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thiourea dioxide chemiluminescence system and its application for selective and sensitive dopamine detection
Sensors and Actuators B 238 (2017) 468–472
Contents lists available at ScienceDirect
Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb
Efficient lucigenin/thiourea dioxide chemiluminescence system and its application for selective and sensitive dopamine detection Wenyue Gao a,b , Liming Qi a,b , Zhongyuan Liu a , Saadat Majeed a,b , Shimeles Addisu Kitte a,b , Guobao Xu a,∗ a State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, PR China b University of Chinese Academy of Sciences, Chinese Academy of Sciences, No. 19A Yuquanlu, Beijing 100049, PR China
a r t i c l e
i n f o
Article history: Received 11 March 2016 Received in revised form 15 July 2016 Accepted 18 July 2016 Available online 20 July 2016 Keywords: Lucigenin Thiourea dioxide Chemiluminescence Dopamine
a b s t r a c t Thiourea dioxide, a well-known eco-friendly, stable and cost-effective industrial reductant, has been used as the coreactant of lucigenin chemiluminescence for the first time. This chemiluminescence system is highly efficient, and its chemiluminescence peak intensity is about 75 times higher than that of the famous lucigenin/H2 O2 system. Interestingly, dopamine dramatically suppresses the chemiluminescence of lucigenin/thiourea dioxide system. Based on this newly-developed system, highly sensitive detection of dopamine, lucigenin, and thiourea dioxide was achieved. The linear ranges are 20–800 nM, 20 nM–0.1 mM, and 0.01–10 mM for dopamine, lucigenin, and thiourea dioxide, respectively. The detection limits are 14.7 nM, 8.0 nM, and 2.4 M for dopamine, lucigenin, and thiourea dioxide, respectively. Moreover, this method shows excellent selectivity for the detection of dopamine against many compounds, such as ascorbic acid, uric acid, amino acids and sugars. This study suggests that the newly-found user-friendly lucigenin/thiourea dioxide system is a promising chemiluminescence system with broad applications. © 2016 Elsevier B.V. All rights reserved.
1. Introduction Chemiluminescence (CL) analysis is attractive because of its simple, fast, sensitive feature and has been widely used in many fields [1–3]. Lucigenin (N,N -dimethylbiacridinium dinitrate) is one of the most popular CL luminophores. Its CL properties were first observed by Gleu and Petsch in 1935 [4]. Since that time many researchers have investigated the mechanism of the CL reaction. Lucigenin emit chemiluminescent light in alkaline medium in the presence of oxidizing agents (e.g., hydrogen peroxide) [5]. The emission reaction could be enhanced by metal ions [6], and different metal ions may have different enhancement effects on the lucigenin CL [7]. These properties expand the application range of lucigenin CL. However, the application of lucigenin in CL analysis is usually limited by lack of specificity [7]. So it is highly desired to develop new lucigenin CL systems, particularly new lucigenin CL systems with high selectivity and good stability for bioassays in which lucigenin is often used as label.
∗ Corresponding author. E-mail address: [email protected] (G. Xu). http://dx.doi.org/10.1016/j.snb.2016.07.093 0925-4005/© 2016 Elsevier B.V. All rights reserved.
Thiourea dioxide (TD) is a well-known industrial reducing agent [8,9]. It is eco-friendly, low-cost, facile and stable, thus it has been vastly used in paper, textile and leather-processing industries. A unique property of this reductant is that it can decompose to generate oxygen [10,11]. It implies that TD may also react with lucigenin to generate CL. In addition, it is necessary to develop new methods for TD detection because of the broad applications of TD. Dopamine (DA) is an important neurotransmitter and plays a significant role in the function of human metabolism, central nervous, renal and hormonal systems [12]. Abnormal concentrations of DA could cause neurological disorders, Parkinson’s disease, and schizophrenia [13]. Therefore, it is of great importance to develop effective, selective and sensitive approaches to detect DA. Up to now, various analytical methods have been exploited for the detection of DA, such as chromatography coupled with spectroscopy (e.g., high-pressure liquid chromatographymass spectrometry (HPLC–MS)) [14], electrochemistry [15,16], spectrophotometry [17,18], fluorescence [19], chemiluminescence [20,21] and electrochemiluminescence [22–24]. These methods, however, have some limitations. For instance, chromatographic methods are time-consuming, labor intensive, and expensive with complicated procedures. Similarly, the synthesis of fluorescent or colorimetric probes for DA detection involves complicated and
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time-consuming procedures. Electrochemical methods usually suffer from the interferences of uric acid (UA) and ascorbic acid (AA). Although some CL methods have also been reported to detect DA, they involve the use of oxidizing agents and metal ions, making the detection methods less selective [21]. In this study, TD has been developed as the coreactant of lucigenin CL for the first time and the effect of DA on this new CL system was investigated. DA dramatically suppresses the CL of lucigenin/TD. The lucigenin/TD system was used to detect lucigenin, TD and DA with excellent sensitivity. The inhibition mechanism of DA on the CL of lucigenin/TD is discussed and the sensitive detection of DA based on this inhibition mechanism has been demonstrated. This DA detection method is simple, fast and shows excellent selectivity against many compounds, such as ascorbic acid, uric acid, amino acids and sugars. 2. Experimental section 2.1. Materials and apparatus Ascorbic acid and hydrogen peroxide were purchased from Beijing Chemical Reagent Company (Beijing, China). Lucigenin was purchased from TCI (Shanghai, China). TD was obtained from Aladdin (Shanghai, China). Lysine, aspartic acid, alanine, arginine, uric acid, glucose and sucrose were purchased from Sinopharm Chemical Reagent Co. Ltd. (Beijing, China). Lucigenin stock solution (1.0 mM) was prepared by dissolving 0.0510 g lucigenin in 100 mL water. All the chemicals were analytical-reagent grade and were used without further purification. Doubly distilled water was used throughout all experiments. The CL was measured by a flow injection CL system consisting of a Biophysics Chemiluminescence (BPCL) ultra-weak luminescence analyzer (the Institute of Biophysics, Chinese Academic of Sciences), an intelligent flow injection sampler (IFIS-C mode) (ReMax Inc., Xi’an, China) and a home-made flow cell. The flow cell was put in a light-tight box of the luminescent analyzer. The loop injector was equipped with an injection loop of 50 L. 2.2. Detection procedure for TD Scheme 1 shows the schematic diagram of the flow system for TD detection. 10 M lucigenin in water and 0.5 M NaOH solution were pumped into the flow cell through channels I and II at a flow rate of 2.0 mL/min, respectively. Different concentrations of TD in water were injected through the loop injector.
Fig. 1. The CL intensity-time curves for the lucigenin/H2 O2 (red line) and lucigenin/TD systems (blue line). Inset: enlarged CL intensity–time curve for the lucigenin/H2 O2 system. c(lucigenin): 10.0 M; c(TD): 1.0 mM; c(H2 O2 ): 1.0 mM; c(NaOH): 0.5 M; photomultiplier tube voltage: 700 V. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.).
2.4. Detection procedure for dopamine 10 M Lucigenin in water and 0.5 M NaOH solution were pumped into the flow cell through channels I and II at a flow rate of 2.0 mL/min, respectively. Different concentrations of dopamine were mixed with 1.0 mM TD first, and then the mixture were injected through the loop injector. 3. Results and discussion 3.1. Chemiluminescence of lucigenin/TD system Fig. 1 shows the CL intensity-time curves of lucigenin/TD system and lucigenin/H2 O2 system. By comparison, the CL peak intensity of lucigenin/TD system is about 75 times higher than that of lucigenin/H2 O2 system. It indicates that TD is an effective coreactant for lucigenin CL. The CL spectrum of this new system was measured by using various band pass filters at wavelengths of 400 nm, 425 nm, 440 nm, 460 nm, 490 nm, 535 nm, 555 nm, 575 nm, 620 nm, and 640 nm. As shown in Fig. 2, the maximum emission wavelength is about 490 nm, which is consistent with the typical
2.3. Detection procedure for lucigenin 10 mM TD in water and 0.5 M NaOH solution were pumped into the flow cell through channels I and II at a flow rate of 2.0 mL/min, respectively. Different concentrations of lucigenin in water were injected through the loop injector.
Scheme 1. A schematic diagram of the flow system for this CL system.
Fig. 2. CL spectrum of lucigenin/TD system. c(lucigenin): 10.0 M; c(TD): 1.0 mM; c(NaOH): 0.5 M; photomultiplier tube voltage: 1000 V.
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Fig. 4. Linear calibration curve of DA. I represents the CL intensity of the system at a specific concentration of DA, I0 represents the CL intensity of the control sample. c(lucigenin): 10.0 M; c(TD): 1.0 mM; c(NaOH): 0.5 M; c(DA): 0, 0.02, 0.05, 0.1, 0.2, 0.4, 0.6 and 0.8 M; photomultiplier tube voltage: 1000 V.
Scheme 2. Reaction mechanism for the lucigenin/TD CL system.
maximum emission wavelength of lucigenin CL. The possible reaction mechanism is shown in Scheme 2. It has been reported that TD can tautamerize and liberate oxygen in aqueous solutions (Eq. (1) in Scheme 2)[10]. The hyproperoxide intermediate (compound A in Eq. (1)) generated from the decomposition of TD in alkaline solutions may oxidize lucigenin to produce dioxetane as shown in Eq. (2) of Scheme 2. Then the dioxetane produced the primary emitter, singlet N-methylacridone, and subsequently generated strong CL (Eqs. (3) and (4) in Scheme 2). 3.2. Optimization of conditions Lucigenin produces CL in basic media, such as, in the solution of sodium hydroxide, and the concentration of sodium hydroxide has significant effect on the CL intensities. So we tested CL intensities of lucigenin/TD system in different concentrations of NaOH solution. As shown in Fig. 3, the CL intensities increase with increasing concentrations of NaOH. This may be attributed to the faster
Fig. 3. Dependence of CL intensities on the concentrations of NaOH. c(TD): 10.0 mM; c(lucigenin): 0.1 mM; c(NaOH): 0.05, 0.1, 0.2, 0.5, 1.0, 2.0, 5.0 and 10.0 M; photomultiplier tube voltage: 500 V.
generation of effective hyproperoxide intermediates from TD at higher pH. The CL intensities increase less rapidly at NaOH concentrations higher than 0.5 M. Therefore, 0.5 M NaOH was used in subsequent experiments. 3.3. Detection for TD and lucigenin In order to evaluate the performance of this new CL system, we tested different concentrations of TD and lucigenin. The logarithm of CL intensities (logI) has good linear relationship with logarithm of concentrations of TD (logc) from 0.01 to 10 mM with correlation coefficient (r) of 0.9985 (Fig. S1). The linear equation is logI = 3.77 + 1.40 logc (where c is the concentration in mM). The limit of detection (LOD) for TD is calculated to be 2.4 M at a signalto-noise ratio of 3. Moreover, the logarithm of CL intensities (logI) has good linear relationship with logarithm of concentrations of lucigenin (logc) from 20 nM to 0.1 mM (Fig. S2). The linear equation is logI = 8.48 + 1.01 logc (where c is the concentration in M) (r = 0.9970). The LOD at a signal-to-noise ratio of 3 is 8.0 nM, which
Fig. 5. Selectivity for the detection of DA. DA concentration is 0.6 M and concentration of other substances is 10.0 M. I represents the CL intensity of the system after the addition of DA and other substances, I0 represents the CL intensity of the control sample. c(lucigenin): 10.0 M; c(TD): 1.0 mM; c(NaOH): 0.5 M; photomultiplier tube voltage: 1000 V. (Glc, glucose; Suc, sucrose; Lys, lysine; Asp, aspartic acid; Ala, alanine; Arg, arginine).
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Table 1 Comparison of different methods for DA detection. Methods
Probes
Linear range
LOD
Ref.
Fluorescence Colorimetry Surface Plasmon Resonance Electrochemistry Electrochemiluminescence Chemiluminescence Chemiluminescence
Polydopamine Nanoparticles Gold nanoparticles Silver nanoparticles Tyrosinase/NiO/ITO electrode CdSeTe/ZnS core–shell quantum dots Luminol–H2 O2 -HKUST-1 Lucigenin/TD
0.5 − 20 M 0 − 1 M 0.2 − 30 M 2 − 100 M 0.375 − 450 M 0.01 − 0.7 M 0.02 − 0.8 M
40 nM 33 nM 20 nM 1.0 M 100 nM 2.3 nM 14.7 nM
30 34 32 31 29 33 This work
is comparable to the best LOD of other reported lucigenin detection methods using lucigenin/H2 O2 system [25]. 3.4. Detection for dopamine We investigated the effect of DA concentrations on the CL intensities of the lucigenin/TD system. The experiment results show that DA can significantly decrease the CL intensities of the lucigenin/TD system. The relationship between the CL quenching efficiencies and the concentrations of DA was analyzed by the Stern–Volmer equation [26–29]: I 0 /I = 1 + K SV c where I0 represents the CL intensity of the control sample, I represents the CL intensity at a specific concentration of quencher, c is the concentration of DA and KSV is the Stern−Volmer quenching constant. The Stern–Volmer plot shown in Fig. 4 shows a linear relationship between I0 /I and the concentrations of DA from 0.02 to 0.8 M. The linear equation is I0 /I = 0.99 + 1.78c (where c is the concentration in M) (r = 0.9950). The quenching constant is 1.78. The LOD is calculated to be 14.7 nM at a signal-to-noise ratio of 3. Relative standard deviations (RSD) of three consecutive experiments are between 0.2% and 2.1%, indicating the good reproducibility of this detection method. These results indicate that this proposed CL method has good linearity and high sensitivity towards the quantitative determination of DA. In comparison with other reported CL methods for the detection of DA (Table 1) [29–34], the present work is simpler, avoiding the troubles of preparing specific luminescent materials or catalysts. 3.5. Selectivity of dopamine detection We tested the selectivity of the newly-developed DA detection method using compounds, such as AA, UA, amino acids and sugars. The concentration of interfering substances investigated is 10.0 M, while the concentration of DA is 0.6 M. As shown in Fig. 5, the CL intensity decreases dramatically in the presence of DA. In contrast, CL intensities change negligibly in the presence of other substances. The results suggest that the DA detection method based on the lucigenin/TD CL system has nice selectivity. 4. Conclusions Lucigenin CL using an eco-friendly, stable and cheap coreactant TD has been reported for the first time. The CL intensities of the lucigenin/TD system can be significantly decreased by DA. The newly-developed lucigenin/TD CL system enables the highly sensitive detection of lucigenin, TD and DA. Moreover, the lucigenin/TD CL system exhibit excellent selectivity for the detection of DA against substances, such as AA, UA, amino acids and sugars. Because of the popularity of lucigenin CL, the newly found user-friendly lucigenin/thiourea dioxide system may find broad applications.
Acknowledgements This project was supported by the National Natural Science Foundation of China (Nos. 21475123), and Faculty Development Programm of Bahauddin Zakaryia University, Multan, Pakistan (100 Foreign Scholarships) (No. PF/Cont./2-50/Admin/5398), the Chinese Academy of Sciences (CAS)-the Academy of Sciences for the Developing World (TWAS) President’s Fellowship Programme. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.snb.2016.07.093. References [1] H.-Z. He, K.-H. Leung, W. Wang, D.S.-H. Chan, C.-H. Leung, D.-L. Ma, Label-free luminescence switch-on detection of T4 polynucleotide kinase activity using a G-quadruplex-selective probe, Chem. Commun. 50 (2014) 5313–5315. [2] L. Lu, D. Shiu-Hin Chan, D.W.J. Kwong, H.-Z. He, C.-H. Leung, D.-L. Ma, Detection of nicking endonuclease activity using a G-quadruplex-selective luminescent switch-on probe, Chem. Sci. 5 (2014) 4561–4568. [3] D.-L. Ma, H.-Z. He, H.-J. Zhong, S. Lin, D.S.-H. Chan, L. Wang, S.M.-Y. Lee, C.-H. Leung, C.-Y. Wong, Visualization of Zn2+ ions in live zebrafish using a luminescent Iridium(III) chemosensor, ACS Appl. Mater. Interfaces 6 (2014) 14008–14015. [4] K. Gleu, W. Petsch, Die chemiluminescenz der dimethyl-diacridyliumsalze, Angew. Chem. 48 (1935) 57–59. [5] C.F. Duan, H. Cui, Time-tunable autocatalytic lucigenin chemiluminescence initiated by platinum nanoparticles and ethanol, Chem. Commun. 18 (2009) 2574–2576. [6] L.A. Montano, J.D. Ingle, Investigation of the lucigenin chemiluminescence reaction, Anal. Chem. 51 (1979) 919–926. [7] Y. He, H. Cui, Synthesis of dendritic platinum nanoparticles/lucigenin/reduced graphene oxide hybrid with chemiluminescence activity, Chem. Eur. J. 18 (2012) 4823–4826. [8] S.V. Makarov, A.K. Horvath, R. Silaghi-Dumitrescu, Q.Y. Gao, Recent developments in the chemistry of thiourea oxides, Chem. Eur. J. 20 (2014) 1–14. [9] L. Zhou, X.Y. Liu, J.Z. Shao, Y.N. Chen, Study on thiourea dioxide’s reducing capacity and its reactivity with reactive dyes, Adv. Mater. Res. 396–398 (2012) 1174–1179. [10] Z. Kis, S.V. Makarov, R. Silaghi-Dumitrescu, Computational investigations on the electronic structure and reactivity of thiourea dioxide: sulfoxylate formation, tautomerism and dioxygen liberation, J. Sulfur Chem. 31 (2010) 27–39. [11] W. Gao, W. Qi, J. Lai, L. Qi, S. Majeed, G. Xu, Thiourea dioxide as a unique eco-friendly coreactant for luminol chemiluminescence in the sensitive detection of luminol, thiourea dioxide and cobalt ions, Chem. Commun. 51 (2015) 1620–1623. [12] B. Yu, D. Kuang, S. Liu, C. Liu, T. Zhang, Template-assisted self-assembly method to prepare three-dimensional reduced graphene oxide for dopamine sensing, Sens. Actuators B—Chem. 205 (2014) 120–126. [13] M. Amjadi, J.L. Manzoori, T. Hallaj, M.H. Sorouraddin, Strong enhancement of the chemiluminescence of the cerium(IV)-thiosulfate reaction by carbon dots, and its application to the sensitive determination of dopamine, Microchim. Acta 181 (2014) 671–677. [14] V. Carrera, E. Sabater, E. Vilanova, M.A. Sogorb, A simple and rapid HPLC–MS method for the simultaneous determination of epinephrine, norepinephrine, dopamine and 5-hydroxytryptamine: application to the secretion of bovine chromaffin cell cultures, J. Chromatogr. B 847 (2007) 88–94. [15] F. Gao, X. Cai, X. Wang, C. Gao, S. Liu, F. Gao, Q. Wang, Highly sensitive and selective detection of dopamine in the presence of ascorbic acid at graphene oxide modified electrode, Sensor. Actuat. B—Chem. 186 (2013) 380–387. [16] W.-C. Wu, H.-W. Chang, Y.-C. Tsai, Electrocatalytic detection of dopamine in the presence of ascorbic acid and uric acid at silicon carbide coated electrodes, Chem. Commun. 47 (2011) 6458–6460.
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Biographies Wenyue Gao received her B. S. degree from Shandong Normal University in 2012. Currently she is a Ph. D. student under the guidance of Prof. Guobao Xu at Changchun Institute of Applied Chemistry, Chinese Academy of Sciences. Her research interests focus on electroanalytical applications of nanomaterials, chemiluminescence, electrochemiluminescence and fluorescence. Liming Qi received her B. S. degree from Jilin University in 2013. Currently she is a Ph. D. student under the guidance of Prof. Guobao Xu at Changchun Institute of Applied Chemistry, Chinese Academy of Sciences. Her current research interests include electroanalytical chemistry, electrochemiluminescence and chemiluminescence, and electrochemical devices. Zhongyuan Liu obtained both her BSc and MSc in chemistry from Southwest University. She joined Changchun Institute of Applied Chemistry as an assistant professor in 2009. Her research interests focus on electrochemiluminescence, electrochemistry, aptasensors and immunosensors. Saadat Majeed obtained her Ph.D under the supervision of Professor Guobao Xu at State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences. Her main current interests are synthesis and luminescent applications of quantum dots, carbon nanomaterials and biosensors. Shimeles Addisu Kitte received his BSc and MSc degree from Jimma University, Ethiopia in 2008 and 2011, respectively. Currently he is a Ph. D. student under the guidance of Prof. Guobao Xu at Changchun Institute of Applied Chemistry, Chinese Academy of Sciences. His current research interests include electroanalytical chemistry, applications of nanomaterials, chemiluminescence and electrochemiluminescence. Guobao Xu received his BSc, MSc, and PhD from Jilin University, Xiamen University, and Changchun Institute of Applied Chemistry, respectively. He did postdoctoral research at the University of Hong Kong, the Hong Kong Polytechnic University, and NTT. He is a professor of the State Key Laboratory of Electroanalytical Chemistry. His research focuses on electrochemiluminescence, biosensors and nanomaterial-based bioanalysis.
Contents lists available at ScienceDirect
Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb
Efficient lucigenin/thiourea dioxide chemiluminescence system and its application for selective and sensitive dopamine detection Wenyue Gao a,b , Liming Qi a,b , Zhongyuan Liu a , Saadat Majeed a,b , Shimeles Addisu Kitte a,b , Guobao Xu a,∗ a State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, PR China b University of Chinese Academy of Sciences, Chinese Academy of Sciences, No. 19A Yuquanlu, Beijing 100049, PR China
a r t i c l e
i n f o
Article history: Received 11 March 2016 Received in revised form 15 July 2016 Accepted 18 July 2016 Available online 20 July 2016 Keywords: Lucigenin Thiourea dioxide Chemiluminescence Dopamine
a b s t r a c t Thiourea dioxide, a well-known eco-friendly, stable and cost-effective industrial reductant, has been used as the coreactant of lucigenin chemiluminescence for the first time. This chemiluminescence system is highly efficient, and its chemiluminescence peak intensity is about 75 times higher than that of the famous lucigenin/H2 O2 system. Interestingly, dopamine dramatically suppresses the chemiluminescence of lucigenin/thiourea dioxide system. Based on this newly-developed system, highly sensitive detection of dopamine, lucigenin, and thiourea dioxide was achieved. The linear ranges are 20–800 nM, 20 nM–0.1 mM, and 0.01–10 mM for dopamine, lucigenin, and thiourea dioxide, respectively. The detection limits are 14.7 nM, 8.0 nM, and 2.4 M for dopamine, lucigenin, and thiourea dioxide, respectively. Moreover, this method shows excellent selectivity for the detection of dopamine against many compounds, such as ascorbic acid, uric acid, amino acids and sugars. This study suggests that the newly-found user-friendly lucigenin/thiourea dioxide system is a promising chemiluminescence system with broad applications. © 2016 Elsevier B.V. All rights reserved.
1. Introduction Chemiluminescence (CL) analysis is attractive because of its simple, fast, sensitive feature and has been widely used in many fields [1–3]. Lucigenin (N,N -dimethylbiacridinium dinitrate) is one of the most popular CL luminophores. Its CL properties were first observed by Gleu and Petsch in 1935 [4]. Since that time many researchers have investigated the mechanism of the CL reaction. Lucigenin emit chemiluminescent light in alkaline medium in the presence of oxidizing agents (e.g., hydrogen peroxide) [5]. The emission reaction could be enhanced by metal ions [6], and different metal ions may have different enhancement effects on the lucigenin CL [7]. These properties expand the application range of lucigenin CL. However, the application of lucigenin in CL analysis is usually limited by lack of specificity [7]. So it is highly desired to develop new lucigenin CL systems, particularly new lucigenin CL systems with high selectivity and good stability for bioassays in which lucigenin is often used as label.
∗ Corresponding author. E-mail address: [email protected] (G. Xu). http://dx.doi.org/10.1016/j.snb.2016.07.093 0925-4005/© 2016 Elsevier B.V. All rights reserved.
Thiourea dioxide (TD) is a well-known industrial reducing agent [8,9]. It is eco-friendly, low-cost, facile and stable, thus it has been vastly used in paper, textile and leather-processing industries. A unique property of this reductant is that it can decompose to generate oxygen [10,11]. It implies that TD may also react with lucigenin to generate CL. In addition, it is necessary to develop new methods for TD detection because of the broad applications of TD. Dopamine (DA) is an important neurotransmitter and plays a significant role in the function of human metabolism, central nervous, renal and hormonal systems [12]. Abnormal concentrations of DA could cause neurological disorders, Parkinson’s disease, and schizophrenia [13]. Therefore, it is of great importance to develop effective, selective and sensitive approaches to detect DA. Up to now, various analytical methods have been exploited for the detection of DA, such as chromatography coupled with spectroscopy (e.g., high-pressure liquid chromatographymass spectrometry (HPLC–MS)) [14], electrochemistry [15,16], spectrophotometry [17,18], fluorescence [19], chemiluminescence [20,21] and electrochemiluminescence [22–24]. These methods, however, have some limitations. For instance, chromatographic methods are time-consuming, labor intensive, and expensive with complicated procedures. Similarly, the synthesis of fluorescent or colorimetric probes for DA detection involves complicated and
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time-consuming procedures. Electrochemical methods usually suffer from the interferences of uric acid (UA) and ascorbic acid (AA). Although some CL methods have also been reported to detect DA, they involve the use of oxidizing agents and metal ions, making the detection methods less selective [21]. In this study, TD has been developed as the coreactant of lucigenin CL for the first time and the effect of DA on this new CL system was investigated. DA dramatically suppresses the CL of lucigenin/TD. The lucigenin/TD system was used to detect lucigenin, TD and DA with excellent sensitivity. The inhibition mechanism of DA on the CL of lucigenin/TD is discussed and the sensitive detection of DA based on this inhibition mechanism has been demonstrated. This DA detection method is simple, fast and shows excellent selectivity against many compounds, such as ascorbic acid, uric acid, amino acids and sugars. 2. Experimental section 2.1. Materials and apparatus Ascorbic acid and hydrogen peroxide were purchased from Beijing Chemical Reagent Company (Beijing, China). Lucigenin was purchased from TCI (Shanghai, China). TD was obtained from Aladdin (Shanghai, China). Lysine, aspartic acid, alanine, arginine, uric acid, glucose and sucrose were purchased from Sinopharm Chemical Reagent Co. Ltd. (Beijing, China). Lucigenin stock solution (1.0 mM) was prepared by dissolving 0.0510 g lucigenin in 100 mL water. All the chemicals were analytical-reagent grade and were used without further purification. Doubly distilled water was used throughout all experiments. The CL was measured by a flow injection CL system consisting of a Biophysics Chemiluminescence (BPCL) ultra-weak luminescence analyzer (the Institute of Biophysics, Chinese Academic of Sciences), an intelligent flow injection sampler (IFIS-C mode) (ReMax Inc., Xi’an, China) and a home-made flow cell. The flow cell was put in a light-tight box of the luminescent analyzer. The loop injector was equipped with an injection loop of 50 L. 2.2. Detection procedure for TD Scheme 1 shows the schematic diagram of the flow system for TD detection. 10 M lucigenin in water and 0.5 M NaOH solution were pumped into the flow cell through channels I and II at a flow rate of 2.0 mL/min, respectively. Different concentrations of TD in water were injected through the loop injector.
Fig. 1. The CL intensity-time curves for the lucigenin/H2 O2 (red line) and lucigenin/TD systems (blue line). Inset: enlarged CL intensity–time curve for the lucigenin/H2 O2 system. c(lucigenin): 10.0 M; c(TD): 1.0 mM; c(H2 O2 ): 1.0 mM; c(NaOH): 0.5 M; photomultiplier tube voltage: 700 V. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.).
2.4. Detection procedure for dopamine 10 M Lucigenin in water and 0.5 M NaOH solution were pumped into the flow cell through channels I and II at a flow rate of 2.0 mL/min, respectively. Different concentrations of dopamine were mixed with 1.0 mM TD first, and then the mixture were injected through the loop injector. 3. Results and discussion 3.1. Chemiluminescence of lucigenin/TD system Fig. 1 shows the CL intensity-time curves of lucigenin/TD system and lucigenin/H2 O2 system. By comparison, the CL peak intensity of lucigenin/TD system is about 75 times higher than that of lucigenin/H2 O2 system. It indicates that TD is an effective coreactant for lucigenin CL. The CL spectrum of this new system was measured by using various band pass filters at wavelengths of 400 nm, 425 nm, 440 nm, 460 nm, 490 nm, 535 nm, 555 nm, 575 nm, 620 nm, and 640 nm. As shown in Fig. 2, the maximum emission wavelength is about 490 nm, which is consistent with the typical
2.3. Detection procedure for lucigenin 10 mM TD in water and 0.5 M NaOH solution were pumped into the flow cell through channels I and II at a flow rate of 2.0 mL/min, respectively. Different concentrations of lucigenin in water were injected through the loop injector.
Scheme 1. A schematic diagram of the flow system for this CL system.
Fig. 2. CL spectrum of lucigenin/TD system. c(lucigenin): 10.0 M; c(TD): 1.0 mM; c(NaOH): 0.5 M; photomultiplier tube voltage: 1000 V.
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Fig. 4. Linear calibration curve of DA. I represents the CL intensity of the system at a specific concentration of DA, I0 represents the CL intensity of the control sample. c(lucigenin): 10.0 M; c(TD): 1.0 mM; c(NaOH): 0.5 M; c(DA): 0, 0.02, 0.05, 0.1, 0.2, 0.4, 0.6 and 0.8 M; photomultiplier tube voltage: 1000 V.
Scheme 2. Reaction mechanism for the lucigenin/TD CL system.
maximum emission wavelength of lucigenin CL. The possible reaction mechanism is shown in Scheme 2. It has been reported that TD can tautamerize and liberate oxygen in aqueous solutions (Eq. (1) in Scheme 2)[10]. The hyproperoxide intermediate (compound A in Eq. (1)) generated from the decomposition of TD in alkaline solutions may oxidize lucigenin to produce dioxetane as shown in Eq. (2) of Scheme 2. Then the dioxetane produced the primary emitter, singlet N-methylacridone, and subsequently generated strong CL (Eqs. (3) and (4) in Scheme 2). 3.2. Optimization of conditions Lucigenin produces CL in basic media, such as, in the solution of sodium hydroxide, and the concentration of sodium hydroxide has significant effect on the CL intensities. So we tested CL intensities of lucigenin/TD system in different concentrations of NaOH solution. As shown in Fig. 3, the CL intensities increase with increasing concentrations of NaOH. This may be attributed to the faster
Fig. 3. Dependence of CL intensities on the concentrations of NaOH. c(TD): 10.0 mM; c(lucigenin): 0.1 mM; c(NaOH): 0.05, 0.1, 0.2, 0.5, 1.0, 2.0, 5.0 and 10.0 M; photomultiplier tube voltage: 500 V.
generation of effective hyproperoxide intermediates from TD at higher pH. The CL intensities increase less rapidly at NaOH concentrations higher than 0.5 M. Therefore, 0.5 M NaOH was used in subsequent experiments. 3.3. Detection for TD and lucigenin In order to evaluate the performance of this new CL system, we tested different concentrations of TD and lucigenin. The logarithm of CL intensities (logI) has good linear relationship with logarithm of concentrations of TD (logc) from 0.01 to 10 mM with correlation coefficient (r) of 0.9985 (Fig. S1). The linear equation is logI = 3.77 + 1.40 logc (where c is the concentration in mM). The limit of detection (LOD) for TD is calculated to be 2.4 M at a signalto-noise ratio of 3. Moreover, the logarithm of CL intensities (logI) has good linear relationship with logarithm of concentrations of lucigenin (logc) from 20 nM to 0.1 mM (Fig. S2). The linear equation is logI = 8.48 + 1.01 logc (where c is the concentration in M) (r = 0.9970). The LOD at a signal-to-noise ratio of 3 is 8.0 nM, which
Fig. 5. Selectivity for the detection of DA. DA concentration is 0.6 M and concentration of other substances is 10.0 M. I represents the CL intensity of the system after the addition of DA and other substances, I0 represents the CL intensity of the control sample. c(lucigenin): 10.0 M; c(TD): 1.0 mM; c(NaOH): 0.5 M; photomultiplier tube voltage: 1000 V. (Glc, glucose; Suc, sucrose; Lys, lysine; Asp, aspartic acid; Ala, alanine; Arg, arginine).
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Table 1 Comparison of different methods for DA detection. Methods
Probes
Linear range
LOD
Ref.
Fluorescence Colorimetry Surface Plasmon Resonance Electrochemistry Electrochemiluminescence Chemiluminescence Chemiluminescence
Polydopamine Nanoparticles Gold nanoparticles Silver nanoparticles Tyrosinase/NiO/ITO electrode CdSeTe/ZnS core–shell quantum dots Luminol–H2 O2 -HKUST-1 Lucigenin/TD
0.5 − 20 M 0 − 1 M 0.2 − 30 M 2 − 100 M 0.375 − 450 M 0.01 − 0.7 M 0.02 − 0.8 M
40 nM 33 nM 20 nM 1.0 M 100 nM 2.3 nM 14.7 nM
30 34 32 31 29 33 This work
is comparable to the best LOD of other reported lucigenin detection methods using lucigenin/H2 O2 system [25]. 3.4. Detection for dopamine We investigated the effect of DA concentrations on the CL intensities of the lucigenin/TD system. The experiment results show that DA can significantly decrease the CL intensities of the lucigenin/TD system. The relationship between the CL quenching efficiencies and the concentrations of DA was analyzed by the Stern–Volmer equation [26–29]: I 0 /I = 1 + K SV c where I0 represents the CL intensity of the control sample, I represents the CL intensity at a specific concentration of quencher, c is the concentration of DA and KSV is the Stern−Volmer quenching constant. The Stern–Volmer plot shown in Fig. 4 shows a linear relationship between I0 /I and the concentrations of DA from 0.02 to 0.8 M. The linear equation is I0 /I = 0.99 + 1.78c (where c is the concentration in M) (r = 0.9950). The quenching constant is 1.78. The LOD is calculated to be 14.7 nM at a signal-to-noise ratio of 3. Relative standard deviations (RSD) of three consecutive experiments are between 0.2% and 2.1%, indicating the good reproducibility of this detection method. These results indicate that this proposed CL method has good linearity and high sensitivity towards the quantitative determination of DA. In comparison with other reported CL methods for the detection of DA (Table 1) [29–34], the present work is simpler, avoiding the troubles of preparing specific luminescent materials or catalysts. 3.5. Selectivity of dopamine detection We tested the selectivity of the newly-developed DA detection method using compounds, such as AA, UA, amino acids and sugars. The concentration of interfering substances investigated is 10.0 M, while the concentration of DA is 0.6 M. As shown in Fig. 5, the CL intensity decreases dramatically in the presence of DA. In contrast, CL intensities change negligibly in the presence of other substances. The results suggest that the DA detection method based on the lucigenin/TD CL system has nice selectivity. 4. Conclusions Lucigenin CL using an eco-friendly, stable and cheap coreactant TD has been reported for the first time. The CL intensities of the lucigenin/TD system can be significantly decreased by DA. The newly-developed lucigenin/TD CL system enables the highly sensitive detection of lucigenin, TD and DA. Moreover, the lucigenin/TD CL system exhibit excellent selectivity for the detection of DA against substances, such as AA, UA, amino acids and sugars. Because of the popularity of lucigenin CL, the newly found user-friendly lucigenin/thiourea dioxide system may find broad applications.
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Biographies Wenyue Gao received her B. S. degree from Shandong Normal University in 2012. Currently she is a Ph. D. student under the guidance of Prof. Guobao Xu at Changchun Institute of Applied Chemistry, Chinese Academy of Sciences. Her research interests focus on electroanalytical applications of nanomaterials, chemiluminescence, electrochemiluminescence and fluorescence. Liming Qi received her B. S. degree from Jilin University in 2013. Currently she is a Ph. D. student under the guidance of Prof. Guobao Xu at Changchun Institute of Applied Chemistry, Chinese Academy of Sciences. Her current research interests include electroanalytical chemistry, electrochemiluminescence and chemiluminescence, and electrochemical devices. Zhongyuan Liu obtained both her BSc and MSc in chemistry from Southwest University. She joined Changchun Institute of Applied Chemistry as an assistant professor in 2009. Her research interests focus on electrochemiluminescence, electrochemistry, aptasensors and immunosensors. Saadat Majeed obtained her Ph.D under the supervision of Professor Guobao Xu at State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences. Her main current interests are synthesis and luminescent applications of quantum dots, carbon nanomaterials and biosensors. Shimeles Addisu Kitte received his BSc and MSc degree from Jimma University, Ethiopia in 2008 and 2011, respectively. Currently he is a Ph. D. student under the guidance of Prof. Guobao Xu at Changchun Institute of Applied Chemistry, Chinese Academy of Sciences. His current research interests include electroanalytical chemistry, applications of nanomaterials, chemiluminescence and electrochemiluminescence. Guobao Xu received his BSc, MSc, and PhD from Jilin University, Xiamen University, and Changchun Institute of Applied Chemistry, respectively. He did postdoctoral research at the University of Hong Kong, the Hong Kong Polytechnic University, and NTT. He is a professor of the State Key Laboratory of Electroanalytical Chemistry. His research focuses on electrochemiluminescence, biosensors and nanomaterial-based bioanalysis.