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Detection of hydrogen peroxide at a palladium nanoparticle-bilayer graphene hybrid-modified electrode
Sensors and Actuators B 230 (2016) 690–696
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Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb
Detection of hydrogen peroxide at a palladium nanoparticle-bilayer graphene hybrid-modified electrode Jue Wang a,b , Hai-bin Sun b , Hai-yang Pan b , Yan-yue Ding a,b , Jian-guo Wan b , Guang-hou Wang a,b , Min Han a,b,∗ a b
National Laboratory of Solid State Microstructures and Department of Materials Science and Engineering, Nanjing University, Nanjing 210093, China Collaborative Innovation Centre of Advanced Microstructures, Nanjing University, Nanjing 210093, China
a r t i c l e
i n f o
Article history: Received 3 November 2015 Received in revised form 13 February 2016 Accepted 23 February 2016 Available online 3 March 2016 Keywords: Gas phase cluster beam deposition Bilayer graphene Hydrogen peroxide detection Palladium nanoparticle
a b s t r a c t We report a nonenzymatic H2 O2 sensor based on a glassy carbon electrode modified with bilayer graphene films (BGFs) that were decorated with well-defined Pd nanoparticles. The BGFs were synthesized with a chemical vapor deposition process, and the Pd nanoparticle films were produced by gas phase cluster beam deposition. The BGFs provide great accessible active surface area and excellent conductive interfaces for electron transfer, which largely enhance the electrocatalytic performance of the modified electrodes. A rapid response time of less than 3 s and a wide linear range from 4 M to 13.5 mM was exhibited in the amperometric detection of H2 O2 . © 2016 Elsevier B.V. All rights reserved.
1. Introduction Fast quantitative determination of hydrogen peroxide (H2 O2 ) is important in many fields, such as clinical chemistry, biotechnology, environmental monitoring, pharmaceuticals, and food analysis [1–5]. Among various analytical methods that have been used for the detection of H2 O2 , electrochemical (amperometric and potentiometric) techniques have received great attention because of their high efficiency, low cost, and high sensitivity [6–9]. In practice, amperometric determination of H2 O2 is suitable for quick test applications. However, amperometric sensors with bulk electrodes require high overpotential for H2 O2 oxidation, which results in interference from other species in real samples, such as ascorbic acid, urea, and paracetamol [10,11]. Furthermore, the electrode reactions are so irreversible that the responses obtained are usually unstable with poor linearity [12,13]. Efforts have been focused on modifying the electrode surfaces using suitable materials, including enzymes, to improve the selectivity and stability of H2 O2 sensors. Recently, development of enzyme-free electrodes modified with metal nanoparticles (NPs) has become a trend [14–23]. The
∗ Corresponding author at: National Laboratory of Solid State Microstructures and Department of Materials Science and Engineering, Nanjing University, Nanjing 210093, China. E-mail address: [email protected] (M. Han). http://dx.doi.org/10.1016/j.snb.2016.02.117 0925-4005/© 2016 Elsevier B.V. All rights reserved.
nanoparticle-based non-enzymatic H2 O2 sensors were found to be versatile, with a low detection limit and wide response range. Non-enzymatic H2 O2 sensors based on noble metal nanoparticles, such as silver [24,25], and palladium [26,27], have attracted considerable attention because of their excellent catalytic activity and electrical conductivity. Liao et al. [28] fabricated a highly adhesive Ag nanoparticle coating on a glass carbon electrode (GCE) using gas phase nanoparticle beam deposition. The Ag NP-modified GCE exhibited high electrocatalytic activity toward the reduction of H2 O2 with a detection limit as low as 1 × 10−6 M and a very fast response time of less than 1 s. Recently, we used a similar method to fabricate Pd NP-deposited-GCE, which enabled highly selective amperometric detection of H2 O2 at a sufficiently low applied potential (∼−0.12 V) [29]. Although both the lower detection limit and the linear response range of the Pd NP-modified GCE were superior to those of the Ag NP-modified GCE, its response time was approximately one order of magnitude slower. Graphene sheets (GS) have excellent electrical conduction in two dimensions with good chemical stability. They have been the subject of considerable interest in recent years because of their excellent electrocatalytic activities [6,30–32]. Graphenemetal nanoparticle hybrids may have much higher electrocatalytic activity than that of GS, providing a new way to develop catalytic materials [33]. Phan and Chung synthesized graphene-supported Pd nanocubes for hydrogen detection [6]. Zhou et al. prepared a
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Au NP/GS nanocomposite-modified GCE for the detection of H2 O2 [34]. Rosy et al. developed a graphene-modified Pd sensor for the determination of norepinephrine [7]. Until now, GSs used for electrode modifications were generally the chemically reduced graphite oxide (rGO) sheets, with some intrinsic limitations such as a lack of control of the film thickness as well as the use of toxic chemicals. Recently, GSs produced by chemical vapor deposition (CVD) have been considered for electrode modifications [8,9,35,36]. Compared with rGO, they have better quality control and higher electron conductivity. CVD-synthesized bilayer graphene has an electric-field-controllable band gap and thus has attracted special interests [37,38]. However, the chemistry and sensor application of bilayer graphene sheets and their metal NP hybrids have not been much studied. Their electrocatalytic activity and non-enzymatic sensing behavior have not been fully understood. In this work, for the first time, Pd NPs were deposited on bilayer GSs supported with glass carbon electrodes in the gas phase. The loading amount and size of Pd NPs were well controlled. The electrocatalytic performance of Pd NPs/bilayer graphene films (BGFs)/GCEs toward H2 O2 detection were investigated, with the main focus being their linear response range and response time. 2. Materials and method 2.1. Preparation of bilayer graphene covered electrodes BGFs were synthesized by CVD with copper foil as the growth substrate; the details on the fabrication process can be found elsewhere [39]. In order to transfer the bilayer graphene to the electrode, a thin layer of poly(methyl methacrylate) (PMMA) (9% in anisole) was spin-coated on top of the BGF. The copper foil was then submerged in a 1.0 M FeCl3 solution and removed completely after etching for 2 h, leaving a continuous film of PMMA/BGF floating on the solution. The films of PMMA/BGFs were picked up from the solution with a glass slide and washed carefully in deionized water. Finally, the PMMA/BGFs were picked up on the GCE surface from the deionized water and dried in vacuum at 80 ◦ C for 30 min. The PMMA layer was then removed with acetone. Before covered with BGFs, the GCEs (3 mm in diameter) were carefully polished to obtain a mirror-like surface and washed in absolute ethanol and ultrapure water. All the specimens were inspected with an optical microscope to insure that the surfaces of the GCEs were fully covered with BGFs uniformly. BGFs were also transferred to the surface of indium tin oxide (ITO) films. The ITO conductive glass (10 × 10 mm2 ) were purchased from YaRong Chemical Reagent Co. (Nanjing, PR China). 2.2. Preparation of Pd NPs and deposition of Pd NPs/BGF hybrid-modified GCEs Fig. 1 schematically depicts the preparation of Pd NPs/BGF/GCE. Pd nanoparticles were generated by a gas aggregation cluster source. The deposition was performed in a high vacuum chamber equipped with the cluster source. Pd atoms were sputtered from a Pd target in an argon buffer gas (purity, 99.999%) in a liquid nitrogen-cooled aggregation tube. In order to produce Pd nanoparticles with a controlled size, three buffer gas pressures of 90 Pa, 110 Pa, and 130 Pa were used. A stable magnetron discharge ran with an input power of 130 W. Pd nanoparticles were formed in the argon gas through the aggregation process. The nanoparticles were swept by the gas stream into high vacuum through a nozzle, forming a nanoparticle beam with a high speed of ∼1000 m/s [40]. The deposition was carried out at a precisely controlled rate of 0.42 Å s−1 for 30 min. The corresponding nanoparticle coverage was about 85%, as characterized with transmission electron microscopy.
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2.3. Chemical reagents All chemicals from commercial sources were of analytical grade. All solutions were prepared using distilled water. 2.4. Characterization The microstructures of the Pd nanoparticles and Pd NPs/graphene hybrid were characterized with transmission electron microscopy (TEM, TecnaiF20). For TEM, the nanoparticles were either deposited simultaneously on amorphous carbon films supported with copper grids, or deposited on the bilayer graphene transferred on the copper grid surface. The graphene films were characterized using a Raman spectrometer (NTMDT NTEGRA spectra). For Raman spectroscopy, the graphene films were transferred to the surface of a Si wafer. 2.5. Electrochemical measurements Electrochemical measurements were performed on an electrochemical workstation (CHI660D, Shanghai Chenhua Instruments Co., Shanghai, China). A three-electrode cell was used, with a bare or modified electrode as the working electrode, a Ag/AgCl electrode (saturated with KCl) as the reference electrode, and platinum wire as a counter electrode. Phosphate buffer solutions (PBSs) (pH = 7.4, 0.05 M) were used as the electrolyte solution throughout the electrochemical measurements. 3. Results and discussion 3.1. Characterization of graphene and Pd nanoparticles In order to investigate the influence of nanoparticle size on the reduction of H2 O2 , Pd NPs with three different sizes were prepared by changing the argon gas pressure. Fig. 2 shows TEM images of Pd NPs prepared with different buffer gas pressures. As shown in Fig. 2(a)–(c), the sizes of the Pd NPs increase with increasing argon gas pressure. Corresponding to the buffer gas pressures that were used (90 Pa, 110 Pa, and 130 Pa), the average diameters of the nanoparticles were measured to be ∼6.5 nm, 10.6 nm, and 12.0 nm, respectively. The Pd NPs are randomly distributed on the substrate with uniform size. Fig. 2(d) shows a TEM image of Pd NPs deposited on BGF. The sample was prepared with similar experimental condition as that of the NPs shown in Fig. 2(b). We can see that the morphologies of the nanoparticle assemblies of the two samples are quite similar. Fig. 2(e) shows the Raman spectrum of the graphene sheets used to modify the GCEs. The spectrum reveals two intense peaks at ∼1590 cm−1 and ∼2650 cm−1 , which can be assigned to the G mode and 2D mode of graphene, respectively. The peak intensity ratio between the G- and 2D-bands was calculated to be ∼1.0, and the full width at half-maximum (FWHM) of the 2D-band was ∼55 cm−1 , corresponding well to the Raman characteristic of the AB-stacked bilayer graphene [41]. The high crystallinity of carbon in the bilayer graphene will be highly beneficial for achieving better electronic conduction between adjacent Pd nanoparticles. 3.2. Electrocatalytic activity toward H2 O2 reduction The electrocatalytic activity of Pd NPs/BGF/GCEs toward H2 O2 reduction was investigated by cyclic voltammetry (CV). Fig. 3(a) shows the CV curves obtained for the bare GCE, Pd NPs/GCE, BGF/GCE, and GCE modified with Pd NPs/BGF hybrid, in PBS containing 10 mM H2 O2 . For the bare GCE and BGF/GCE, no significant current change could be observed, indicating that there was no electrocatalytic activity toward H2 O2 reduction for them. For the
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Fig. 1. Schematic diagram of the process of Pd NPs/BGF/GCE preparation.
Fig. 2. TEM images of Pd NPs produced with argon gas pressure of (a) 90 Pa, (b) 110 Pa, and (c) 130 Pa and the corresponding size distributions. (d) TEM image of the Pd NPs deposited on bilayer graphene film surface. (e) Raman spectrum of the BGF.
Pd NPs-modified GCE, there was obvious electrocatalytic current for H2 O2 . A prominent cathodic peak current appeared at approximately −0.12 V. For the GCE modified with Pd NPs/BGF hybrid, a drastic increase in the reduction current was observed, with a well-defined reduction peak at approximately −0.17 V applied voltage. The redox peak could be attributed to the enhanced electron transfer between H2 O2 and the Pd NPs//BGF hybrid. The results indicate that GCEs modified either with Pd NPs or with Pd NPs/BGF hybrid have effective electrocatalytic ability in H2 O2 reduction. However, a quantitative comparison with the cyclic voltammogram obtained at GCE that is merely covered with Pd NPs shows a tremendous improvement in the catalytic properties of Pd NPs/BGF/GCE for hydrogen peroxide reduction. The anodic peak current of the
latter is increased by more than 2-folds. Although the reduction peak potential of Pd NPs/BGF/GCE is somewhat increased (from −0.12 eV to −0.17 eV), it is still much smaller than the applied overpotential reported for silver-based electrodes [28], and low enough to eliminate the influence from most of the chemicals other than H2 O2 , such as ascorbic acid, uric acid, glucose and ethanol. This particular aspect is appealing for highly selective detection of H2 O2 . In Fig. 3(b), CV curves obtained in PBS containing 10 mM H2 O2 for the Pd NPs/BGF hybrid-modified GCEs with three different Pd nanoparticle sizes are compared. The coverage of the samples was carefully controlled to be the same by maintaining a constant deposition condition (depositing 30 min with a 0.42 Å s−1 deposition rate). A small variation of peak potential as well as the
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Fig. 3. (a) CV curves of bare GCE, BGF/GCE, Pd NPs/GCE, and Pd NPs/BGF/GCE in 0.05 M PBS (pH 7.4) containing 0.01 M H2 O2 . Inset: a rescaled plot of the CV curves to show the very small (in subnano-ampere range) cathodic currents for bare GCE and BGF/GCE. (b) CV curves of the Pd NPs/BGF/GCEs with different average sizes of Pd nanoparticles measured in 0.01 M H2 O2 (0.05 M PBS, pH 7.4) at a scan rate of 50 mV/s.
current of H2 O2 reduction is exhibited. However, such changes are much smaller than those induced by incorporating bilayer graphene sheets into the electrodes, as shown in Fig. 3(a). We have repeated similar experiments with nanoparticle size-relevant specimens for three times, the peak current and peak potential of H2 O2 reduction did not change significantly from electrode to electrode. Evidently, the significant enhancement in the electrocatalytic activity of the electrodes should be attributed to the effect of the modification with Pd NPs/BGF hybrid, rather than the size effect of the Pd nanoparticles, although the nanoparticle size does have some influence on the electrocatalytic activity in H2 O2 detection [28,42]. Therefore, in the following discussion we omit the influence of the nanoparticle size and use Pd nanoparticles with ∼10 nm average diameter in the experiments. Detailed characterization of the response of the Pd NPs/BGF/GCEs toward H2 O2 was performed at a constant applied potential of −0.17 V. Measurements were performed in 0.05 M stirred phosphate buffer solution. The limit of detection, linear response range, sensitivity, and response time were studied. Fig. 4(a) shows the stable amperometric responses (steady-state current vs. time) of Pd NPs/BGF/GCEs to the additions of H2 O2 into PBS. Well-defined responses can be observed for the successive additions of 4 M of H2 O2 at the low H2 O2 concentrations and 13.5 mM of H2 O2 at the higher H2 O2 concentrations. From the insert it can be seen that the Pd NPs/BGF/GCEs respond rapidly to the addition of H2 O2 , reaching 95% of the steady current in less than 3 s. The response time is much shorter than that of the GCE covered barely with Pd NPs, for which a response time of 6 s is estimated. Such a fast response time may be attributed to the excellent electrical conduction of the 2D graphene sheets and the high conductive interface between Pd NPs and BGF, due to the high quality of their crystal lattices. Similar response time was also observed in other electrodes based on CVD-fabricated functionalized three-dimensional graphene [9,35]. In practice, electrochemical sensors are often applied for measuring hydrogen peroxide when a quick test is required, therefore a short response time is of great concern. We also performed measurements on the amperometric responses of the Pd NPs/BGF hybrid-based electrode to the addition of H2 O2 into PBS, by replacing the glassy carbon electrodes with ITO films. As shown in Fig. 4(b), the Pd NPs/BGF/ITO electrode responds rapidly and sensitively to the changes in H2 O2 concentration. A response time of 3 s can be estimated, which is as short as that of the Pd NPs/BGF/GCE. This therefore demonstrates that it is the highly conductive interface between Pd NPs and BGF that contributes much to the fast response to H2 O2 , rather than the interface between BGF and supporting electrode.
The corresponding calibration curve (steady-state response current vs. H2 O2 concentration) is shown in Fig. 4(c). The Pd NPs/BGF/GCE shows excellent linearity up to 13.5 mM. At higher H2 O2 concentration, the plot deviates from linearity, which may be attributed to the saturation of the electrocatalytic activity of the electrode. With the increasing of H2 O2 concentration, the electrodes adsorb more and more H2 O2 and ultimately approach saturation. The saturation of absorption results in the saturation of the electrocatalytic activity of the electrode, so that the current change becomes smaller and smaller, and the calibration curve deviates from linearity. Also, at higher H2 O2 concentrations, we can observe a significant increase in the noise of the measured anodic current. Such noise may correlate with the diffusion of the reactants on the electrode surface. With the increase of H2 O2 concentration, the diffusion of the reactants which have not been absorbed becomes significant, which will contribute to the anodic current as noise. A detection limit of 1.5 × 10−6 M is determined at a signal-tonoise ratio of 3. The sensitivity estimated using the slope of the calibration plot is 115.1 A mM −1 . For Pd NPs-modified GCE without graphene, a linear response in the H2 O2 concentration range from 1 M to 6.0 mM can be observed, with a sensitivity of approximately 57.1 A mM−1 . Evidently, GCEs modified with Pd NPs/BGF hybrids offer more advantages in H2 O2 detection over GCEs covered merely with Pd NPs, such as their much wider linear range and much higher sensitivity. In fact, the linear response range and sensitivity of the Pd NPs/BGF/GCE are significantly higher than those of nonenzyme H2 O2 sensors reported previously based on silver nanoparticles [28], Cu2 O [43], Fe3 O4 [44], Pd nanoparticles [29,45], and even enzyme-based electrodes [46,47]. Based on the modified electrodes of different materials, a comparison for H2O2 determination is presented in Table 1. H2 O2 concentrations typically range from micromolar for in vivo conditions and residual levels analysis in foods to tens of millimolar for bleaching applications; therefore, nonenzyme H2 O2 sensors with a response range up to several tens of millimolar are considered important. As we pointed out in our previous paper [29], the electrocatalytic activity of Pd nanoparticles toward H2 O2 reduction might be attributed to their excellent catalytic properties and good electronic conductivity. The small size and clean surface of nanoparticles enable high specific surface area and provide a large number of active sites, leading to electrocatalytic reduction of H2 O2 at lower overpotentials. The nanoparticles also play an important role in transferring electrons between H2 O2 and the conducting sites of the electrodes, resulting in an increase in electron transfer rate. When Pd NPs are combined with BGF, the electrocatalytic activity of the hybrid can be significantly enhanced because of the synergistic effect of BGF and Pd NPs. The 2D graphene sheets have
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Fig. 4. (a) Amperometric responses of the Pd NPs/GCE and Pd NPs/BGF/GCEs upon successive addition of H2 O2 into gently stirred 0.05 M PBS (pH 7.4) at −0.11 and −0.17 V applied potentials, respectively. Inset: rescaled plots of amperometric responses from 40 to 120 s. (b) Amperometric responses of the Pd NPs/BGF/ITO upon successive addition of H2 O2 into gently stirred 0.05 M PBS (pH 7.4) at −0.08 V. For comparison, the corresponding data of Pd NPs/BGF/GCEs is also plotted. Inset: a rescaled plot of amperometric responses of the Pd NPs/BGF/ITO from 40 to 120 s. (c) Calibration plots of the relationship between the response current and the H2 O2 concentration at Pd NPs/GCEs and Pd NPs/BGF/GCEs (The error bars were determined from a statistical analysis of the data from 20 separate measurements). Inset: rescaled calibration plots of the relationship between the response current and the H2 O2 concentration in the 0 to 20000 M H2 O2 concentration range. Table 1 Comparison of different H2 O2 sensors. Electrode used b
3DGN/PtNP PdNP/GNs-GCEc Pd-PEI/GO/GCd (DNA-AgNCs)/GN/GCEe PdNP-CNF/GPEf Pd-NPs/BGFs/GCE a b c d e f
Potential (V)
LOD (M)a
LRR (M)
pH used
Reference
0.45 −0.25 0 −0.6 −0.2 −0.17
0.125 0.05 0.2 3 0.2 1.5
0.167–7.486 0.1–1000 0.5–459 15–23,000 0.2–20,000 4–13,500
7.8 7.4 7.2 7.0 7.4 7.4
[30] [48] [49] [50] [51] This work
LOD: the limit of detection. 3DGN/PtNP: three-dimensional graphene networks/Pt nanoparticle. PdNP/GNs-GCE: palladium nanoparticles/graphene nanosheets-glassy carbon electrode. Pd-PEI/GO/GC: palladium- branched polyethylenimine/graphene oxide/glassy carbon. (DNA-AgNCs)/GN/GCE: polynucleotide-templated silver nanoclusters/graphene composite film/glassy carbon electrode. PdNPs-CNF/CPE: palladinumnanoparticles-carbonnanofibers/carbonpasteelectrode.
excellent electrical conduction because of the high quality of their crystal lattices and can make contact with Pd NPs well, resulting in a highly conductive interface, which could accelerate the electron transfer rate between H2 O2 molecules and the electrode and speed up the response time of the measurements. Furthermore, because of the highly accessible active surface area of BGF, the accumulation of OH (ads) intermediates on the electrode surface could be largely enhanced, enabling the Pd NP-catalyzed reduction of the secondary H2 O2 molecule to take place continuously at a faster rate [28]. Fig. 5 shows the CV curves of Pd NPs/BGF/GCE and Pd NPs/GCE in 0.1 M NaOH, with a mean Pd NP diameter of approximately 10.6 nm. From Fig. 5, the active surface area of GCEs modified with Pd NPs and Pd NPs/BGF hybrid was determined to be 4.3 cm2 and 8.5 cm2 , respectively. This confirms that the BGFs and hence their modified electrodes have a large active surface area which is approximately double that of the bare GCE. The long-term stability of the fabricated electrodes was examined. The used Pd NPs/BGF/GCE was stored in air at room temperature for one week, and its CV to H2 O2 was measured. As can be seen in Fig. 6, the CV peak currents are still 100%. From TEM and
Fig. 5. CV curves of Pd NPs/BGF/GCE and Pd NPs/GCE in 0.1 M NaOH.
Raman spectrum observation, we confirmed that the morphology of the Pd nanoparticles as well as their decorated bilayer graphene sheets did not change over time, even after H2 O2 immersion.
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Fig. 6. CV curves measured in 0.05 M PBS (pH 7.4) containing 0.01 M H2 O2 with the as-prepared Pd NPs/BGF/GCE and that of the same electrode stored in air at room temperature for one week after its first usage.
4. Conclusion In conclusion, we have demonstrated the synthesis of a Pd NPs/Bilayer graphene film hybrid-modified electrode and its application for fast and sensitive nonenzymatic detection of H2 O2 . The CVD synthesized bilayer graphene possesses a highly accessible active surface area, which enhances the accumulation of OH intermediates on the electrode surface and enables the Pd NP-catalyzed reduction of the secondary H2 O2 molecule to take place continuously with a faster rate. Moreover, the 2D graphene sheets have excellent electrical conduction and can make contact with Pd NPs well. This results in highly conductive interfaces, which accelerate the electron transfer rate between H2 O2 molecules and the electrode. All these features provide a favorable environment for the electrocatalytic reduction of H2 O2 and allow fast and sensitive detection of H2 O2 . With the introduction of BGF, the catalytic activity of the Pd NP-modified electrodes toward H2 O2 reduction was largely enhanced. The fabricated Pd NPs/BGFs/GCE showed a large linear range from 4 M to 13.5 mM, and a rapid response time less than 3 s. Acknowledgments The authors thank the National Natural Science Foundation of China (Grant no. 51171077), and the National Basic Research Program of China (973 Program, Grant no. 2014CB932302). This research was also supported by a project funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions. References [1] P.E. Gomez, M.C. Lopez, A review on micro-oxygenation of red wines: claims, benefits and the underlying chemistry, Food Chem. 125 (2011) 1131–1140. [2] B.M. Andersen, M. Rasch, K. Hochlin, F.H. Jensen, P. Wismar, J.E. Fredriksen, Decontamination of rooms, medical equipment and ambulances using an aerosol of hydrogen peroxide disinfectant, J. Hosp. Infect. 62 (2006) 149–155. [3] T. Ruzgas, E. Csoregi, J. Emneus, L. Gorton, G. Marko-Varga, Peroxidase-modified electrodes: fundamentals and application, Anal. Chim. Acta 330 (1996) 123–138. [4] W. Chen, S. Cai, Q.Q. Ren, W. Wen, Y.D. Zhao, Recent advances in electrochemical sensing for hydrogen peroxide: a review, Analyst 137 (2012) 49–58. [5] P. Niethammer, C. Grabher, A.T. Look, T.J. Mitchison, A tissue-scale gradient of hydrogen peroxide mediates rapid wound detection in zebrafish, Nature 459 (2009) 996–1000. [6] D.T. Phan, G.S. Chung, A novel Pd nanocube-graphene hybrid for hydrogen detection, Sens. Actuator B: Chem. 199 (2014) 354–360. [7] S.K. Rosy, B. Yadav, M. Agrawal, R.N. Goyal Oyama, Graphene modified palladium sensor for electrochemical analysis of norepinephrine in pharmaceuticals and biological fluids, Electrochim. Acta 125 (2014) 622–629. [8] G. Albert, C. Carlo, M. Roya, Single-layer CVD-grown graphene decorated with metal nanoparticles as a promising biosensing platform, Biosens. Bioelectron. 33 (2012) 56–59.
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Biographies Jue Wang in 2009 received the B.S. degree in Materials Chemistry from Jiangxi University of Science and Technology, in 2012 she received the M.S. degree in Applied Chemistry from Jiangsu University of Science and Technology, She is currently working as a Ph.D. student in the Department of Materials Science and Engineering, Nanjing University. Her research cover metal nanostructures, especially metal
nanoparticle arrays, as well as the applications of these nanostructures in sensors and gas phase catalysis. Hai-bin Sun received the B.S. degree with physics in 2003 from Xinyang Normal University. In 2006, he received the M.S. degree in Material Physics and Chemistry from the Zhengzhou University. In 2015 he received Ph.D. degree in Condensed Matter Physics from the Nanjing University. He is now a lecturer in the Department of Physics and Electronic Engineering at Xinyang Normal University. His research are related to two dimension film materials and noble metal nanomaterials, including controllable preparation, plasmon resonance property and optical-electric properties. Hai-yang Pan received the B.S. degree in 2011 with Physics from Zhenzhou University, He is currently student of master leading to Ph.D. in Nanjing University, and his work includes the synthesis and electron transport of semiconductor nanowires. His researches also include the two dimension materials and device fabrication. Yan-yue Ding received the B.S. degree in Materials Physics from Nanjing University, in 2015. She is currently master student in Nanjing University. Her research is related to optic properties of semiconductor nanoparticle arrays. Jian-guo Wan in 1997 obtained doctoral degree from Nanjing University Aeronautics and Astronautics. He was a visiting associate researcher in Department of Applied Physics and Intelligent Materials Research Center in the Hong Kong Polytechnic University, in 2002. He is now a professor of physics in Nanjing University, His research is related to atomic clusters and cluster-based nanostructures and nanomaterials, preparation and physical properties of Multiferroic Materials, the preparation, properties and application of low-dimensional Nanofunctional materials. Guang-hou Wang was born in Anhui Province, in 1939. He obtained his bachelor’s degree in Beijing Normal University in 1963. He was a visiting professor in New York State University from 1980 to 1982. He is a senior professor of physics in Nanjing University. He was also elected in 2011 as a Academician in Chinese Academy of Sciences, His research is related to atomic clusters and cluster-based 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 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 in condensed matter physics from Nanjing University, 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 Freiburg University in Germany. From 2003, he was elected 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. Particularly 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, nano-optics and quantum transport in clusterbased nanostructures, molecular and gas sensors based on densely packed clusters films.
Contents lists available at ScienceDirect
Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb
Detection of hydrogen peroxide at a palladium nanoparticle-bilayer graphene hybrid-modified electrode Jue Wang a,b , Hai-bin Sun b , Hai-yang Pan b , Yan-yue Ding a,b , Jian-guo Wan b , Guang-hou Wang a,b , Min Han a,b,∗ a b
National Laboratory of Solid State Microstructures and Department of Materials Science and Engineering, Nanjing University, Nanjing 210093, China Collaborative Innovation Centre of Advanced Microstructures, Nanjing University, Nanjing 210093, China
a r t i c l e
i n f o
Article history: Received 3 November 2015 Received in revised form 13 February 2016 Accepted 23 February 2016 Available online 3 March 2016 Keywords: Gas phase cluster beam deposition Bilayer graphene Hydrogen peroxide detection Palladium nanoparticle
a b s t r a c t We report a nonenzymatic H2 O2 sensor based on a glassy carbon electrode modified with bilayer graphene films (BGFs) that were decorated with well-defined Pd nanoparticles. The BGFs were synthesized with a chemical vapor deposition process, and the Pd nanoparticle films were produced by gas phase cluster beam deposition. The BGFs provide great accessible active surface area and excellent conductive interfaces for electron transfer, which largely enhance the electrocatalytic performance of the modified electrodes. A rapid response time of less than 3 s and a wide linear range from 4 M to 13.5 mM was exhibited in the amperometric detection of H2 O2 . © 2016 Elsevier B.V. All rights reserved.
1. Introduction Fast quantitative determination of hydrogen peroxide (H2 O2 ) is important in many fields, such as clinical chemistry, biotechnology, environmental monitoring, pharmaceuticals, and food analysis [1–5]. Among various analytical methods that have been used for the detection of H2 O2 , electrochemical (amperometric and potentiometric) techniques have received great attention because of their high efficiency, low cost, and high sensitivity [6–9]. In practice, amperometric determination of H2 O2 is suitable for quick test applications. However, amperometric sensors with bulk electrodes require high overpotential for H2 O2 oxidation, which results in interference from other species in real samples, such as ascorbic acid, urea, and paracetamol [10,11]. Furthermore, the electrode reactions are so irreversible that the responses obtained are usually unstable with poor linearity [12,13]. Efforts have been focused on modifying the electrode surfaces using suitable materials, including enzymes, to improve the selectivity and stability of H2 O2 sensors. Recently, development of enzyme-free electrodes modified with metal nanoparticles (NPs) has become a trend [14–23]. The
∗ Corresponding author at: National Laboratory of Solid State Microstructures and Department of Materials Science and Engineering, Nanjing University, Nanjing 210093, China. E-mail address: [email protected] (M. Han). http://dx.doi.org/10.1016/j.snb.2016.02.117 0925-4005/© 2016 Elsevier B.V. All rights reserved.
nanoparticle-based non-enzymatic H2 O2 sensors were found to be versatile, with a low detection limit and wide response range. Non-enzymatic H2 O2 sensors based on noble metal nanoparticles, such as silver [24,25], and palladium [26,27], have attracted considerable attention because of their excellent catalytic activity and electrical conductivity. Liao et al. [28] fabricated a highly adhesive Ag nanoparticle coating on a glass carbon electrode (GCE) using gas phase nanoparticle beam deposition. The Ag NP-modified GCE exhibited high electrocatalytic activity toward the reduction of H2 O2 with a detection limit as low as 1 × 10−6 M and a very fast response time of less than 1 s. Recently, we used a similar method to fabricate Pd NP-deposited-GCE, which enabled highly selective amperometric detection of H2 O2 at a sufficiently low applied potential (∼−0.12 V) [29]. Although both the lower detection limit and the linear response range of the Pd NP-modified GCE were superior to those of the Ag NP-modified GCE, its response time was approximately one order of magnitude slower. Graphene sheets (GS) have excellent electrical conduction in two dimensions with good chemical stability. They have been the subject of considerable interest in recent years because of their excellent electrocatalytic activities [6,30–32]. Graphenemetal nanoparticle hybrids may have much higher electrocatalytic activity than that of GS, providing a new way to develop catalytic materials [33]. Phan and Chung synthesized graphene-supported Pd nanocubes for hydrogen detection [6]. Zhou et al. prepared a
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Au NP/GS nanocomposite-modified GCE for the detection of H2 O2 [34]. Rosy et al. developed a graphene-modified Pd sensor for the determination of norepinephrine [7]. Until now, GSs used for electrode modifications were generally the chemically reduced graphite oxide (rGO) sheets, with some intrinsic limitations such as a lack of control of the film thickness as well as the use of toxic chemicals. Recently, GSs produced by chemical vapor deposition (CVD) have been considered for electrode modifications [8,9,35,36]. Compared with rGO, they have better quality control and higher electron conductivity. CVD-synthesized bilayer graphene has an electric-field-controllable band gap and thus has attracted special interests [37,38]. However, the chemistry and sensor application of bilayer graphene sheets and their metal NP hybrids have not been much studied. Their electrocatalytic activity and non-enzymatic sensing behavior have not been fully understood. In this work, for the first time, Pd NPs were deposited on bilayer GSs supported with glass carbon electrodes in the gas phase. The loading amount and size of Pd NPs were well controlled. The electrocatalytic performance of Pd NPs/bilayer graphene films (BGFs)/GCEs toward H2 O2 detection were investigated, with the main focus being their linear response range and response time. 2. Materials and method 2.1. Preparation of bilayer graphene covered electrodes BGFs were synthesized by CVD with copper foil as the growth substrate; the details on the fabrication process can be found elsewhere [39]. In order to transfer the bilayer graphene to the electrode, a thin layer of poly(methyl methacrylate) (PMMA) (9% in anisole) was spin-coated on top of the BGF. The copper foil was then submerged in a 1.0 M FeCl3 solution and removed completely after etching for 2 h, leaving a continuous film of PMMA/BGF floating on the solution. The films of PMMA/BGFs were picked up from the solution with a glass slide and washed carefully in deionized water. Finally, the PMMA/BGFs were picked up on the GCE surface from the deionized water and dried in vacuum at 80 ◦ C for 30 min. The PMMA layer was then removed with acetone. Before covered with BGFs, the GCEs (3 mm in diameter) were carefully polished to obtain a mirror-like surface and washed in absolute ethanol and ultrapure water. All the specimens were inspected with an optical microscope to insure that the surfaces of the GCEs were fully covered with BGFs uniformly. BGFs were also transferred to the surface of indium tin oxide (ITO) films. The ITO conductive glass (10 × 10 mm2 ) were purchased from YaRong Chemical Reagent Co. (Nanjing, PR China). 2.2. Preparation of Pd NPs and deposition of Pd NPs/BGF hybrid-modified GCEs Fig. 1 schematically depicts the preparation of Pd NPs/BGF/GCE. Pd nanoparticles were generated by a gas aggregation cluster source. The deposition was performed in a high vacuum chamber equipped with the cluster source. Pd atoms were sputtered from a Pd target in an argon buffer gas (purity, 99.999%) in a liquid nitrogen-cooled aggregation tube. In order to produce Pd nanoparticles with a controlled size, three buffer gas pressures of 90 Pa, 110 Pa, and 130 Pa were used. A stable magnetron discharge ran with an input power of 130 W. Pd nanoparticles were formed in the argon gas through the aggregation process. The nanoparticles were swept by the gas stream into high vacuum through a nozzle, forming a nanoparticle beam with a high speed of ∼1000 m/s [40]. The deposition was carried out at a precisely controlled rate of 0.42 Å s−1 for 30 min. The corresponding nanoparticle coverage was about 85%, as characterized with transmission electron microscopy.
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2.3. Chemical reagents All chemicals from commercial sources were of analytical grade. All solutions were prepared using distilled water. 2.4. Characterization The microstructures of the Pd nanoparticles and Pd NPs/graphene hybrid were characterized with transmission electron microscopy (TEM, TecnaiF20). For TEM, the nanoparticles were either deposited simultaneously on amorphous carbon films supported with copper grids, or deposited on the bilayer graphene transferred on the copper grid surface. The graphene films were characterized using a Raman spectrometer (NTMDT NTEGRA spectra). For Raman spectroscopy, the graphene films were transferred to the surface of a Si wafer. 2.5. Electrochemical measurements Electrochemical measurements were performed on an electrochemical workstation (CHI660D, Shanghai Chenhua Instruments Co., Shanghai, China). A three-electrode cell was used, with a bare or modified electrode as the working electrode, a Ag/AgCl electrode (saturated with KCl) as the reference electrode, and platinum wire as a counter electrode. Phosphate buffer solutions (PBSs) (pH = 7.4, 0.05 M) were used as the electrolyte solution throughout the electrochemical measurements. 3. Results and discussion 3.1. Characterization of graphene and Pd nanoparticles In order to investigate the influence of nanoparticle size on the reduction of H2 O2 , Pd NPs with three different sizes were prepared by changing the argon gas pressure. Fig. 2 shows TEM images of Pd NPs prepared with different buffer gas pressures. As shown in Fig. 2(a)–(c), the sizes of the Pd NPs increase with increasing argon gas pressure. Corresponding to the buffer gas pressures that were used (90 Pa, 110 Pa, and 130 Pa), the average diameters of the nanoparticles were measured to be ∼6.5 nm, 10.6 nm, and 12.0 nm, respectively. The Pd NPs are randomly distributed on the substrate with uniform size. Fig. 2(d) shows a TEM image of Pd NPs deposited on BGF. The sample was prepared with similar experimental condition as that of the NPs shown in Fig. 2(b). We can see that the morphologies of the nanoparticle assemblies of the two samples are quite similar. Fig. 2(e) shows the Raman spectrum of the graphene sheets used to modify the GCEs. The spectrum reveals two intense peaks at ∼1590 cm−1 and ∼2650 cm−1 , which can be assigned to the G mode and 2D mode of graphene, respectively. The peak intensity ratio between the G- and 2D-bands was calculated to be ∼1.0, and the full width at half-maximum (FWHM) of the 2D-band was ∼55 cm−1 , corresponding well to the Raman characteristic of the AB-stacked bilayer graphene [41]. The high crystallinity of carbon in the bilayer graphene will be highly beneficial for achieving better electronic conduction between adjacent Pd nanoparticles. 3.2. Electrocatalytic activity toward H2 O2 reduction The electrocatalytic activity of Pd NPs/BGF/GCEs toward H2 O2 reduction was investigated by cyclic voltammetry (CV). Fig. 3(a) shows the CV curves obtained for the bare GCE, Pd NPs/GCE, BGF/GCE, and GCE modified with Pd NPs/BGF hybrid, in PBS containing 10 mM H2 O2 . For the bare GCE and BGF/GCE, no significant current change could be observed, indicating that there was no electrocatalytic activity toward H2 O2 reduction for them. For the
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Fig. 1. Schematic diagram of the process of Pd NPs/BGF/GCE preparation.
Fig. 2. TEM images of Pd NPs produced with argon gas pressure of (a) 90 Pa, (b) 110 Pa, and (c) 130 Pa and the corresponding size distributions. (d) TEM image of the Pd NPs deposited on bilayer graphene film surface. (e) Raman spectrum of the BGF.
Pd NPs-modified GCE, there was obvious electrocatalytic current for H2 O2 . A prominent cathodic peak current appeared at approximately −0.12 V. For the GCE modified with Pd NPs/BGF hybrid, a drastic increase in the reduction current was observed, with a well-defined reduction peak at approximately −0.17 V applied voltage. The redox peak could be attributed to the enhanced electron transfer between H2 O2 and the Pd NPs//BGF hybrid. The results indicate that GCEs modified either with Pd NPs or with Pd NPs/BGF hybrid have effective electrocatalytic ability in H2 O2 reduction. However, a quantitative comparison with the cyclic voltammogram obtained at GCE that is merely covered with Pd NPs shows a tremendous improvement in the catalytic properties of Pd NPs/BGF/GCE for hydrogen peroxide reduction. The anodic peak current of the
latter is increased by more than 2-folds. Although the reduction peak potential of Pd NPs/BGF/GCE is somewhat increased (from −0.12 eV to −0.17 eV), it is still much smaller than the applied overpotential reported for silver-based electrodes [28], and low enough to eliminate the influence from most of the chemicals other than H2 O2 , such as ascorbic acid, uric acid, glucose and ethanol. This particular aspect is appealing for highly selective detection of H2 O2 . In Fig. 3(b), CV curves obtained in PBS containing 10 mM H2 O2 for the Pd NPs/BGF hybrid-modified GCEs with three different Pd nanoparticle sizes are compared. The coverage of the samples was carefully controlled to be the same by maintaining a constant deposition condition (depositing 30 min with a 0.42 Å s−1 deposition rate). A small variation of peak potential as well as the
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Fig. 3. (a) CV curves of bare GCE, BGF/GCE, Pd NPs/GCE, and Pd NPs/BGF/GCE in 0.05 M PBS (pH 7.4) containing 0.01 M H2 O2 . Inset: a rescaled plot of the CV curves to show the very small (in subnano-ampere range) cathodic currents for bare GCE and BGF/GCE. (b) CV curves of the Pd NPs/BGF/GCEs with different average sizes of Pd nanoparticles measured in 0.01 M H2 O2 (0.05 M PBS, pH 7.4) at a scan rate of 50 mV/s.
current of H2 O2 reduction is exhibited. However, such changes are much smaller than those induced by incorporating bilayer graphene sheets into the electrodes, as shown in Fig. 3(a). We have repeated similar experiments with nanoparticle size-relevant specimens for three times, the peak current and peak potential of H2 O2 reduction did not change significantly from electrode to electrode. Evidently, the significant enhancement in the electrocatalytic activity of the electrodes should be attributed to the effect of the modification with Pd NPs/BGF hybrid, rather than the size effect of the Pd nanoparticles, although the nanoparticle size does have some influence on the electrocatalytic activity in H2 O2 detection [28,42]. Therefore, in the following discussion we omit the influence of the nanoparticle size and use Pd nanoparticles with ∼10 nm average diameter in the experiments. Detailed characterization of the response of the Pd NPs/BGF/GCEs toward H2 O2 was performed at a constant applied potential of −0.17 V. Measurements were performed in 0.05 M stirred phosphate buffer solution. The limit of detection, linear response range, sensitivity, and response time were studied. Fig. 4(a) shows the stable amperometric responses (steady-state current vs. time) of Pd NPs/BGF/GCEs to the additions of H2 O2 into PBS. Well-defined responses can be observed for the successive additions of 4 M of H2 O2 at the low H2 O2 concentrations and 13.5 mM of H2 O2 at the higher H2 O2 concentrations. From the insert it can be seen that the Pd NPs/BGF/GCEs respond rapidly to the addition of H2 O2 , reaching 95% of the steady current in less than 3 s. The response time is much shorter than that of the GCE covered barely with Pd NPs, for which a response time of 6 s is estimated. Such a fast response time may be attributed to the excellent electrical conduction of the 2D graphene sheets and the high conductive interface between Pd NPs and BGF, due to the high quality of their crystal lattices. Similar response time was also observed in other electrodes based on CVD-fabricated functionalized three-dimensional graphene [9,35]. In practice, electrochemical sensors are often applied for measuring hydrogen peroxide when a quick test is required, therefore a short response time is of great concern. We also performed measurements on the amperometric responses of the Pd NPs/BGF hybrid-based electrode to the addition of H2 O2 into PBS, by replacing the glassy carbon electrodes with ITO films. As shown in Fig. 4(b), the Pd NPs/BGF/ITO electrode responds rapidly and sensitively to the changes in H2 O2 concentration. A response time of 3 s can be estimated, which is as short as that of the Pd NPs/BGF/GCE. This therefore demonstrates that it is the highly conductive interface between Pd NPs and BGF that contributes much to the fast response to H2 O2 , rather than the interface between BGF and supporting electrode.
The corresponding calibration curve (steady-state response current vs. H2 O2 concentration) is shown in Fig. 4(c). The Pd NPs/BGF/GCE shows excellent linearity up to 13.5 mM. At higher H2 O2 concentration, the plot deviates from linearity, which may be attributed to the saturation of the electrocatalytic activity of the electrode. With the increasing of H2 O2 concentration, the electrodes adsorb more and more H2 O2 and ultimately approach saturation. The saturation of absorption results in the saturation of the electrocatalytic activity of the electrode, so that the current change becomes smaller and smaller, and the calibration curve deviates from linearity. Also, at higher H2 O2 concentrations, we can observe a significant increase in the noise of the measured anodic current. Such noise may correlate with the diffusion of the reactants on the electrode surface. With the increase of H2 O2 concentration, the diffusion of the reactants which have not been absorbed becomes significant, which will contribute to the anodic current as noise. A detection limit of 1.5 × 10−6 M is determined at a signal-tonoise ratio of 3. The sensitivity estimated using the slope of the calibration plot is 115.1 A mM −1 . For Pd NPs-modified GCE without graphene, a linear response in the H2 O2 concentration range from 1 M to 6.0 mM can be observed, with a sensitivity of approximately 57.1 A mM−1 . Evidently, GCEs modified with Pd NPs/BGF hybrids offer more advantages in H2 O2 detection over GCEs covered merely with Pd NPs, such as their much wider linear range and much higher sensitivity. In fact, the linear response range and sensitivity of the Pd NPs/BGF/GCE are significantly higher than those of nonenzyme H2 O2 sensors reported previously based on silver nanoparticles [28], Cu2 O [43], Fe3 O4 [44], Pd nanoparticles [29,45], and even enzyme-based electrodes [46,47]. Based on the modified electrodes of different materials, a comparison for H2O2 determination is presented in Table 1. H2 O2 concentrations typically range from micromolar for in vivo conditions and residual levels analysis in foods to tens of millimolar for bleaching applications; therefore, nonenzyme H2 O2 sensors with a response range up to several tens of millimolar are considered important. As we pointed out in our previous paper [29], the electrocatalytic activity of Pd nanoparticles toward H2 O2 reduction might be attributed to their excellent catalytic properties and good electronic conductivity. The small size and clean surface of nanoparticles enable high specific surface area and provide a large number of active sites, leading to electrocatalytic reduction of H2 O2 at lower overpotentials. The nanoparticles also play an important role in transferring electrons between H2 O2 and the conducting sites of the electrodes, resulting in an increase in electron transfer rate. When Pd NPs are combined with BGF, the electrocatalytic activity of the hybrid can be significantly enhanced because of the synergistic effect of BGF and Pd NPs. The 2D graphene sheets have
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Fig. 4. (a) Amperometric responses of the Pd NPs/GCE and Pd NPs/BGF/GCEs upon successive addition of H2 O2 into gently stirred 0.05 M PBS (pH 7.4) at −0.11 and −0.17 V applied potentials, respectively. Inset: rescaled plots of amperometric responses from 40 to 120 s. (b) Amperometric responses of the Pd NPs/BGF/ITO upon successive addition of H2 O2 into gently stirred 0.05 M PBS (pH 7.4) at −0.08 V. For comparison, the corresponding data of Pd NPs/BGF/GCEs is also plotted. Inset: a rescaled plot of amperometric responses of the Pd NPs/BGF/ITO from 40 to 120 s. (c) Calibration plots of the relationship between the response current and the H2 O2 concentration at Pd NPs/GCEs and Pd NPs/BGF/GCEs (The error bars were determined from a statistical analysis of the data from 20 separate measurements). Inset: rescaled calibration plots of the relationship between the response current and the H2 O2 concentration in the 0 to 20000 M H2 O2 concentration range. Table 1 Comparison of different H2 O2 sensors. Electrode used b
3DGN/PtNP PdNP/GNs-GCEc Pd-PEI/GO/GCd (DNA-AgNCs)/GN/GCEe PdNP-CNF/GPEf Pd-NPs/BGFs/GCE a b c d e f
Potential (V)
LOD (M)a
LRR (M)
pH used
Reference
0.45 −0.25 0 −0.6 −0.2 −0.17
0.125 0.05 0.2 3 0.2 1.5
0.167–7.486 0.1–1000 0.5–459 15–23,000 0.2–20,000 4–13,500
7.8 7.4 7.2 7.0 7.4 7.4
[30] [48] [49] [50] [51] This work
LOD: the limit of detection. 3DGN/PtNP: three-dimensional graphene networks/Pt nanoparticle. PdNP/GNs-GCE: palladium nanoparticles/graphene nanosheets-glassy carbon electrode. Pd-PEI/GO/GC: palladium- branched polyethylenimine/graphene oxide/glassy carbon. (DNA-AgNCs)/GN/GCE: polynucleotide-templated silver nanoclusters/graphene composite film/glassy carbon electrode. PdNPs-CNF/CPE: palladinumnanoparticles-carbonnanofibers/carbonpasteelectrode.
excellent electrical conduction because of the high quality of their crystal lattices and can make contact with Pd NPs well, resulting in a highly conductive interface, which could accelerate the electron transfer rate between H2 O2 molecules and the electrode and speed up the response time of the measurements. Furthermore, because of the highly accessible active surface area of BGF, the accumulation of OH (ads) intermediates on the electrode surface could be largely enhanced, enabling the Pd NP-catalyzed reduction of the secondary H2 O2 molecule to take place continuously at a faster rate [28]. Fig. 5 shows the CV curves of Pd NPs/BGF/GCE and Pd NPs/GCE in 0.1 M NaOH, with a mean Pd NP diameter of approximately 10.6 nm. From Fig. 5, the active surface area of GCEs modified with Pd NPs and Pd NPs/BGF hybrid was determined to be 4.3 cm2 and 8.5 cm2 , respectively. This confirms that the BGFs and hence their modified electrodes have a large active surface area which is approximately double that of the bare GCE. The long-term stability of the fabricated electrodes was examined. The used Pd NPs/BGF/GCE was stored in air at room temperature for one week, and its CV to H2 O2 was measured. As can be seen in Fig. 6, the CV peak currents are still 100%. From TEM and
Fig. 5. CV curves of Pd NPs/BGF/GCE and Pd NPs/GCE in 0.1 M NaOH.
Raman spectrum observation, we confirmed that the morphology of the Pd nanoparticles as well as their decorated bilayer graphene sheets did not change over time, even after H2 O2 immersion.
J. Wang et al. / Sensors and Actuators B 230 (2016) 690–696
Fig. 6. CV curves measured in 0.05 M PBS (pH 7.4) containing 0.01 M H2 O2 with the as-prepared Pd NPs/BGF/GCE and that of the same electrode stored in air at room temperature for one week after its first usage.
4. Conclusion In conclusion, we have demonstrated the synthesis of a Pd NPs/Bilayer graphene film hybrid-modified electrode and its application for fast and sensitive nonenzymatic detection of H2 O2 . The CVD synthesized bilayer graphene possesses a highly accessible active surface area, which enhances the accumulation of OH intermediates on the electrode surface and enables the Pd NP-catalyzed reduction of the secondary H2 O2 molecule to take place continuously with a faster rate. Moreover, the 2D graphene sheets have excellent electrical conduction and can make contact with Pd NPs well. This results in highly conductive interfaces, which accelerate the electron transfer rate between H2 O2 molecules and the electrode. All these features provide a favorable environment for the electrocatalytic reduction of H2 O2 and allow fast and sensitive detection of H2 O2 . With the introduction of BGF, the catalytic activity of the Pd NP-modified electrodes toward H2 O2 reduction was largely enhanced. The fabricated Pd NPs/BGFs/GCE showed a large linear range from 4 M to 13.5 mM, and a rapid response time less than 3 s. Acknowledgments The authors thank the National Natural Science Foundation of China (Grant no. 51171077), and the National Basic Research Program of China (973 Program, Grant no. 2014CB932302). This research was also supported by a project funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions. References [1] P.E. Gomez, M.C. Lopez, A review on micro-oxygenation of red wines: claims, benefits and the underlying chemistry, Food Chem. 125 (2011) 1131–1140. [2] B.M. Andersen, M. Rasch, K. Hochlin, F.H. Jensen, P. Wismar, J.E. Fredriksen, Decontamination of rooms, medical equipment and ambulances using an aerosol of hydrogen peroxide disinfectant, J. Hosp. Infect. 62 (2006) 149–155. [3] T. Ruzgas, E. Csoregi, J. Emneus, L. Gorton, G. Marko-Varga, Peroxidase-modified electrodes: fundamentals and application, Anal. Chim. Acta 330 (1996) 123–138. [4] W. Chen, S. Cai, Q.Q. Ren, W. Wen, Y.D. Zhao, Recent advances in electrochemical sensing for hydrogen peroxide: a review, Analyst 137 (2012) 49–58. [5] P. Niethammer, C. Grabher, A.T. Look, T.J. Mitchison, A tissue-scale gradient of hydrogen peroxide mediates rapid wound detection in zebrafish, Nature 459 (2009) 996–1000. [6] D.T. Phan, G.S. Chung, A novel Pd nanocube-graphene hybrid for hydrogen detection, Sens. Actuator B: Chem. 199 (2014) 354–360. [7] S.K. Rosy, B. Yadav, M. Agrawal, R.N. Goyal Oyama, Graphene modified palladium sensor for electrochemical analysis of norepinephrine in pharmaceuticals and biological fluids, Electrochim. Acta 125 (2014) 622–629. [8] G. Albert, C. Carlo, M. Roya, Single-layer CVD-grown graphene decorated with metal nanoparticles as a promising biosensing platform, Biosens. Bioelectron. 33 (2012) 56–59.
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Biographies Jue Wang in 2009 received the B.S. degree in Materials Chemistry from Jiangxi University of Science and Technology, in 2012 she received the M.S. degree in Applied Chemistry from Jiangsu University of Science and Technology, She is currently working as a Ph.D. student in the Department of Materials Science and Engineering, Nanjing University. Her research cover metal nanostructures, especially metal
nanoparticle arrays, as well as the applications of these nanostructures in sensors and gas phase catalysis. Hai-bin Sun received the B.S. degree with physics in 2003 from Xinyang Normal University. In 2006, he received the M.S. degree in Material Physics and Chemistry from the Zhengzhou University. In 2015 he received Ph.D. degree in Condensed Matter Physics from the Nanjing University. He is now a lecturer in the Department of Physics and Electronic Engineering at Xinyang Normal University. His research are related to two dimension film materials and noble metal nanomaterials, including controllable preparation, plasmon resonance property and optical-electric properties. Hai-yang Pan received the B.S. degree in 2011 with Physics from Zhenzhou University, He is currently student of master leading to Ph.D. in Nanjing University, and his work includes the synthesis and electron transport of semiconductor nanowires. His researches also include the two dimension materials and device fabrication. Yan-yue Ding received the B.S. degree in Materials Physics from Nanjing University, in 2015. She is currently master student in Nanjing University. Her research is related to optic properties of semiconductor nanoparticle arrays. Jian-guo Wan in 1997 obtained doctoral degree from Nanjing University Aeronautics and Astronautics. He was a visiting associate researcher in Department of Applied Physics and Intelligent Materials Research Center in the Hong Kong Polytechnic University, in 2002. He is now a professor of physics in Nanjing University, His research is related to atomic clusters and cluster-based nanostructures and nanomaterials, preparation and physical properties of Multiferroic Materials, the preparation, properties and application of low-dimensional Nanofunctional materials. Guang-hou Wang was born in Anhui Province, in 1939. He obtained his bachelor’s degree in Beijing Normal University in 1963. He was a visiting professor in New York State University from 1980 to 1982. He is a senior professor of physics in Nanjing University. He was also elected in 2011 as a Academician in Chinese Academy of Sciences, His research is related to atomic clusters and cluster-based 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 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 in condensed matter physics from Nanjing University, 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 Freiburg University in Germany. From 2003, he was elected 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. Particularly 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, nano-optics and quantum transport in clusterbased nanostructures, molecular and gas sensors based on densely packed clusters films.