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A direct comparison of nanosilver particles and nanosilver plates for the oxidation of ascorbic acid
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 326–328
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
A direct comparison of nanosilver particles and nanosilver plates for the oxidation of ascorbic acid Babak Sadeghi a,⇑, Masoumeh Meskinfam b a b
Department of Chemistry, Tonekabon Branch, Islamic Azad University, Tonekabon, Iran Department of Chemistry, Lahijan Branch, Islamic Azad University, Lahijan, Iran
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
" Silver nanoparticles and silver
nanoplates have been grown on zinc tin oxide (ZTO) electrode. " Silver nanoplates modified ZTO has higher catalytic activity. " Ag nanoplates modified ZTO electrode towards oxidation of ascorbic acid.
a r t i c l e
i n f o
Article history: Received 27 April 2012 Received in revised form 23 May 2012 Accepted 29 May 2012 Available online 23 June 2012 Keywords: Silver nanoparticles Surfaces Polymers Ascorbic acid
a b s t r a c t We study of spherical silver nanoparticles of different size and Ag nanoplates were grown at zinc tin oxide (ZTO) surface and characterized using SEM. The application of different electrodes in voltammetry for determination ascorbic acid indicated that oxidation of this biomolecule occurs at these electrodes in diffusion controlled process. Ag nanoplates modified zinc tin oxide electrodes exhibit at least two to three times higher current than spherical nanosilver particles. The observed behavior suggests that Ag nanoplates exhibit higher electrocatalytic activity than spherical silver nanoparticles. The reason for such behavior may be due to lattice plane as well as due to more available surface edges. As dimensions of nanoplates are increased surface area in the case of nanoplates also appears to play a significant role. Ó 2012 Elsevier B.V. All rights reserved.
Introduction The nanomaterials modified electrodes have attracted considerable attention in last few years as sensors and biosensors for variety of biomolecules and metal ions [1–7]. Recently, the nanomaterial-composite modified electrodes have been claimed to exhibit much higher sensitivity in comparison to only nanomaterials modified electrodes [8,9]. The usefulness of these nanoparticles is further enhanced if they are deposited on substrate like ⇑ Corresponding author. Tel.: +98 912 289 8500; fax: +98 192 428 2205. E-mail addresses: [email protected], [email protected] (B. Sadeghi). 1386-1425/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2012.05.082
zinc tin oxide (ZTO). Such electrodes have been proved as an excellent working electrode having properties such as high electroactive surface area, excellent electronic conductivity and wide available potential window. The applications and catalytic properties of nanosilver modified zinc tin oxide electrode have already been demonstrated in recent years in the determination of dopamine, uric acid and many other biologically important compounds [7,10]. We have recently developed a reduction method of converting Ag nanospheres into nanorods [11], nanoplates [12], their antibacterial activity [13,14], an improved an easy synthetic route for silver nano-particles in poly (diallyldimethylammonium chloride) (PDDA) [15] and synthesis of Gold/HPC hybrid nanocomposite
B. Sadeghi, M. Meskinfam / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 326–328
327
[16]. In this communication an attempt has been made to prepare spherical nanosilver particles of different sizes and the electrochemical behavior of biologically important compound ascorbic acid at spherical nanosilver modified ZTO electrodes with Ag nanoplate modified electrode. Three different sizes of spherical nanosilver particles (30 nm; medium 30–60 nm and large 60–100 nm) were prepared. Experimental Materials Cetyltrimethylammonium bromide, ascorbic acid, and AgNO3 were obtained from Sigma–Aldrich. ZTO coated glass plates were procured from CBC Optics. SEM images were recorded using a scanning electron microscopy model LEO 440i. The detailed procedure to attach and growth of Ag nanoparticles or nanoplates on the surface of ZTO similar to inidium tin oxide (ITO) and has been described by M. Oyama and et al. [17,18].
Fig. 1. Typical SEM images of nanosilver, (a) with modified ZTO electrodes (after 30 min) and (b) after changing growth solution to AgNO3 and poly(vinylpyrrolidone).
Methods In this seed mediated growth procedure, when another growth solution containing AgNO3 and poly (vinylpyrrolidone) (PVP) was used, we could prepare Ag nanoplate-attached ZTO substrates as reported previously for ITO M. Oyama and et al. [18]. In the present work, to increase the coverage amount of Ag nanoplates, the contents of the growth solution used was prepared by adding 0.2 ml of 0.15 M ascorbic acid into a solution that contained 0.5 ml of 0.01 M AgNO3, 9 ml of 1 mM PVP, 10 ml of 0.1 M CTAB and 3 ml pure water, and then a piece of ZTO was immersed for 15 h after the seeding treatment. As reduction chemical method was used for preparation of Ag nanoplates, a few nanorods and spherical nanoparticles also formed [11,12]. Results and discussion It was observed [17,18] during preparation of nanosilver particles that seed mediated growth approach leads to growth of spherical nanoparticles of different size (30–100 nm) depending upon the time allowed in the growth solution. In the present studies the time allowed in growth solution was 30 min, 1 h and 24 h. At these times spherical nanosilver particles of different size were deposited. They have been named as small (<30 nm), medium (30–60 nm), large (>60 nm) nanosilver particles and nanosilver plates [11,12].
Fig. 2. A comparison of linear sweep voltammograms of 1.0 mM potassium ferrocyanide at different electrodes at sweep rate of 25 mV s 1. Curves were recorded at (a) ZTO, (b) spherical nanosilver particles >60 nm, (c) bulk silver and (d) silver nanoplates.
nanoparticles. Meanwhile, the current would not depend on the 2D surface of the silver. Linear sweep voltammograms characterization Fig. 3 presents a comparison of voltammograms observed for ascorbic acid at pH 7.2. It was observed that electrodes having spherical nanosilver particles of different sizes exhibit oxidation
SEM Characterization Fig. 1(a and b), shows the SEM images of different spherical nanoparticles and nanoplates grown on zinc tin oxide (ZTO), and clearly indicates the deposition of spherical and nanosilver plates. Sweep voltammograms characterization Fig. 2 presents a comparison of voltammograms at silver nanoparticles attached electrode with bare silver electrode at sweep rate of 25 mV s 1. The current magnitude of ferrocyanide at ZTO electrode is presented by curve in Fig. 2. The curves b and d present current magnitude of spherical Ag nanoparticles (>60 nm) and nanoplates. However, bare and bulk silver electrode is presented by curve c. It is clear from the figure that for the standard redox couple the response of nanoplates is larger in comparison to spherical Ag
Fig. 3. Linear sweep voltammograms of 1.0 mM ascorbic acid in pH 7.2 phosphate buffer observed at a sweep rate of 20 mV s 1 at (a) plate type, (b) spherical small, (c) medium and (d) large nanosilver modified electrode.
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B. Sadeghi, M. Meskinfam / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 326–328
peak at same potential (cf. 695 mV) with identical current. In contrast to electrode having spherical nanosilver particles, the oxidation of ascorbic acid was observed at 628 mV at nanosilver plate electrode and current was found to increase to 3.4 lA. A linear relationship was observed between the peak current and the square root of scan rate with a slope of 0.55 and correlation coefficient -0.983. This behavior indicates that the electrode process is diffusion-controlled within the scan rate range studied [19]. The slope of 0.55 is close to the theoretically expected value of 0.50 for an ideal diffusion controlled process. Similar behavior was observed for ascorbic acid in square wave voltammetry. At bare silver electrode ascorbic acid exhibited a broad oxidation peak, whereas, no peak was observed at bare ZTO electrode. It was found that oxidation of ascorbic acid occurred in a single peak having Ep 575 mV at three spherical nanosilver modified ZTO electrodes. The peak current observed was close to 3.2 lA at spherical nanosilver electrodes. However, when nanoplate modified ZTO electrode was used, the Ep value remained same, whereas, the peak current was found to increase to 7.5 lA. The geometric area was used for current density calculations effective electrode calculations showed a variation of nearly 10% for nanoplates. However, as rough estimate the ratio of effective/ geometric area of nanoplates was found between 0.6 and 0.7. This clearly indicates that silver nanoplate modified ZTO has higher catalytic activity in comparison to spherical nanosilver particles modified ZTO electrode [12]. The dependence of peak current for oxidation peak of ascorbic acid was studied on scan frequency at all the electrodes. This behavior suggested the diffusion controlled nature of electrode reaction [20]. Also, the peak potential of ascorbic acid shifted towards more positive potentials with increase in sweep rate. This peak shift indicates a quasi-reversible process or a chemical reaction associated with the electron transfer. Thus, use of nanoplates modified ZTO electrode provides better peak current and hence lower detection limit can be easily achieved for ascorbic acid and possibly for other biomolecules also. The above studies clearly indicate that Ag nanoplate modified ZTO electrode exhibit higher electrocatalytic activity in comparison to spherical silver nano modified ZTO electrodes towards oxidation of biomolecule particularly ascorbic acid. One of the reasons for such behavior may be due to very sharp edges of triangular Ag nanoplates with average width 5–10 lm. The lattice plane may also provide more edges in comparison to spherical nanosilver particles. The edge plane has been found to exhibit more catalytic activity in comparison plane of pyrolytic graphite [21,22]. Another possibility is the role of the electroactive area of the electrode. The spherical nanoparticles are indeed rather small (<100 nm) so that their dimension does not exceed the dimension of the diffusion layer, therefore they should not contribute significantly to increasing the electroactive area. This agrees with well with what is recently demonstrated for the case of electrodes made of arrays of silver nanowires with different length [23]. A comparison of catalytic behavior of the different shaped nanosilver particles has also reported in literature [12,24–27] that Ag nanoplates exhibit superior catalytic properties to other shaped nanosilver particles for liberating hydrogen gas for HCHO solutions. Thus, it is suggested that electrodes modified with Ag nanoplates are better in comparison to spherical nanosilver particles.
Further studies on comparative aspects of electrochemical activity of silver nanoplates and spherical nanosilver particles are in progress. Conclusion In summary, we observed that the peak currents at Ag nanoplates modified ZTO electrode are nearly two to three times larger than spherical silver nanoparticles. This clearly indicates that silver nanoplate modified ZTO has higher catalytic activity in comparison to spherical nanosilver particles modified ZTO electrode. One of the reasons for such behavior may be due to very sharp edges of triangular Ag nanoplates with average width 5–10 lm. It is thus expected that the sensitivity and detection limit will be much better at Ag nanoplates modified ZTO electrode in linear sweep voltammetry in comparison to spherical nanosilver particles. Acknowledgements The financial and encouragement support provided by the Research vice Presidency of Tonekabon Branch, Islamic Azad University and Executive Director of Iran-Nanotechnology Organization (Govt. of Iran). References [1] S. Lu, K. Wu, X. Dang, S. Hu, Talanta 63 (2004) 653–657. [2] R.N. Goyal, M. Oyama, V.K. Gupta, S.P. Singh, R.A. Sharma, Sensors Actuat. B 134 (2008) 816–821. [3] O. Niwa, D. Kato, H. Shigeru, Chem. Sensors 24 (2008) 6–12. [4] L. Xiao, G.G. Wildgoose, R.G. Compton, New J. Chem. 32 (2008) 1628–1633. [5] F. Kurusu, H. Tsunoda, A. SaZTO, A. Tomita, A. Kayahara, I. Karube, et al., Analyst 131 (2006) 1292–1298. [6] F. Valentini, S. Orlanducci, M. Terranova, A. Letizia, P.G. Aziz, Sensors Actuat. B 100 (2004) 117–125. [7] R.N. Goyal, M. Oyama, A. Tyagi, S.P. Singh, Talanta 72 (2007) 140–144. [8] M. Li, F. Gao, P. Yang, L. Wang, B. Fang, Surf. Sci. 602 (2007) 151–155. [9] H.L. Zhang, X.Z. Zou, G.S. Lai, D.Y. Han, F. Wang, Electroanalysis 19 (2007) 1869–1874. [10] R.N. Goyal, V.K. Gupta, M. Oyama, N. Bachheti, Electrochem. Commun. 8 (2006) 65–70. [11] M.A.S. Sadjadi, B. Sadeghi, M. Meskinfam, K. Zare, J. Azizian, Physica E 40 (2008) 3183–3186. [12] B. Sadeghi, M.A.S. Sadjadi, R.A.R. Vahdati, Superlattices Microstruct. 46 (2009) 858–863. [13] B. Sadeghi, M. Jamali, Sh. Kia, A. Amininia, S. Ghafari, Int. J. Nano Dimens. 1 (2010) 119–124. [14] B. Sadeghi, F.S. Garmaroudi, M. Hashemi, H.R. Nezhad, A. Nasrollahi, Sima. Ardalan, Sahar. Ardalan, Adv. Powder Technol. 23 (2012) 22–26. [15] B. Sadeghi, A. Pourahmad, Adv. Powder Technol. 22 (2011) 669–673. [16] B. Sadeghi, Sh. Ghammamy, Z. Gholipour, M. Ghorchibeigy, A. Amininia, Mic & Nano Letters 6 (2011) 209–213. [17] M. Kambayashi, J. Zhang, M. Oyama, Cryst. Growth Des. 5 (2005) 81–84. [18] A.A. Umar, M. Oyama, Cryst. Growth Des. 6 (2006) 818–821. [19] A. Bard, L.R.F. Aglkner, Electrochemical Methods, Wiley, NY, 1980. [20] J. Osteryoung, R.A. Osteryoung, Anal. Chem. 57 (1985) 101–110. [21] R.H. Wopschall, I. Shain, Anal. Chem. 39 (1967) 1514–1527. [22] R.T. Kachoosangi, R.G. Compton, Anal. Bioanal. Chem. 387 (2007) 2793–2800. [23] M. De Leo, A. Kuhn, P. Ugo, Electroanalysis 19 (2007) 227–236. [24] Y. Bi, G. Lu, Mater. Lett. 62 (2008) 2696–2699. [25] A. Miyazaki, T. Asakawa, Y. Nakano, I. Balint, Chem. Commun. (2005) 3730– 3732. [26] M. Li, Z. Zhao, R. Geng, H. Hu, Bioelectrochemistry 74 (2008) 217–221. [27] N.N. Horimoto, K. Imura, H. Okamoto, Chem. Phys. Lett. 467 (2008) 105–109.
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
A direct comparison of nanosilver particles and nanosilver plates for the oxidation of ascorbic acid Babak Sadeghi a,⇑, Masoumeh Meskinfam b a b
Department of Chemistry, Tonekabon Branch, Islamic Azad University, Tonekabon, Iran Department of Chemistry, Lahijan Branch, Islamic Azad University, Lahijan, Iran
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
" Silver nanoparticles and silver
nanoplates have been grown on zinc tin oxide (ZTO) electrode. " Silver nanoplates modified ZTO has higher catalytic activity. " Ag nanoplates modified ZTO electrode towards oxidation of ascorbic acid.
a r t i c l e
i n f o
Article history: Received 27 April 2012 Received in revised form 23 May 2012 Accepted 29 May 2012 Available online 23 June 2012 Keywords: Silver nanoparticles Surfaces Polymers Ascorbic acid
a b s t r a c t We study of spherical silver nanoparticles of different size and Ag nanoplates were grown at zinc tin oxide (ZTO) surface and characterized using SEM. The application of different electrodes in voltammetry for determination ascorbic acid indicated that oxidation of this biomolecule occurs at these electrodes in diffusion controlled process. Ag nanoplates modified zinc tin oxide electrodes exhibit at least two to three times higher current than spherical nanosilver particles. The observed behavior suggests that Ag nanoplates exhibit higher electrocatalytic activity than spherical silver nanoparticles. The reason for such behavior may be due to lattice plane as well as due to more available surface edges. As dimensions of nanoplates are increased surface area in the case of nanoplates also appears to play a significant role. Ó 2012 Elsevier B.V. All rights reserved.
Introduction The nanomaterials modified electrodes have attracted considerable attention in last few years as sensors and biosensors for variety of biomolecules and metal ions [1–7]. Recently, the nanomaterial-composite modified electrodes have been claimed to exhibit much higher sensitivity in comparison to only nanomaterials modified electrodes [8,9]. The usefulness of these nanoparticles is further enhanced if they are deposited on substrate like ⇑ Corresponding author. Tel.: +98 912 289 8500; fax: +98 192 428 2205. E-mail addresses: [email protected], [email protected] (B. Sadeghi). 1386-1425/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2012.05.082
zinc tin oxide (ZTO). Such electrodes have been proved as an excellent working electrode having properties such as high electroactive surface area, excellent electronic conductivity and wide available potential window. The applications and catalytic properties of nanosilver modified zinc tin oxide electrode have already been demonstrated in recent years in the determination of dopamine, uric acid and many other biologically important compounds [7,10]. We have recently developed a reduction method of converting Ag nanospheres into nanorods [11], nanoplates [12], their antibacterial activity [13,14], an improved an easy synthetic route for silver nano-particles in poly (diallyldimethylammonium chloride) (PDDA) [15] and synthesis of Gold/HPC hybrid nanocomposite
B. Sadeghi, M. Meskinfam / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 326–328
327
[16]. In this communication an attempt has been made to prepare spherical nanosilver particles of different sizes and the electrochemical behavior of biologically important compound ascorbic acid at spherical nanosilver modified ZTO electrodes with Ag nanoplate modified electrode. Three different sizes of spherical nanosilver particles (30 nm; medium 30–60 nm and large 60–100 nm) were prepared. Experimental Materials Cetyltrimethylammonium bromide, ascorbic acid, and AgNO3 were obtained from Sigma–Aldrich. ZTO coated glass plates were procured from CBC Optics. SEM images were recorded using a scanning electron microscopy model LEO 440i. The detailed procedure to attach and growth of Ag nanoparticles or nanoplates on the surface of ZTO similar to inidium tin oxide (ITO) and has been described by M. Oyama and et al. [17,18].
Fig. 1. Typical SEM images of nanosilver, (a) with modified ZTO electrodes (after 30 min) and (b) after changing growth solution to AgNO3 and poly(vinylpyrrolidone).
Methods In this seed mediated growth procedure, when another growth solution containing AgNO3 and poly (vinylpyrrolidone) (PVP) was used, we could prepare Ag nanoplate-attached ZTO substrates as reported previously for ITO M. Oyama and et al. [18]. In the present work, to increase the coverage amount of Ag nanoplates, the contents of the growth solution used was prepared by adding 0.2 ml of 0.15 M ascorbic acid into a solution that contained 0.5 ml of 0.01 M AgNO3, 9 ml of 1 mM PVP, 10 ml of 0.1 M CTAB and 3 ml pure water, and then a piece of ZTO was immersed for 15 h after the seeding treatment. As reduction chemical method was used for preparation of Ag nanoplates, a few nanorods and spherical nanoparticles also formed [11,12]. Results and discussion It was observed [17,18] during preparation of nanosilver particles that seed mediated growth approach leads to growth of spherical nanoparticles of different size (30–100 nm) depending upon the time allowed in the growth solution. In the present studies the time allowed in growth solution was 30 min, 1 h and 24 h. At these times spherical nanosilver particles of different size were deposited. They have been named as small (<30 nm), medium (30–60 nm), large (>60 nm) nanosilver particles and nanosilver plates [11,12].
Fig. 2. A comparison of linear sweep voltammograms of 1.0 mM potassium ferrocyanide at different electrodes at sweep rate of 25 mV s 1. Curves were recorded at (a) ZTO, (b) spherical nanosilver particles >60 nm, (c) bulk silver and (d) silver nanoplates.
nanoparticles. Meanwhile, the current would not depend on the 2D surface of the silver. Linear sweep voltammograms characterization Fig. 3 presents a comparison of voltammograms observed for ascorbic acid at pH 7.2. It was observed that electrodes having spherical nanosilver particles of different sizes exhibit oxidation
SEM Characterization Fig. 1(a and b), shows the SEM images of different spherical nanoparticles and nanoplates grown on zinc tin oxide (ZTO), and clearly indicates the deposition of spherical and nanosilver plates. Sweep voltammograms characterization Fig. 2 presents a comparison of voltammograms at silver nanoparticles attached electrode with bare silver electrode at sweep rate of 25 mV s 1. The current magnitude of ferrocyanide at ZTO electrode is presented by curve in Fig. 2. The curves b and d present current magnitude of spherical Ag nanoparticles (>60 nm) and nanoplates. However, bare and bulk silver electrode is presented by curve c. It is clear from the figure that for the standard redox couple the response of nanoplates is larger in comparison to spherical Ag
Fig. 3. Linear sweep voltammograms of 1.0 mM ascorbic acid in pH 7.2 phosphate buffer observed at a sweep rate of 20 mV s 1 at (a) plate type, (b) spherical small, (c) medium and (d) large nanosilver modified electrode.
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B. Sadeghi, M. Meskinfam / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 326–328
peak at same potential (cf. 695 mV) with identical current. In contrast to electrode having spherical nanosilver particles, the oxidation of ascorbic acid was observed at 628 mV at nanosilver plate electrode and current was found to increase to 3.4 lA. A linear relationship was observed between the peak current and the square root of scan rate with a slope of 0.55 and correlation coefficient -0.983. This behavior indicates that the electrode process is diffusion-controlled within the scan rate range studied [19]. The slope of 0.55 is close to the theoretically expected value of 0.50 for an ideal diffusion controlled process. Similar behavior was observed for ascorbic acid in square wave voltammetry. At bare silver electrode ascorbic acid exhibited a broad oxidation peak, whereas, no peak was observed at bare ZTO electrode. It was found that oxidation of ascorbic acid occurred in a single peak having Ep 575 mV at three spherical nanosilver modified ZTO electrodes. The peak current observed was close to 3.2 lA at spherical nanosilver electrodes. However, when nanoplate modified ZTO electrode was used, the Ep value remained same, whereas, the peak current was found to increase to 7.5 lA. The geometric area was used for current density calculations effective electrode calculations showed a variation of nearly 10% for nanoplates. However, as rough estimate the ratio of effective/ geometric area of nanoplates was found between 0.6 and 0.7. This clearly indicates that silver nanoplate modified ZTO has higher catalytic activity in comparison to spherical nanosilver particles modified ZTO electrode [12]. The dependence of peak current for oxidation peak of ascorbic acid was studied on scan frequency at all the electrodes. This behavior suggested the diffusion controlled nature of electrode reaction [20]. Also, the peak potential of ascorbic acid shifted towards more positive potentials with increase in sweep rate. This peak shift indicates a quasi-reversible process or a chemical reaction associated with the electron transfer. Thus, use of nanoplates modified ZTO electrode provides better peak current and hence lower detection limit can be easily achieved for ascorbic acid and possibly for other biomolecules also. The above studies clearly indicate that Ag nanoplate modified ZTO electrode exhibit higher electrocatalytic activity in comparison to spherical silver nano modified ZTO electrodes towards oxidation of biomolecule particularly ascorbic acid. One of the reasons for such behavior may be due to very sharp edges of triangular Ag nanoplates with average width 5–10 lm. The lattice plane may also provide more edges in comparison to spherical nanosilver particles. The edge plane has been found to exhibit more catalytic activity in comparison plane of pyrolytic graphite [21,22]. Another possibility is the role of the electroactive area of the electrode. The spherical nanoparticles are indeed rather small (<100 nm) so that their dimension does not exceed the dimension of the diffusion layer, therefore they should not contribute significantly to increasing the electroactive area. This agrees with well with what is recently demonstrated for the case of electrodes made of arrays of silver nanowires with different length [23]. A comparison of catalytic behavior of the different shaped nanosilver particles has also reported in literature [12,24–27] that Ag nanoplates exhibit superior catalytic properties to other shaped nanosilver particles for liberating hydrogen gas for HCHO solutions. Thus, it is suggested that electrodes modified with Ag nanoplates are better in comparison to spherical nanosilver particles.
Further studies on comparative aspects of electrochemical activity of silver nanoplates and spherical nanosilver particles are in progress. Conclusion In summary, we observed that the peak currents at Ag nanoplates modified ZTO electrode are nearly two to three times larger than spherical silver nanoparticles. This clearly indicates that silver nanoplate modified ZTO has higher catalytic activity in comparison to spherical nanosilver particles modified ZTO electrode. One of the reasons for such behavior may be due to very sharp edges of triangular Ag nanoplates with average width 5–10 lm. It is thus expected that the sensitivity and detection limit will be much better at Ag nanoplates modified ZTO electrode in linear sweep voltammetry in comparison to spherical nanosilver particles. Acknowledgements The financial and encouragement support provided by the Research vice Presidency of Tonekabon Branch, Islamic Azad University and Executive Director of Iran-Nanotechnology Organization (Govt. of Iran). References [1] S. Lu, K. Wu, X. Dang, S. Hu, Talanta 63 (2004) 653–657. [2] R.N. Goyal, M. Oyama, V.K. Gupta, S.P. Singh, R.A. Sharma, Sensors Actuat. B 134 (2008) 816–821. [3] O. Niwa, D. Kato, H. Shigeru, Chem. Sensors 24 (2008) 6–12. [4] L. Xiao, G.G. Wildgoose, R.G. Compton, New J. Chem. 32 (2008) 1628–1633. [5] F. Kurusu, H. Tsunoda, A. SaZTO, A. Tomita, A. Kayahara, I. Karube, et al., Analyst 131 (2006) 1292–1298. [6] F. Valentini, S. Orlanducci, M. Terranova, A. Letizia, P.G. Aziz, Sensors Actuat. B 100 (2004) 117–125. [7] R.N. Goyal, M. Oyama, A. Tyagi, S.P. Singh, Talanta 72 (2007) 140–144. [8] M. Li, F. Gao, P. Yang, L. Wang, B. Fang, Surf. Sci. 602 (2007) 151–155. [9] H.L. Zhang, X.Z. Zou, G.S. Lai, D.Y. Han, F. Wang, Electroanalysis 19 (2007) 1869–1874. [10] R.N. Goyal, V.K. Gupta, M. Oyama, N. Bachheti, Electrochem. Commun. 8 (2006) 65–70. [11] M.A.S. Sadjadi, B. Sadeghi, M. Meskinfam, K. Zare, J. Azizian, Physica E 40 (2008) 3183–3186. [12] B. Sadeghi, M.A.S. Sadjadi, R.A.R. Vahdati, Superlattices Microstruct. 46 (2009) 858–863. [13] B. Sadeghi, M. Jamali, Sh. Kia, A. Amininia, S. Ghafari, Int. J. Nano Dimens. 1 (2010) 119–124. [14] B. Sadeghi, F.S. Garmaroudi, M. Hashemi, H.R. Nezhad, A. Nasrollahi, Sima. Ardalan, Sahar. Ardalan, Adv. Powder Technol. 23 (2012) 22–26. [15] B. Sadeghi, A. Pourahmad, Adv. Powder Technol. 22 (2011) 669–673. [16] B. Sadeghi, Sh. Ghammamy, Z. Gholipour, M. Ghorchibeigy, A. Amininia, Mic & Nano Letters 6 (2011) 209–213. [17] M. Kambayashi, J. Zhang, M. Oyama, Cryst. Growth Des. 5 (2005) 81–84. [18] A.A. Umar, M. Oyama, Cryst. Growth Des. 6 (2006) 818–821. [19] A. Bard, L.R.F. Aglkner, Electrochemical Methods, Wiley, NY, 1980. [20] J. Osteryoung, R.A. Osteryoung, Anal. Chem. 57 (1985) 101–110. [21] R.H. Wopschall, I. Shain, Anal. Chem. 39 (1967) 1514–1527. [22] R.T. Kachoosangi, R.G. Compton, Anal. Bioanal. Chem. 387 (2007) 2793–2800. [23] M. De Leo, A. Kuhn, P. Ugo, Electroanalysis 19 (2007) 227–236. [24] Y. Bi, G. Lu, Mater. Lett. 62 (2008) 2696–2699. [25] A. Miyazaki, T. Asakawa, Y. Nakano, I. Balint, Chem. Commun. (2005) 3730– 3732. [26] M. Li, Z. Zhao, R. Geng, H. Hu, Bioelectrochemistry 74 (2008) 217–221. [27] N.N. Horimoto, K. Imura, H. Okamoto, Chem. Phys. Lett. 467 (2008) 105–109.