- Email: [email protected]
A promising method for fabricating Ag nanoparticle modified nonenzyme hydrogen peroxide sensors
Sensors and Actuators B 181 (2013) 125–129
Contents lists available at SciVerse ScienceDirect
Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb
A promising method for fabricating Ag nanoparticle modified nonenzyme hydrogen peroxide sensors Kaiming Liao, Peng Mao, Yuhua Li, Yali Nan, Fengqi Song, Guanghou Wang, Min Han ∗ National Laboratory of Solid State Microstructures and Department of Materials Science and Engineering, Nanjing University, Nanjing 210093, China
a r t i c l e
i n f o
Article history: Received 11 October 2012 Received in revised form 15 January 2013 Accepted 18 January 2013 Available online 28 January 2013 Keywords: Silver nanoparticles Cluster beam deposition Hydrogen peroxide Nonenzyme sensors
a b s t r a c t We demonstrate a promising method to fabricate highly adhesive silver nanoparticle coating on glass carbon electrode with good dispersity by using gas phase cluster beam deposition. The fabricated nanoparticles have clean surface and show enhanced electrocatalytic activity toward the reduction of H2 O2 with a considerably decreased overpotential. A nonenzyme sensing platform for stable detection of H2 O2 with a very rapid response time (less than 1 s), high sensitivity (63 A/mM) as well as a low detection limit (1.3 M) is realized from the silver nanoparticle based electrode with a optimized nanoparticle coverage. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Rapid, accurate, stable, sensitive and low cost detection of H2 O2 is very important in various fields including clinical diagnostics, environmental analysis and food industry. [1–3]. Many techniques have been reported for the H2 O2 determination [4,5], among which amperometric technique is especially attractive because of its simplicity and high sensitivity. [6]. Nanoparticles, especially noble metal nanoparticles, such as gold [7], silver [8], platinum [9], iridium [10], palladium [11] and their hybrids [12], have attracted considerable attention in preparing biosensors due to their unique electronic and catalytic properties. They were found to be versatile in applying for biosensors based on the oxidation of H2 O2 on platinum based electrodes [9,12,13]. However, the amperometric detection of H2 O2 at a positive potential often suffers from electrochemical interference by oxidizable species, such as acetaminophen, l-ascorbic acid, and uric acid. [13,14] Recently, silver nanostructures have attracted much interest in the sensor applications due to their low costs and excellent conductivities. Silver nanoparticle (AgNP) based electrodes, such as DNA/silver [15], hemoglobin/silver [16], peroxidase/DNA/silver electrode [17], have been widely investigated for the H2 O2 detection. However, due to the intrinsic nature of enzymes and DNA, such sensors suffer from the stability problem. To resolve this issue, silver electrodes free from enzyme or DNA were proposed [8,18–21].
∗ Corresponding author. Tel.: +86 25 83686248; fax: +86 25 83686248. E-mail address: [email protected] (M. Han). 0925-4005/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.snb.2013.01.038
In the fabrication of the silver electrodes, a two-step procedure was commonly used. The silver nanoparticles were firstly synthesized chemically in solution and then the nanoparticle dispersion was dripped onto the electrode as catalyzer. The adhesion of the nanoparticle catalyzers on the electrode was not strong and stable problems would emerge in sensor applications. To improve the adhesion of the catalyzers on the electrodes, conducting polymers were widely employed to fix the catalyzers [22–24]. In practice, the conducting polymer may have an influence on the catalyzers so that its application is limited [25]. Although certain progresses have been made on catalyzer immobilization, it is still a big challenge to fabricate catalyzer layers that are tightly bonded on electrode with a good dispersity. In this work, we report an Ag nanoparticle modified glass carbon electrode (GCE) fabricated by means of gas phase cluster beam deposition with controlled coverage and size distribution. The nanostructures fabricated by this method have the merits of high adhesion, good dispersity as well as clean surface. The asprepared electrode shows excellent catalytic activity toward the electrochemical reduction of H2 O2 .
2. Experimental In the experiment, the GCEs with 3 mm diameter were carefully polished to obtain a mirror-like surface. AgNPs were generated in gas phase with a magnetron plasma gas aggregation cluster source [26] and deposited on GCEs in a high vacuum chamber. To operate the cluster source, 130 sccm of argon was introduced into the liquid nitrogen cooled aggregation tube to maintain a stable
126
K. Liao et al. / Sensors and Actuators B 181 (2013) 125–129
Fig. 1. Sketch illustrating the depositing of AgNPs on the GCEs by cluster beam deposition.
pressure of 110 Pa. A stable magnetron discharge ran with an input power of 55 W. Atoms were sputtered from the silver target and silver clusters were formed through the aggregation process in the argon gas. The clusters were swept by the gas stream into high vacuum through a nozzle and formed a nanoparticle beam with a high speed of ∼1000 m/s [27]. Then, the nanoparticles deposited and stuck on the GCEs surface firmly. Fig. 1 illustrates a sketch of depositing AgNPs on the GCEs. The coverage and size distribution of the AgNPs was characterized with a transmission electron microscopy (TEM, Tecnai F20). For TEM imaging, AgNPs were deposited on the surface of amorphous carbon film supported with copper grid. The size distribution and nanoparticle coverage were measured from the TEM images. Electrochemical measurements were carried out on a CHI 660D electrochemical workstation (CH instruments) by using a conventional three-electrode system. An AgNPs/GCE, a platinum wire and a saturated Ag/AgCl electrode were used as the working, counter, and reference electrodes, respectively. The cyclic voltammetric (CV) and amperometric measurements were performed at 25 ◦ C in an electrochemical cell containing 10 mL of 0.05 M phosphate buffer solutions (PBS) with pH = 7.4, which was deaerated with high purity nitrogen for 10 min. The PBS was prepared with NaH2 PO4 and Na2 HPO4 . The supporting electrolyte was 0.9% NaCl. 3. Results and discussion Fig. 2a depicts the CV curves of the AgNP modified electrode (∼60% coverage) in 0.05 M PBS (pH 7.4) at different scan rates. A redox peak can be observed between −0.6 and −0.4 V. On the other hand, no obvious electrochemical reduction peak was observed in the current experiment when the CV scans were performed on bare GCE in H2 O2 , bare GCE in PBS, AgNPs/GCE in PBS and AgNPs/GCE in NaCl supporting electrolyte (as shown in inset of Fig. 2a, which were measured at a typical scan rate of 0.1 V/s). Obviously, the redox peaks were attributed to the electrochemical reaction of H2 O2 on AgNPs/GCE. The reaction mechanism is proposed as follows: Ag
H2 O2 + e− −→OH(ads) + OH− Ag
H2 O2 + H+ + OH(ads) + e− −→2OH(ads) + H2 O In the first step, the “activated” step, the reduction of the first H2 O2 molecule provides the initial source of OH(ads) at a small overpotential, which, in turn, allows the reduction of the secondary H2 O2 molecule at a faster rate. The activated process also results in the accumulation of OH(ads) intermediates on the electrode surface, provided that the reduction of H2 O2 takes place continuously [28,29]. The above H2 O2 reduction process can only take place efficiently under the catalysis of Ag on the eletrode [30]. It is worthwhile to notice that the peak potential appears at around −0.4 V at a scan rate of 0.1 V/s, which is about −0.2 V lower
than the reported over-potential of AgNP-modified nonenzyme electrodes [8,18–21]. This prominent electrocatalytic activity of the AgNPs may be ascribed to their clean surface, large area-to-volume ratio and high adhesion on the electrode with good dispersity. In Fig. 2b the reduction peak currents are shown as a function of the scan rate. It shows that the reduction peak current increases linearly with the square root of the scan rate (v1/2 ) from 0.1 to 0.9 V/s. This result reveals the electron transfer between H2 O2 and AgNPs/GCE in a diffusive electrochemical process. Fig. 2c shows the typical amperometric responses of the AgNPs/GCE to the successive addition of H2 O2 of different concentrations measured at −0.4 V under optimized experimental conditions. The electrode shows a very quick response to the concentration change of H2 O2 , with a current rise time of less than 1 s (inset in Fig. 2c), which is faster than all the silver based electrodes [8,15–21]. The fast response may be attributed to the small size and clean surface of the AgNPs. Furthermore, a linear relationship between the catalytic current and the H2 O2 concentration could be obtained with a correlation coefficient of 0.9998 in the H2 O2 concentration range from 4 × 10−6 M to 7.6 × 10−5 M, as shown in Fig. 2d. A detection limit of 1.3 × 10−6 M is reached at the signal-to-noise ratio of 3 and the sensitivity of the AgNPs/GCE is 63 A/mM, which is higher than those reported for the silver nonenzyme electrodes [8,18–21], Cu2 O modified electrode [22], Fe3 O4 modified electrode [31], and even enzyme-based electrode [16,17]. The electrode also shows a good repeatability. In Fig. 2d, standard deviations estimated from five repeated amperometric measurements with the same electrode are shown as the associated error bars. As can be seen, the dispersion of the measurement data is reasonably small. Such behaviors indicate that the present fabricated electrode functions well in detecting H2 O2 and is promising for nonenzyme sensor. To examine the effects of the coverage and size distribution of the AgNPs on the reduction of the H2 O2 for optimizing the electrode conformation, we fabricated AgNPs/GCE electrodes with different deposition durations. Fig. 3a–c show the TEM images of the AgNPs ˚ fabricated by cluster beam deposition at a depositing rate of 0.3 A/s for 1 min, 5 min and 10 min, respectively. The coverage and size distribution of the AgNPs were measured from the TEM images that represent those nanoparticles deposited on the GCE surface. The nanoparticle coverage is estimated to be ∼15%, ∼60% and ∼70% correspondingly. As can be seen in Fig. 3a–c, the size of the AgNPs keeps unchanged with 1 min and 5 min deposition, and starts to increase with 10 min deposition. At high coverage, the size of the Ag nanoparticles increases due to the diffusive aggregation and coalescence. It is known that the catalytic behaviors of the metal nanoparticles are strongly affected by their size. Such examples include Pt nanoparticles used in the reduction of oxygen [32] and Pd nanoparticles used for the catalytic hydrogenation of allyl alcohol [33]. To evaluate the morphology dependent catalytic activity of the AgNPs/GCE electrodes toward the reduction of H2 O2 , the linear sweep stripping voltammetry (LSSV) was conducted for 4 mM H2 O2 (0.05 M PBS pH = 7.4) in the potential range from −0.2 V to −0.7 V (vs. Ag/AgCl) at a scan rate of 0.1 V/s and in N2 saturated. It can be found that the catalytic activity of the AgNPs/GCE is influenced by the nanoparticle coverage in H2 O2 reduction. As shown in Fig. 3d, the reduction peak current of H2 O2 increases remarkably when the deposition time increases from 1 to 5 min, while it decreases slowly when further increasing the deposition time to 10 min. In order to compare the electrochemical responses of AgNPs/GCE with different deposition time (indicated in the legend) in the reduction of H2 O2 , the time dependent current responses to the continuous addition of H2 O2 were recorded and the results are shown in Fig. 3e. It can be seen that the catalytic reduction current of H2 O2 is directly proportional to the H2 O2 concentration in the range of 4–60 M (shown in Fig. 3f). From the slope of the curves, the sensitivity of the AgNPs/GCE sensors was calculated to
K. Liao et al. / Sensors and Actuators B 181 (2013) 125–129
127
Fig. 2. (a) The CV curves of the as-prepared AgNPs/GCE in 10 mM H2 O2 and 0.05 M PBS (pH 7.4) at different scan rates (from top to bottom: 0.1–0.9 V/s). The inset shows the CV scans performed on bare GCE in H2 O2 , bare GCE in PBS, AgNPs/GCE in PBS and AgNPs/GCE in NaCl supporting electrolyte at a scan rate 0.1 V/s. (b) The linear dependence of peak current on the square root of the scan rate. (c) Typical amperometric responses of the AgNPs/GCE upon successive addition of H2 O2 into gently stirred 0.05 M PBS (pH 7.4) at −0.4 V. (d) The linear relationship between the catalytic current and the H2 O2 concentration.
Fig. 3. (a–c) Size distributions and TEM images of the AgNPs with different deposition times ((a) 1 min, (b) 5 min and (c) 10 min) on the GCEs. (d) The linear sweep stripping voltammetry (LSSV) measurements of the AgNPs/GCE with different deposition times (indicated in the legend) in 4 mM H2 O2 (0.05 M PBS pH = 7.4) at the scan rates of 0.1 V/s. (e) The amperometric responses of the AgNPs/GCE with different deposition times (indicated in the legend) upon successive addition of H2 O2 into gently stirred 0.05 M PBS (pH 7.4) at −0.4 V. (f) The linear relationship between the catalytic current and the concentration.
128
K. Liao et al. / Sensors and Actuators B 181 (2013) 125–129
also supported by a project funded by the PAPD of Jiangsu Higher Education Institutions.
References
Fig. 4. A comparison of measurements within ten consecutive scans of the same electrode by LSSV in 4 mM H2 O2 (0.05 M PBS pH = 7.4) at the scan rates of 0.1 V/s.
be 24, 63 and 54 A/mM for the corresponding nanoparticle deposition time of 1, 5 and 10 min respectively. It seems that there is an optimized deposition time to realize the best sensitivity and linearity. With a deposition time of 10 min, both the sensitivity and linearity of the AgNPs/GCE sensor become worse than that of the sensor with a deposition time of 5 min. It thus demonstrates that the electrode consists of small nanoparticles which are densely closely spaced but sufficiently isolated from each other and has significantly advantages in electroanalysis. The stability of the electrode was also tested. Fig. 4 compares the LSSV obtained within ten consecutive measurements on the AgNPs/GCE electrode in 4 mM H2 O2 at the constant scan rate of 0.1 V/s. No obvious changes on the peak current and peak potential can be observed from those curves, which indicates the as-prepared sensor is quite stable in detection H2 O2 . The stable response should be ascribed to the high adhesion of the AgNPs on the given electrode. The long-term stability of the electrode in air was also examined. When the used electrode was stored at room temperature in air for 1 week, the CV peak currents still retained ∼90% and in the next 2 weeks the response still retained ∼85% of the initial value. From TEM observation, we confirmed that the coverage grade of the AgNPs deposited on carbon surface didn’t change over time, even after H2 O2 immersion. 4. Conclusion The present study demonstrates a novel method to coat Ag nanoparticles on glass carbon electrodes with high adhesion and good dispersity by performing gas phase cluster beam deposition. The AgNPs generated with this approach have clean surface as compared with those obtained from the chemical route. As a result, the fabricated AgNP-modified-GCE shows enhanced electrocatalytic activity toward the reduction of H2 O2 with a much reduced detection limit (typically 1 × 10−6 M) and response time (typically less than 1 s) as compared with those have been previously reported. Moreover, this technique is a promising technology for fabricating various metal nanoparticle based electrodes with great promise for electrochemical sensors design. Acknowledgments We acknowledge the financial support from NSFC (grant nos. 10974092, 51171077 and 11075076), the National Basic Research Program of China (973 Program, contract no. 2009CB930501), and the Industrialization Promotion of University Research Program in Jiangsu Province under contract no. JH10-2. This research was
[1] S. Ashok Kumar, S.F. Wang, Y.T. Chang, Poly(BCB)/Au-nanoparticles hybrid film modified electrode: preparation, characterization and its application as a nonenzymatic sensor, Thin Solid Films 518 (2010) 5832–5838. [2] G.H. Zhang, N.B. Yang, Y.L. Ni, J. Shen, W.B. Zhao, X.H. Huang, A H2 O2 electrochemical biosensor based on biocompatible PNIPAM-g-P (NIPAM-co-St) nanoparticles and multi-walled carbon nanotubes modified glass carbon electrode, Sensors and Actuators B: Chemical 158 (2011) 130–137. [3] M. Delvaux, A. Walcarius, S. Demoustier-Champagne, Electrocatalytic H2 O2 amperometric detection using gold nanotube electrode ensembles, Analytica Chimica Acta 525 (2004) 221–230. [4] C. Matsubara, N. Kawamoto, K. Takamura, Oxo [5,10, 15, 20-tetra(4pyridyl)porphyrinato] titanium(IV): an ultra-high sensitivity spectrophotometric reagent for hydrogen peroxide, Analyst 117 (1992) 1781–1784. [5] S. Hanaoka, J. Lin, M. Yamada, Chemiluminescent flow sensor for H2 O2 based on the decomposition of H2 O2 catalyzed by cobalt(II)-ethanolamine complex immobilized on resin, Analytica Chimica Acta 426 (2001) 57–64. [6] V. Tripathi, V. Kandimalla, H. Ju, Amperometric biosensor for hydrogen peroxide based on ferrocene-bovine serum albumin and multiwall carbon nanotube modified ormosil composite, Biosensors and Bioelectronics 21 (2006) 1529–1535. [7] Z.M. Liu, Y. Yang, H. Wang, Y.L. Liu, G.L. Shen, R.Q. Yu, A hydrogen peroxide biosensor based on nano-Au/PAMAM dendrimer/cystamine modified gold electrode, Sensors and Actuators B: Chemical 106 (2005) 394–400. [8] S. Liu, J.Q. Tian, L. Wang, X.P. Sun, A method for the production of reduced graphene oxide using benzylamine as a reducing and stabilizing agent and its subsequent decoration with Ag nanoparticles for enzymeless hydrogen peroxide detection, Carbon 49 (2011) 3158–3164. [9] J. Ren, W. Shi, K. Li, Z.F. Ma, Ultrasensitive platinum nanocubes enhanced amperometric glucose biosensor based on chitosan and nafion film, Sensors and Actuators B: Chemical 163 (2012) 115–120. [10] M.C. Rodriguez, G.A. Rivas, Glucose biosensor prepared by the deposition of iridium and glucose oxidase on glassy carbon transducer, Electroanalysis 11 (1999) 558–564. [11] P. Zhou, Z.H. Dai, M. Fang, X.H. Huang, J.C. Bao, Novel dendritic palladium nanostructure and its application in biosensing, The Journal of Physical Chemistry C 111 (2007) 12609–12616. [12] M. Janyasupab, C.W. Liu, Y. Zhang, K.W. Wang, C.C. Liu, Bimetallic Pt–M (M = Cu, Ni, Pd, and Rh) nanoporous for H2 O2 based amperometric biosensors, Sensors and Actuators B: Chemical (2012), http://dx.doi.org/ 10.1016/j.snb.2012.09.099. [13] M. Ammam, E.B. Easton, High-performance glucose sensor based on glucose oxidase encapsulated in new synthesized platinum nanoparticles supported on carbon Vulcan/Nafion composite deposited on glassy carbon, Sensors and Actuators B: Chemical 155 (2011) 340–346. [14] J. Wang, G. Chen, M.P. Chatrathi, M. Musameh, Capillary electrophoresis microchip with a carbon nanotube-modified electrochemical detector, Analytical Chemistry 76 (2004) 298–302. [15] S. Wu, H. Zhao, H. Ju, C. Shi, J. Zhao, Electrodeposition of silver–DNA hybrid nanoparticles for electrochemical sensing of hydrogen peroxide and glucose, Electrochemistry Communications 8 (2006) 1197–1203. [16] Y.H. Wang, H.Y. Gu, Hemoglobin co-immobilized with silver–silver oxide nanoparticles on a bare silver electrode for hydrogen peroxide electroanalysis, Mikrochimica Acta 164 (2009) 41–47. [17] L. Ma, R. Yuan, Y. Chai, S. Chen, Amperometric hydrogen peroxide biosensor based on the immobilization of HRP on DNA–silver nanohybrids and PDDAprotected gold nanoparticles, Journal of Molecular Catalysis B: Enzymatic 56 (2009) 215–220. [18] X. Gao, L.Y. Jin, Q. Wu, Z.C. Chen, X.F. Lin, A nonenzymatic hydrogen peroxide sensor based on silver nanowires and chitosan film, Electroanalysis 24 (2012) 1771–1777. [19] X.P. Sun, X.Y. Qin, J.M. Hu, Y.L. Luo, W.B. Lu, G.H. Chang, A.M. Asiri, A.O. Al-Youbi, Heat treatment-based one-step preparation of highly concentrated, well-stable silver colloids that can form stable films on bare electrodes for H2 O2 detection, Current Nanoscience 8 (2012) 335–342. [20] G.H. Chang, Y.L. Luo, W.B. Lu, F. Liao, X.P. Sun, Hydrothermal synthesis of ultrahighly concentrated, well-stable Ag nanoparticles and their application for enzymeless hydrogen peroxide detection, Journal of Nanoparticle Research 13 (2011) 2689–2695. [21] Y.W. Zhang, S. Liu, L. Wang, X.Y. Qin, J.Q. Tian, W.B. Lu, G.H. Chang, X.P. Sun, One-pot green synthesis of Ag nanoparticles–graphene nanocomposites and their applications in SERS, H2 O2 , and glucose sensing, RSC Advances 2 (2012) 538–545. [22] L. Zhang, H. Li, Y.H. Ni, J. Li, K.M. Liao, G.C. Zhao, Porous cuprous oxide microcubes for non-enzymatic amperometric hydrogen peroxide and glucose sensing, Electrochemistry Communications 11 (2009) 812–815. [23] Q. Wang, Y.B. Yun, J.B. Zheng, Nonenzymatic hydrogen peroxide sensor based on a polyaniline-single walled carbon nanotubes composite in a room temperature ionic liquid, Mikrochimica Acta 167 (2009) 153–157.
K. Liao et al. / Sensors and Actuators B 181 (2013) 125–129 [24] J. Wang, M. Musameh, Y. Lin, Solubilization of carbon nanotubes by nafion toward the preparation of amperometric biosensors, Journal of the American Chemical Society 125 (2003) 2408–2409. [25] M.A. Rahman, P. Kumar, D.S. Park, Y.B. Shim, Electrochemical sensors based on organic conjugated polymers, Sensors 8 (2008) 118–141. [26] H. Haberland, M. Mall, M. Moseler, Y. Qian, T. Reiners, Y. Thurner, Filling of micron-sized contact holes with copper by energetic cluster impact, Journal Vacuum Science and Technology A 12 (1994) 2925–2930. [27] M. Han, C.H. Xu, D. Zhu, L. Yang, J.L. Zhang, Y.P. Chen, K. Ding, F.Q. Song, G.H. Wang, Controllable synthesis of two-dimensional metal nanoparticle arrays with oriented size and number density gradients, Advanced Materials 19 (2007) 2979–2983. [28] G. Flätgen, S. Wasle, M. Lübke, C. Eickes, G. Radhakrishnan, K. Doblhofer, G. Ertl, Autocatalytic mechanism of H2 O2 reduction on Ag electrodes in acidic electrolyte: experiments and simulations, Electrochimica Acta 44 (1999) 4499–4506. [29] W. Zhao, H. Wang, X. Qin, X. Wang, Z. Zhao, Z. Miao, L. Chen, M. Shan, Y. Fang, Q. Chen, A novel nonenzymatic hydrogen peroxide sensor based on multiwall carbon nanotube/silver nanoparticle nanohybrids modified gold electrode, Talanta 80 (2009) 1029–1033. [30] X. He, C. Hu, H. Liu, G. Du, Y. Xi, Y. Jiang, Building Ag nanoparticle 3D catalyst via Na2 Ti3 O7 nanowires for the detection of hydrogen peroxide, Sensors and Actuators B: Chemical 144 (2010) 289–294. [31] M.S. Lin, H.J. Leu, A Fe3 O4 -based chemical sensor for cathodic determination of hydrogen peroxide, Electroanalysis 17 (2005) 2068–2073. [32] H. Ye, J.A. Crooks, R.M. Crooks, Effect of particle size on the kinetics of the electrocatalytic oxygen reduction reaction catalyzed by Pt dendrimer-encapsulated nanoparticles, Langmuir 23 (2007) 11901–11906. [33] O.M. Wilson, M.R. Knecht, J.C. Garcia-Martinez, R.M. Crooks, Effect of Pd nanoparticle size on the catalytic hydrogenation of allyl alcohol, Journal of the American Chemical Society 128 (2006) 4510–4511.
Biographies Kaiming Liao was born in 1983 in Anhui Province, China. He got a B.S. and M.S. degree in Chemistry and Materials Science from Anhui Normal University, China, in 2006 and 2009, respectively. In 2011, he worked as a visiting scholar in the National Institute of Advanced Industrial Science and Technology (AIST) in Japan. He is currently working in his Ph.D. at the Department of Materials Science and Engineering, Nanjing University. His research interests cover metal nanostructures, especially metal nanoparticle arrays, as well as the applications of these nanostructures in sensors, electronics, and energy. Peng Mao received the B.E. degree in Materials Chemistry from Nanjing University of Technology, China, in 2010. He is currently working on Ph.D. at the Department of Materials Science and Engineering, Nanjing University. His research interests cover
129
metal nanostructures, dielectric nanostructures, especially optic properties of metal and dielectric nanoparticle arrays, as well as the applications of these nanostructures in light emission device, sensors, photocatalysis and energy. Yuhua Li received the B.S. degree in Electronic and Information Engineering from Xiàn University of Architecture and Technology, China, in 2010. She is currently studying on the nanostructured photovoltaic device toward her M.S. degree in Materials Science at Nanjing University. Yali Nan received the B.S. degree in Materials Physics and chemistry from Hebei University of technology, China, in 2010. She is currently studying on the semicondutor nanoparticles toward her M.S. degree in Materials Physics and Chemistry at Nanjing University. Fengqi Song received the B.S. degree in Particle Physics and Nuclear Physics from Lanzhou University, China, in 2000. In 2005 he received Ph.D. degree in Condensed Matter Physics from the Nanjing University. He is now an associate professor in the Department of Physics at Nanjing University. His research interests span a wide range of experimental and theoretical topics in electronic structure of nanoscale materials and thermal properties of small particles, nanocrystals, and nanotubes. Guanghou Wang was born in Anhui Province, China in 1939. He obtained his bachelor’s degree in Beijing Normal University in 1963. He was a visiting scholar in New York State University from 1980 to 1982. He was employed as a professor of physics in Nanjing University in 1988. He was elected in the Academician of Chinese Academy of Sciences in 2011. His research is related to atomic clusters and clusterbased nanostructures and nanomaterials, including theoretical simulation of atomic clusters and design of cluster-based microstructures; controllable preparation, plasmon resonance property and nano-optics of cluster arrays; thermal physical properties as well as mass and/or energy transport through cluster-assembled system; magnetic and electric properties of nanostructured diluted magnetic oxides and multiferroic nanomaterial. Min Han got his B.S. degree in 1986, master degree in 1989 and doctoral degree in 1997 on condensed matter physics from Nanjing University, China. He was a STA fellow in National Institute of Advanced Industrial Science and Technology (AIST) in Japan in 1997–1999, and then appointed as a senior visiting scholar to AIST in 2001. In 2002, he worked as a visiting scholar in the Department of Physics and the Research Institute of Material Science of Freiburg University in Germany. From 2003, he was employed as a professor of materials science in Nanjing University. His research is concerned with the physical properties and applications of nanoclusters and their related nanostructures. Particular interests include gas phase cluster generation, low energy cluster beam deposition, metal cluster-block copolymer hybrid nanostructures, controllable fabrication of closely spaced nanocluster arrays, thermodynamic behaviors of nanoclusters and cluster assemblies, nanooptics and quantum transport in cluster-based nanostructures, molecular and gas sensors based on densely packed clusters.
Contents lists available at SciVerse ScienceDirect
Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb
A promising method for fabricating Ag nanoparticle modified nonenzyme hydrogen peroxide sensors Kaiming Liao, Peng Mao, Yuhua Li, Yali Nan, Fengqi Song, Guanghou Wang, Min Han ∗ National Laboratory of Solid State Microstructures and Department of Materials Science and Engineering, Nanjing University, Nanjing 210093, China
a r t i c l e
i n f o
Article history: Received 11 October 2012 Received in revised form 15 January 2013 Accepted 18 January 2013 Available online 28 January 2013 Keywords: Silver nanoparticles Cluster beam deposition Hydrogen peroxide Nonenzyme sensors
a b s t r a c t We demonstrate a promising method to fabricate highly adhesive silver nanoparticle coating on glass carbon electrode with good dispersity by using gas phase cluster beam deposition. The fabricated nanoparticles have clean surface and show enhanced electrocatalytic activity toward the reduction of H2 O2 with a considerably decreased overpotential. A nonenzyme sensing platform for stable detection of H2 O2 with a very rapid response time (less than 1 s), high sensitivity (63 A/mM) as well as a low detection limit (1.3 M) is realized from the silver nanoparticle based electrode with a optimized nanoparticle coverage. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Rapid, accurate, stable, sensitive and low cost detection of H2 O2 is very important in various fields including clinical diagnostics, environmental analysis and food industry. [1–3]. Many techniques have been reported for the H2 O2 determination [4,5], among which amperometric technique is especially attractive because of its simplicity and high sensitivity. [6]. Nanoparticles, especially noble metal nanoparticles, such as gold [7], silver [8], platinum [9], iridium [10], palladium [11] and their hybrids [12], have attracted considerable attention in preparing biosensors due to their unique electronic and catalytic properties. They were found to be versatile in applying for biosensors based on the oxidation of H2 O2 on platinum based electrodes [9,12,13]. However, the amperometric detection of H2 O2 at a positive potential often suffers from electrochemical interference by oxidizable species, such as acetaminophen, l-ascorbic acid, and uric acid. [13,14] Recently, silver nanostructures have attracted much interest in the sensor applications due to their low costs and excellent conductivities. Silver nanoparticle (AgNP) based electrodes, such as DNA/silver [15], hemoglobin/silver [16], peroxidase/DNA/silver electrode [17], have been widely investigated for the H2 O2 detection. However, due to the intrinsic nature of enzymes and DNA, such sensors suffer from the stability problem. To resolve this issue, silver electrodes free from enzyme or DNA were proposed [8,18–21].
∗ Corresponding author. Tel.: +86 25 83686248; fax: +86 25 83686248. E-mail address: [email protected] (M. Han). 0925-4005/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.snb.2013.01.038
In the fabrication of the silver electrodes, a two-step procedure was commonly used. The silver nanoparticles were firstly synthesized chemically in solution and then the nanoparticle dispersion was dripped onto the electrode as catalyzer. The adhesion of the nanoparticle catalyzers on the electrode was not strong and stable problems would emerge in sensor applications. To improve the adhesion of the catalyzers on the electrodes, conducting polymers were widely employed to fix the catalyzers [22–24]. In practice, the conducting polymer may have an influence on the catalyzers so that its application is limited [25]. Although certain progresses have been made on catalyzer immobilization, it is still a big challenge to fabricate catalyzer layers that are tightly bonded on electrode with a good dispersity. In this work, we report an Ag nanoparticle modified glass carbon electrode (GCE) fabricated by means of gas phase cluster beam deposition with controlled coverage and size distribution. The nanostructures fabricated by this method have the merits of high adhesion, good dispersity as well as clean surface. The asprepared electrode shows excellent catalytic activity toward the electrochemical reduction of H2 O2 .
2. Experimental In the experiment, the GCEs with 3 mm diameter were carefully polished to obtain a mirror-like surface. AgNPs were generated in gas phase with a magnetron plasma gas aggregation cluster source [26] and deposited on GCEs in a high vacuum chamber. To operate the cluster source, 130 sccm of argon was introduced into the liquid nitrogen cooled aggregation tube to maintain a stable
126
K. Liao et al. / Sensors and Actuators B 181 (2013) 125–129
Fig. 1. Sketch illustrating the depositing of AgNPs on the GCEs by cluster beam deposition.
pressure of 110 Pa. A stable magnetron discharge ran with an input power of 55 W. Atoms were sputtered from the silver target and silver clusters were formed through the aggregation process in the argon gas. The clusters were swept by the gas stream into high vacuum through a nozzle and formed a nanoparticle beam with a high speed of ∼1000 m/s [27]. Then, the nanoparticles deposited and stuck on the GCEs surface firmly. Fig. 1 illustrates a sketch of depositing AgNPs on the GCEs. The coverage and size distribution of the AgNPs was characterized with a transmission electron microscopy (TEM, Tecnai F20). For TEM imaging, AgNPs were deposited on the surface of amorphous carbon film supported with copper grid. The size distribution and nanoparticle coverage were measured from the TEM images. Electrochemical measurements were carried out on a CHI 660D electrochemical workstation (CH instruments) by using a conventional three-electrode system. An AgNPs/GCE, a platinum wire and a saturated Ag/AgCl electrode were used as the working, counter, and reference electrodes, respectively. The cyclic voltammetric (CV) and amperometric measurements were performed at 25 ◦ C in an electrochemical cell containing 10 mL of 0.05 M phosphate buffer solutions (PBS) with pH = 7.4, which was deaerated with high purity nitrogen for 10 min. The PBS was prepared with NaH2 PO4 and Na2 HPO4 . The supporting electrolyte was 0.9% NaCl. 3. Results and discussion Fig. 2a depicts the CV curves of the AgNP modified electrode (∼60% coverage) in 0.05 M PBS (pH 7.4) at different scan rates. A redox peak can be observed between −0.6 and −0.4 V. On the other hand, no obvious electrochemical reduction peak was observed in the current experiment when the CV scans were performed on bare GCE in H2 O2 , bare GCE in PBS, AgNPs/GCE in PBS and AgNPs/GCE in NaCl supporting electrolyte (as shown in inset of Fig. 2a, which were measured at a typical scan rate of 0.1 V/s). Obviously, the redox peaks were attributed to the electrochemical reaction of H2 O2 on AgNPs/GCE. The reaction mechanism is proposed as follows: Ag
H2 O2 + e− −→OH(ads) + OH− Ag
H2 O2 + H+ + OH(ads) + e− −→2OH(ads) + H2 O In the first step, the “activated” step, the reduction of the first H2 O2 molecule provides the initial source of OH(ads) at a small overpotential, which, in turn, allows the reduction of the secondary H2 O2 molecule at a faster rate. The activated process also results in the accumulation of OH(ads) intermediates on the electrode surface, provided that the reduction of H2 O2 takes place continuously [28,29]. The above H2 O2 reduction process can only take place efficiently under the catalysis of Ag on the eletrode [30]. It is worthwhile to notice that the peak potential appears at around −0.4 V at a scan rate of 0.1 V/s, which is about −0.2 V lower
than the reported over-potential of AgNP-modified nonenzyme electrodes [8,18–21]. This prominent electrocatalytic activity of the AgNPs may be ascribed to their clean surface, large area-to-volume ratio and high adhesion on the electrode with good dispersity. In Fig. 2b the reduction peak currents are shown as a function of the scan rate. It shows that the reduction peak current increases linearly with the square root of the scan rate (v1/2 ) from 0.1 to 0.9 V/s. This result reveals the electron transfer between H2 O2 and AgNPs/GCE in a diffusive electrochemical process. Fig. 2c shows the typical amperometric responses of the AgNPs/GCE to the successive addition of H2 O2 of different concentrations measured at −0.4 V under optimized experimental conditions. The electrode shows a very quick response to the concentration change of H2 O2 , with a current rise time of less than 1 s (inset in Fig. 2c), which is faster than all the silver based electrodes [8,15–21]. The fast response may be attributed to the small size and clean surface of the AgNPs. Furthermore, a linear relationship between the catalytic current and the H2 O2 concentration could be obtained with a correlation coefficient of 0.9998 in the H2 O2 concentration range from 4 × 10−6 M to 7.6 × 10−5 M, as shown in Fig. 2d. A detection limit of 1.3 × 10−6 M is reached at the signal-to-noise ratio of 3 and the sensitivity of the AgNPs/GCE is 63 A/mM, which is higher than those reported for the silver nonenzyme electrodes [8,18–21], Cu2 O modified electrode [22], Fe3 O4 modified electrode [31], and even enzyme-based electrode [16,17]. The electrode also shows a good repeatability. In Fig. 2d, standard deviations estimated from five repeated amperometric measurements with the same electrode are shown as the associated error bars. As can be seen, the dispersion of the measurement data is reasonably small. Such behaviors indicate that the present fabricated electrode functions well in detecting H2 O2 and is promising for nonenzyme sensor. To examine the effects of the coverage and size distribution of the AgNPs on the reduction of the H2 O2 for optimizing the electrode conformation, we fabricated AgNPs/GCE electrodes with different deposition durations. Fig. 3a–c show the TEM images of the AgNPs ˚ fabricated by cluster beam deposition at a depositing rate of 0.3 A/s for 1 min, 5 min and 10 min, respectively. The coverage and size distribution of the AgNPs were measured from the TEM images that represent those nanoparticles deposited on the GCE surface. The nanoparticle coverage is estimated to be ∼15%, ∼60% and ∼70% correspondingly. As can be seen in Fig. 3a–c, the size of the AgNPs keeps unchanged with 1 min and 5 min deposition, and starts to increase with 10 min deposition. At high coverage, the size of the Ag nanoparticles increases due to the diffusive aggregation and coalescence. It is known that the catalytic behaviors of the metal nanoparticles are strongly affected by their size. Such examples include Pt nanoparticles used in the reduction of oxygen [32] and Pd nanoparticles used for the catalytic hydrogenation of allyl alcohol [33]. To evaluate the morphology dependent catalytic activity of the AgNPs/GCE electrodes toward the reduction of H2 O2 , the linear sweep stripping voltammetry (LSSV) was conducted for 4 mM H2 O2 (0.05 M PBS pH = 7.4) in the potential range from −0.2 V to −0.7 V (vs. Ag/AgCl) at a scan rate of 0.1 V/s and in N2 saturated. It can be found that the catalytic activity of the AgNPs/GCE is influenced by the nanoparticle coverage in H2 O2 reduction. As shown in Fig. 3d, the reduction peak current of H2 O2 increases remarkably when the deposition time increases from 1 to 5 min, while it decreases slowly when further increasing the deposition time to 10 min. In order to compare the electrochemical responses of AgNPs/GCE with different deposition time (indicated in the legend) in the reduction of H2 O2 , the time dependent current responses to the continuous addition of H2 O2 were recorded and the results are shown in Fig. 3e. It can be seen that the catalytic reduction current of H2 O2 is directly proportional to the H2 O2 concentration in the range of 4–60 M (shown in Fig. 3f). From the slope of the curves, the sensitivity of the AgNPs/GCE sensors was calculated to
K. Liao et al. / Sensors and Actuators B 181 (2013) 125–129
127
Fig. 2. (a) The CV curves of the as-prepared AgNPs/GCE in 10 mM H2 O2 and 0.05 M PBS (pH 7.4) at different scan rates (from top to bottom: 0.1–0.9 V/s). The inset shows the CV scans performed on bare GCE in H2 O2 , bare GCE in PBS, AgNPs/GCE in PBS and AgNPs/GCE in NaCl supporting electrolyte at a scan rate 0.1 V/s. (b) The linear dependence of peak current on the square root of the scan rate. (c) Typical amperometric responses of the AgNPs/GCE upon successive addition of H2 O2 into gently stirred 0.05 M PBS (pH 7.4) at −0.4 V. (d) The linear relationship between the catalytic current and the H2 O2 concentration.
Fig. 3. (a–c) Size distributions and TEM images of the AgNPs with different deposition times ((a) 1 min, (b) 5 min and (c) 10 min) on the GCEs. (d) The linear sweep stripping voltammetry (LSSV) measurements of the AgNPs/GCE with different deposition times (indicated in the legend) in 4 mM H2 O2 (0.05 M PBS pH = 7.4) at the scan rates of 0.1 V/s. (e) The amperometric responses of the AgNPs/GCE with different deposition times (indicated in the legend) upon successive addition of H2 O2 into gently stirred 0.05 M PBS (pH 7.4) at −0.4 V. (f) The linear relationship between the catalytic current and the concentration.
128
K. Liao et al. / Sensors and Actuators B 181 (2013) 125–129
also supported by a project funded by the PAPD of Jiangsu Higher Education Institutions.
References
Fig. 4. A comparison of measurements within ten consecutive scans of the same electrode by LSSV in 4 mM H2 O2 (0.05 M PBS pH = 7.4) at the scan rates of 0.1 V/s.
be 24, 63 and 54 A/mM for the corresponding nanoparticle deposition time of 1, 5 and 10 min respectively. It seems that there is an optimized deposition time to realize the best sensitivity and linearity. With a deposition time of 10 min, both the sensitivity and linearity of the AgNPs/GCE sensor become worse than that of the sensor with a deposition time of 5 min. It thus demonstrates that the electrode consists of small nanoparticles which are densely closely spaced but sufficiently isolated from each other and has significantly advantages in electroanalysis. The stability of the electrode was also tested. Fig. 4 compares the LSSV obtained within ten consecutive measurements on the AgNPs/GCE electrode in 4 mM H2 O2 at the constant scan rate of 0.1 V/s. No obvious changes on the peak current and peak potential can be observed from those curves, which indicates the as-prepared sensor is quite stable in detection H2 O2 . The stable response should be ascribed to the high adhesion of the AgNPs on the given electrode. The long-term stability of the electrode in air was also examined. When the used electrode was stored at room temperature in air for 1 week, the CV peak currents still retained ∼90% and in the next 2 weeks the response still retained ∼85% of the initial value. From TEM observation, we confirmed that the coverage grade of the AgNPs deposited on carbon surface didn’t change over time, even after H2 O2 immersion. 4. Conclusion The present study demonstrates a novel method to coat Ag nanoparticles on glass carbon electrodes with high adhesion and good dispersity by performing gas phase cluster beam deposition. The AgNPs generated with this approach have clean surface as compared with those obtained from the chemical route. As a result, the fabricated AgNP-modified-GCE shows enhanced electrocatalytic activity toward the reduction of H2 O2 with a much reduced detection limit (typically 1 × 10−6 M) and response time (typically less than 1 s) as compared with those have been previously reported. Moreover, this technique is a promising technology for fabricating various metal nanoparticle based electrodes with great promise for electrochemical sensors design. Acknowledgments We acknowledge the financial support from NSFC (grant nos. 10974092, 51171077 and 11075076), the National Basic Research Program of China (973 Program, contract no. 2009CB930501), and the Industrialization Promotion of University Research Program in Jiangsu Province under contract no. JH10-2. This research was
[1] S. Ashok Kumar, S.F. Wang, Y.T. Chang, Poly(BCB)/Au-nanoparticles hybrid film modified electrode: preparation, characterization and its application as a nonenzymatic sensor, Thin Solid Films 518 (2010) 5832–5838. [2] G.H. Zhang, N.B. Yang, Y.L. Ni, J. Shen, W.B. Zhao, X.H. Huang, A H2 O2 electrochemical biosensor based on biocompatible PNIPAM-g-P (NIPAM-co-St) nanoparticles and multi-walled carbon nanotubes modified glass carbon electrode, Sensors and Actuators B: Chemical 158 (2011) 130–137. [3] M. Delvaux, A. Walcarius, S. Demoustier-Champagne, Electrocatalytic H2 O2 amperometric detection using gold nanotube electrode ensembles, Analytica Chimica Acta 525 (2004) 221–230. [4] C. Matsubara, N. Kawamoto, K. Takamura, Oxo [5,10, 15, 20-tetra(4pyridyl)porphyrinato] titanium(IV): an ultra-high sensitivity spectrophotometric reagent for hydrogen peroxide, Analyst 117 (1992) 1781–1784. [5] S. Hanaoka, J. Lin, M. Yamada, Chemiluminescent flow sensor for H2 O2 based on the decomposition of H2 O2 catalyzed by cobalt(II)-ethanolamine complex immobilized on resin, Analytica Chimica Acta 426 (2001) 57–64. [6] V. Tripathi, V. Kandimalla, H. Ju, Amperometric biosensor for hydrogen peroxide based on ferrocene-bovine serum albumin and multiwall carbon nanotube modified ormosil composite, Biosensors and Bioelectronics 21 (2006) 1529–1535. [7] Z.M. Liu, Y. Yang, H. Wang, Y.L. Liu, G.L. Shen, R.Q. Yu, A hydrogen peroxide biosensor based on nano-Au/PAMAM dendrimer/cystamine modified gold electrode, Sensors and Actuators B: Chemical 106 (2005) 394–400. [8] S. Liu, J.Q. Tian, L. Wang, X.P. Sun, A method for the production of reduced graphene oxide using benzylamine as a reducing and stabilizing agent and its subsequent decoration with Ag nanoparticles for enzymeless hydrogen peroxide detection, Carbon 49 (2011) 3158–3164. [9] J. Ren, W. Shi, K. Li, Z.F. Ma, Ultrasensitive platinum nanocubes enhanced amperometric glucose biosensor based on chitosan and nafion film, Sensors and Actuators B: Chemical 163 (2012) 115–120. [10] M.C. Rodriguez, G.A. Rivas, Glucose biosensor prepared by the deposition of iridium and glucose oxidase on glassy carbon transducer, Electroanalysis 11 (1999) 558–564. [11] P. Zhou, Z.H. Dai, M. Fang, X.H. Huang, J.C. Bao, Novel dendritic palladium nanostructure and its application in biosensing, The Journal of Physical Chemistry C 111 (2007) 12609–12616. [12] M. Janyasupab, C.W. Liu, Y. Zhang, K.W. Wang, C.C. Liu, Bimetallic Pt–M (M = Cu, Ni, Pd, and Rh) nanoporous for H2 O2 based amperometric biosensors, Sensors and Actuators B: Chemical (2012), http://dx.doi.org/ 10.1016/j.snb.2012.09.099. [13] M. Ammam, E.B. Easton, High-performance glucose sensor based on glucose oxidase encapsulated in new synthesized platinum nanoparticles supported on carbon Vulcan/Nafion composite deposited on glassy carbon, Sensors and Actuators B: Chemical 155 (2011) 340–346. [14] J. Wang, G. Chen, M.P. Chatrathi, M. Musameh, Capillary electrophoresis microchip with a carbon nanotube-modified electrochemical detector, Analytical Chemistry 76 (2004) 298–302. [15] S. Wu, H. Zhao, H. Ju, C. Shi, J. Zhao, Electrodeposition of silver–DNA hybrid nanoparticles for electrochemical sensing of hydrogen peroxide and glucose, Electrochemistry Communications 8 (2006) 1197–1203. [16] Y.H. Wang, H.Y. Gu, Hemoglobin co-immobilized with silver–silver oxide nanoparticles on a bare silver electrode for hydrogen peroxide electroanalysis, Mikrochimica Acta 164 (2009) 41–47. [17] L. Ma, R. Yuan, Y. Chai, S. Chen, Amperometric hydrogen peroxide biosensor based on the immobilization of HRP on DNA–silver nanohybrids and PDDAprotected gold nanoparticles, Journal of Molecular Catalysis B: Enzymatic 56 (2009) 215–220. [18] X. Gao, L.Y. Jin, Q. Wu, Z.C. Chen, X.F. Lin, A nonenzymatic hydrogen peroxide sensor based on silver nanowires and chitosan film, Electroanalysis 24 (2012) 1771–1777. [19] X.P. Sun, X.Y. Qin, J.M. Hu, Y.L. Luo, W.B. Lu, G.H. Chang, A.M. Asiri, A.O. Al-Youbi, Heat treatment-based one-step preparation of highly concentrated, well-stable silver colloids that can form stable films on bare electrodes for H2 O2 detection, Current Nanoscience 8 (2012) 335–342. [20] G.H. Chang, Y.L. Luo, W.B. Lu, F. Liao, X.P. Sun, Hydrothermal synthesis of ultrahighly concentrated, well-stable Ag nanoparticles and their application for enzymeless hydrogen peroxide detection, Journal of Nanoparticle Research 13 (2011) 2689–2695. [21] Y.W. Zhang, S. Liu, L. Wang, X.Y. Qin, J.Q. Tian, W.B. Lu, G.H. Chang, X.P. Sun, One-pot green synthesis of Ag nanoparticles–graphene nanocomposites and their applications in SERS, H2 O2 , and glucose sensing, RSC Advances 2 (2012) 538–545. [22] L. Zhang, H. Li, Y.H. Ni, J. Li, K.M. Liao, G.C. Zhao, Porous cuprous oxide microcubes for non-enzymatic amperometric hydrogen peroxide and glucose sensing, Electrochemistry Communications 11 (2009) 812–815. [23] Q. Wang, Y.B. Yun, J.B. Zheng, Nonenzymatic hydrogen peroxide sensor based on a polyaniline-single walled carbon nanotubes composite in a room temperature ionic liquid, Mikrochimica Acta 167 (2009) 153–157.
K. Liao et al. / Sensors and Actuators B 181 (2013) 125–129 [24] J. Wang, M. Musameh, Y. Lin, Solubilization of carbon nanotubes by nafion toward the preparation of amperometric biosensors, Journal of the American Chemical Society 125 (2003) 2408–2409. [25] M.A. Rahman, P. Kumar, D.S. Park, Y.B. Shim, Electrochemical sensors based on organic conjugated polymers, Sensors 8 (2008) 118–141. [26] H. Haberland, M. Mall, M. Moseler, Y. Qian, T. Reiners, Y. Thurner, Filling of micron-sized contact holes with copper by energetic cluster impact, Journal Vacuum Science and Technology A 12 (1994) 2925–2930. [27] M. Han, C.H. Xu, D. Zhu, L. Yang, J.L. Zhang, Y.P. Chen, K. Ding, F.Q. Song, G.H. Wang, Controllable synthesis of two-dimensional metal nanoparticle arrays with oriented size and number density gradients, Advanced Materials 19 (2007) 2979–2983. [28] G. Flätgen, S. Wasle, M. Lübke, C. Eickes, G. Radhakrishnan, K. Doblhofer, G. Ertl, Autocatalytic mechanism of H2 O2 reduction on Ag electrodes in acidic electrolyte: experiments and simulations, Electrochimica Acta 44 (1999) 4499–4506. [29] W. Zhao, H. Wang, X. Qin, X. Wang, Z. Zhao, Z. Miao, L. Chen, M. Shan, Y. Fang, Q. Chen, A novel nonenzymatic hydrogen peroxide sensor based on multiwall carbon nanotube/silver nanoparticle nanohybrids modified gold electrode, Talanta 80 (2009) 1029–1033. [30] X. He, C. Hu, H. Liu, G. Du, Y. Xi, Y. Jiang, Building Ag nanoparticle 3D catalyst via Na2 Ti3 O7 nanowires for the detection of hydrogen peroxide, Sensors and Actuators B: Chemical 144 (2010) 289–294. [31] M.S. Lin, H.J. Leu, A Fe3 O4 -based chemical sensor for cathodic determination of hydrogen peroxide, Electroanalysis 17 (2005) 2068–2073. [32] H. Ye, J.A. Crooks, R.M. Crooks, Effect of particle size on the kinetics of the electrocatalytic oxygen reduction reaction catalyzed by Pt dendrimer-encapsulated nanoparticles, Langmuir 23 (2007) 11901–11906. [33] O.M. Wilson, M.R. Knecht, J.C. Garcia-Martinez, R.M. Crooks, Effect of Pd nanoparticle size on the catalytic hydrogenation of allyl alcohol, Journal of the American Chemical Society 128 (2006) 4510–4511.
Biographies Kaiming Liao was born in 1983 in Anhui Province, China. He got a B.S. and M.S. degree in Chemistry and Materials Science from Anhui Normal University, China, in 2006 and 2009, respectively. In 2011, he worked as a visiting scholar in the National Institute of Advanced Industrial Science and Technology (AIST) in Japan. He is currently working in his Ph.D. at the Department of Materials Science and Engineering, Nanjing University. His research interests cover metal nanostructures, especially metal nanoparticle arrays, as well as the applications of these nanostructures in sensors, electronics, and energy. Peng Mao received the B.E. degree in Materials Chemistry from Nanjing University of Technology, China, in 2010. He is currently working on Ph.D. at the Department of Materials Science and Engineering, Nanjing University. His research interests cover
129
metal nanostructures, dielectric nanostructures, especially optic properties of metal and dielectric nanoparticle arrays, as well as the applications of these nanostructures in light emission device, sensors, photocatalysis and energy. Yuhua Li received the B.S. degree in Electronic and Information Engineering from Xiàn University of Architecture and Technology, China, in 2010. She is currently studying on the nanostructured photovoltaic device toward her M.S. degree in Materials Science at Nanjing University. Yali Nan received the B.S. degree in Materials Physics and chemistry from Hebei University of technology, China, in 2010. She is currently studying on the semicondutor nanoparticles toward her M.S. degree in Materials Physics and Chemistry at Nanjing University. Fengqi Song received the B.S. degree in Particle Physics and Nuclear Physics from Lanzhou University, China, in 2000. In 2005 he received Ph.D. degree in Condensed Matter Physics from the Nanjing University. He is now an associate professor in the Department of Physics at Nanjing University. His research interests span a wide range of experimental and theoretical topics in electronic structure of nanoscale materials and thermal properties of small particles, nanocrystals, and nanotubes. Guanghou Wang was born in Anhui Province, China in 1939. He obtained his bachelor’s degree in Beijing Normal University in 1963. He was a visiting scholar in New York State University from 1980 to 1982. He was employed as a professor of physics in Nanjing University in 1988. He was elected in the Academician of Chinese Academy of Sciences in 2011. His research is related to atomic clusters and clusterbased nanostructures and nanomaterials, including theoretical simulation of atomic clusters and design of cluster-based microstructures; controllable preparation, plasmon resonance property and nano-optics of cluster arrays; thermal physical properties as well as mass and/or energy transport through cluster-assembled system; magnetic and electric properties of nanostructured diluted magnetic oxides and multiferroic nanomaterial. Min Han got his B.S. degree in 1986, master degree in 1989 and doctoral degree in 1997 on condensed matter physics from Nanjing University, China. He was a STA fellow in National Institute of Advanced Industrial Science and Technology (AIST) in Japan in 1997–1999, and then appointed as a senior visiting scholar to AIST in 2001. In 2002, he worked as a visiting scholar in the Department of Physics and the Research Institute of Material Science of Freiburg University in Germany. From 2003, he was employed as a professor of materials science in Nanjing University. His research is concerned with the physical properties and applications of nanoclusters and their related nanostructures. Particular interests include gas phase cluster generation, low energy cluster beam deposition, metal cluster-block copolymer hybrid nanostructures, controllable fabrication of closely spaced nanocluster arrays, thermodynamic behaviors of nanoclusters and cluster assemblies, nanooptics and quantum transport in cluster-based nanostructures, molecular and gas sensors based on densely packed clusters.