Journal of Colloid and Interface Science 447 (2015) 50–57
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Journal of Colloid and Interface Science www.elsevier.com/locate/jcis
A nanoporous palladium-nickel alloy with high sensing performance towards hydrogen peroxide and glucose Dianyun Zhao, Caixia Xu ⇑ Key Laboratory of Chemical Sensing & Analysis in Universities of Shandong, School of Chemistry and Chemical Engineering, University of Jinan, Jinan 250022, China
g r a p h i c a l a b s t r a c t
a r t i c l e
i n f o
Article history: Received 17 December 2014 Accepted 20 January 2015 Available online 4 February 2015 Keywords: Nanoporous Hydrogen peroxide Glucose Electrochemical sensor Palladium
a b s t r a c t The nanoporous (NP) PdNi alloy is easily fabricated by one-step mild dealloying of PdNiAl precursor alloy in NaOH solution. Characterized by the nanoporous network architecture with the ligament size as small as 5 nm, NP-PdNi alloy exhibits higher electrocatalytic activity towards the oxidation of H2O2 and glucose compared with NP-Pd and Pd/C catalysts. The electrochemical sensor constructed based on NP-PdNi alloy shows high sensing performance towards H2O2 and glucose with a wide linear range, long-term stability, and fast amperometric response. Moreover, NP-PdNi alloy exhibits high resistance towards Cl poisoning as well as good anti-interference towards ascorbic acid, urci acid, and dopamine. This work provides a simple and green route to construct highly active and sensitive electrochemical sensor for detecting H2O2 and glucose. Ó 2015 Elsevier Inc. All rights reserved.
1. Introduction Hydrogen peroxide (H2O2) as an intermediate plays a fundamental role in many reactions, such as an antiseptic or disinfectant agent, a bleaching agent, and a cleaning agent [1–4]. Glucose detection is vital in diabetes management, wastewater treatment, food industries, and environmental monitoring [5–8]. Consequently, development of highly sensitive, accurate, and selective method for determination of H2O2 and glucose is of significant ⇑ Corresponding author. Fax: +86 531 82765969. E-mail address: [email protected] (C. Xu). http://dx.doi.org/10.1016/j.jcis.2015.01.053 0021-9797/Ó 2015 Elsevier Inc. All rights reserved.
importance in food, pharmaceutical, industrial, and environmental analyses. Different analytical methods for the detection of H2O2 and glucose have been reported, such as colorimetric assay, fluoroimmunoassay, and electrochemiluminescence [9–11]. Among these methods, electrochemical sensors based on electrooxidation of small molecules have gained remarkable attention owing to the advantages of convenient operation, fast response time, and low cost [12–15]. In recent years, advanced nanomaterials modified electrodes have attracted much attention as the platform for the H2O2 and glucose electrochemical sensor. Anu Prathap et al. developed a simple nonenzymatic H2O2 and glucose sensor based on CuO nanostructures modified electrode, finding unique electro-
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chemical sensing performance for H2O2 and glucose detections [6]. The nanomaterial is indeed successful in achieving high electrochemical activity as the platform to construct the electrochemical sensor. Therefore, the design of highly efficient nanostructured materials with controllable preparation is much important in order to maximize the entire advantages of electrochemical sensors. Among various nanostructured materials, palladium (Pd) nanostructured materials have attracted considerable interests due to their high electrocatalytic efficiency, the relatively cheaper price, and abundant yielding [16–18]. Especially, incorporation of other transition metals into Pd can further improve its electrochemical performance by changing its electronic structure as well as correlating the ligand effect and strain effect. Thus, great attentions have been paid to explore highly active Pd-based catalysts for various electrochemical detections. Nickel(Ni) as one of the 3d metals shows a dramatically synergistic effect to enhance the electrochemical activity of Pd [19–23]. Shen et al. synthesized PdNi catalysts by simultaneous reduction method using NaBH4 as reductant, finding high oxidation activity towards ethanol in alkaline solution [24]. Zhang et al. synthesized carbon-supported PdNi nanoparticles by controlling coreduction of PdCl2 and Ni (NO3)2, finding excellent ascorbic acid sensing capability [25]. However, these preparation methods usually involve the reduction of various Pd precursors with organic agents and the excessive use of surfactants, which may cause undesired environmental issues. Consequently, it is essential to develop a simple and highly effective method to fabricate PdNi bimetallic nanostructure in high through-put under mild conditions. Recently, nanoporous (NP) bimetallic structures have attracted great attention in the application of electrochemical sensing because their bicontinuous nanoscale skeletons and interconnected hollow channels are favourable for easy mass transport and high electron conductivity [26–30]. Nanoporous materials prepared by dealloying have the advantages of extremely clean metal surface, controllable and simple preparation, and excellent reproducibility [31–33]. In our previous work, it has been reported that NP-PdNi alloy was simply fabricated by a straightforward dealloy-
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Fig. 2. XRD patterns of the dealloyed NP-PdNi sample. The standard patterns of Pd (JCPDS 65-2867) and Ni (JCPDS 65-2865) are attached for clear comparison.
ing from the ternary PdNiAl source alloy in NaOH solution. It is found that NP-PdNi show superior electrocatalytic activity towards oxygen reduction reaction with higher specific and mass activities as well as higher methanol tolerance compared with Pt/C catalyst [32]. In current work, it is interesting to explore the sensing ability of NP-PdNi alloy as the platform for the electrochemical detection of H2O2 and glucose. On the basis of the unique electroxidation activity towards H2O2 and glucose, NP-PdNi alloy shows promising application potential to construct highly sensitive and stable electrochemical sensors. 2. Experimental Pd15Ni5Al80 and Pd20Al80 alloy foils with a thickness of 50 lm were prepared by refining respective pure (>99.9%) Pd, Al, and Ni metal in an arc furnace, followed by melt-spinning under an
Fig. 1. SEM (a) and (b), TEM (c) and HRTEM (d) images of the resulted samples by dealloying Pd15Ni5Al80 alloy in 0.5 M NaOH solution for 48 h at room temperature.
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Fig. 3. CV curves of (a) NP-PdNi, (b) Pd/C, (c) NP-Pd in PBS solution with and without 1 mM H2O2. (d) CV curves of all samples in PBS + 1 mM H2O2 solution. (e) CV curves of NP-PdNi in PBS + 1 mM H2O2 solution at different scan rates of 20, 40, 60, 80, 100, and 120 mV/s. (f) Plots of current on NP-PdNi at 1.0 V.
argon-protected atmosphere. The NP-Pd75Ni25 and NP-Pd were respectively prepared by etching PdNiAl and PdAl alloy foils in 0.5 M NaOH solution for 48 h at room temperature. H2O2 (30%) and glucose were purchased from Sinopharm Chemical Reagent Co. Ltd. The phosphate buffered saline solution was prepared using Na2HPO4 and KH2PO4 solutions. Ultra-pure water (18.2 MX) was used in all measurements. Ascorbic acid (AA), uric acid (UA), and dopamine (DA) were purchased from Sigma–Aldrich. All the reagents were of analytical reagent grade and used without further treatment. The structure characterizations were carried out on a JEM-2100 transmission electron microscope (TEM) and a JSM-6700 field emission scanning electron microscope (SEM). Powder X-ray diffraction (XRD) was carried out on a Bruker D8 advanced X-ray diffractometer using Cu KR radiation at a step rate of 0.04°s 1. All electrochemical measurements were performed using CHI 760D
electrochemical workstation (Shanghai CH Instruments Co., China). A conventional three-electrode cell was used with Pt foil as a counter electrode, mercury sulphate electrode as the reference electrode, and 4-mm-diameter glassy carbon electrode as work electrode. Catalyst ink was prepared by mixing 1.5 mg carbon powder, 1.0 mg NP-PdNi, 400 lL isopropanol, and 200 lL nafion solutions (0.5 wt.%) under sonication for 30 min. The working electrode was made by dropping appropriate catalyst ink on a polished glassy carbon electrode and dried. The NP-Pd and Pd/C electrodes were prepared in a similar way. The electrochemical surface areas (ECSA) of Pd in all catalysts were evaluated by integrating the reduction charges during the stripping of surface monolayer oxide in N2-purged 0.5 M H2SO4 solution in the range of 0–1.35 V at the scan rate of 50 mV s 1, in which the used charge density is 420 lC cm 2 Pd [23].
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Fig. 4. (a) Amperometric responses of NP-PdNi on successive addition of 0.05 mM H2O2 into stirring PBS solution at 1.0 V. (b) Plots of currents vs. H2O2 concentrations. (c) Effects of the pH on the oxidation current of 1 mM H2O2 on NP-PdNi at 1.0 V (d) Sensing stability of NP-PdNi, Pd/C, and NP-Pd in a stirred PBS solution containing 1 mM H2O2 for 2000 s at 1.0 V.
Table 1 A comparison of the performance of some sensor platforms using different electrodes for H2O2 detection. H2O2 sensor
Linear range (mM)
Sensitivity (lA cm
Pd nanoparticle assemblies Graphene–AuNPs/GCE ERGO–ATP–Pd Palladized aluminum NP-PdNi
0.001–0.82 0.02–0.28 0.0001–10 0.005–0.034 0.05–1.0
– 3000 1176 – 208.6
3. Results and discussion 3.1. Characterization of the prepared PdNi alloy Fig. 1 illustrates the resulted structure after dealloying PdNiAl alloy in 0.5 M NaOH solution for 48 h. From the SEM image in Fig. 1a, it is clearly observed that selectively etching Al has successfully generated an open nanosponge morphology consisting of uniform ligaments distribution around 5 nm. The cross-sectional SEM image (Fig. 1b) indicates that the whole sample has been penetrated with interconnected hollow channels extending in all dimensions upon dealloying. As shows in the TEM image (Fig. 1c), a clear contrast between the dark skeletons and bright central region indicates the formation of nanoporous network structure with bicontinuous nanoscaled skeleton run through interconnected hollow channels. High-resolution TEM (HRTEM) image (Fig. 1d) provides more details for this structure, in which the ordered lattice fringes were well resolved across several interconnected ligaments with the lattice spacing calculated to be 2.18 Å, corresponding to the (1 1 1) crystal plane of a PdNi alloy structure. According to the SEM and TEM images of the resulted sample, it can be concluded that uniform nanoporous PdNi architecture can be simply fabricated by means of the simple dealloying method.
2
mM
1
)
Detection limit (lM)
Response time
Ref.
0.68 6 0.016 4.0 2.1
10 – 10 – 1.2
[35] [36] [37] [38] This work
XRD was used to examine the crystal structure of the dealloyed sample. As shown in Fig. 2, it is clear that the after selective leaching of Al from the ternary alloy, only a set of three diffraction peaks emerged at 40.3, 45.3, and 68.2 (2h), which can be assigned to the (1 1 1), (2 0 0), and (2 2 0) diffractions for a face centred cubic (fcc) PdNi alloy structure. It is noted that there are no other diffraction peaks emerged related to individual Pd and Ni, indicating the formation of a homogenous single-phase PdNi alloy. 3.2. Electrochemical behaviours of H2O2 over the NP-PdNi Characterized by the desirable nanoporous architecture with bicontinuous skeleton and hollow interconnected channels, NPPdNi is favourable for the molecules transport and electron conductivity. Consequently, it is interesting to explore the sensing performance towards H2O2 on the NP-PdNi alloy. Fig. 3 shows the cyclic voltammetric curves (CVs) of the modifed electrodes in PBS solution in the presence and absence of H2O2. It is observed that the NP-PdNi alloy exhibits higher oxidation current towards H2O2 starting from 0.42 V compared with that in pure PBS solution (Fig. 3a). As shown in Fig. 3b and c, Pd/C and NP-Pd shows similar electrochemical behaviour to NP-PdNi for H2O2 oxidation. However, the current density for H2O2 oxidation on NP-PdNi in the
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Fig. 5. CV curves of (a) NP-PdNi, (b) Pd/C, and (c) NP-Pd in 0.1 M NaOH solution with the presence and absence of 10 mM glucose. (d) CV curves of NP-PdNi, Pd/C, and NP-Pd in 10 mM glucose + 0.1 M NaOH solution.
range of 0.9–1.2 V is more than 3 times higher than those of Pd/C and NP-Pd, while the onset oxidation potential negatively shifted more than 100 mV (Fig. 3a–d). The much enhanced electrochemical activities towards H2O2 on NP-PdNi alloy may be due to the synergistic effect between Ni and Pd atoms as well as the nanoporous structure. The electrochemical behaviour of NP-PdNi towards H2O2 oxidation was further investigated by changing the scan rate. As displayed in Fig. 3e, the currents at 1.0 V are linear as a function of the scan rate in a range from 20 to 120 mV s 1 and the corresponding linear equation for the currents is I (mA) = 31.22 + 2.13 with a linear correlation coefficient of 0.997. This indicates that the electrochemical oxidation of H2O2 on the NP-PdNi modifed electrode is a surface-controlled process [34]. It can be concluded that the as prepared NP-PdNi alloy has greatly enhanced electrochemical activities towards H2O2, providing a substantial basis for its electrochemical sensing application. Based on the high electrooxidation activity towards H2O2, the sensing performance on NP-PdNi alloy is evaluated by amperometric detection upon the successive addition of H2O2. Fig. 4a shows the typical amperometric responses of NP-PdNi, Pd/C, and NP-Pd at a fixed potential. It is noted that NP-PdNi electrode responds rapidly (1.2 s) to each addition of H2O2. The rapid response could be attributed to the fact that H2O2 could diffuse freely into the bicontinuous nanoscaled skeleton as well rapidly be oxidized on the NP-PdNi surface duto the smaller structure dimension. In addition, NP-PdNi electrode shows larger response signals to the each addition of H2O2 compared with NP-Pd and Pd/C electrodes. As shown in Fig. 4b, Pd/C sample has a linear relationship in the range of 0.05–0.9 mM (linear equation: y = 39.91 x + 3.31, R = 0.995) with a detection limit of 2.7 lM. NP-Pd alloy has a better linear response to H2O2 in the range of 0.05 to 0.95 mM (linear equation:
y = 1.15 + 66.88 x, R = 0.995) with a detection limit of 2.3 lM (S/ N = 3). By comparison, NP-PdNi alloy exhibits the highest sensitivity and the widest linear range up to 1.0 mM (linear equation: y = 0.21 + 165.02 x, R = 0.998) with the lowest detection limit of 2.1 lM. These analytical parameters of NP-PdNi are better than other reported catalysts based H2O2 sensors as shown in Table 1 [35–38]. The remarkable performance of NP-PdNi modified electrode towards the detection of H2O2 indicates that NP-PdNi holds great potential to construct H2O2 sensor. The pH effect on the electrochemical response of H2O2 on NPPdNi was investigated in the pH range of 5.5–8.0. As shown in Fig. 4c, the current response was increased with the range from 5.5 to 6.5, and kept higher in pH range of 6.5–7.5. Indicating that neutral solution was the optimized condition for the electrochemical oxidation of H2O2. The decrease of the current value on alkaline conditions might be related to the self-degradation of H2O2 [14]. So pH around 7.0 was preferable in the H2O2 detection. The long-term sensing stability of the electrochemical sensor is significant for continuous and reliable monitoring of H2O2, which was evaluated by detecting the steady-state specific activity by using potentiostatic method. As is shown in Fig. 4d, NP-PdNi shows a more stable amperometric response to the addition of 1 mM H2O2 in stirring PBS after running for 2000 s compared with NP-Pd and Pd/C, indicating the higher sensing durability. The current degradation of NP-PdNi was 8.5% within 2000 s. The reproducibility of the sensors was evaluated by using ten equally proposed electrodes in the mixture of 1.0 mM H2O2. The relative standard deviation (RSD) of peak currents was 3.2%. The result indicated that the reproducibility of NP-PdNi was acceptable. The better performance of NP-PdNi modified electrode towards the detection of H2O2 indicates that NP-PdNi holds great potential to construct H2O2 sensor.
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Fig. 6. (a) CV curves of NP-PdNi alloy in 0.1 M NaOH and 10 mM glucose solution with and without 0.1 M NaCl. (b) Sensing stability NP-Pd, Pd/C, and NP-PdNi in a stirred NaOH solution containing 10 mM glucose for 2000 s at 0.35 V. (c) Amperometric current responses of NP-Pd, Pd/C, and NP-PdNi on successive addition of 1 mM glucose into stirring NaOH solution at 0.35 V. (d) Plots of current vs. glucose concentrations. (e) Amperometric current responses of NP-PdNi alloy on successive addition of 0.1-2.5 mM glucose into stirring NaOH solution at 0.35 V. (f) Glucose sensitivities of NP-PdNi as a function of the concentration of glucose.
Table 2 A comparison of the performance of some sensor platforms using different electrodes for glucose detection. Glucose sensor PdCu/GE GOx/Pd NPAs Pd–Ni/SiNWs PtPd–RGO NP-PdNi
Linear range (mM) 1–18 0.040–22 0–20 0.1–22 1–25
2
Sensitivity (lA cm 48(lA mg – 190.72 1.47 0.75
3.3. Electrochemical behaviours of glucose over the NP-PdNi Fig. 5a shows CVs of the NP-PdNi modified electrode in 0.1 M NaOH solution with and without glucose. In the presence of glucose, NP-PdNi electrode exhibits high oxidation currents starting from 0.3 V. The anodic peak located at 0.2 V could be attributed
1
mM
1
)
mM
1
)
Applied potential
Ref.
0.2 +0.25 +0.14 0 +0.35
[5] [35] [41] [42] This work
to glucose electroadsorption, causing the generation of adsorbed intermediates [39]. However, the accumulation of the intermediates inhibited the further electroadsorption of glucose, resulting in current decrease. When the potential was higher than 0.6V, Pd-OH species generated in the alkaline solution, which is beneficial for the oxidation of reaction intermediates on alloy surface,
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Fig. 7. (a) Interference of 0.1 mM AA, 0.02 mM UA, and 0.01 mM DA on the response of 1 mM H2O2 in 0.1 M PBS solution at 1.0 V (b) interference of 0.02 mM UA, 0.1 mM AA, and 0.01 mM DA on the response of 10 mM glucose in 0.1 M NaOH solution at 0.35 V.
leading to the current increases again. Moreover, the electrooxidation current also increased due to the direct oxidation of glucose on the surface. In the negative scan, the oxidized Pd is reduced at a potential around 0.1 V. As shown in Fig. 5b and c, Pd/C and NPPd catalysts show the similar electrochemical behaviour to NPPdNi for glucose oxidation. However, compared with NP-Pd and Pd/C catalysts, the much higher current density on NP-PdNi alloy indicates that its high glucose electrooxidation activity originates from the synergetic catalytic effect between Pd and Ni atoms as well as specific nanoporous architecture. It has been reported that Cl has a serious poisoning effect on some metallic electrocatalysts, leading to the activity loss towards the glucose electrooxidation [15]. The effect of Cl on the glucose oxidation over NP-PdNi alloy was evaluated by adding NaCl into 0.1 M NaOH and 10 mM glucose solution. As shown in Fig. 6a, the glucose oxidation current and potention on NP-PdNi has almost no change after adding NaCl, suggesting that NP-PdNi can well maintain its electrochemical property in the presence of Cl . However, it is noted that the current starting from 0.2 V became higher after adding Cl , which is consistent with the previous reports in Cl poisoning effect on some catalysts [40]. The longterm sensing stability of NP-PdNi alloy towards glucose oxidation is significant for continuous and reliable monitoring of glucose. As is shown in Fig. 6b, NP-PdNi shows much higher sensing durability and more stable amperometric response to the addition of 10 mM glucose in stirring NaOH after running for 2000 s compared with NP-Pd and Pd/C. Based on the excellent electrochemical activity towards glucose oxidation, the sensing performance of the all catalysts are evaluated by amperometric detection upon the successive addition of glucose. Fig. 6c shows the typical amperometric response of NP-PdNi alloy towards the successive addition of glucose at a fixed potential. NP-PdNi electrode responds rapidly to each addition of glucose and reaches the maximum steady-state current within 1.8 s. The rapid response could be attributed to the fact that glucose could diffuse freely into the bicontinuous nanoporous structure as well rapidly be oxidized on NP-PdNi surface. In addition, NP-PdNi electrode shows higher current response signals to the addition of glucose compared with NP-Pd and Pd/C electrodes with the current response intensity in NaOH system due to the synergistic effect between Ni and Pd atoms. As shown in Fig. 6d, the NP-PdNi alloy exhibits the high sensitivity and wide linear range up to 25 mM (linear equation: y = 4.1310 + 2.4619 x, R = 0.994) with the lowest detection limit of 1.9 lM. In comparison, the sensing range of Pd/ C and NP-Pd are respective up to 16 mM and 14 mM (linear equation: y = 0.57 + 0.23 x, R = 0.986 and y = 0.46 + 0.36 x, R = 0.996) with the detection limit of 2.1 lM and 2.3 lM. The analytical
parameters of NP-PdNi are better than other reported catalysts based glucose sensors as shown in Table 2 [5,35,41,42]. The better performance of NP-PdNi modified electrode towards the detection of glucose indicates that NP-PdNi holds great potential to fabricate glucose sensor. The sensing performance of the NP-PdNi alloy is also evaluated by successive addition of glucose with different concentrations. Fig. 6e gives the amperometric responses of NP-PdNi alloy on successive addition of 0.1–2.5 mM glucose. Owing to the synergistic electrocatalytic activity of PdNi alloy and the excellent conductivity of nanoporous architecture, the amperometric response of the NP-PdNi exhibits stable step curve with dramatically enhanced current density. It should be noted that the response time is less than 2 s to research steady-state current. In addition, the glucose biosensors based on NP-PdNi show multi-linear detection ranges with different sensitivities up to 71 mM, displaying a strong dependence on the concentration of added glucose (Fig. 6f). As the concentration decreases to 1 mM, the sensitivity of NP-PdNi increases up to 2.5 lA mM 1 cm 2. 3.4. The anti-interference for electrochemical detection of H2O2 and glucose over NP-PdNi One of the major challenges in nonenzymatic H2O2 and glucose detections are the interfering electrochemical signals caused by some easily oxidizable compounds such as AA, UA, and DA [43]. So, it is essential to investigate the anti-interference of NP-PdNi towards the H2O2 and glucose sensing. Fig. 7a shows the chronoamperometry curves of NP-PdNi electrode with successive addition of 0.1 mM AA, 0.02 mM UA, 0.01 mM DA, and 1 mM H2O2. The interferences from AA, UA, or DA were 4.1%, 0.3% or 7.8% of the response generated by H2O2 on NP-PdNi modified electrode. In addition, Fig. 7b shows the chronoamperometry curves of NPPdNi electrode with successive addition of 0.1 mM AA, 0.02 mM UA, 0.01 mM DA, and 1 mM H2O2. The interferences from UA, AA or DA were 0.38%, 7.8% or 2.4% of the response generated by glucose on NP-PdNi modified electrode. The result demonstrated that electrochemical detection of H2O2 and glucose on NP-PdNi modified electrodes could be performed with little interference from AA, DA, and UA. 4. Conclusions In this work, NP-PdNi alloy is successfully fabricated with bicontinuous nanoporous architecture by a simple dealloying strategy. Based on enhanced electrochemical activities towards
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the oxidation of H2O2 and glucose, NP-PdNi can achieve sensitive detection for H2O2 and glucose with wide linear range, fast response, long-term sensing durability as well as little interference from DA, UA, and AA. Along with these attractive features, NP-PdNi alloy holds great application potential in constructing electrochemical sensors. Acknowledgment This work was supported by the National Science Foundation of China (51001053, 21271085). References [1] Y.H. Wang, X.J. Yang, J. Bai, X. Jiang, G.Y. Fan, Biosens. Bioelectron. 43 (2013) 180–185. [2] K. Sato, E. Abe, M. Takahashi, J. Anzai, J. Colloid Interf. Sci. 432 (2014) 92–97. [3] W.N. Liu, D. Ding, Z.L. Song, X. Bian, X.K. Nie, X.B. Zhang, Z. Chen, W.H. Tan, Biosens. Bioelectron. 52 (2014) 438–444. [4] X.J. Yang, Y.H. Wang, Y.W. Liu, X. Jiang, Electrochim. Acta 108 (2013) 39–44. [5] M. Yuan, A. Liu, M. Zhao, W.J. Dong, T.Y. Zhao, J.J. Wang, W.H. Tang, Sens. Actuat. B 190 (2014) 707–714. [6] M.U.Anu. Prathap, B. Kaur, R. Srivastava, J. Colloid Interf. Sci. 370 (2012) 144– 154. _ Boyacı, Z. [7] V.K. Gupta, N. Atar, M.L. Yola, M. Eryılmaz, H. Torul, U. Tamer, I.H. Üstündag˘, J. Colloid Interf. Sci. 406 (2013) 231–237. [8] A.K. Dutta, S.K. Maji, P. Biswas, B. Adhikary, Sens. Actuat. B 177 (2013) 676– 683. [9] T. Wen, F. Qu, N.B. Li, H.Q. Luo, Anal. Chim. Acta 749 (2012) 56–62. [10] Y.F. Cheng, R. Yuan, Y.Q. Chai, H. Niu, Y.L. Cao, H.J. Liu, L.J. Bai, Y.L. Yuan, Anal. Chim. Acta 745 (2012) 137–142. [11] M. Abo, Y. Urano, K. Hanaoka, T. Terai, T. Komatsu, T. Nagano, J. Am. Chem. Soc. 133 (2011) 10629–10637. [12] H.B. Noh, K.S. Lee, P. Chandra, M.S. Won, Y.B. Shim, Electrochim. Acta 61 (2012) 36–43. [13] X. Yuan, Y.Q. Tay, X.Y. Dou, Z.T. Luo, D.T. Leong, J.P. Xie, Anal. Chem. 85 (2013) 1913–1919. [14] N.M. Jia, B.Z. Huang, L. Chen, L. Tan, S.Z. Yao, Sens. Actuat. B 195 (2014) 165– 170. [15] X.M. Chen, Z.J. Lin, D.J. Chen, T.T. Jia, Z.M. Cai, X.R. Wang, X. Chen, Biosens. Bioelectron. 25 (2010) 1803–1808.
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Journal of Colloid and Interface Science www.elsevier.com/locate/jcis
A nanoporous palladium-nickel alloy with high sensing performance towards hydrogen peroxide and glucose Dianyun Zhao, Caixia Xu ⇑ Key Laboratory of Chemical Sensing & Analysis in Universities of Shandong, School of Chemistry and Chemical Engineering, University of Jinan, Jinan 250022, China
g r a p h i c a l a b s t r a c t
a r t i c l e
i n f o
Article history: Received 17 December 2014 Accepted 20 January 2015 Available online 4 February 2015 Keywords: Nanoporous Hydrogen peroxide Glucose Electrochemical sensor Palladium
a b s t r a c t The nanoporous (NP) PdNi alloy is easily fabricated by one-step mild dealloying of PdNiAl precursor alloy in NaOH solution. Characterized by the nanoporous network architecture with the ligament size as small as 5 nm, NP-PdNi alloy exhibits higher electrocatalytic activity towards the oxidation of H2O2 and glucose compared with NP-Pd and Pd/C catalysts. The electrochemical sensor constructed based on NP-PdNi alloy shows high sensing performance towards H2O2 and glucose with a wide linear range, long-term stability, and fast amperometric response. Moreover, NP-PdNi alloy exhibits high resistance towards Cl poisoning as well as good anti-interference towards ascorbic acid, urci acid, and dopamine. This work provides a simple and green route to construct highly active and sensitive electrochemical sensor for detecting H2O2 and glucose. Ó 2015 Elsevier Inc. All rights reserved.
1. Introduction Hydrogen peroxide (H2O2) as an intermediate plays a fundamental role in many reactions, such as an antiseptic or disinfectant agent, a bleaching agent, and a cleaning agent [1–4]. Glucose detection is vital in diabetes management, wastewater treatment, food industries, and environmental monitoring [5–8]. Consequently, development of highly sensitive, accurate, and selective method for determination of H2O2 and glucose is of significant ⇑ Corresponding author. Fax: +86 531 82765969. E-mail address: [email protected] (C. Xu). http://dx.doi.org/10.1016/j.jcis.2015.01.053 0021-9797/Ó 2015 Elsevier Inc. All rights reserved.
importance in food, pharmaceutical, industrial, and environmental analyses. Different analytical methods for the detection of H2O2 and glucose have been reported, such as colorimetric assay, fluoroimmunoassay, and electrochemiluminescence [9–11]. Among these methods, electrochemical sensors based on electrooxidation of small molecules have gained remarkable attention owing to the advantages of convenient operation, fast response time, and low cost [12–15]. In recent years, advanced nanomaterials modified electrodes have attracted much attention as the platform for the H2O2 and glucose electrochemical sensor. Anu Prathap et al. developed a simple nonenzymatic H2O2 and glucose sensor based on CuO nanostructures modified electrode, finding unique electro-
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chemical sensing performance for H2O2 and glucose detections [6]. The nanomaterial is indeed successful in achieving high electrochemical activity as the platform to construct the electrochemical sensor. Therefore, the design of highly efficient nanostructured materials with controllable preparation is much important in order to maximize the entire advantages of electrochemical sensors. Among various nanostructured materials, palladium (Pd) nanostructured materials have attracted considerable interests due to their high electrocatalytic efficiency, the relatively cheaper price, and abundant yielding [16–18]. Especially, incorporation of other transition metals into Pd can further improve its electrochemical performance by changing its electronic structure as well as correlating the ligand effect and strain effect. Thus, great attentions have been paid to explore highly active Pd-based catalysts for various electrochemical detections. Nickel(Ni) as one of the 3d metals shows a dramatically synergistic effect to enhance the electrochemical activity of Pd [19–23]. Shen et al. synthesized PdNi catalysts by simultaneous reduction method using NaBH4 as reductant, finding high oxidation activity towards ethanol in alkaline solution [24]. Zhang et al. synthesized carbon-supported PdNi nanoparticles by controlling coreduction of PdCl2 and Ni (NO3)2, finding excellent ascorbic acid sensing capability [25]. However, these preparation methods usually involve the reduction of various Pd precursors with organic agents and the excessive use of surfactants, which may cause undesired environmental issues. Consequently, it is essential to develop a simple and highly effective method to fabricate PdNi bimetallic nanostructure in high through-put under mild conditions. Recently, nanoporous (NP) bimetallic structures have attracted great attention in the application of electrochemical sensing because their bicontinuous nanoscale skeletons and interconnected hollow channels are favourable for easy mass transport and high electron conductivity [26–30]. Nanoporous materials prepared by dealloying have the advantages of extremely clean metal surface, controllable and simple preparation, and excellent reproducibility [31–33]. In our previous work, it has been reported that NP-PdNi alloy was simply fabricated by a straightforward dealloy-
51
Fig. 2. XRD patterns of the dealloyed NP-PdNi sample. The standard patterns of Pd (JCPDS 65-2867) and Ni (JCPDS 65-2865) are attached for clear comparison.
ing from the ternary PdNiAl source alloy in NaOH solution. It is found that NP-PdNi show superior electrocatalytic activity towards oxygen reduction reaction with higher specific and mass activities as well as higher methanol tolerance compared with Pt/C catalyst [32]. In current work, it is interesting to explore the sensing ability of NP-PdNi alloy as the platform for the electrochemical detection of H2O2 and glucose. On the basis of the unique electroxidation activity towards H2O2 and glucose, NP-PdNi alloy shows promising application potential to construct highly sensitive and stable electrochemical sensors. 2. Experimental Pd15Ni5Al80 and Pd20Al80 alloy foils with a thickness of 50 lm were prepared by refining respective pure (>99.9%) Pd, Al, and Ni metal in an arc furnace, followed by melt-spinning under an
Fig. 1. SEM (a) and (b), TEM (c) and HRTEM (d) images of the resulted samples by dealloying Pd15Ni5Al80 alloy in 0.5 M NaOH solution for 48 h at room temperature.
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Fig. 3. CV curves of (a) NP-PdNi, (b) Pd/C, (c) NP-Pd in PBS solution with and without 1 mM H2O2. (d) CV curves of all samples in PBS + 1 mM H2O2 solution. (e) CV curves of NP-PdNi in PBS + 1 mM H2O2 solution at different scan rates of 20, 40, 60, 80, 100, and 120 mV/s. (f) Plots of current on NP-PdNi at 1.0 V.
argon-protected atmosphere. The NP-Pd75Ni25 and NP-Pd were respectively prepared by etching PdNiAl and PdAl alloy foils in 0.5 M NaOH solution for 48 h at room temperature. H2O2 (30%) and glucose were purchased from Sinopharm Chemical Reagent Co. Ltd. The phosphate buffered saline solution was prepared using Na2HPO4 and KH2PO4 solutions. Ultra-pure water (18.2 MX) was used in all measurements. Ascorbic acid (AA), uric acid (UA), and dopamine (DA) were purchased from Sigma–Aldrich. All the reagents were of analytical reagent grade and used without further treatment. The structure characterizations were carried out on a JEM-2100 transmission electron microscope (TEM) and a JSM-6700 field emission scanning electron microscope (SEM). Powder X-ray diffraction (XRD) was carried out on a Bruker D8 advanced X-ray diffractometer using Cu KR radiation at a step rate of 0.04°s 1. All electrochemical measurements were performed using CHI 760D
electrochemical workstation (Shanghai CH Instruments Co., China). A conventional three-electrode cell was used with Pt foil as a counter electrode, mercury sulphate electrode as the reference electrode, and 4-mm-diameter glassy carbon electrode as work electrode. Catalyst ink was prepared by mixing 1.5 mg carbon powder, 1.0 mg NP-PdNi, 400 lL isopropanol, and 200 lL nafion solutions (0.5 wt.%) under sonication for 30 min. The working electrode was made by dropping appropriate catalyst ink on a polished glassy carbon electrode and dried. The NP-Pd and Pd/C electrodes were prepared in a similar way. The electrochemical surface areas (ECSA) of Pd in all catalysts were evaluated by integrating the reduction charges during the stripping of surface monolayer oxide in N2-purged 0.5 M H2SO4 solution in the range of 0–1.35 V at the scan rate of 50 mV s 1, in which the used charge density is 420 lC cm 2 Pd [23].
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Fig. 4. (a) Amperometric responses of NP-PdNi on successive addition of 0.05 mM H2O2 into stirring PBS solution at 1.0 V. (b) Plots of currents vs. H2O2 concentrations. (c) Effects of the pH on the oxidation current of 1 mM H2O2 on NP-PdNi at 1.0 V (d) Sensing stability of NP-PdNi, Pd/C, and NP-Pd in a stirred PBS solution containing 1 mM H2O2 for 2000 s at 1.0 V.
Table 1 A comparison of the performance of some sensor platforms using different electrodes for H2O2 detection. H2O2 sensor
Linear range (mM)
Sensitivity (lA cm
Pd nanoparticle assemblies Graphene–AuNPs/GCE ERGO–ATP–Pd Palladized aluminum NP-PdNi
0.001–0.82 0.02–0.28 0.0001–10 0.005–0.034 0.05–1.0
– 3000 1176 – 208.6
3. Results and discussion 3.1. Characterization of the prepared PdNi alloy Fig. 1 illustrates the resulted structure after dealloying PdNiAl alloy in 0.5 M NaOH solution for 48 h. From the SEM image in Fig. 1a, it is clearly observed that selectively etching Al has successfully generated an open nanosponge morphology consisting of uniform ligaments distribution around 5 nm. The cross-sectional SEM image (Fig. 1b) indicates that the whole sample has been penetrated with interconnected hollow channels extending in all dimensions upon dealloying. As shows in the TEM image (Fig. 1c), a clear contrast between the dark skeletons and bright central region indicates the formation of nanoporous network structure with bicontinuous nanoscaled skeleton run through interconnected hollow channels. High-resolution TEM (HRTEM) image (Fig. 1d) provides more details for this structure, in which the ordered lattice fringes were well resolved across several interconnected ligaments with the lattice spacing calculated to be 2.18 Å, corresponding to the (1 1 1) crystal plane of a PdNi alloy structure. According to the SEM and TEM images of the resulted sample, it can be concluded that uniform nanoporous PdNi architecture can be simply fabricated by means of the simple dealloying method.
2
mM
1
)
Detection limit (lM)
Response time
Ref.
0.68 6 0.016 4.0 2.1
10 – 10 – 1.2
[35] [36] [37] [38] This work
XRD was used to examine the crystal structure of the dealloyed sample. As shown in Fig. 2, it is clear that the after selective leaching of Al from the ternary alloy, only a set of three diffraction peaks emerged at 40.3, 45.3, and 68.2 (2h), which can be assigned to the (1 1 1), (2 0 0), and (2 2 0) diffractions for a face centred cubic (fcc) PdNi alloy structure. It is noted that there are no other diffraction peaks emerged related to individual Pd and Ni, indicating the formation of a homogenous single-phase PdNi alloy. 3.2. Electrochemical behaviours of H2O2 over the NP-PdNi Characterized by the desirable nanoporous architecture with bicontinuous skeleton and hollow interconnected channels, NPPdNi is favourable for the molecules transport and electron conductivity. Consequently, it is interesting to explore the sensing performance towards H2O2 on the NP-PdNi alloy. Fig. 3 shows the cyclic voltammetric curves (CVs) of the modifed electrodes in PBS solution in the presence and absence of H2O2. It is observed that the NP-PdNi alloy exhibits higher oxidation current towards H2O2 starting from 0.42 V compared with that in pure PBS solution (Fig. 3a). As shown in Fig. 3b and c, Pd/C and NP-Pd shows similar electrochemical behaviour to NP-PdNi for H2O2 oxidation. However, the current density for H2O2 oxidation on NP-PdNi in the
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Fig. 5. CV curves of (a) NP-PdNi, (b) Pd/C, and (c) NP-Pd in 0.1 M NaOH solution with the presence and absence of 10 mM glucose. (d) CV curves of NP-PdNi, Pd/C, and NP-Pd in 10 mM glucose + 0.1 M NaOH solution.
range of 0.9–1.2 V is more than 3 times higher than those of Pd/C and NP-Pd, while the onset oxidation potential negatively shifted more than 100 mV (Fig. 3a–d). The much enhanced electrochemical activities towards H2O2 on NP-PdNi alloy may be due to the synergistic effect between Ni and Pd atoms as well as the nanoporous structure. The electrochemical behaviour of NP-PdNi towards H2O2 oxidation was further investigated by changing the scan rate. As displayed in Fig. 3e, the currents at 1.0 V are linear as a function of the scan rate in a range from 20 to 120 mV s 1 and the corresponding linear equation for the currents is I (mA) = 31.22 + 2.13 with a linear correlation coefficient of 0.997. This indicates that the electrochemical oxidation of H2O2 on the NP-PdNi modifed electrode is a surface-controlled process [34]. It can be concluded that the as prepared NP-PdNi alloy has greatly enhanced electrochemical activities towards H2O2, providing a substantial basis for its electrochemical sensing application. Based on the high electrooxidation activity towards H2O2, the sensing performance on NP-PdNi alloy is evaluated by amperometric detection upon the successive addition of H2O2. Fig. 4a shows the typical amperometric responses of NP-PdNi, Pd/C, and NP-Pd at a fixed potential. It is noted that NP-PdNi electrode responds rapidly (1.2 s) to each addition of H2O2. The rapid response could be attributed to the fact that H2O2 could diffuse freely into the bicontinuous nanoscaled skeleton as well rapidly be oxidized on the NP-PdNi surface duto the smaller structure dimension. In addition, NP-PdNi electrode shows larger response signals to the each addition of H2O2 compared with NP-Pd and Pd/C electrodes. As shown in Fig. 4b, Pd/C sample has a linear relationship in the range of 0.05–0.9 mM (linear equation: y = 39.91 x + 3.31, R = 0.995) with a detection limit of 2.7 lM. NP-Pd alloy has a better linear response to H2O2 in the range of 0.05 to 0.95 mM (linear equation:
y = 1.15 + 66.88 x, R = 0.995) with a detection limit of 2.3 lM (S/ N = 3). By comparison, NP-PdNi alloy exhibits the highest sensitivity and the widest linear range up to 1.0 mM (linear equation: y = 0.21 + 165.02 x, R = 0.998) with the lowest detection limit of 2.1 lM. These analytical parameters of NP-PdNi are better than other reported catalysts based H2O2 sensors as shown in Table 1 [35–38]. The remarkable performance of NP-PdNi modified electrode towards the detection of H2O2 indicates that NP-PdNi holds great potential to construct H2O2 sensor. The pH effect on the electrochemical response of H2O2 on NPPdNi was investigated in the pH range of 5.5–8.0. As shown in Fig. 4c, the current response was increased with the range from 5.5 to 6.5, and kept higher in pH range of 6.5–7.5. Indicating that neutral solution was the optimized condition for the electrochemical oxidation of H2O2. The decrease of the current value on alkaline conditions might be related to the self-degradation of H2O2 [14]. So pH around 7.0 was preferable in the H2O2 detection. The long-term sensing stability of the electrochemical sensor is significant for continuous and reliable monitoring of H2O2, which was evaluated by detecting the steady-state specific activity by using potentiostatic method. As is shown in Fig. 4d, NP-PdNi shows a more stable amperometric response to the addition of 1 mM H2O2 in stirring PBS after running for 2000 s compared with NP-Pd and Pd/C, indicating the higher sensing durability. The current degradation of NP-PdNi was 8.5% within 2000 s. The reproducibility of the sensors was evaluated by using ten equally proposed electrodes in the mixture of 1.0 mM H2O2. The relative standard deviation (RSD) of peak currents was 3.2%. The result indicated that the reproducibility of NP-PdNi was acceptable. The better performance of NP-PdNi modified electrode towards the detection of H2O2 indicates that NP-PdNi holds great potential to construct H2O2 sensor.
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Fig. 6. (a) CV curves of NP-PdNi alloy in 0.1 M NaOH and 10 mM glucose solution with and without 0.1 M NaCl. (b) Sensing stability NP-Pd, Pd/C, and NP-PdNi in a stirred NaOH solution containing 10 mM glucose for 2000 s at 0.35 V. (c) Amperometric current responses of NP-Pd, Pd/C, and NP-PdNi on successive addition of 1 mM glucose into stirring NaOH solution at 0.35 V. (d) Plots of current vs. glucose concentrations. (e) Amperometric current responses of NP-PdNi alloy on successive addition of 0.1-2.5 mM glucose into stirring NaOH solution at 0.35 V. (f) Glucose sensitivities of NP-PdNi as a function of the concentration of glucose.
Table 2 A comparison of the performance of some sensor platforms using different electrodes for glucose detection. Glucose sensor PdCu/GE GOx/Pd NPAs Pd–Ni/SiNWs PtPd–RGO NP-PdNi
Linear range (mM) 1–18 0.040–22 0–20 0.1–22 1–25
2
Sensitivity (lA cm 48(lA mg – 190.72 1.47 0.75
3.3. Electrochemical behaviours of glucose over the NP-PdNi Fig. 5a shows CVs of the NP-PdNi modified electrode in 0.1 M NaOH solution with and without glucose. In the presence of glucose, NP-PdNi electrode exhibits high oxidation currents starting from 0.3 V. The anodic peak located at 0.2 V could be attributed
1
mM
1
)
mM
1
)
Applied potential
Ref.
0.2 +0.25 +0.14 0 +0.35
[5] [35] [41] [42] This work
to glucose electroadsorption, causing the generation of adsorbed intermediates [39]. However, the accumulation of the intermediates inhibited the further electroadsorption of glucose, resulting in current decrease. When the potential was higher than 0.6V, Pd-OH species generated in the alkaline solution, which is beneficial for the oxidation of reaction intermediates on alloy surface,
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Fig. 7. (a) Interference of 0.1 mM AA, 0.02 mM UA, and 0.01 mM DA on the response of 1 mM H2O2 in 0.1 M PBS solution at 1.0 V (b) interference of 0.02 mM UA, 0.1 mM AA, and 0.01 mM DA on the response of 10 mM glucose in 0.1 M NaOH solution at 0.35 V.
leading to the current increases again. Moreover, the electrooxidation current also increased due to the direct oxidation of glucose on the surface. In the negative scan, the oxidized Pd is reduced at a potential around 0.1 V. As shown in Fig. 5b and c, Pd/C and NPPd catalysts show the similar electrochemical behaviour to NPPdNi for glucose oxidation. However, compared with NP-Pd and Pd/C catalysts, the much higher current density on NP-PdNi alloy indicates that its high glucose electrooxidation activity originates from the synergetic catalytic effect between Pd and Ni atoms as well as specific nanoporous architecture. It has been reported that Cl has a serious poisoning effect on some metallic electrocatalysts, leading to the activity loss towards the glucose electrooxidation [15]. The effect of Cl on the glucose oxidation over NP-PdNi alloy was evaluated by adding NaCl into 0.1 M NaOH and 10 mM glucose solution. As shown in Fig. 6a, the glucose oxidation current and potention on NP-PdNi has almost no change after adding NaCl, suggesting that NP-PdNi can well maintain its electrochemical property in the presence of Cl . However, it is noted that the current starting from 0.2 V became higher after adding Cl , which is consistent with the previous reports in Cl poisoning effect on some catalysts [40]. The longterm sensing stability of NP-PdNi alloy towards glucose oxidation is significant for continuous and reliable monitoring of glucose. As is shown in Fig. 6b, NP-PdNi shows much higher sensing durability and more stable amperometric response to the addition of 10 mM glucose in stirring NaOH after running for 2000 s compared with NP-Pd and Pd/C. Based on the excellent electrochemical activity towards glucose oxidation, the sensing performance of the all catalysts are evaluated by amperometric detection upon the successive addition of glucose. Fig. 6c shows the typical amperometric response of NP-PdNi alloy towards the successive addition of glucose at a fixed potential. NP-PdNi electrode responds rapidly to each addition of glucose and reaches the maximum steady-state current within 1.8 s. The rapid response could be attributed to the fact that glucose could diffuse freely into the bicontinuous nanoporous structure as well rapidly be oxidized on NP-PdNi surface. In addition, NP-PdNi electrode shows higher current response signals to the addition of glucose compared with NP-Pd and Pd/C electrodes with the current response intensity in NaOH system due to the synergistic effect between Ni and Pd atoms. As shown in Fig. 6d, the NP-PdNi alloy exhibits the high sensitivity and wide linear range up to 25 mM (linear equation: y = 4.1310 + 2.4619 x, R = 0.994) with the lowest detection limit of 1.9 lM. In comparison, the sensing range of Pd/ C and NP-Pd are respective up to 16 mM and 14 mM (linear equation: y = 0.57 + 0.23 x, R = 0.986 and y = 0.46 + 0.36 x, R = 0.996) with the detection limit of 2.1 lM and 2.3 lM. The analytical
parameters of NP-PdNi are better than other reported catalysts based glucose sensors as shown in Table 2 [5,35,41,42]. The better performance of NP-PdNi modified electrode towards the detection of glucose indicates that NP-PdNi holds great potential to fabricate glucose sensor. The sensing performance of the NP-PdNi alloy is also evaluated by successive addition of glucose with different concentrations. Fig. 6e gives the amperometric responses of NP-PdNi alloy on successive addition of 0.1–2.5 mM glucose. Owing to the synergistic electrocatalytic activity of PdNi alloy and the excellent conductivity of nanoporous architecture, the amperometric response of the NP-PdNi exhibits stable step curve with dramatically enhanced current density. It should be noted that the response time is less than 2 s to research steady-state current. In addition, the glucose biosensors based on NP-PdNi show multi-linear detection ranges with different sensitivities up to 71 mM, displaying a strong dependence on the concentration of added glucose (Fig. 6f). As the concentration decreases to 1 mM, the sensitivity of NP-PdNi increases up to 2.5 lA mM 1 cm 2. 3.4. The anti-interference for electrochemical detection of H2O2 and glucose over NP-PdNi One of the major challenges in nonenzymatic H2O2 and glucose detections are the interfering electrochemical signals caused by some easily oxidizable compounds such as AA, UA, and DA [43]. So, it is essential to investigate the anti-interference of NP-PdNi towards the H2O2 and glucose sensing. Fig. 7a shows the chronoamperometry curves of NP-PdNi electrode with successive addition of 0.1 mM AA, 0.02 mM UA, 0.01 mM DA, and 1 mM H2O2. The interferences from AA, UA, or DA were 4.1%, 0.3% or 7.8% of the response generated by H2O2 on NP-PdNi modified electrode. In addition, Fig. 7b shows the chronoamperometry curves of NPPdNi electrode with successive addition of 0.1 mM AA, 0.02 mM UA, 0.01 mM DA, and 1 mM H2O2. The interferences from UA, AA or DA were 0.38%, 7.8% or 2.4% of the response generated by glucose on NP-PdNi modified electrode. The result demonstrated that electrochemical detection of H2O2 and glucose on NP-PdNi modified electrodes could be performed with little interference from AA, DA, and UA. 4. Conclusions In this work, NP-PdNi alloy is successfully fabricated with bicontinuous nanoporous architecture by a simple dealloying strategy. Based on enhanced electrochemical activities towards
D. Zhao, C. Xu / Journal of Colloid and Interface Science 447 (2015) 50–57
the oxidation of H2O2 and glucose, NP-PdNi can achieve sensitive detection for H2O2 and glucose with wide linear range, fast response, long-term sensing durability as well as little interference from DA, UA, and AA. Along with these attractive features, NP-PdNi alloy holds great application potential in constructing electrochemical sensors. Acknowledgment This work was supported by the National Science Foundation of China (51001053, 21271085). References [1] Y.H. Wang, X.J. Yang, J. Bai, X. Jiang, G.Y. Fan, Biosens. Bioelectron. 43 (2013) 180–185. [2] K. Sato, E. Abe, M. Takahashi, J. Anzai, J. Colloid Interf. Sci. 432 (2014) 92–97. [3] W.N. Liu, D. Ding, Z.L. Song, X. Bian, X.K. Nie, X.B. Zhang, Z. Chen, W.H. Tan, Biosens. Bioelectron. 52 (2014) 438–444. [4] X.J. Yang, Y.H. Wang, Y.W. Liu, X. Jiang, Electrochim. Acta 108 (2013) 39–44. [5] M. Yuan, A. Liu, M. Zhao, W.J. Dong, T.Y. Zhao, J.J. Wang, W.H. Tang, Sens. Actuat. B 190 (2014) 707–714. [6] M.U.Anu. Prathap, B. Kaur, R. Srivastava, J. Colloid Interf. Sci. 370 (2012) 144– 154. _ Boyacı, Z. [7] V.K. Gupta, N. Atar, M.L. Yola, M. Eryılmaz, H. Torul, U. Tamer, I.H. Üstündag˘, J. Colloid Interf. Sci. 406 (2013) 231–237. [8] A.K. Dutta, S.K. Maji, P. Biswas, B. Adhikary, Sens. Actuat. B 177 (2013) 676– 683. [9] T. Wen, F. Qu, N.B. Li, H.Q. Luo, Anal. Chim. Acta 749 (2012) 56–62. [10] Y.F. Cheng, R. Yuan, Y.Q. Chai, H. Niu, Y.L. Cao, H.J. Liu, L.J. Bai, Y.L. Yuan, Anal. Chim. Acta 745 (2012) 137–142. [11] M. Abo, Y. Urano, K. Hanaoka, T. Terai, T. Komatsu, T. Nagano, J. Am. Chem. Soc. 133 (2011) 10629–10637. [12] H.B. Noh, K.S. Lee, P. Chandra, M.S. Won, Y.B. Shim, Electrochim. Acta 61 (2012) 36–43. [13] X. Yuan, Y.Q. Tay, X.Y. Dou, Z.T. Luo, D.T. Leong, J.P. Xie, Anal. Chem. 85 (2013) 1913–1919. [14] N.M. Jia, B.Z. Huang, L. Chen, L. Tan, S.Z. Yao, Sens. Actuat. B 195 (2014) 165– 170. [15] X.M. Chen, Z.J. Lin, D.J. Chen, T.T. Jia, Z.M. Cai, X.R. Wang, X. Chen, Biosens. Bioelectron. 25 (2010) 1803–1808.
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