14.91 μA mM−1 with R2 0.9995–15.92 μA mM−1 with R2 0.9995. Fig. 7(c) presents the relationship between the peak current and the concentration of NADH before and after UV/ozone modification. For original SPCE, the peak current is in the range of 0.42–80.88 µA with R2 0.9946 before UV/ozone modification, and is in the range of 0.48–91.59 µA with R2 0.9998 after UV/ozone modification. The sensitivity of original SPCE increases from 17.45 μA mM−1 to 19.11 μA mM−1. For CNT-modified SPCE, the peak current is in the range of 0.35–80.62 µA with R2 0.9988 before UV/ozone modification, and is in the range of 0.45–83.65 µA with R2 0.9994 after modification. Correspondingly, the sensitivity of CNT-modified SPCE increases from 16.01 μA mM−1 to 16.33 μA mM−1 via UV/ozone modification. 4. Conclusion A simple and economic method of UV/ozone modification is proposed to improve the EC performance of SPCE. The improved EC performance is mainly attributed to the increase of the number of surface oxygen functional groups. After UV/ozone modification, the oxidation potential and peak current responses of K3[Fe(CN)6] and NADH were obviously improved in both original and CNT-modified SPCEs, which is agreement with the obtained results of potentiodynamic polarization and EIS with K3[Fe(CN)6]. In terms of NADH, it is noteworthy that NAD+ has stronger adsorption on CNT-modified SPCE than original one, which leads to a lower electron transfer rate for CNT-modified SPCE.
3.3.3. Improved EC response of SPCEs by UV/ozone modification To further verify the improved EC response of both original and CNT-modified SPCEs by UV/ozone modification, a series of K3[Fe (CN)6] concentrations varying from 0.156 to 5 mM and NADH concentrations varying from 0.019 to 5 mM were measured by cyclic voltammetry at the scan rate of 50 mV s−1. Fig. 7(a) presents the relationship between peak current and concentration of K3[Fe(CN)6] for original SPCE. The anodic peak current is in the range of 1.85–58.81 µA before UV/ozone modification and in the range of 2.18–63.28 µA after UV/ozone modification. In addition, the sensitivity of anodic peak current increases from 12.46 μA mM−1 with R2 0.9989–12.78 μA mM−1 with R2 0.9998. The cathodic peak current is in the range of 2.14–68.16 µA before UV/ozone modification and in the range of 2.59–74.13 µA after modification. In addition, the sensitivity of cathodic peak current increases from 14.13 μA mM−1 with R2 0.9986–14.91 μA mM−1 with R2 0.9991 after modification. Fig. 7(b) presents the relationship between peak current and concentration of K3[Fe(CN)6] for CNT-modified SPCE. The anodic peak current is in the range of 2.16–61.58 µA before UV/ozone modification and in the range of 2.49–66.94 µ after modification. And the sensitivity of anodic peak current increases from 12.59 μA mM−1 with R2 0.9992–13.63 μA mM−1 with R2 0.9995 after UV/ozone modification.
Acknowledgments Authors wishing to acknowledge assistance received from National Natural Science Foundation of China (No. 51621064) and Fundamental Research Funds for the Central Universities (No. DUT16TD20). References [1] R.L. Mccreery, Advanced carbon electrode materials for molecular electrochemistry, Chem. Rev. 39 (41) (2008) 2646–2687. [2] N. Ralph, Electrochem. Solid Electrodes (1969). [3] J. Wang, Analytical Electochemistry, second ed., (2002). [4] M.E. Rice, Z. Galus, R.N. Adams, Graphite paste electrodes: effects of paste composition and surface states on electron-transfer rates, J. Electroanal. Chem. 143 (1) (1983) 89–102. [5] M. Alvarezicaza, U. Bilitewski, Mass production of biosensors, Anal. Chem. 65 (11) (1999) 525A–533A. [6] P. Ekabutr, O. Chailapakul, P. Supaphol, Modification of disposable screen‐printed carbon electrode surfaces with conductive electrospun nanofibers for biosensor applications, J. Appl. Polym. Sci. 130 (6) (2013) 3885–3893. [7] P. Fanjul-Bolado, P. Queipo, P.J. Lamas-Ardisana, A. Costa-García, Manufacture and
44
Talanta 192 (2019) 40–45
J. Wang et al.
[8]
[9]
[10] [11]
[12]
[13] [14]
[15]
[16]
[17]
[18] [19]
[20]
[21]
[22]
[23] K. Teshima, H. Sugimura, Y. Inoue, O. Takai, A. Takano, Transparent ultra waterrepellent poly(ethylene terephthalate) substrates fabricated by oxygen plasma treatment and subsequent hydrophobic coating, Appl. Surf. Sci. 244 (1) (2005) 619–622. [24] A. Ueda, K. Dai, R. Kurita, T. Kamata, H. Inokuchi, S. Umemura, S. Hirono, O. Niwa, Efficient direct electron transfer with enzyme on a nanostructured carbon film fabricated with a maskless top-down UV/ozone process, J. Am. Chem. Soc. 133 (13) (2011) 4840. [25] M.I. González-Sánchez, B. Gómez-Monedero, J. Agrisuelas, J. Iniesta, E. Valero, Highly activated screen-printed carbon electrodes by electrochemical treatment with hydrogen peroxide, Electrochem. Commun. 91 (2018). [26] K.J. Kim, S.W. Lee, T. Yim, J.G. Kim, J.W. Choi, J.H. Kim, M.S. Park, Y.J. Kim, A new strategy for integrating abundant oxygen functional groups into carbon felt electrode for vanadium redox flow batteries, Sci. Rep. 4 (27) (2014) 6906. [27] J. Kong, N.R. Franklin, C. Zhou, M.G. Chapline, S. Peng, K. Cho, H. Dai, Nanotube molecular wires as chemical sensors, Science 287 (5453) (2000) 622–625. [28] E.S. Snow, F.K. Perkins, E.J. Houser, S.C. Badescu, T.L. Reinecke, Chemical detection with a single-walled carbon nanotube capacitor, Science 307 (5717) (2005) 1942–1945. [29] A.F. Kanta, M.P. Planche, G. Montavon, Electrochemical characterisations of Al2O3, Plasma Chem. Plasma Process. 31 (6) (2011) 867–877. [30] R. Oriňaková, A. Oriňak, M. Kupková, M. Hrubovčáková, L. Škantárová, A.M. Turoňová, L.M. Bučková, C. Muhmann, H.F. Arlinghaus, Study of electrochemical deposition and degradation of hydroxyapatite coated iron biomaterials, Int. J. Electrochem. Sci. 10 (1) (2015) 659–670. [31] A. Muhammad, R. Hajian, N.A. Yusof, N. Shams, J. Abdullah, M.W. Pei, H. Garmestani, A screen printed carbon electrode modified with carbon nanotubes and gold nanoparticles as a sensitive electrochemical sensor for determination of thiamphenicol residue in milk, RSC Adv. 8 (5) (2018) 2714–2722. [32] R. Cisneros, M. Beley, J.F. Fauvarque, F. Lapicque, Investigation of electron transfer processes involved in DSSC's by wavelength dependent electrochemical impedance spectroscopy (λ-EIS), Electrochim. Acta 171 (2015) 49–58. [33] S. Amin, M.T. Soomro, N. Memon, A.R. Solangi, Sirajuddin, T. Qureshi, A.R. Behzad, Disposable screen printed graphite electrode for the direct electrochemical determination of ibuprofen in surface water, Environ. Nanotechnol. Monit. Manag. 1–2 (2014) 8–13. [34] A. Sudarvizhi, K. Pandian, O.S. Oluwafemi, S.C.B. Gopinath, Amperometry detection of nitrite in food samples using tetrasulfonated copper phthalocyanine modified glassy carbon electrode, Sens. Actuators B Chem. (2018). [35] M. Pumera, R. Scipioni, H. Iwai, T. Ohno, Y. Miyahara, M. Boero, A mechanism of adsorption of beta-nicotinamide adenine dinucleotide on graphene sheets: experiment and theory, Chemistry 15 (41) (2009) 10851. [36] C.R. Raj, S. Behera, Mediatorless voltammetric oxidation of NADH and sensing of ethanol, Biosens. Bioelectron. 21 (6) (2005) 949–956.
evaluation of carbon nanotube modified screen-printed electrodes as electrochemical tools, Talanta 74 (3) (2007) 427–433. P. Fanjul-Bolado, D. Hernández-Santos, P.J. Lamas-Ardisana, A. Martín-Pernía, A. Costa-García, Electrochemical characterization of screen-printed and conventional carbon paste electrodes, Electrochim. Acta 53 (10) (2008) 3635–3642. H. Wei, J.J. Sun, Y. Xie, C.G. Lin, Y.M. Wang, W.H. Yin, G.N. Chen, Enhanced electrochemical performance at screen-printed carbon electrodes by a new pretreating procedure, Anal. Chim. Acta 588 (2) (2007) 297–303. J.L. Figueiredo, M.F.R. Pereira, M.M.A. Freitas, J.J.M. Órfão, Modification of the surface chemistry of activated carbons, Carbon 37 (9) (1999) 1379–1389. V. Datsyuk, M. Kalyva, K. Papagelis, J. Parthenios, D. Tasis, A. Siokou, I. Kallitsis, C. Galiotis, Chemical oxidation of multiwalled carbon nanotubes, Carbon 46 (6) (2008) 833–840. G. Cui, J.H. Yoo, J.S. Lee, J. Yoo, J.H. Uhm, G.S. Cha, H. Nam, Effect of pretreatment on the surface and electrochemical properties of screen-printed carbon paste electrodes, Analyst 126 (8) (2001) 1399. J. Wang, M. Pedrero, H. Sakslund, O. Hammerich, J. Pingarron, Electrochemical activation of screen-printed carbon strips, Analyst 121 (3) (1996) 345–350. S.C. Wang, K.S. Chang, C.J. Yuan, Enhancement of electrochemical properties of screen-printed carbon electrodes by oxygen plasma treatment, Electrochim. Acta 54 (21) (2009) 4937–4943. F. Ghamouss, P.Y. Tessier, M.A. Djouadi, M.P. Besland, M. Boujtita, Examination of the electrochemical reactivity of screen printed carbon electrode treated by radiofrequency argon plasma, Electrochem. Commun. 9 (7) (2007) 1798–1804. M. Chikae, K. Idegami, K. Kerman, N. Nagatani, M. Ishikawa, Y. Takamura, E. Tamiya, Direct fabrication of catalytic metal nanoparticles onto the surface of a screen-printed carbon electrode, Electrochem. Commun. 8 (8) (2006) 1375–1380. S.H. Lee, H.Y. Fang, W.C. Chen, Electrochemical characterization of screen-printed carbon electrodes by modification with chitosan oligomers, Electroanalysis 17 (23) (2010) 2170–2174. J. Wang, M. Musameh, Carbon nanotube screen-printed electrochemical sensors, Analyst 129 (1) (2004) 1–2. Y. Liu, X. Feng, J. Shen, J.J. Zhu, W. Hou, Fabrication of a novel glucose biosensor based on a highly electroactive polystyrene/polyaniline/Au nanocomposite, J. Phys. Chem. B 112 (30) (2008) 9237–9242. C. Karuwan, C. Sriprachuabwong, A. Wisitsoraat, D. Phokharatkul, P. Sritongkham, A. Tuantranont, Inkjet-printed graphene-poly(3,4-ethylenedioxythiophene):poly (styrene-sulfonate) modified on screen printed carbon electrode for electrochemical sensing of salbutamol, Sens. Actuators B Chem. 161 (1) (2012) 549–555. Y.W. Ju, G.R. Choi, H.R. Jung, W.J. Lee, Electrochemical properties of electrospun PAN/MWCNT carbon nanofibers electrodes coated with polypyrrole, Electrochim. Acta 53 (19) (2008) 5796–5803. K.S. Kim, K.H. Lee, K. Cho, C.E. Park, Surface modification of polysulfone ultrafiltration membrane by oxygen plasma treatment, J. Membr. Sci. 199 (1) (2002) 135–145.
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Talanta journal homepage: www.elsevier.com/locate/talanta
Improvement of electrochemical performance of screen-printed carbon electrodes by UV/ozone modification
T
⁎
Jing Wanga, Zheng Xua, , Mengqi Zhanga, Junshan Liua, Hongqun Zoub, Liding Wangb a b
Dalian University of Technology, Key Laboratory for Micro/Nano Technology and System of Liaoning Province, Dalian 116085, China Dalian University of Technology, Key Laboratory for Precision and Non-traditional Machining Technology of Ministry of Education, Dalian 116085, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Screen-printed carbon electrode UV/ozone Electron transfer
Screen-printed carbon electrode (SPCE) has been widely used in electrochemical (EC) field. Nevertheless, compared with some metal electrodes, SPCE is not sensitive to small amounts of reagent owing to its relatively low electron transfer rate. In this paper, the UV/ozone modification was proposed to treat SPCE to improve its electron transfer rate and EC performance. The changes of SPCE morphology and composition induced by UV/ ozone modification were investigated in detail. The results show that the improved electron transfer rate can be mainly attributed to the increase of oxygen functional groups. To clarify the essential EC characterization, potentiodynamic polarization and electrochemical impedance spectroscopy of K3[Fe(CN)6] was studied. Furthermore, to demonstrate the improved EC effect, two typical samples: small-molecule K3[Fe(CN)6] and macro-molecule nicotinamide adenine dinucleotide (NADH), were measured by cyclic voltammetry. After UV/ ozone modification, the oxidation potential and peak current responses to K3[Fe(CN)6] and NADH were obviously improved in both original and CNT-modified SPCEs. Whereas, the original SPCE is more suitable to measure macromolecule NADH rather than CNT-modified one as the oxidative products of NADH are more likely to adsorb on rough surface.
1. Introduction Screen-printed carbon electrode (SPCE) has been widely used in electrochemical (EC) field, owing to its excellent properties, such as low background current, wide potential window, high chemical stability etc [1–5]. Furthermore, SPCE is inexpensive as disposable unit [6]. However, compared with platinum electrode etc, SPCE is not sensitive to small amounts of reagent due to its relatively low electron transfer rate which limits its application [7,8]. In order to improve the EC performance of SPCE, several methods had been employed, including chemical treatment [9–11], EC activation [12,13], plasma treatment [14,15], surface modification with various catalysts [16,17] and nanomaterials [18–21]. For example, Wei et al. [9] modified SPCE by chemical treatment. SPCE was soaked into 3 M NaOH solution for 1 h, and then was anodized at 1.2 V in 0.5 M NaOH solution for 20 s. The peak to peak separation of modified SPCE for Fe(CN)63-/4- couple was reduced from 480 to 84 mV. Cui et al. [12] activated SPCE in saturated Na2CO3 solution at 1.2 V for 5 min, the peak to peak separation of activated SPCE for Fe(CN)63-/4- couple was reduced from 122 to 72 mV. Generally, chemical or EC activation of
SPCE utilizes anodization to increase the EC activity of SPCE through the increase of surface functionalities and roughness. However, these chemical methods are not fully suitable for SPCEs that are composed of counter/reference electrode made of silver or copper since these metals are more likely to be corroded by alkaline solution. On the other hand, the oxygen plasma treatment of SPCE can etch SPCE, and both vacuum pump and gas resource are indispensable to produce plasma too [22,23]. Herein, the method of UV/ozone modification is presented to improve electron transfer rate and EC performance of SPCE. Both original and carbon nanotubes (CNT) modified SPCEs were treated with UV/ ozone. The changes of SPCE morphology and composition induced by UV/ozone modification were investigated. The improved EC responses of modified SPCEs were evaluated by the measurement of two typical electroactive samples: small-molecule K3[Fe(CN)6] and macro-molecule nicotinamide adenine dinucleotide (NADH). The results show that UV/ ozone modification is helpful to improve the EC performance of SPCEs. Compared with other methods, UV/ozone modification is cost-effective since it doesn’t require both extra reagents and external gas source. In addition, the price of UV/ozone cleaner is acceptable.
⁎ Correspondence to: Dalian University of Technology, School of Mechanical Engineering, Key Laboratory for Micro/Nano Technology, No.2 Linggong Road, Dalian City, Liaoning Province, China. E-mail address: [email protected] (Z. Xu).
https://doi.org/10.1016/j.talanta.2018.08.065 Received 18 May 2018; Received in revised form 19 August 2018; Accepted 27 August 2018 0039-9140/ © 2018 Elsevier B.V. All rights reserved.
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Fig. 1. Scanning electron micrographs of original SPCE (a) before and (b) after UV/ozone modification. Scanning electron micrographs of CNT-modified SPCE (c) before and (d) after UV/ozone modification. The red circles are for step-like carbon sheets.
2. Experimental section
3. Results and discussion
2.1. Materials
3.1. Investigation on the surface characteristics of SPCEs
Two kinds of SPCE strips: SPCE modified with CNT and original SPCE without CNT, were purchased from Dropsens. Both SPCE strips consist of a carbon electrode as working electrode, silver electrode as reference electrode, and another carbon electrode as counter electrode. NADH was purchased from Roche. NAD+ was purchased from SigmaAldrich. K3[Fe(CN)6] was purchased from Dalian Meilun. NADH and K3[Fe(CN)6] samples were freshly prepared in PBS (0.1 M, pH 7.4) and KCL (0.1 M) solutions respectively.
Surface morphology of original and CNT-modified SPCEs was investigated by SEM. A series of images were analyzed for each surface morphology (40 images). One image selected for each type of surface morphology is shown in Fig. 1. It can be seen that the step-like carbon sheets increase after UV/ozone modification of both original and CNTmodified SPCEs. This is because ozone or single oxygen molecules could slowly etch the carbon surface to form oxygen-containing groups which would let the carbon surface become rough [24]. Besides, some organic binders existed on the electrode surface can be removed via UV/ozone modification [25]. Therefore, the morphology of both original and CNT-modified SPCEs becomes rougher after modification. The change of chemical composition of original and CNT-modified SPCEs was investigated by XPS. As shown in Fig. 2, O1 s peak intensity obviously increases for both original and CNT-modified SPCEs after UV/ ozone modification. The ratio of O1 s increases from 0.04 to 0.13 for original SPCE and from 0.06 to 0.12 for CNT-modified one. The reason is that oxygen-containing functional groups were generated on SPCE surface [24]. Since the oxygen-containing groups on the SPCE surface can improve the wettability which could promote the diffusion-controlled process and thus enhance the electron transfer rate of SPCE [26]. The detailed change of oxygen atoms was further studied through Gaussian decompositions of O1 s spectra as follows. For original SPCE, there is only one C-O bond peak before UV/ozone modification. It becomes the mixture of C-O and C˭O bonds via UV/ozone modification, and the ratio of C-O and C˭O bonds are 37.8% and 62.2% respectively. For CNTmodified SPCE, the ratio of C-O and C˭O bonds are 45.9% and 54.1% before UV/ozone modification, and the ratio of C-O and C˭O bonds become to 53.7% and 46.3% via UV/ozone modification.
2.2. Apparatus A UV/ozone cleaner (144AX-220, JELIGHT Co., Ltd., USA) was used to modify SPCEs, in which a 10 mW/cm2 Hg lamp provided 185 and 254 nm UV light. The lamp was warmed for 15 min, and then SPCE strips were placed in chamber and modified at 6 cm distance from the Hg lamp for 5 min. In the process, oxygen molecules (O2) absorbed 185 nm UV light and formed ozone, then ozone molecules (O3) absorbed 254 nm UV light and broke into atomic oxygen (O). The electrochemical impedance spectroscopy (EIS) of SPCE was determinated with an impedance analyzer (E4990A, Keysight Co., USA). The surface morphology of SPCE was characterized by a scanning electron microscope (SEM, JSM-6360, LV JEOL Co., Japan). Chemical compositions of SPCE were analyzed by an X-ray photoelectron spectroscope (ESCALAB 250Xi, ThermoFisher Co., USA). All EC experiments were carried out with an electrochemical workstation (Reference 600 +, Gamry Co., USA).
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Fig. 2. O1s spectra and Gaussian decompositions of O1s spectra before and after UV/ozone modification for (a) original SPCE and (b) CNT-modified SPCE.
Therefore, the interfacial impedance was measured from 20 to 500 Hz. From Fig. 3, it can be seen that the impedances are decreased for both original and CNT-modified SPCEs by UV/ozone modification, and the interfacial impedance of CNT-modified SPCE is lower than that of original SPCE. The decrease of interfacial impedance is primarily contributed to the incremental C-O and C˭O bonds that can anchor H2O molecules via intermolecular bonding and then the interfacial reaction between SPCE and electrolyte was enhanced [27,28]. 3.3. Electrochemical tests 3.3.1. Measurement of essential EC characterizations To clarify the EC characterization of modified SPCEs, two EC methods: potentiodynamic polarization and EC impedance spectroscopy, were used. Both original and CNT-modified SPCEs were measured with 1 mM K3[Fe(CN)6] solution. Test of potentiodynamic polarization was performed after stabilization of open-circuit potential (OCP). And the test was carried out from −500–500 mV/OCP at a scanning rate of 0.1 mV s−1 [29]. Fig. 4(a) and (b) present the results for original and CNT-modified SPCEs respectively. It can be seen that the potential negative shift and the current density increase slightly after UV/ozone modification for both original and CNT-modified SPCEs. Higher current density or more negative potential means the UV/ozone modified SPCEs is of less EC resistance compared with the unmodified SPCEs [30]. EIS is a powerful technique to characterize the charge transfer
Fig. 3. Interfacial impedance of SPCEs before and after UV/ozone modification.
3.2. Measurement of interfacial impedance Since the interfacial impedance plays an important role in electron transfer process, it was measured with 10 mM NaCl solution. When the scanning rate is too high, the mass transfer rate can't keep up with the change of external potential, resulting in the saturation of EC reaction. Thus, limited by mass transfer, most EC detections are carried out in the relatively low frequency region. For example, the scan rate of cyclic voltammetry (CV) is often limited in the range of 10–100 mV s−1. 42
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Fig. 4. Potentiodynamic polarization curves of (a) original SPCE and (b) CNT-modified SPCE before and after UV/ozone modification.
Fig. 5. Nyquist plots of (a) original SPCE and (b) CNT-modified SPCE in a 1.0 mM K3Fe(CN)6 solution containing 0.1 KCl in the frequency range of 20 Hz to 100 kHz.
Fig. 6. Cyclic voltammograms of (a) 1 mM K3[Fe(CN)6] and (b) 1 mM NADH with original and CNT-modified SPCEs before and after UV/ozone modification.
Cyclic voltammograms (CVs) of 1 mM K3[Fe(CN)6] are shown in Fig. 6(a). For K3[Fe(CN)6], the scanning range is −0.3–0.5 V and the scanning rate is 50 mV s−1. From Fig. 6(a), the anodic potential peak (original SPCE: 200 mV, CNT-modified SPCE: 178 mV) is lower and the anodic current peak (original SPCE: 11.01 µA. CNT-modified SPCE: 12.62 µA) is higher for CNT-modified SPCE than that of original SPCE. After UV/ozone modification, the peak-to-peak potential separation (ΔEp) between oxidative (Epa) and reductive peak potentials (Epc) becomes narrower (original SPCE: from 170 to 112 mV, CNT-modified SPCE: from 108 to 90 mV), and anodic current becomes higher (original SPCE: from 11.01 to 12.97 µA, CNT-modified SPCE: from 12.62 to 14.58 µA). Compared with other methods, the peak-to-peak potential separation of K3[Fe(CN)6] on UV/ozone modified SPCE is narrower than that of oxygen plasma treated SPCE (from 440 to 156 mV) [14], and is comparable with that of chemical modified SPCEs [9,12]. CVs of 1 mM NADH are shown in Fig. 6(b). For NADH, the scanning
process at various electrode surfaces [25,31,32]. Here the EIS experiment was performed in a solution of 1 mM K3[Fe(CN)6] containing 0.1 M KCl with the frequency range from 20 Hz to 100 kHz. As shown in Fig. 5(a) and (b), there are two approximately linear curves in EIS Nyquist plots for both original and CNT-modified SPCEs. And the slopes of lines become lower via UV/ozone modification, indicating that the electron transfer becomes easier [33]. In addition, the linear relationship for both original and CNT-modified SPCEs shows that the EC process is mainly mass-diffusion controlled [34]. In summary, the electron transfer rate was obviously improved in both original and CNT-modified SPCEs via UV/ozone modification.
3.3.2. Test of the effect of UV/ozone modification on EC performance To evaluate the effect of UV/ozone modification on EC performance, the cyclic voltammetric behavior was investigated with two samples: small molecule K3[Fe(CN)6] and macromolecule NADH. 43
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Fig. 7. Amperometric response to K3[Fe(CN)6] concentration for (a) original SPCE and (b) CNT-modified SPCE before and after UV/ozone modification. (c) Amperometric response to NADH concentration for SPCEs before and after UV/ozone modification.
range is −0.2–0.7 V and the scanning rate is 50 mV s−1. The anodic peak current increases from 18.83 to 21.75 µA and the oxidation potential reduces from 320 to 292 mV for original SPCE via UV/ozone modification. Similarly, the anodic peak current increases from 16.85 to 17.68 µA and the oxidation potential reduces from 310 to 260 mV for CNT-modified SPCE. In the above measurement of K3[Fe(CN)6] and NADH, the improved amplitudes of anodic peak current are 17.81% and 15.53% respectively in original SPCE, 15.51% and 4.93% in CNT-modified SPCE. In terms of NADH, the improved amplitude of CNT-modified SPCE is relatively lower than that of original SPCE. It is due to NAD+ (EC oxidative product of NADH [35]), which has stronger adsorption for CNT-modified SPCE than original one since the CNT-modified SPCE has larger surface area [36]. The interfacial impedance can be used to demonstrate the difference of NAD+ adsorption on the original and CNT-modified SPCEs surface too. After SPCEs were immersed into 5 mM NAD+ solution for 30 min, the interfacial impedances increased by 12.53% and 30.33% in 20 Hz for original and CNT-modified SPCEs, respectively (original SPCE: from 1.34 to 1.51 KΩ mm−2, CNT-modified SPCE: from 0.54 to 0.71 KΩ mm−2). Because the improved amplitude of interfacial impedance is higher for CNT-modified SPCE than original one, more quantity of NAD+ is absorbed on the CNT-modified SPCE surface. And NAD+ might hinder the EC activity of SPCE and increase the resistance which will slow the total kinetic of reaction.
The cathodic peak currents is in the range of 2.63–74.07 µA before UV/ ozone modification and in the range of 2.97–80.44 µA after modification. Correspondingly, the sensitivity of cathodic peak current increases from 14.91 μA mM−1 with R2 0.9995–15.92 μA mM−1 with R2 0.9995. Fig. 7(c) presents the relationship between the peak current and the concentration of NADH before and after UV/ozone modification. For original SPCE, the peak current is in the range of 0.42–80.88 µA with R2 0.9946 before UV/ozone modification, and is in the range of 0.48–91.59 µA with R2 0.9998 after UV/ozone modification. The sensitivity of original SPCE increases from 17.45 μA mM−1 to 19.11 μA mM−1. For CNT-modified SPCE, the peak current is in the range of 0.35–80.62 µA with R2 0.9988 before UV/ozone modification, and is in the range of 0.45–83.65 µA with R2 0.9994 after modification. Correspondingly, the sensitivity of CNT-modified SPCE increases from 16.01 μA mM−1 to 16.33 μA mM−1 via UV/ozone modification. 4. Conclusion A simple and economic method of UV/ozone modification is proposed to improve the EC performance of SPCE. The improved EC performance is mainly attributed to the increase of the number of surface oxygen functional groups. After UV/ozone modification, the oxidation potential and peak current responses of K3[Fe(CN)6] and NADH were obviously improved in both original and CNT-modified SPCEs, which is agreement with the obtained results of potentiodynamic polarization and EIS with K3[Fe(CN)6]. In terms of NADH, it is noteworthy that NAD+ has stronger adsorption on CNT-modified SPCE than original one, which leads to a lower electron transfer rate for CNT-modified SPCE.
3.3.3. Improved EC response of SPCEs by UV/ozone modification To further verify the improved EC response of both original and CNT-modified SPCEs by UV/ozone modification, a series of K3[Fe (CN)6] concentrations varying from 0.156 to 5 mM and NADH concentrations varying from 0.019 to 5 mM were measured by cyclic voltammetry at the scan rate of 50 mV s−1. Fig. 7(a) presents the relationship between peak current and concentration of K3[Fe(CN)6] for original SPCE. The anodic peak current is in the range of 1.85–58.81 µA before UV/ozone modification and in the range of 2.18–63.28 µA after UV/ozone modification. In addition, the sensitivity of anodic peak current increases from 12.46 μA mM−1 with R2 0.9989–12.78 μA mM−1 with R2 0.9998. The cathodic peak current is in the range of 2.14–68.16 µA before UV/ozone modification and in the range of 2.59–74.13 µA after modification. In addition, the sensitivity of cathodic peak current increases from 14.13 μA mM−1 with R2 0.9986–14.91 μA mM−1 with R2 0.9991 after modification. Fig. 7(b) presents the relationship between peak current and concentration of K3[Fe(CN)6] for CNT-modified SPCE. The anodic peak current is in the range of 2.16–61.58 µA before UV/ozone modification and in the range of 2.49–66.94 µ after modification. And the sensitivity of anodic peak current increases from 12.59 μA mM−1 with R2 0.9992–13.63 μA mM−1 with R2 0.9995 after UV/ozone modification.
Acknowledgments Authors wishing to acknowledge assistance received from National Natural Science Foundation of China (No. 51621064) and Fundamental Research Funds for the Central Universities (No. DUT16TD20). References [1] R.L. Mccreery, Advanced carbon electrode materials for molecular electrochemistry, Chem. Rev. 39 (41) (2008) 2646–2687. [2] N. Ralph, Electrochem. Solid Electrodes (1969). [3] J. Wang, Analytical Electochemistry, second ed., (2002). [4] M.E. Rice, Z. Galus, R.N. Adams, Graphite paste electrodes: effects of paste composition and surface states on electron-transfer rates, J. Electroanal. Chem. 143 (1) (1983) 89–102. [5] M. Alvarezicaza, U. Bilitewski, Mass production of biosensors, Anal. Chem. 65 (11) (1999) 525A–533A. [6] P. Ekabutr, O. Chailapakul, P. Supaphol, Modification of disposable screen‐printed carbon electrode surfaces with conductive electrospun nanofibers for biosensor applications, J. Appl. Polym. Sci. 130 (6) (2013) 3885–3893. [7] P. Fanjul-Bolado, P. Queipo, P.J. Lamas-Ardisana, A. Costa-García, Manufacture and
44
Talanta 192 (2019) 40–45
J. Wang et al.
[8]
[9]
[10] [11]
[12]
[13] [14]
[15]
[16]
[17]
[18] [19]
[20]
[21]
[22]
[23] K. Teshima, H. Sugimura, Y. Inoue, O. Takai, A. Takano, Transparent ultra waterrepellent poly(ethylene terephthalate) substrates fabricated by oxygen plasma treatment and subsequent hydrophobic coating, Appl. Surf. Sci. 244 (1) (2005) 619–622. [24] A. Ueda, K. Dai, R. Kurita, T. Kamata, H. Inokuchi, S. Umemura, S. Hirono, O. Niwa, Efficient direct electron transfer with enzyme on a nanostructured carbon film fabricated with a maskless top-down UV/ozone process, J. Am. Chem. Soc. 133 (13) (2011) 4840. [25] M.I. González-Sánchez, B. Gómez-Monedero, J. Agrisuelas, J. Iniesta, E. Valero, Highly activated screen-printed carbon electrodes by electrochemical treatment with hydrogen peroxide, Electrochem. Commun. 91 (2018). [26] K.J. Kim, S.W. Lee, T. Yim, J.G. Kim, J.W. Choi, J.H. Kim, M.S. Park, Y.J. Kim, A new strategy for integrating abundant oxygen functional groups into carbon felt electrode for vanadium redox flow batteries, Sci. Rep. 4 (27) (2014) 6906. [27] J. Kong, N.R. Franklin, C. Zhou, M.G. Chapline, S. Peng, K. Cho, H. Dai, Nanotube molecular wires as chemical sensors, Science 287 (5453) (2000) 622–625. [28] E.S. Snow, F.K. Perkins, E.J. Houser, S.C. Badescu, T.L. Reinecke, Chemical detection with a single-walled carbon nanotube capacitor, Science 307 (5717) (2005) 1942–1945. [29] A.F. Kanta, M.P. Planche, G. Montavon, Electrochemical characterisations of Al2O3, Plasma Chem. Plasma Process. 31 (6) (2011) 867–877. [30] R. Oriňaková, A. Oriňak, M. Kupková, M. Hrubovčáková, L. Škantárová, A.M. Turoňová, L.M. Bučková, C. Muhmann, H.F. Arlinghaus, Study of electrochemical deposition and degradation of hydroxyapatite coated iron biomaterials, Int. J. Electrochem. Sci. 10 (1) (2015) 659–670. [31] A. Muhammad, R. Hajian, N.A. Yusof, N. Shams, J. Abdullah, M.W. Pei, H. Garmestani, A screen printed carbon electrode modified with carbon nanotubes and gold nanoparticles as a sensitive electrochemical sensor for determination of thiamphenicol residue in milk, RSC Adv. 8 (5) (2018) 2714–2722. [32] R. Cisneros, M. Beley, J.F. Fauvarque, F. Lapicque, Investigation of electron transfer processes involved in DSSC's by wavelength dependent electrochemical impedance spectroscopy (λ-EIS), Electrochim. Acta 171 (2015) 49–58. [33] S. Amin, M.T. Soomro, N. Memon, A.R. Solangi, Sirajuddin, T. Qureshi, A.R. Behzad, Disposable screen printed graphite electrode for the direct electrochemical determination of ibuprofen in surface water, Environ. Nanotechnol. Monit. Manag. 1–2 (2014) 8–13. [34] A. Sudarvizhi, K. Pandian, O.S. Oluwafemi, S.C.B. Gopinath, Amperometry detection of nitrite in food samples using tetrasulfonated copper phthalocyanine modified glassy carbon electrode, Sens. Actuators B Chem. (2018). [35] M. Pumera, R. Scipioni, H. Iwai, T. Ohno, Y. Miyahara, M. Boero, A mechanism of adsorption of beta-nicotinamide adenine dinucleotide on graphene sheets: experiment and theory, Chemistry 15 (41) (2009) 10851. [36] C.R. Raj, S. Behera, Mediatorless voltammetric oxidation of NADH and sensing of ethanol, Biosens. Bioelectron. 21 (6) (2005) 949–956.
evaluation of carbon nanotube modified screen-printed electrodes as electrochemical tools, Talanta 74 (3) (2007) 427–433. P. Fanjul-Bolado, D. Hernández-Santos, P.J. Lamas-Ardisana, A. Martín-Pernía, A. Costa-García, Electrochemical characterization of screen-printed and conventional carbon paste electrodes, Electrochim. Acta 53 (10) (2008) 3635–3642. H. Wei, J.J. Sun, Y. Xie, C.G. Lin, Y.M. Wang, W.H. Yin, G.N. Chen, Enhanced electrochemical performance at screen-printed carbon electrodes by a new pretreating procedure, Anal. Chim. Acta 588 (2) (2007) 297–303. J.L. Figueiredo, M.F.R. Pereira, M.M.A. Freitas, J.J.M. Órfão, Modification of the surface chemistry of activated carbons, Carbon 37 (9) (1999) 1379–1389. V. Datsyuk, M. Kalyva, K. Papagelis, J. Parthenios, D. Tasis, A. Siokou, I. Kallitsis, C. Galiotis, Chemical oxidation of multiwalled carbon nanotubes, Carbon 46 (6) (2008) 833–840. G. Cui, J.H. Yoo, J.S. Lee, J. Yoo, J.H. Uhm, G.S. Cha, H. Nam, Effect of pretreatment on the surface and electrochemical properties of screen-printed carbon paste electrodes, Analyst 126 (8) (2001) 1399. J. Wang, M. Pedrero, H. Sakslund, O. Hammerich, J. Pingarron, Electrochemical activation of screen-printed carbon strips, Analyst 121 (3) (1996) 345–350. S.C. Wang, K.S. Chang, C.J. Yuan, Enhancement of electrochemical properties of screen-printed carbon electrodes by oxygen plasma treatment, Electrochim. Acta 54 (21) (2009) 4937–4943. F. Ghamouss, P.Y. Tessier, M.A. Djouadi, M.P. Besland, M. Boujtita, Examination of the electrochemical reactivity of screen printed carbon electrode treated by radiofrequency argon plasma, Electrochem. Commun. 9 (7) (2007) 1798–1804. M. Chikae, K. Idegami, K. Kerman, N. Nagatani, M. Ishikawa, Y. Takamura, E. Tamiya, Direct fabrication of catalytic metal nanoparticles onto the surface of a screen-printed carbon electrode, Electrochem. Commun. 8 (8) (2006) 1375–1380. S.H. Lee, H.Y. Fang, W.C. Chen, Electrochemical characterization of screen-printed carbon electrodes by modification with chitosan oligomers, Electroanalysis 17 (23) (2010) 2170–2174. J. Wang, M. Musameh, Carbon nanotube screen-printed electrochemical sensors, Analyst 129 (1) (2004) 1–2. Y. Liu, X. Feng, J. Shen, J.J. Zhu, W. Hou, Fabrication of a novel glucose biosensor based on a highly electroactive polystyrene/polyaniline/Au nanocomposite, J. Phys. Chem. B 112 (30) (2008) 9237–9242. C. Karuwan, C. Sriprachuabwong, A. Wisitsoraat, D. Phokharatkul, P. Sritongkham, A. Tuantranont, Inkjet-printed graphene-poly(3,4-ethylenedioxythiophene):poly (styrene-sulfonate) modified on screen printed carbon electrode for electrochemical sensing of salbutamol, Sens. Actuators B Chem. 161 (1) (2012) 549–555. Y.W. Ju, G.R. Choi, H.R. Jung, W.J. Lee, Electrochemical properties of electrospun PAN/MWCNT carbon nanofibers electrodes coated with polypyrrole, Electrochim. Acta 53 (19) (2008) 5796–5803. K.S. Kim, K.H. Lee, K. Cho, C.E. Park, Surface modification of polysulfone ultrafiltration membrane by oxygen plasma treatment, J. Membr. Sci. 199 (1) (2002) 135–145.
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