- Email: [email protected]
ZnO coaxial nanocable microelectrode for electrochemical sensing of ascorbic acid
Materials Letters 181 (2016) 265–267
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
RF magnetron sputtering synthesis of carbon fibers/ZnO coaxial nanocable microelectrode for electrochemical sensing of ascorbic acid Baoxiang Gu a, Zhong Liu b, Xinyang Wang a,n, Xiuxiu Dong c,n a
College of Resource and Environmental, Henan University of Engineering, Zhengzhou 451191, China Key Laboratory of Comprehensive and Highly Efficient Utilization of Salt Resources, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, China c State Key Laboratory of Bioelectronics, School of Biological Science and Medical Engineering, Southeast University, Nanjing 210096, China b
art ic l e i nf o
a b s t r a c t
Article history: Received 31 March 2016 Received in revised form 18 May 2016 Accepted 12 June 2016 Available online 14 June 2016
A simple and “green” radio frequency (RF) magnetron sputtering-assisted hydrothermal method was utilized to synthesize carbon fibers/ZnO coaxial nanocable with sharp control. The X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the crystal phase and morphology of the obtained material. Based on the electrocatalytical activity of the material towards ascorbic acid (AA), the material was used to develop a biosensor which make the diagnosis easy and convenient. The property of the electrode was investigated by cyclic voltammetry (CV). Differential pulse voltammograms (DPV) was used to sensing AA with wide range detection capabilities. This work provides a portable and green route to construct biomedical sensor, which is promising for clinical diagnosis. & 2016 Elsevier B.V. All rights reserved.
Keywords: Semiconductors Coaxial nanocable Composite materials Sensors Ascorbic acid
1. Introduction Remarkable efforts have been dedicated to ZnO-based chemosensors and biosensors over the last few years, mainly driven by its unique properties such as its high exciton binding energy, high physicochemical stability, and high-electron transfer [1,2]. Various kinds of ZnO nanostructures including nanoparticles, plates, floccus, nanorods, and branched submicrorods were synthesized to construct the biosensor [1]. Almost all the ZnO-based sensors were constructed by modified ZnO or its hybrids which pre-synthesized by a series of methods onto the electrode surface by physical absorption to improve the electrochemical performance [3,4]. These modification methods should be not ignored for preparation of biosensor to examine some biomolecules in the earlier work. Compared to the modified carbon electrode or gold electrode, microelectrodes have drawn considerable attention, because of the promise of reaching the excellent trade-off between performance, affordability, simplicity and good repeatability [5]. However, the ZnO alone cannot reach excellent electrochemical properties as a work electrode like carbon electrode because of its intrinsic nature. Considering that the similar properties of carbon electrode can obtain from carbon fibers [6–8], we synthesized carbon fibers/ ZnO coaxial nanocable which can be used as the microelectrode n
Corresponding authors. E-mail address: [email protected] (X. Dong).
http://dx.doi.org/10.1016/j.matlet.2016.06.055 0167-577X/& 2016 Elsevier B.V. All rights reserved.
with the aid of RF magnetron sputtering technique. RF magnetron sputtering technique is a widespread and cost-efficient method used to prepared nanomaterials [9,10]. Much attention has been paid on RF magnetron sputtering -based approaches due to their advantages, such as rapid, in-situ, simplicity and high purity of the product. It provides a platform for the growth of materials with an abundance of energy with extremely fast kinetics, promoting chemical reactions, and thus makes it possible to synthesis carbon fibers/ZnO coaxial nanocable. In the current work, we proposed a facile and rapid plasma sputtering route for the preparation of carbon fibers/ZnO coaxial nanocable for the first time. The morphological and structural are described. Based on their excellent electrocatalytic properties toward AA, they were used as microelectrode and structure a biosensor.
2. Experimental section Carbon fibers/ZnO coaxial nanocable was synthesized through two steps. Briefly, Sputter ZnO seed (5 N, 7.5 cm diameter) on the surface of carbon fibers (the length and diameter is 4 cm and 2 mm, respectively) using the reactive RF magnetron sputtering technique (MSP-300C). A high purity gas mixture of Ar (50%) and N2 (10%) at a total pressure of 1.0 Pa was used as the sputtering gas. The sputtering parameters were 5 min of sputtering time, 3.3 Pa of sputtering pressure, 50 L min 1 of sputtering speed for
266
B. Gu et al. / Materials Letters 181 (2016) 265–267
Fig. 1. (A) XRD pattern; (B) a low-magnification and (C) a high-magnification SEM images of carbon fibers/ZnO coaxial nanocable.
Fig. 2. Electrochemical mechanism for electro-oxidation of AA.
Ar, and 10 L min 1 of sputtering speed for N2. And then, the obtained material template was immersed a Teflon-lined stainless steel autoclave with 50 mL deionized water, 50 mM zinc acetate dehydrate and hexamethylenetetramine, and keep the temperature at 90 °C for 18 h. The obtained hybrids were rinsed with ethanol and deionized water for several times, and then dried in a vacuum at 60 °C for 6 h. The SEM images were obtained with a Hitachi X650 and the XRD analysis was performed with a Japanese Rigaku D/max-cA rotating anode X-ray diffractometer at 2 theta-theta mode. The carbon fibers/ZnO coaxial nanocable microelectrode (denoted as CF/ZnO CN-ME) was obtained by tightening carbon fibers/ZnO coaxial nanocable onto the copper wire with the aid of moderate conductive gel. Electrochemical measurements were performed on a CHI 660 electrochemical analyzer (Co. CHI, USA) with a conventional three-electrode system comprised of Pt rod as the auxiliary electrode, an Ag/AgCl electrode as the reference, and a CF/ ZnO CN-ME as the working electrode.
3. Results and discussion Carbon fibers/ZnO coaxial nanocable was obtained by plasma sputtering-assisted method and characterized by XRD and SEM. The XRD pattern of the carbon fibers/ZnO coaxial nanocable is represented in Fig. 1(A). It contains the characteristic peak of ZnO and carbon fibers. The broad peak at 25.2° was ascribed to the disordered carbon of carbon fibers and all other diffraction peaks
was assigned to the hexagonal wurtzite of ZnO (JCPDS 36-1451). No other impurity peak is detected. This result indicated that the hexagonal wurtzite ZnO wrapped on the surface of carbon fibers. In addition, the morphology of carbon fibers/ZnO coaxial nanocable was studied by SEM. From the low-magnification SEM image in Fig. 1(B), we can see that the bare carbon fibers exhibited long and continuous cylindrical morphologies with smooth surface while carbon fibers/ZnO coaxial nanocable showed bumpy surface. The high-resolution SEM image in Fig. 1(C) shows that carbon fibers/ZnO coaxial nanocable was formed by doping dense ZnO nanowires on the carbon fibers uniformly and tidily. The averaged diameter of ZnO nanowires was 50 nm. As-obtained carbon fibers/ZnO coaxial nanocable was applied to prepare an electrochemical biosensor. In this case, AA was chosen. AA is adsorbed on the CF/ZnO CN-ME and then oxidized on the ZnO surface resulted from the electron transfer between AA and ZnO, which the –OH group in the AA molecular was converted into ¼O group [10,11]. The electro-oxidation process for AA is showed in Fig. 2. The electrochemical behavior of CF/ZnO CN-ME was studied in the absence and presence of AA. As shown in Fig. 3 (A), a significantly anodic peak appears at 266 mV for CF/ZnO CNME in the presence of AA. It indicates that CF/ZnO CN-ME plays an excellent electrocatalytic properties toward AA. Then, the microelectrode property was investigated. Fig. 3(B) shows the effect of the potential scan rate on the electrochemical oxidation of AA at CF/ZnO CN-ME. The oxidation current versus the potential scan rate was plotted and resulted in a straight line (R2 ¼0.9920), shown in Fig. 3(C). This linearity suggests that electrochemical reaction of AA on the surface of CF/ZnO CN-ME are adsorption controlled processes. Those indicate that carbon fibers/ZnO coaxial nanocable could use as new materials for electrochemical sensing of AA. In order to validate the possibility, differential pulse voltammograms (DPV) was performed due to their high sensitivity and better resolution. Fig. 4(A) shows the DPV response of CF/ZnO CN-
Fig. 3. (A) CV of CF electrode in PBS (pH 7.0) in the presence (black line) of 1 mM AA, and CVs of CF/ZnO CN-ME in PBS (pH 7.0) in the absence (red line) and presence (green line) of 1 mM AA; (B) CVs recorded at CF/ZnO CN-ME at various rates: 10, 20, 40, 60, 80, 100, and 120 mV; (C) The linear dependence of peak current with scan rate. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
B. Gu et al. / Materials Letters 181 (2016) 265–267
267
Fig. 4. (A) Schematic diagram of CF/ZnO CN-ME; (B) DPV curves of CF/ZnO CN-ME to successive injection of AA into PBS (pH 7.0); (C) The linear relationships between the catalytic current and the concentration.
ME towards AA. The peak current increased with increasing the concentration of AA. The peak current of AA is linear to the AA concentration in the range of 0.6–1.8 mM (Fig. 4(B)) and the linear equation is I¼0.08318 þ1.44471*CAA (R2 ¼0.99172) with the limit of detection of 156.7 μM (Fig. 4(C)). For electrochemical sensors, most previous reports have focused on the improvement of limits of detection [12]. However, very few efforts have concentrated on the range of detection, another essential aspect for evaluating the sensing performance. Analysis of unpretreated, ‘real world’ samples that span a broad range of concentrations requires the sensors with wide range detection capabilities [13]. Thus, AA could be quantifiably measured by DPV according to our requirement. However, it is well known that AA, dopamine (DA), and UA usually coexist in human body fluids. Thus, selectivity is the important quota for this sensor. The selectivity of the obtained sensor was evaluated, and electroactive substances such as DA and AA had no obvious interference on the detection of AA. The phenomenon may be decided by the ZnO content and charge distribution of carbon fibers/ZnO coaxial nanocable [10]. The stability and reproducibility were also studied. The experimental results showed that the microelectrode had good stability and excellent reproducibility. It may be caused by the three-dimensional structure of carbon fibers/ZnO coaxial nanocable which has super surface area and excellent electron transfer.
4. Conclusions In summary, a novel carbon fibers/ZnO coaxial nanocable was synthesized via plasma sputtering-assisted hydrothermal method for the first time. Based on obtained hybrid material microelectrode demonstrated an excellent electrocatalytic activity towards AA, and was utilized to construct an electrochemical microsensor with wide range detection capabilities. The microelectrode
showed excellent selectivity and sensitivity, convenient, reusable, and low cost. The proposed strategy was allowed to determine the concentration of AA with a microminiaturization. This work may provide a valuable clue for the nanomaterials to clinical diagnose.
Acknowledgements This work was financially supported by NSFC (61404075, 21405029, 61171015 and BK20130394), Henan Institute of Engineering Innovation Team Building Program Funded Projects (CXTD2014005) and the State Key Laboratory of Analytical Chemistry for Life Science (SKLACLS1305).
References [1] D. Panda, T. Tseng, J. Mater. Sci. 48 (2013) 6849–6877. [2] X.X. Dong, Y.X. Liu, Y.M. Sun, C. Yang, Z.L. Xu, Mater. Lett. 162 (2016) 246–249. [3] J.H. Han, D. Lee, C.H.C. Chew, T. Kim, J.J. Park, Sens. Actuators B 228 (2016) 36–42. [4] H. Chao, H.Y. Liu, D. Zhang, C. Yang, M.Z. Zhang, J. Alloy. Compd. 666 (2016) 178e184. [5] H.Y. Liu, C.C. Gu, C. Hou, Z.Z. Yin, K. Fan, M.Z. Zhang, Sens. Actuators B 224 (2016) 857–862. [6] H.L. Luo, G.Y. Xiong, X.Q. Chen, Q.P. Li, C.Y. Ma, D.Y. Li, et al., J. Alloy. Compd. 593 (2014) 7–15. [7] K. Kong, B.K. Deka, M. Kim, A. Oh, H. Kim, Y.B. Park, et al., Compos. Sci. Technol. 100 (2014) 83–91. [8] Y. Ko, D. Ramana, J. Yu, Nanoscale Res. Lett. 8 (2013) 262–268. [9] C. Yang, L.W. Hu, H.Y. Zhu, Y. Ling, J.H. Tao, C.X. Xu, J. Mater. Chem. B 3 (2015) 2651–2659. [10] C. Yang, B.X. Gu, D. Zhang, C.W. Ge, H.M. Tao, Anal. Methods 8 (2016) 650–655. [11] A. Pardakhty, S. Ahmadzadeh, S. Avazpour, V.K. Gupta, J. Mol. liq. 216 (2016) 387–391. [12] J.C. Kemmegne-Mbouguen, L. Angnes, Sens. Actuators B 212 (2015) 464-47. [13] X.W. Mao, W.D. Tian, T.A. Hatton, G.C. Rutledge, Anal. Bioanal. Chem. 408 (2016) 1307–1326.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
RF magnetron sputtering synthesis of carbon fibers/ZnO coaxial nanocable microelectrode for electrochemical sensing of ascorbic acid Baoxiang Gu a, Zhong Liu b, Xinyang Wang a,n, Xiuxiu Dong c,n a
College of Resource and Environmental, Henan University of Engineering, Zhengzhou 451191, China Key Laboratory of Comprehensive and Highly Efficient Utilization of Salt Resources, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, China c State Key Laboratory of Bioelectronics, School of Biological Science and Medical Engineering, Southeast University, Nanjing 210096, China b
art ic l e i nf o
a b s t r a c t
Article history: Received 31 March 2016 Received in revised form 18 May 2016 Accepted 12 June 2016 Available online 14 June 2016
A simple and “green” radio frequency (RF) magnetron sputtering-assisted hydrothermal method was utilized to synthesize carbon fibers/ZnO coaxial nanocable with sharp control. The X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the crystal phase and morphology of the obtained material. Based on the electrocatalytical activity of the material towards ascorbic acid (AA), the material was used to develop a biosensor which make the diagnosis easy and convenient. The property of the electrode was investigated by cyclic voltammetry (CV). Differential pulse voltammograms (DPV) was used to sensing AA with wide range detection capabilities. This work provides a portable and green route to construct biomedical sensor, which is promising for clinical diagnosis. & 2016 Elsevier B.V. All rights reserved.
Keywords: Semiconductors Coaxial nanocable Composite materials Sensors Ascorbic acid
1. Introduction Remarkable efforts have been dedicated to ZnO-based chemosensors and biosensors over the last few years, mainly driven by its unique properties such as its high exciton binding energy, high physicochemical stability, and high-electron transfer [1,2]. Various kinds of ZnO nanostructures including nanoparticles, plates, floccus, nanorods, and branched submicrorods were synthesized to construct the biosensor [1]. Almost all the ZnO-based sensors were constructed by modified ZnO or its hybrids which pre-synthesized by a series of methods onto the electrode surface by physical absorption to improve the electrochemical performance [3,4]. These modification methods should be not ignored for preparation of biosensor to examine some biomolecules in the earlier work. Compared to the modified carbon electrode or gold electrode, microelectrodes have drawn considerable attention, because of the promise of reaching the excellent trade-off between performance, affordability, simplicity and good repeatability [5]. However, the ZnO alone cannot reach excellent electrochemical properties as a work electrode like carbon electrode because of its intrinsic nature. Considering that the similar properties of carbon electrode can obtain from carbon fibers [6–8], we synthesized carbon fibers/ ZnO coaxial nanocable which can be used as the microelectrode n
Corresponding authors. E-mail address: [email protected] (X. Dong).
http://dx.doi.org/10.1016/j.matlet.2016.06.055 0167-577X/& 2016 Elsevier B.V. All rights reserved.
with the aid of RF magnetron sputtering technique. RF magnetron sputtering technique is a widespread and cost-efficient method used to prepared nanomaterials [9,10]. Much attention has been paid on RF magnetron sputtering -based approaches due to their advantages, such as rapid, in-situ, simplicity and high purity of the product. It provides a platform for the growth of materials with an abundance of energy with extremely fast kinetics, promoting chemical reactions, and thus makes it possible to synthesis carbon fibers/ZnO coaxial nanocable. In the current work, we proposed a facile and rapid plasma sputtering route for the preparation of carbon fibers/ZnO coaxial nanocable for the first time. The morphological and structural are described. Based on their excellent electrocatalytic properties toward AA, they were used as microelectrode and structure a biosensor.
2. Experimental section Carbon fibers/ZnO coaxial nanocable was synthesized through two steps. Briefly, Sputter ZnO seed (5 N, 7.5 cm diameter) on the surface of carbon fibers (the length and diameter is 4 cm and 2 mm, respectively) using the reactive RF magnetron sputtering technique (MSP-300C). A high purity gas mixture of Ar (50%) and N2 (10%) at a total pressure of 1.0 Pa was used as the sputtering gas. The sputtering parameters were 5 min of sputtering time, 3.3 Pa of sputtering pressure, 50 L min 1 of sputtering speed for
266
B. Gu et al. / Materials Letters 181 (2016) 265–267
Fig. 1. (A) XRD pattern; (B) a low-magnification and (C) a high-magnification SEM images of carbon fibers/ZnO coaxial nanocable.
Fig. 2. Electrochemical mechanism for electro-oxidation of AA.
Ar, and 10 L min 1 of sputtering speed for N2. And then, the obtained material template was immersed a Teflon-lined stainless steel autoclave with 50 mL deionized water, 50 mM zinc acetate dehydrate and hexamethylenetetramine, and keep the temperature at 90 °C for 18 h. The obtained hybrids were rinsed with ethanol and deionized water for several times, and then dried in a vacuum at 60 °C for 6 h. The SEM images were obtained with a Hitachi X650 and the XRD analysis was performed with a Japanese Rigaku D/max-cA rotating anode X-ray diffractometer at 2 theta-theta mode. The carbon fibers/ZnO coaxial nanocable microelectrode (denoted as CF/ZnO CN-ME) was obtained by tightening carbon fibers/ZnO coaxial nanocable onto the copper wire with the aid of moderate conductive gel. Electrochemical measurements were performed on a CHI 660 electrochemical analyzer (Co. CHI, USA) with a conventional three-electrode system comprised of Pt rod as the auxiliary electrode, an Ag/AgCl electrode as the reference, and a CF/ ZnO CN-ME as the working electrode.
3. Results and discussion Carbon fibers/ZnO coaxial nanocable was obtained by plasma sputtering-assisted method and characterized by XRD and SEM. The XRD pattern of the carbon fibers/ZnO coaxial nanocable is represented in Fig. 1(A). It contains the characteristic peak of ZnO and carbon fibers. The broad peak at 25.2° was ascribed to the disordered carbon of carbon fibers and all other diffraction peaks
was assigned to the hexagonal wurtzite of ZnO (JCPDS 36-1451). No other impurity peak is detected. This result indicated that the hexagonal wurtzite ZnO wrapped on the surface of carbon fibers. In addition, the morphology of carbon fibers/ZnO coaxial nanocable was studied by SEM. From the low-magnification SEM image in Fig. 1(B), we can see that the bare carbon fibers exhibited long and continuous cylindrical morphologies with smooth surface while carbon fibers/ZnO coaxial nanocable showed bumpy surface. The high-resolution SEM image in Fig. 1(C) shows that carbon fibers/ZnO coaxial nanocable was formed by doping dense ZnO nanowires on the carbon fibers uniformly and tidily. The averaged diameter of ZnO nanowires was 50 nm. As-obtained carbon fibers/ZnO coaxial nanocable was applied to prepare an electrochemical biosensor. In this case, AA was chosen. AA is adsorbed on the CF/ZnO CN-ME and then oxidized on the ZnO surface resulted from the electron transfer between AA and ZnO, which the –OH group in the AA molecular was converted into ¼O group [10,11]. The electro-oxidation process for AA is showed in Fig. 2. The electrochemical behavior of CF/ZnO CN-ME was studied in the absence and presence of AA. As shown in Fig. 3 (A), a significantly anodic peak appears at 266 mV for CF/ZnO CNME in the presence of AA. It indicates that CF/ZnO CN-ME plays an excellent electrocatalytic properties toward AA. Then, the microelectrode property was investigated. Fig. 3(B) shows the effect of the potential scan rate on the electrochemical oxidation of AA at CF/ZnO CN-ME. The oxidation current versus the potential scan rate was plotted and resulted in a straight line (R2 ¼0.9920), shown in Fig. 3(C). This linearity suggests that electrochemical reaction of AA on the surface of CF/ZnO CN-ME are adsorption controlled processes. Those indicate that carbon fibers/ZnO coaxial nanocable could use as new materials for electrochemical sensing of AA. In order to validate the possibility, differential pulse voltammograms (DPV) was performed due to their high sensitivity and better resolution. Fig. 4(A) shows the DPV response of CF/ZnO CN-
Fig. 3. (A) CV of CF electrode in PBS (pH 7.0) in the presence (black line) of 1 mM AA, and CVs of CF/ZnO CN-ME in PBS (pH 7.0) in the absence (red line) and presence (green line) of 1 mM AA; (B) CVs recorded at CF/ZnO CN-ME at various rates: 10, 20, 40, 60, 80, 100, and 120 mV; (C) The linear dependence of peak current with scan rate. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
B. Gu et al. / Materials Letters 181 (2016) 265–267
267
Fig. 4. (A) Schematic diagram of CF/ZnO CN-ME; (B) DPV curves of CF/ZnO CN-ME to successive injection of AA into PBS (pH 7.0); (C) The linear relationships between the catalytic current and the concentration.
ME towards AA. The peak current increased with increasing the concentration of AA. The peak current of AA is linear to the AA concentration in the range of 0.6–1.8 mM (Fig. 4(B)) and the linear equation is I¼0.08318 þ1.44471*CAA (R2 ¼0.99172) with the limit of detection of 156.7 μM (Fig. 4(C)). For electrochemical sensors, most previous reports have focused on the improvement of limits of detection [12]. However, very few efforts have concentrated on the range of detection, another essential aspect for evaluating the sensing performance. Analysis of unpretreated, ‘real world’ samples that span a broad range of concentrations requires the sensors with wide range detection capabilities [13]. Thus, AA could be quantifiably measured by DPV according to our requirement. However, it is well known that AA, dopamine (DA), and UA usually coexist in human body fluids. Thus, selectivity is the important quota for this sensor. The selectivity of the obtained sensor was evaluated, and electroactive substances such as DA and AA had no obvious interference on the detection of AA. The phenomenon may be decided by the ZnO content and charge distribution of carbon fibers/ZnO coaxial nanocable [10]. The stability and reproducibility were also studied. The experimental results showed that the microelectrode had good stability and excellent reproducibility. It may be caused by the three-dimensional structure of carbon fibers/ZnO coaxial nanocable which has super surface area and excellent electron transfer.
4. Conclusions In summary, a novel carbon fibers/ZnO coaxial nanocable was synthesized via plasma sputtering-assisted hydrothermal method for the first time. Based on obtained hybrid material microelectrode demonstrated an excellent electrocatalytic activity towards AA, and was utilized to construct an electrochemical microsensor with wide range detection capabilities. The microelectrode
showed excellent selectivity and sensitivity, convenient, reusable, and low cost. The proposed strategy was allowed to determine the concentration of AA with a microminiaturization. This work may provide a valuable clue for the nanomaterials to clinical diagnose.
Acknowledgements This work was financially supported by NSFC (61404075, 21405029, 61171015 and BK20130394), Henan Institute of Engineering Innovation Team Building Program Funded Projects (CXTD2014005) and the State Key Laboratory of Analytical Chemistry for Life Science (SKLACLS1305).
References [1] D. Panda, T. Tseng, J. Mater. Sci. 48 (2013) 6849–6877. [2] X.X. Dong, Y.X. Liu, Y.M. Sun, C. Yang, Z.L. Xu, Mater. Lett. 162 (2016) 246–249. [3] J.H. Han, D. Lee, C.H.C. Chew, T. Kim, J.J. Park, Sens. Actuators B 228 (2016) 36–42. [4] H. Chao, H.Y. Liu, D. Zhang, C. Yang, M.Z. Zhang, J. Alloy. Compd. 666 (2016) 178e184. [5] H.Y. Liu, C.C. Gu, C. Hou, Z.Z. Yin, K. Fan, M.Z. Zhang, Sens. Actuators B 224 (2016) 857–862. [6] H.L. Luo, G.Y. Xiong, X.Q. Chen, Q.P. Li, C.Y. Ma, D.Y. Li, et al., J. Alloy. Compd. 593 (2014) 7–15. [7] K. Kong, B.K. Deka, M. Kim, A. Oh, H. Kim, Y.B. Park, et al., Compos. Sci. Technol. 100 (2014) 83–91. [8] Y. Ko, D. Ramana, J. Yu, Nanoscale Res. Lett. 8 (2013) 262–268. [9] C. Yang, L.W. Hu, H.Y. Zhu, Y. Ling, J.H. Tao, C.X. Xu, J. Mater. Chem. B 3 (2015) 2651–2659. [10] C. Yang, B.X. Gu, D. Zhang, C.W. Ge, H.M. Tao, Anal. Methods 8 (2016) 650–655. [11] A. Pardakhty, S. Ahmadzadeh, S. Avazpour, V.K. Gupta, J. Mol. liq. 216 (2016) 387–391. [12] J.C. Kemmegne-Mbouguen, L. Angnes, Sens. Actuators B 212 (2015) 464-47. [13] X.W. Mao, W.D. Tian, T.A. Hatton, G.C. Rutledge, Anal. Bioanal. Chem. 408 (2016) 1307–1326.