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A portable wireless single-electrode system for electrochemiluminescent analysis
Electrochimica Acta 308 (2019) 20e24
Contents lists available at ScienceDirect
Electrochimica Acta journal homepage: www.elsevier.com/locate/electacta
A portable wireless single-electrode system for electrochemiluminescent analysis Xiangui Ma a, b, Liming Qi a, c, Wenyue Gao a, c, Fan Yuan a, b, Yong Xia a, b, Baohua Lou a, b, Guobao Xu a, b, * a
State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin, 130022, PR China University of Science and Technology of China, Hefei, Anhui, 230026, PR China c University of Chinese Academy of Sciences, No. 19A Yuquanlu, Beijing, 100049, PR China b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 21 December 2018 Received in revised form 3 April 2019 Accepted 3 April 2019 Available online 4 April 2019
A wireless single-electrode electrochemiluminescence (ECL) system is for the first time designed by coupling single-electrode ECL system with wireless energy transfer. It consists of a wireless energy transfer module, a single-electrode ECL system and a diode. The electric current in this system is supplied through the wireless energy transfer and then rectified by the diode. The potential difference is induced by the resistance of ITO of the single-electrode ECL system, which leads to the ECL reaction of luminol and hydrogen peroxide. With this system, linear range of hydrogen peroxide from 1 to 150 mM is obtained by photomultiplier tube (PMT) detector with a detection limit of 0.26 mM. Moreover, visual detection was carried out using a smart phone as detector. And the linear range of hydrogen peroxide was from 10 to 100 mM. Because of its advantages like low cost, high sensitivity and portability, this wireless single-electrode system has great potential for the applications in on-site detection, drug screening and point of care testing. © 2019 Elsevier Ltd. All rights reserved.
Keywords: Wireless energy transfer Single-electrode system Electrochemiluminescence Visual detection Portable device
1. Introduction As a low-cost, simple and highly efficient tool, bipolar electrode has drawn extensive attention [1] in recent years and shown broad applications in various fields, including biological and chemical sensing [2e4], catalysts evaluation and screening [5,6], electrochemical synthesis [7] and scanning microscopy [8]. Except for direct electrical signals, there are many ways to read out signals of bipolar system such as electrochemiluminescence (ECL) [9,10], fluorescence [11], electrochromism [12], light of LED [13] and anodic dissolution [6]. ECL is a simple and highly sensitive method with low background [14,15]. Since ECL was coupled with bipolar electrochemistry [16,17] from 2001, it becomes a popular method especially in biological and chemical analysis. Recently our group has developed a single-electrode electrochemical system (SEES) for ECL detection [18]. Unlike conventional bipolar electrode system,
* Corresponding author. State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin, 130022, PR China. E-mail address: [email protected] (G. Xu). https://doi.org/10.1016/j.electacta.2019.04.015 0013-4686/© 2019 Elsevier Ltd. All rights reserved.
the SEES is a special kind of bipolar electrode using only one electrode and generates ECL reactions through the potential difference induced by the resistance of electrode. Moreover, it avoids the background ECL signal of driving electrodes. This low-cost system enables ECL analysis and provides new applications for the bipolar electrode ECL analysis. To date, new interdisciplinary technologies are emerging to meet the need of miniaturized and portable devices for point of care sensing and on-site detection [19,20]. For example, visual detections using portable devices [2,21,22] and wireless sensor devices [23] have been wildly explored. Our group has reported an ECL detection device powered by wireless power transfer (WPT) [24] and a WPT electrode array chip with a rectifying diode for ECL visual detection based on digital camera [25]. The WPT technology was first proposed by Nicola Tesla in the 1890s. The mechanism of WPT can be categorized as capacitive coupling, inductive coupling, magnetic resonant coupling and electromagnetic radiation. Because of its convenience, simplicity and safety, inductive coupling is the most common WPT technology in daily life, such as charging phones, electric toothbrushes and implantable medical devices [26e28]. WPT technology can simplify electrical circuit,
X. Ma et al. / Electrochimica Acta 308 (2019) 20e24
avoid the direct connections between power sources and electrodes and benefit the development of portable and facile ECL detection devices. In this study, taking advantages of WPT and SEES technique, a new wireless single-electrode system for ECL detection is developed. The application of wireless energy transfer as power supply will bring considerable convenience to the ECL detection because no direct electrical connection in this system. And the use of singleelectrode system can eliminate the interference ECL signals from driving electrode. Finally hydrogen peroxide is quantitatively measured with satisfactory sensitivity by photomultiplier tube (PMT) and smart phone as detectors. 2. Experimental 2.1. Chemicals and materials Hydrogen peroxide, luminol, sodium bicarbonate and sodium hydroxide were obtained from Beijing Chemical Reagent Company. Triton X-100 was purchased from Sinopharm Chemical Reagent Company Ltd. (Shanghai, China). Indium tin oxide (ITO) conductive glass and conductive carbon ink CH-8 were bought from Foshan
21
City Meijingyuan Glass Co., Ltd and Jujo Printing Supplies & Technology Co., Ltd, China, respectively. Polyethylene terephthalate (PET) label was bought from Jinfuzhou Paper Co. Ltd. NaHCO3eNaOH buffer solution (0.1 M, pH 10.5) was used in the ECL detection experiments. All the reagents were used directly in the experiments without any further purification. Doubly distilled water was used in all solutions. 2.2. Apparatus The direct current was supplied from a digitally regulated direct current (DC) power supply (CE0120010T, Shanghai Kalaifei Company, China). ECL intensities were recorded by a BPCL ultraweak luminescence analyzer from the Institute of Biophysics, Chinese Academic of Sciences. The wireless energy transfer modules (XKT412-27) and copper coils were bought from Shenzhen Xinketai Electronic Co, Ltd. And the RB520S-30 diodes were bought from Shenzhen Jiechengnuo Electronics Co, Ltd. The alternating potentialtime profiles were monitored in parallel with the singleelectrode using the digital storage oscilloscope (ADS1112CAL) from Nanjing Glarun-Atten Technology Co, Ltd. For visual detections, the
Fig. 1. Schematic diagram of wireless single-electrode system.
Fig. 2. The principle of wireless single-electrode system and its equivalent electrical circuit.
Fig. 3. The effect of diode on the ECL intensity. (A) Alternating potentialtime profiles of the system without and with diode. (B) Comparison of ECL intensities between the system without diode and with diode. Inset: A zoom of ECL intensity of the system without diode. Luminol 0.1 mM, H2O2 1 mM, 1% (V/V) Triton X-100, 0.1 M CBS, pH 10.5, PMT: 600 V, ITO resistance 500 U.
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images of the ECL emission were taken in a dark box using a smart phone (Xiaomi 6). 2.3. Procedure for detection of H2O2 A volume of 8 mL of carbonate buffer solution (pH 10.5, 0.1 M) containing 0.01 mM luminol, 1% (V/V) Triton X-100 and different concentrations of hydrogen peroxide were pipetted into the cell. Then two copper coils were aligned on both sides of a glass slide (thickness: 1 mm), and an input voltage of 5 V for wireless energy transfer module was adopted. With this wireless single-electrode system, ECL intensities were measured using a BPCL ultraweak luminescence analyzer. Visual detection of hydrogen peroxide had the similar procedures. A volume of 8 mL of 0.1 M carbonate buffer solution (pH 10.5) containing 1% (V/V) Triton X-100, 0.1 mM luminol and different concentrations of hydrogen peroxide were dropped into the cell. The images of ECL emission were captured in a dark box using a smart phone (exposure time: 16 s, ISO parameter: 3200). Then intensities of the light spots were analyzed using ImageJ software. 3. Results and discussion 3.1. Fabrication and principle of wireless single-electrode system The schematic diagram of wireless single-electrode system is illustrated in Fig. 1. This system consists of a wireless energy transmission module, a single-electrode, a diode and two copper coils. The fabrication of the single-electrode was similar to the procedures in previous work of our group [18]. In short, PET label was cut with a rectangular hole (1.0 cm, 0.8 cm) and attached onto a piece of ITO conductive glass (2.0 cm, 1.0 cm). Then two copper wires were connected by both ends of the PET label with conductive carbon ink. Fig. 2 illustrates the principle of single-electrode system. When an external voltage (Etot) is applied, the current (itot) between two copper wires passes though the ITO glass (ie) and the solution (is) in
the cell. Because the resistance of solution (Rs) is much larger than resistance of ITO electrode (Rs) [18], it can be believed that current is carried through the ITO film mostly. An approximately uniform electric field is built in this single-electrode system. And the potential difference (Ec) across the cell is estimated using the following equation: Ec ¼ Etot Lc/Ltot. If Ec reaches certain amount, hydrogen peroxide and dissolved oxygen will be reduced on the ITO surface at the cathode. At the same time, luminol and hydrogen peroxide are oxidized at the anode side of cell and emit blue light. 3.2. The effect of diode on the wireless single-electrode system The alternating potentialtime profile in Fig. 3A was measured by oscilloscope in parallel with the single-electrode. So the potentials can be regarded as the external voltage (Etot) in the system. When diode was not used, high frequency alternating potential from 9.7 to 4.2 V was applied, and the corresponding ECL intensity (Fig. 3B, red line) was quite weak. The reactive intermediates generated by the oxidization of luminol and hydrogen peroxide at positive potentials would be reduced at the negative potentials and lost activity before the ECL emission reaction, leading to a weak ECL emission. To avoid this problem, diode was employed to rectify the alternating current (AC) to enhance ECL efficiency. Fig. 3B shows that the use of diode remarkably enhances ECL intensity by about 200 times. Therefore, the diode was employed in subsequent experiments. 3.3. The effect of different ITO resistances on the wireless singleelectrode system As presented in Fig. 4, the ECL intensities increased with the increasing resistances of ITO, and ITO resistance of 500 U per square had the best ECL performance. On the one hand, the ITO electrodes with higher resistance have thinner indium tin oxide layers and higher transparency. On the other hand, the ITO electrodes of different resistances may have difference electron transfer rates. These factors lead to the increase in ECL intensities as resistances
Fig. 4. Effect of different ITO resistances on the ECL intensity. Luminol 0.1 mM, H2O2 1 mM, 1% (V/V) Triton X-100, 0.1 M CBS, pH 10.5, PMT: 600 V.
X. Ma et al. / Electrochimica Acta 308 (2019) 20e24
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with this wireless single-electrode system in carbonate buffer solution (pH 10.5) containing 1% (V/V) Triton X-100 and 0.01 mM luminol using a PMT-based detector. The ECL intensities increased with the increasing H2O2 concentrations. As depicted in the inset of Fig. 5B, ECL intensities had a good linear relationship with the concentrations of H2O2 from 1 mM to 150 mM with a correlation coefficient (r) of 0.9996. And the regression equation is described as I ¼ 106.36 þ 7.85 c (H2O2/mM). The detection limit for hydrogen peroxide was calculated to be 0.26 mM, which is comparable to the previously reported detection methods in Table 1. 3.5. Visual detection of H2O2 For further application of this system, visual detection of hydrogen peroxide was explored using a smart phone. 8 mL of 0.1 M carbonate buffer solution (pH 10.5) containing 1% (V/V) Triton X100, 0.1 mM luminol and different concentrations of H2O2 were analyzed by taking photos in a dark box. Fig. 6A shows the ECL emission images of luminol/H2O2 system with 0, 10, 20, 50, 70, 100, 200, 500 mM H2O2. As shown in Fig. 6B, the relative light units (RLU)
Fig. 5. Detection of H2O2 using PMT. (A) ECL profiles (three consecutive measurements) with different H2O2 concentrations. (B) ECL intensities versus the concentrations of H2O2. Inset: Linear calibration curve. Luminol 0.01 mM, 1% (V/V) Triton X-100, 0.1 M CBS, pH 10.5, PMT: 600 V, ITO resistance 500 U.
increase. Moreover, ITO electrodes of higher resistance are cheaper. Thus the single-electrodes made by ITO glass of 500 U per square were used in the following experiments.
3.4. Detection of H2O2 by PMT Under the optimal conditions, a wireless single-electrode system for ECL detection toward hydrogen peroxide was developed. As shown in Fig. 5, different concentrations of H2O2 were detected
Fig. 6. (A) ECL images of luminol and different concentrations of H2O2. (B) Visualized quantitative detection of hydrogen peroxide. Luminol 0.1 mM, 1% (V/V) Triton X-100, 0.1 M CBS, pH 10.5.
Table 1 Comparison of some bipolar electrode systems for H2O2 detection based on luminol/H2O2 ECL system. Device
Detector
Linear range (mM)
LOD (mM)
Reference
Cloth-based microfluidic device Paper fluidic closed bipolar electrode Multichannel Closed Bipolar System Glassy carbon based BPE SEES
CCD CCD PMT Smart phone PMT Smart phone PMT Smart phone
25e2500 75e500 50e5000 5e300 1e100 5e100 1e150 10e100
24 41 50 3.67 0.27 e 0.26 e
[29] [30] [31] [2] [18]
wireless single-electrode system
This work
24
X. Ma et al. / Electrochimica Acta 308 (2019) 20e24
of ECL increased as the H2O2 concentrations increased. And a linear correlation between the relative light units and the concentrations of H2O2 is established from 10 to 100 mM. The regression equation could be expressed as I ¼ 238.77 þ 25.46 c (H2O2/mM), R ¼ 0.9987. 4. Conclusions In conclusion, we have designed a facile and portable wireless single-electrode system for ECL detection of hydrogen peroxide with acceptable linear ranges and detection limits. This device can be easily constructed without the need for complicated and expensive materials and equipment. In contrast with other bipolar electrode systems, this system can avoid the interference signal from driving electrode. And it is more convenient to use the wireless transmission as power supply, because frequent electrical connections and disconnections are not necessary. Moreover, this system supports visualized quantitative detection using a smart phone. On the basis of the advantages above, this high performance wireless single-electrode system will contribute to the development of bipolar devices in portable ECL testing. Acknowledgements We thank the support from The National Key Research and Development Program of China (No. 2016YFA0201300), and the National Natural Science Foundation of China (No. 21675148, 21804127, 21874126). References [1] S.E. Fosdick, K.N. Knust, K. Scida, R.M. Crooks, Bipolar electrochemistry, Angew. Chem. Int. Ed. 52 (2013) 10438e10456. [2] F. Yuan, L. Qi, T.H. Fereja, D.V. Snizhko, Z. Liu, W. Zhang, G. Xu, Regenerable bipolar electrochemiluminescence device using glassy carbon bipolar electrode, stainless steel driving electrode and cold patch, Electrochim. Acta 262 (2018) 182e186. [3] H.-R. Zhang, Y.-Z. Wang, W. Zhao, J.-J. Xu, H.-Y. Chen, Visual color-switch electrochemiluminescence biosensing of cancer cell based on multichannel bipolar electrode chip, Anal. Chem. 88 (2016) 2884e2890. [4] Y. Zhuo, H.-J. Wang, Y.-M. Lei, P. Zhang, J.-L. Liu, Y.-Q. Chai, R. Yuan, Electrochemiluminescence biosensing based on different modes of switching signals, Analyst 143 (2018) 3230e3248. [5] V. Eßmann, S. Barwe, J. Masa, W. Schuhmann, Bipolar electrochemistry for concurrently evaluating the stability of anode and cathode electrocatalysts and the overall cell performance during long-term water electrolysis, Anal. Chem. 88 (2016) 8835e8840. [6] S.E. Fosdick, R.M. Crooks, Bipolar electrodes for rapid screening of electrocatalysts, J. Am. Chem. Soc. 134 (2012) 863e866. [7] G. Tisserant, Z. Fattah, C. Ayela, J. Roche, B. Plano, D. Zigah, B. Goudeau, A. Kuhn, L. Bouffier, Generation of metal composition gradients by means of bipolar electrodeposition, Electrochim. Acta 179 (2015) 276e281. [8] V. Eßmann, C. Santana Santos, T. Tarnev, M. Bertotti, W. Schuhmann, Scanning bipolar electrochemical microscopy, Anal. Chem. 90 (2018) 6267e6274. [9] L. Bouffier, S. Arbault, A. Kuhn, N. Sojic, Generation of electrochemiluminescence at bipolar electrodes: concepts and applications, Anal. Bioanal. Chem. 408 (2016) 7003e7011.
[10] R. Liu, C. Liu, H. Li, M. Liu, D. Wang, C. Zhang, Bipolar electrochemiluminescence on thread: a new class of electroanalytical sensors, Biosens. Bioelectron. 94 (2017) 335e343. [11] H. Xing, X. Zhang, Q. Zhai, J. Li, E. Wang, Bipolar electrode based reversible fluorescence switch using prussian blue/Au nanoclusters nanocomposite film, Anal. Chem. 89 (2017) 3867e3872. [12] L. Wang, W. Lian, H. Liu, A resettable keypad lock with visible readout based on closed bipolar electrochemistry and electrochromic poly(3methylthiophene) films, Chem. Eur J. 22 (2016) 4825e4832. [13] X. Zhang, C. Chen, J. Yin, Y. Han, J. Li, E. Wang, Portable and visual electrochemical sensor based on the bipolar light emitting diode electrode, Anal. Chem. 87 (2015) 4612e4616. [14] L. Li, Y. Chen, J.-J. Zhu, Recent advances in electrochemiluminescence analysis, Anal. Chem. 89 (2017) 358e371. [15] Z. Liu, W. Qi, G. Xu, Recent advances in electrochemiluminescence, Chem. Soc. Rev. 44 (2015) 3117e3142. [16] A. Arora, J.C.T. Eijkel, W.E. Morf, A. Manz, A wireless electrochemiluminescence detector applied to direct and indirect detection for electrophoresis on a microfabricated glass device, Anal. Chem. 73 (2001) 3282e3288. [17] W. Zhan, J. Alvarez, R.M. Crooks, Electrochemical sensing in microfluidic systems using electrogenerated chemiluminescence as a photonic reporter of redox reactions, J. Am. Chem. Soc. 124 (2002) 13265e13270. [18] W. Gao, K. Muzyka, X. Ma, B. Lou, G. Xu, A single-electrode electrochemical system for multiplex electrochemiluminescence analysis based on a resistance induced potential difference, Chem. Sci. 9 (2018) 3911e3916. [19] S. Nayak, N.R. Blumenfeld, T. Laksanasopin, S.K. Sia, Point-of-Care diagnostics: recent developments in a connected age, Anal. Chem. 89 (2017) 102e123. [20] R.K. Mishra, L.J. Hubble, A. Martín, R. Kumar, A. Barfidokht, J. Kim, M.M. Musameh, I.L. Kyratzis, J. Wang, Wearable flexible and stretchable glove biosensor for on-site detection of organophosphorus chemical threats, ACS Sens. 2 (2017) 553e561. [21] S. Kanchi, M.I. Sabela, P.S. Mdluli, Inamuddin, K. Bisetty, Smartphone based bioanalytical and diagnosis applications: a review, Biosens. Bioelectron. 102 (2018) 136e149. [22] W. Gao, M. Saqib, L. Qi, W. Zhang, G. Xu, Recent advances in electrochemiluminescence devices for point-of-care testing, Curr. Opin. Electrochem. 3 (2017) 4e10. [23] P. Kassal, M.D. Steinberg, I.M. Steinberg, Wireless chemical sensors and biosensors: a review, Sensor. Actuator. B Chem. 266 (2018) 228e245. [24] W. Qi, J. Lai, W. Gao, S. Li, S. Hanif, G. Xu, Wireless electrochemiluminescence with disposable minidevice, Anal. Chem. 86 (2014) 8927e8931. [25] L. Qi, Y. Xia, W. Qi, W. Gao, F. Wu, G. Xu, Increasing electrochemiluminescence intensity of a wireless electrode array chip by thousands of times using a diode for sensitive visual detection by a digital camera, Anal. Chem. 88 (2016) 1123e1127. [26] Z. Bi, T. Kan, C.C. Mi, Y. Zhang, Z. Zhao, G.A. Keoleian, A review of wireless power transfer for electric vehicles: prospects to enhance sustainable mobility, Appl. Energy 179 (2016) 413e425. [27] L. Sun, D. Ma, H. Tang, A review of recent trends in wireless power transfer technology and its applications in electric vehicle wireless charging, Renew. Sustain. Energy Rev. 91 (2018) 490e503. [28] L. Xie, Y. Shi, Y.T. Hou, A. Lou, Wireless power transfer and applications to sensor networks, IEEE Wirel. Commun. 20 (2013) 140e145. [29] M. Liu, R. Liu, D. Wang, C. Liu, C. Zhang, A low-cost, ultraflexible cloth-based microfluidic device for wireless electrochemiluminescence application, Lab Chip 16 (2016) 2860e2870. [30] C. Liu, D. Wang, C. Zhang, A novel paperfluidic closed bipolar electrodeelectrochemiluminescence sensing platform: potential for multiplex detection at crossing-channel closed bipolar electrodes, Sensor. Actuator. B Chem. 270 (2018) 341e352. [31] X. Zhang, J. Li, X. Jia, D. Li, E. Wang, Full-featured electrochemiluminescence sensing platform based on the multichannel closed bipolar system, Anal. Chem. 86 (2014) 5595e5599.
Contents lists available at ScienceDirect
Electrochimica Acta journal homepage: www.elsevier.com/locate/electacta
A portable wireless single-electrode system for electrochemiluminescent analysis Xiangui Ma a, b, Liming Qi a, c, Wenyue Gao a, c, Fan Yuan a, b, Yong Xia a, b, Baohua Lou a, b, Guobao Xu a, b, * a
State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin, 130022, PR China University of Science and Technology of China, Hefei, Anhui, 230026, PR China c University of Chinese Academy of Sciences, No. 19A Yuquanlu, Beijing, 100049, PR China b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 21 December 2018 Received in revised form 3 April 2019 Accepted 3 April 2019 Available online 4 April 2019
A wireless single-electrode electrochemiluminescence (ECL) system is for the first time designed by coupling single-electrode ECL system with wireless energy transfer. It consists of a wireless energy transfer module, a single-electrode ECL system and a diode. The electric current in this system is supplied through the wireless energy transfer and then rectified by the diode. The potential difference is induced by the resistance of ITO of the single-electrode ECL system, which leads to the ECL reaction of luminol and hydrogen peroxide. With this system, linear range of hydrogen peroxide from 1 to 150 mM is obtained by photomultiplier tube (PMT) detector with a detection limit of 0.26 mM. Moreover, visual detection was carried out using a smart phone as detector. And the linear range of hydrogen peroxide was from 10 to 100 mM. Because of its advantages like low cost, high sensitivity and portability, this wireless single-electrode system has great potential for the applications in on-site detection, drug screening and point of care testing. © 2019 Elsevier Ltd. All rights reserved.
Keywords: Wireless energy transfer Single-electrode system Electrochemiluminescence Visual detection Portable device
1. Introduction As a low-cost, simple and highly efficient tool, bipolar electrode has drawn extensive attention [1] in recent years and shown broad applications in various fields, including biological and chemical sensing [2e4], catalysts evaluation and screening [5,6], electrochemical synthesis [7] and scanning microscopy [8]. Except for direct electrical signals, there are many ways to read out signals of bipolar system such as electrochemiluminescence (ECL) [9,10], fluorescence [11], electrochromism [12], light of LED [13] and anodic dissolution [6]. ECL is a simple and highly sensitive method with low background [14,15]. Since ECL was coupled with bipolar electrochemistry [16,17] from 2001, it becomes a popular method especially in biological and chemical analysis. Recently our group has developed a single-electrode electrochemical system (SEES) for ECL detection [18]. Unlike conventional bipolar electrode system,
* Corresponding author. State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin, 130022, PR China. E-mail address: [email protected] (G. Xu). https://doi.org/10.1016/j.electacta.2019.04.015 0013-4686/© 2019 Elsevier Ltd. All rights reserved.
the SEES is a special kind of bipolar electrode using only one electrode and generates ECL reactions through the potential difference induced by the resistance of electrode. Moreover, it avoids the background ECL signal of driving electrodes. This low-cost system enables ECL analysis and provides new applications for the bipolar electrode ECL analysis. To date, new interdisciplinary technologies are emerging to meet the need of miniaturized and portable devices for point of care sensing and on-site detection [19,20]. For example, visual detections using portable devices [2,21,22] and wireless sensor devices [23] have been wildly explored. Our group has reported an ECL detection device powered by wireless power transfer (WPT) [24] and a WPT electrode array chip with a rectifying diode for ECL visual detection based on digital camera [25]. The WPT technology was first proposed by Nicola Tesla in the 1890s. The mechanism of WPT can be categorized as capacitive coupling, inductive coupling, magnetic resonant coupling and electromagnetic radiation. Because of its convenience, simplicity and safety, inductive coupling is the most common WPT technology in daily life, such as charging phones, electric toothbrushes and implantable medical devices [26e28]. WPT technology can simplify electrical circuit,
X. Ma et al. / Electrochimica Acta 308 (2019) 20e24
avoid the direct connections between power sources and electrodes and benefit the development of portable and facile ECL detection devices. In this study, taking advantages of WPT and SEES technique, a new wireless single-electrode system for ECL detection is developed. The application of wireless energy transfer as power supply will bring considerable convenience to the ECL detection because no direct electrical connection in this system. And the use of singleelectrode system can eliminate the interference ECL signals from driving electrode. Finally hydrogen peroxide is quantitatively measured with satisfactory sensitivity by photomultiplier tube (PMT) and smart phone as detectors. 2. Experimental 2.1. Chemicals and materials Hydrogen peroxide, luminol, sodium bicarbonate and sodium hydroxide were obtained from Beijing Chemical Reagent Company. Triton X-100 was purchased from Sinopharm Chemical Reagent Company Ltd. (Shanghai, China). Indium tin oxide (ITO) conductive glass and conductive carbon ink CH-8 were bought from Foshan
21
City Meijingyuan Glass Co., Ltd and Jujo Printing Supplies & Technology Co., Ltd, China, respectively. Polyethylene terephthalate (PET) label was bought from Jinfuzhou Paper Co. Ltd. NaHCO3eNaOH buffer solution (0.1 M, pH 10.5) was used in the ECL detection experiments. All the reagents were used directly in the experiments without any further purification. Doubly distilled water was used in all solutions. 2.2. Apparatus The direct current was supplied from a digitally regulated direct current (DC) power supply (CE0120010T, Shanghai Kalaifei Company, China). ECL intensities were recorded by a BPCL ultraweak luminescence analyzer from the Institute of Biophysics, Chinese Academic of Sciences. The wireless energy transfer modules (XKT412-27) and copper coils were bought from Shenzhen Xinketai Electronic Co, Ltd. And the RB520S-30 diodes were bought from Shenzhen Jiechengnuo Electronics Co, Ltd. The alternating potentialtime profiles were monitored in parallel with the singleelectrode using the digital storage oscilloscope (ADS1112CAL) from Nanjing Glarun-Atten Technology Co, Ltd. For visual detections, the
Fig. 1. Schematic diagram of wireless single-electrode system.
Fig. 2. The principle of wireless single-electrode system and its equivalent electrical circuit.
Fig. 3. The effect of diode on the ECL intensity. (A) Alternating potentialtime profiles of the system without and with diode. (B) Comparison of ECL intensities between the system without diode and with diode. Inset: A zoom of ECL intensity of the system without diode. Luminol 0.1 mM, H2O2 1 mM, 1% (V/V) Triton X-100, 0.1 M CBS, pH 10.5, PMT: 600 V, ITO resistance 500 U.
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images of the ECL emission were taken in a dark box using a smart phone (Xiaomi 6). 2.3. Procedure for detection of H2O2 A volume of 8 mL of carbonate buffer solution (pH 10.5, 0.1 M) containing 0.01 mM luminol, 1% (V/V) Triton X-100 and different concentrations of hydrogen peroxide were pipetted into the cell. Then two copper coils were aligned on both sides of a glass slide (thickness: 1 mm), and an input voltage of 5 V for wireless energy transfer module was adopted. With this wireless single-electrode system, ECL intensities were measured using a BPCL ultraweak luminescence analyzer. Visual detection of hydrogen peroxide had the similar procedures. A volume of 8 mL of 0.1 M carbonate buffer solution (pH 10.5) containing 1% (V/V) Triton X-100, 0.1 mM luminol and different concentrations of hydrogen peroxide were dropped into the cell. The images of ECL emission were captured in a dark box using a smart phone (exposure time: 16 s, ISO parameter: 3200). Then intensities of the light spots were analyzed using ImageJ software. 3. Results and discussion 3.1. Fabrication and principle of wireless single-electrode system The schematic diagram of wireless single-electrode system is illustrated in Fig. 1. This system consists of a wireless energy transmission module, a single-electrode, a diode and two copper coils. The fabrication of the single-electrode was similar to the procedures in previous work of our group [18]. In short, PET label was cut with a rectangular hole (1.0 cm, 0.8 cm) and attached onto a piece of ITO conductive glass (2.0 cm, 1.0 cm). Then two copper wires were connected by both ends of the PET label with conductive carbon ink. Fig. 2 illustrates the principle of single-electrode system. When an external voltage (Etot) is applied, the current (itot) between two copper wires passes though the ITO glass (ie) and the solution (is) in
the cell. Because the resistance of solution (Rs) is much larger than resistance of ITO electrode (Rs) [18], it can be believed that current is carried through the ITO film mostly. An approximately uniform electric field is built in this single-electrode system. And the potential difference (Ec) across the cell is estimated using the following equation: Ec ¼ Etot Lc/Ltot. If Ec reaches certain amount, hydrogen peroxide and dissolved oxygen will be reduced on the ITO surface at the cathode. At the same time, luminol and hydrogen peroxide are oxidized at the anode side of cell and emit blue light. 3.2. The effect of diode on the wireless single-electrode system The alternating potentialtime profile in Fig. 3A was measured by oscilloscope in parallel with the single-electrode. So the potentials can be regarded as the external voltage (Etot) in the system. When diode was not used, high frequency alternating potential from 9.7 to 4.2 V was applied, and the corresponding ECL intensity (Fig. 3B, red line) was quite weak. The reactive intermediates generated by the oxidization of luminol and hydrogen peroxide at positive potentials would be reduced at the negative potentials and lost activity before the ECL emission reaction, leading to a weak ECL emission. To avoid this problem, diode was employed to rectify the alternating current (AC) to enhance ECL efficiency. Fig. 3B shows that the use of diode remarkably enhances ECL intensity by about 200 times. Therefore, the diode was employed in subsequent experiments. 3.3. The effect of different ITO resistances on the wireless singleelectrode system As presented in Fig. 4, the ECL intensities increased with the increasing resistances of ITO, and ITO resistance of 500 U per square had the best ECL performance. On the one hand, the ITO electrodes with higher resistance have thinner indium tin oxide layers and higher transparency. On the other hand, the ITO electrodes of different resistances may have difference electron transfer rates. These factors lead to the increase in ECL intensities as resistances
Fig. 4. Effect of different ITO resistances on the ECL intensity. Luminol 0.1 mM, H2O2 1 mM, 1% (V/V) Triton X-100, 0.1 M CBS, pH 10.5, PMT: 600 V.
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with this wireless single-electrode system in carbonate buffer solution (pH 10.5) containing 1% (V/V) Triton X-100 and 0.01 mM luminol using a PMT-based detector. The ECL intensities increased with the increasing H2O2 concentrations. As depicted in the inset of Fig. 5B, ECL intensities had a good linear relationship with the concentrations of H2O2 from 1 mM to 150 mM with a correlation coefficient (r) of 0.9996. And the regression equation is described as I ¼ 106.36 þ 7.85 c (H2O2/mM). The detection limit for hydrogen peroxide was calculated to be 0.26 mM, which is comparable to the previously reported detection methods in Table 1. 3.5. Visual detection of H2O2 For further application of this system, visual detection of hydrogen peroxide was explored using a smart phone. 8 mL of 0.1 M carbonate buffer solution (pH 10.5) containing 1% (V/V) Triton X100, 0.1 mM luminol and different concentrations of H2O2 were analyzed by taking photos in a dark box. Fig. 6A shows the ECL emission images of luminol/H2O2 system with 0, 10, 20, 50, 70, 100, 200, 500 mM H2O2. As shown in Fig. 6B, the relative light units (RLU)
Fig. 5. Detection of H2O2 using PMT. (A) ECL profiles (three consecutive measurements) with different H2O2 concentrations. (B) ECL intensities versus the concentrations of H2O2. Inset: Linear calibration curve. Luminol 0.01 mM, 1% (V/V) Triton X-100, 0.1 M CBS, pH 10.5, PMT: 600 V, ITO resistance 500 U.
increase. Moreover, ITO electrodes of higher resistance are cheaper. Thus the single-electrodes made by ITO glass of 500 U per square were used in the following experiments.
3.4. Detection of H2O2 by PMT Under the optimal conditions, a wireless single-electrode system for ECL detection toward hydrogen peroxide was developed. As shown in Fig. 5, different concentrations of H2O2 were detected
Fig. 6. (A) ECL images of luminol and different concentrations of H2O2. (B) Visualized quantitative detection of hydrogen peroxide. Luminol 0.1 mM, 1% (V/V) Triton X-100, 0.1 M CBS, pH 10.5.
Table 1 Comparison of some bipolar electrode systems for H2O2 detection based on luminol/H2O2 ECL system. Device
Detector
Linear range (mM)
LOD (mM)
Reference
Cloth-based microfluidic device Paper fluidic closed bipolar electrode Multichannel Closed Bipolar System Glassy carbon based BPE SEES
CCD CCD PMT Smart phone PMT Smart phone PMT Smart phone
25e2500 75e500 50e5000 5e300 1e100 5e100 1e150 10e100
24 41 50 3.67 0.27 e 0.26 e
[29] [30] [31] [2] [18]
wireless single-electrode system
This work
24
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of ECL increased as the H2O2 concentrations increased. And a linear correlation between the relative light units and the concentrations of H2O2 is established from 10 to 100 mM. The regression equation could be expressed as I ¼ 238.77 þ 25.46 c (H2O2/mM), R ¼ 0.9987. 4. Conclusions In conclusion, we have designed a facile and portable wireless single-electrode system for ECL detection of hydrogen peroxide with acceptable linear ranges and detection limits. This device can be easily constructed without the need for complicated and expensive materials and equipment. In contrast with other bipolar electrode systems, this system can avoid the interference signal from driving electrode. And it is more convenient to use the wireless transmission as power supply, because frequent electrical connections and disconnections are not necessary. Moreover, this system supports visualized quantitative detection using a smart phone. On the basis of the advantages above, this high performance wireless single-electrode system will contribute to the development of bipolar devices in portable ECL testing. Acknowledgements We thank the support from The National Key Research and Development Program of China (No. 2016YFA0201300), and the National Natural Science Foundation of China (No. 21675148, 21804127, 21874126). References [1] S.E. Fosdick, K.N. Knust, K. Scida, R.M. Crooks, Bipolar electrochemistry, Angew. Chem. Int. Ed. 52 (2013) 10438e10456. [2] F. Yuan, L. Qi, T.H. Fereja, D.V. Snizhko, Z. Liu, W. Zhang, G. Xu, Regenerable bipolar electrochemiluminescence device using glassy carbon bipolar electrode, stainless steel driving electrode and cold patch, Electrochim. Acta 262 (2018) 182e186. [3] H.-R. Zhang, Y.-Z. Wang, W. Zhao, J.-J. Xu, H.-Y. Chen, Visual color-switch electrochemiluminescence biosensing of cancer cell based on multichannel bipolar electrode chip, Anal. Chem. 88 (2016) 2884e2890. [4] Y. Zhuo, H.-J. Wang, Y.-M. Lei, P. Zhang, J.-L. Liu, Y.-Q. Chai, R. Yuan, Electrochemiluminescence biosensing based on different modes of switching signals, Analyst 143 (2018) 3230e3248. [5] V. Eßmann, S. Barwe, J. Masa, W. Schuhmann, Bipolar electrochemistry for concurrently evaluating the stability of anode and cathode electrocatalysts and the overall cell performance during long-term water electrolysis, Anal. Chem. 88 (2016) 8835e8840. [6] S.E. Fosdick, R.M. Crooks, Bipolar electrodes for rapid screening of electrocatalysts, J. Am. Chem. Soc. 134 (2012) 863e866. [7] G. Tisserant, Z. Fattah, C. Ayela, J. Roche, B. Plano, D. Zigah, B. Goudeau, A. Kuhn, L. Bouffier, Generation of metal composition gradients by means of bipolar electrodeposition, Electrochim. Acta 179 (2015) 276e281. [8] V. Eßmann, C. Santana Santos, T. Tarnev, M. Bertotti, W. Schuhmann, Scanning bipolar electrochemical microscopy, Anal. Chem. 90 (2018) 6267e6274. [9] L. Bouffier, S. Arbault, A. Kuhn, N. Sojic, Generation of electrochemiluminescence at bipolar electrodes: concepts and applications, Anal. Bioanal. Chem. 408 (2016) 7003e7011.
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