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A ratiometric magnesium sensor using DNAzyme-templated CdTe quantum dots and Cy5
Sensors & Actuators: B. Chemical 272 (2018) 146–150
Contents lists available at ScienceDirect
Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb
A ratiometric magnesium sensor using DNAzyme-templated CdTe quantum dots and Cy5
T
⁎
Jidong Wanga, , Xiaoyu Wanga, Hengshan Tanga, Shengquan Hea, Zehua Gaoa, Ruixu Niua, ⁎ Yue Zhengb, Shumin Hana,c, a
Hebei Key Laboratory of Applied Chemistry, School of Environmental and Chemical Engineering, Yanshan University, Qinhuangdao 066004, China The First Hospital in Qinhuangdao Affiliated to Hebei Medical University, Qinhuangdao 066004, China c State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, China b
A R T I C LE I N FO
A B S T R A C T
Keywords: Ratiometric sensor One-step synthesis DNAzyme-templated CdTe QDs Cy5 Mg2+ detection
DNAzyme-templated CdTe quantum dots (DNAzyme-CdTe QDs) were synthesized through a facile one- step route and the obtained QDs were used to fabricate a novel ratiometric magnesium sensor. Crosslinking and surface modification process of QDs were not the necessary step in this synthesis. By catalyzing the DNAzyme sensing system, composed of DNAzyme- CdTe QDs and Cy5 labeled substrate strand, Mg2+ was detected. The fluorescent intensity ratio between CdTe QDs and Cy5 showed a good linear relationship with Mg2+concentration. The sensor displayed a wide range of linear response (0–20 nM), low detection limit (0.3 nM, (S/N = 3)), good reproducibility, stability and selectivity.
1. Introduction DNAzymes as an artificial deoxyribozyme, due to their highly specific and sensitive for metal ions, have conjugated with various signaling transduction strategies to detect metal ions [1–5]. Semiconductor quantum dots (QDs), for their excellent optical characters and outstanding signal transduction capacity, have attracted great interest in the biosensing community [6–8]. These unique characters make DNAzyme-QDs system as a promising platform using for detecting metal ions in environmental samples and imaging in living cells [9–12]. However, so far, during the synthesis process of DNAzyme-QDs, Crosslinking and surface modification of QDs by specific cross-linking agent, such as EDC/NHS et al., is the essential and prior step. Magnesium ion, as an alkaline earth metal ion, plays an essential role in biological activities. However, due to lack of specific recognizing probe, the efficient methods for detecting Mg2+ are limited. Herein, we reported a ratiometric sensing synthesis for detecting Mg2+ using Mg2+-dependent DNAzyme- CdTe QDs and Cy5. A facile one-step approach was proposed to synthesize DNAzyme- CdTe QDs, in which the process of crosslinking and surface modification with DNAzyme was not the necessary step. Two different domains were designed in the modified DNAzyme strand, including phosphorothioates(ps) and phosphates (po) backbone which served as synthetic agent and corresponding DNAzyme strand, respectively. After DNAzyme strand had hybridized
⁎
with Cy5- labeled DNAzyme substrate strand (S-DNA), the fluorescence of CdTe QDs was quenched by Cy5 due to fluorescence resonance energy transfer(FRET) between QDs and Cy5. When Mg2+ was added into the sensing system, the DNAzyme was catalyzed and substrate strand was cleaved. The small DNA segment with Cy5 fled into solution so that the fluorescence of CdTe QDs recovered. The ratio of signal intensity between QDs and Cy5 showed a good linear relationship with Mg2+ concentration. Therefore, a novel biosensor for detecting Mg2+ was obtained (Scheme 1). 2. Experimental 2.1. Materials and reagents Sodium borohydride (NaBH4, 98%), sodium hydroxide (NaOH, 96%), anhydrous ethanol (99.7%), Cadmium chloride (CdCl2, 99%), anhydrous magnesium chloride (MgCl2, 99%), 3-mercaptopropionic acid (MPA, 98%), Tris-HCl buffer solution, sodium borohydride (NaBH4, 95%), sodium tellurite (NaTeO3, 99.0%) were obtained from Alfa Aesar. DNAzyme: G*G*G*G*G AAAAATTTTGTCAGCGAT CCGGA ACGGC ACCCATGTGAGAGAA (* indicates the phosphorothioate linkage) and S-DNA: T TCT CTC T rA G GAC AAA A-Cy5 were synthesized by Shanghai Sangon Biotechnology Co. Ltd.
Corresponding authors at: College of Environmental and Chemical Engineering, Yanshan University, Qinhuangdao, 066004, China. E-mail addresses: [email protected] (J. Wang), [email protected] (X. Wang), [email protected] (H. Tang), [email protected] (S. He), [email protected] (Z. Gao), [email protected] (R. Niu), [email protected] (Y. Zheng), [email protected] (S. Han). https://doi.org/10.1016/j.snb.2018.05.162 Received 1 October 2017; Received in revised form 17 May 2018; Accepted 28 May 2018 Available online 29 May 2018 0925-4005/ © 2018 Elsevier B.V. All rights reserved.
Sensors & Actuators: B. Chemical 272 (2018) 146–150
J. Wang et al.
Scheme 1. Schematic illustration for one-pot synthesized DNAzyme-CdTe QDs for highly sensitive detection of Mg2+.
2.2. Apparatus
3. Results and discussion
UV–vis absorption spectroscopy and fluorescence spectrum measurements were recorded on a UV-2550 (Shimadzu, Kyoto, Japan) and F-7000 (Hitachi, Tokyo, Japan). Transmission electron microscopic (TEM) was obtained by a HT7700 transmission electron microscope (Hitachi, Tokyo, Japan). FTIR spectral analysis was recorded by a Nicolet iS10 spectrometer (Thermo Fisher Scientific Co., Madison, WI).
3.1. Synthesis and characterization of the DNAzyme – CdTe QDs The synthesis conditions of DNAzyme – CdTe QDs, including the reaction time, pH, the concentration of DNA and the number of ps, were discussed as shown in Fig. 1. The optimum parameters were chosen as follows: the reaction time was 2 h, pH value was 9.0, concentration of DNA1 was 0.03 nM and ps modified G number was five. The distinct exciton absorption peak of DNAzyme – CdTe QDs appeared at 545 nm and a strong fluorescence emission peak was at 607 nm as Fig. 2A shown. The emission spectrum of CdTe QDs would share a broad overlapping with the absorbance of Cy5, because the absorption position peak of Cy5 was about 650 nm as shown in Fig. 2B. The CdTe QDs and Cy5 could be as the donor-acceptor pairs to promise an efficient FRET happened. According to the Peng’s empirical formula [13], we could calculate that the size of CdTe QDs was about 3.1 nm. TEM analysis of as-synthesis QDs also indicated that these QDs had spherical shapes and the average size was about 3.1 nm as shown in Fig. 2C, which was consistent with the calculation of above empirical equation. FT-IR was investigated as shown in Fig. 2D. The functional groups belong to DNAzyme sequence appeared including the stretching vibrations of C]O (1560 cm−1) and eOH (3436 cm−1), the PeO stretches of the main chain (880 cm−1), the eNH2 feature (1620 cm−1), the out of phase symmetrical stretches (1040 cm−1), and the asymmetric stretching vibrations of the PO2−(1380 cm−1). The results confirmed that the DNAzyme strand as ligand agent had participated in the synthesis and had successfully coordinated on the surface of CdTe QDs.
2.3. Preparation of DNAzyme – templated CdTe QDs CdCl2 (0.0183 g), MPA (0.0106 g) and deionized water (50 mL) were loaded in flask together. The mixture solution agitated and pH value was adjusted to 9.0. Then, Na2TeO3 (0.0056 g) and NaBH4 (0.0189 g) were added to provide a Cd2+ to MPA to TeO32− molar ratio of 1:1:0.25 solution. 10 μL DNAzyme (10 μM) was added in 1 mL above mixture solution and heated to 90 °C. The crude DNAzyme-CdTe QDs samples were washed by deionized water and alcohol three times.
2.4. Establishment of the sensing system for Mg2+ 160 μL DNAzyme – CdTe QDs (about 50 μM) and 160 μL S-DNA-Cy5 with some concentration complementary strand were successively added into 0.5 mL calibrated test tube. Then the solution was diluted to 400 μL with Tris-HCl (pH 8.0, 0.1 mol/L) followed by the shaking and incubating for some time at 37 °C. Then, 20 μL Mg2+ (0, 1, 5, 10, 20, 40, 100, 500 nM) was added and shaked for 60 min. The PL intensity was investigated by fluorescence spectrum (λex = 485 nm). 147
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Fig. 1. Optimization of parameter for the synthesis of DNAzyme – CdTe QDs, (A) the reaction time, (B) pH, (C) the concentration of DNA and (D)the number of ps.
Fig. 2. (A) UV-vis and fluorescent emission spectra of DNAzyme-CdTe QDs. (B) Fluorescence emission of DNAzyme – CdTe QDs and UV-vis spectrum of Cy5 solution. The excitation wavelength was set to 485 nm (C)TEM image of DNAzyme-CdTe QDs (D) The FT-IR spectra of DNA1-CdTe QDs. 148
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Fig. 3. (A) Fluorescence emission spectra of DNAzyme – CdTe QDs and S-DNA- Cy5 solution upon the addition of different concentration of Mg2+ (respectively 0, 1, 5, 10, 20, 40, 100, 500 nM). (B) The linear plots of IDye/IQDs versus the Mg2+ concentration in the range of 0–20 nM. Measurement in Tris-HCl (pH 8.0, 0.1 mol/L).
Appendix A. Supplementary data
3.2. The fabrication of DNAzyme-CdTe QDs sensing system for detecting Mg2+
Supplementary data associated with this article can be found, in the online version, at https://doi.org/10.1016/j.snb.2018.05.162.
After S-DNA had hybridized with DNAzyme, the fluorescence intensity of CdTe QDs, whose peak was at 607 nm, decreased gradually with the increase of Cy5, which was 664 nm 10 μM and 3 h were chosen as the best hybridization conditions, after were discussed in Fig. S1A and Fig. S1B. To investigate the influence of Mg2+ on fluorescence intensity, Mg2+ with various concentration (0, 1, 5, 10, 20, 40, 100, 500 nM) was added in the above hybridization system. IDye/IQDs evolved with Mg2+ concentration, which showed a good linear relationship. IDye/IQD = 4.14 + 0.145C (IDye and IQDs was the fluorescence intensity of QDs and Cy5 solution, respectively; C is the concentration of Mg2+, (nM)). The corresponding coefficient is 0.9664. The line ranges from 0 to 20 nM and the detection limit was 0.3 nM (S/ N = 3) (Fig. 3). The reproducibility of sensor was evaluated by DNAzyme – CdTe with 40, 70, 100, μM (DNAzyme – CdTe QDs: S-DNA-Cy5 was about 1:2). The relative standard deviation (RSD) of these batches were 8.0%, 6.4% and 5.2%, respectively. To investigate the stability of sensor, the hybridization mixture solution of DNAzyme – CdTe QDs and S-DNACy5 were stored in the refrigerator at 4 °C. The fluorescence biosensor retained 94% of its original response to Mg2+ after a month storage. To test selectivity, different metal cations were examined. Mg2+ indicated an obvious change in IDye/IQDs, while other metal ions were almost no change (Fig. S1C). The sensor exhibited good selectivity. This sensing system was also applied to the detecting Mg2+ in real water samples from bottled drinking water with the standard addition method. The water samples were spiked with different concentrations of Mg2+. The average recovery was 99–102% as shown in Table S1, which demonstrated that this sensor would meet the requirements for trace analysis of Mg2+ owing to its good precision.
References [1] M.R. Saidur, A.R.A. Aziz, W.J. Basirun, Recent advances in DNAbased electrochemical biosensors for heavy metal ion detection: a review, Biosens. Bioelectron. 90 (2017) 125–139. [2] Y. Du, S. Dong, Nucleic acid biosensors: recent advances and perspectives, Anal. Chem. 89 (2017) 189–215. [3] E. Priyadarshini, N. Pradhan, Gold nanoparticles as efficient sensors in colorimetric detection of toxic metal ions: a review, Sens. Actuators B 238 (2017) 888–902. [4] W. Yun, D. Cai, J. Jiang, P. Zhao, Y. Huang, G. Sang, Enzyme-free and label-free ultra-sensitive colorimetric detection of Pb2+ using molecular beacon and DNAzyme based amplification strategy, Biosens. Bioelectron. 80 (2016) 187–193. [5] M. Hollenstein, C. Hipolito, C. Lam, D. Dietrich, D.M. Perrin, A highly selective DNAzyme sensor for mercuric ions, Angew. Chem. Int. Ed. 47 (23) (2008) 4346–4350. [6] L. Li, J. Liu, X. Yang, Z. Peng, W. Liu, J. Xu, J. Tang, X. He, K. Wang, Quantum dot/ methylene blue FRET mediated NIR fluorescent nanomicelles with large Stokes shift for bioimaging, Chem. Commun. 51 (2015) 14357–14360. [7] E. Sharon, R. Freeman, I. Willner, CdSe/ZnS quantum dots-G-quadruplex/hemin hybrids as optical DNA sensors and aptasensors, Anal. Chem. 82 (2010) 7073–7077. [8] C. Wu, M. Oo, X. Fan, Highly sensitive multiplexed heavy metal detection using quantum-dot labeled DNAzymes, ACS Nano 4 (2010) 5897–5904. [9] H.Y. Liu, Y.B. Lou, F. Zhou, H. Zhu, E.S. Abdel-Halim, J.J. Zhu, An amplified electrochemical strategy using DNA-QDs dendrimer superstructure for the detection of thymine DNA glycosylase activity, Biosens. Bioelectron. 71 (2015) 249–255. [10] Y. Yang, Z. Yuan, X.P. Liu, Q. Liu, C.J. Mao, H.L. Niu, B.K. Jin, S.Y. Zhang, Electrochemical biosensor for Ni2+ detection based on a DNAzyme-CdSe nanocomposite, Biosens. Bioelectron. 77 (2016) 13–18. [11] C.-S. Wu, M.K.K. Oo, X. Fan, Highly sensitive multiplexed heavy metal detection using quantum-dot-labeled DNAzymes, ACS Nano 4 (2010) 5897–5904. [12] H. Wang, R.H. Yang, L. Yang, W.H. Tan, Nucleic acid conjugated nanomaterials for enhanced molecular recognition, ACS Nano 3 (2009) 2451–2460. [13] W.W. Yu, L.H. Qu, W.Z. Guo, X.G. Peng, Experimental determination of the extinction coefficient of CdTe, CdSe and CdS nanocrystals, Chem. Mater. 16 (2004) 560. Jidong Wang received his Ph.D. in chemical engineering and technology in 2013 at Yanshan University, China. He is currently working as an associate professor at Hebei Key Laboratory of Applied Chemistry, School of Environmental and Chemical Engineering, Yanshan University, China. His research interests are the synthesis of semiconductor nanomaterials and organic functional materials and the research of new materials applications in biosensor.
4. Conclusions DNAzyme- templated CdTe QDs were successfully synthesized via a facile one-step route. The obtained QDs were used to fabricate ratiometric magnesium sensor, which showed a wide range of linear response (0–20 nM), low detection limit (0.3 nM, (S/N = 3)), good reproducibility stability and selectivity. This one-step synthesis of DNAzyme- CdTe QDs and the novel construction of ratiometric magnesium sensor would provide a promising and common approach in the nanomaterials synthesis and metal ions detection.
Xiaoyu Wang received his bachelor's degree in chemical engineering and technology in 2015 at school of environmental and chemical engineering, Yanshan University, China. He is currently studying as a graduate student at Yanshan University. His research interests are the synthesis of semiconductor nanomaterials and their applications in electrochemical biosensor.
Acknowledgments
Hengshan Tang received his master's degree in chemical engineering in 2017 at school of environmental and chemical engineering, Yanshan University, China. He is currently working as a patent agent at Guangzhou huajin joint patent trademark agency co. LTD. His current research interests focus on the patent writing.
This research was supported by the Natural Science Foundation of Hebei Province (H2015203231), Youth Foundation Project supported by the Hebei Education Department of China (QN2014004), the Key Research and Development Program of Qin Huangdao (201602A110), Doctoral Fund of Yanshan University (B821).
Shengquan He received his bachelor's degree in chemical engineering and technology in 2016 at school of light industry department, Hubei University of Technology, China. He is currently studying as a graduate student at Yanshan University. His research interests are focus on antineoplastic drugs.
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Yue Zheng received master's degree in Hebei Medical University, China. He is currently working as a professor at the First Hospital in Qinhuangdao Affiliated to Hebei Medical University, China. Her research interests are fabrication of biosensor and the detection of tumor mark and trace metal ions.
Zehua Gao received his bachelor's degree in chemical engineering and technology in 2016 at Institute of Petrochemical Technology from Changzhou University, China. He is currently studying as a graduate student at Yanshan University. His current research interests focus on biosensors.
Shumin Han received his Ph.D. in chemical engineering and technology from Yanshan University, China. He is currently working as a professor at Yanshan University. His current research interests focus on the synthesis of functional semiconductor and polymer materials.
Ruixu Niu received her bachelor's degree in Liren College of Yanshan University in 2016. She is currently studying as a graduate student at Yanshan University. Her research interests are cell microscopic imaging.
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Contents lists available at ScienceDirect
Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb
A ratiometric magnesium sensor using DNAzyme-templated CdTe quantum dots and Cy5
T
⁎
Jidong Wanga, , Xiaoyu Wanga, Hengshan Tanga, Shengquan Hea, Zehua Gaoa, Ruixu Niua, ⁎ Yue Zhengb, Shumin Hana,c, a
Hebei Key Laboratory of Applied Chemistry, School of Environmental and Chemical Engineering, Yanshan University, Qinhuangdao 066004, China The First Hospital in Qinhuangdao Affiliated to Hebei Medical University, Qinhuangdao 066004, China c State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, China b
A R T I C LE I N FO
A B S T R A C T
Keywords: Ratiometric sensor One-step synthesis DNAzyme-templated CdTe QDs Cy5 Mg2+ detection
DNAzyme-templated CdTe quantum dots (DNAzyme-CdTe QDs) were synthesized through a facile one- step route and the obtained QDs were used to fabricate a novel ratiometric magnesium sensor. Crosslinking and surface modification process of QDs were not the necessary step in this synthesis. By catalyzing the DNAzyme sensing system, composed of DNAzyme- CdTe QDs and Cy5 labeled substrate strand, Mg2+ was detected. The fluorescent intensity ratio between CdTe QDs and Cy5 showed a good linear relationship with Mg2+concentration. The sensor displayed a wide range of linear response (0–20 nM), low detection limit (0.3 nM, (S/N = 3)), good reproducibility, stability and selectivity.
1. Introduction DNAzymes as an artificial deoxyribozyme, due to their highly specific and sensitive for metal ions, have conjugated with various signaling transduction strategies to detect metal ions [1–5]. Semiconductor quantum dots (QDs), for their excellent optical characters and outstanding signal transduction capacity, have attracted great interest in the biosensing community [6–8]. These unique characters make DNAzyme-QDs system as a promising platform using for detecting metal ions in environmental samples and imaging in living cells [9–12]. However, so far, during the synthesis process of DNAzyme-QDs, Crosslinking and surface modification of QDs by specific cross-linking agent, such as EDC/NHS et al., is the essential and prior step. Magnesium ion, as an alkaline earth metal ion, plays an essential role in biological activities. However, due to lack of specific recognizing probe, the efficient methods for detecting Mg2+ are limited. Herein, we reported a ratiometric sensing synthesis for detecting Mg2+ using Mg2+-dependent DNAzyme- CdTe QDs and Cy5. A facile one-step approach was proposed to synthesize DNAzyme- CdTe QDs, in which the process of crosslinking and surface modification with DNAzyme was not the necessary step. Two different domains were designed in the modified DNAzyme strand, including phosphorothioates(ps) and phosphates (po) backbone which served as synthetic agent and corresponding DNAzyme strand, respectively. After DNAzyme strand had hybridized
⁎
with Cy5- labeled DNAzyme substrate strand (S-DNA), the fluorescence of CdTe QDs was quenched by Cy5 due to fluorescence resonance energy transfer(FRET) between QDs and Cy5. When Mg2+ was added into the sensing system, the DNAzyme was catalyzed and substrate strand was cleaved. The small DNA segment with Cy5 fled into solution so that the fluorescence of CdTe QDs recovered. The ratio of signal intensity between QDs and Cy5 showed a good linear relationship with Mg2+ concentration. Therefore, a novel biosensor for detecting Mg2+ was obtained (Scheme 1). 2. Experimental 2.1. Materials and reagents Sodium borohydride (NaBH4, 98%), sodium hydroxide (NaOH, 96%), anhydrous ethanol (99.7%), Cadmium chloride (CdCl2, 99%), anhydrous magnesium chloride (MgCl2, 99%), 3-mercaptopropionic acid (MPA, 98%), Tris-HCl buffer solution, sodium borohydride (NaBH4, 95%), sodium tellurite (NaTeO3, 99.0%) were obtained from Alfa Aesar. DNAzyme: G*G*G*G*G AAAAATTTTGTCAGCGAT CCGGA ACGGC ACCCATGTGAGAGAA (* indicates the phosphorothioate linkage) and S-DNA: T TCT CTC T rA G GAC AAA A-Cy5 were synthesized by Shanghai Sangon Biotechnology Co. Ltd.
Corresponding authors at: College of Environmental and Chemical Engineering, Yanshan University, Qinhuangdao, 066004, China. E-mail addresses: [email protected] (J. Wang), [email protected] (X. Wang), [email protected] (H. Tang), [email protected] (S. He), [email protected] (Z. Gao), [email protected] (R. Niu), [email protected] (Y. Zheng), [email protected] (S. Han). https://doi.org/10.1016/j.snb.2018.05.162 Received 1 October 2017; Received in revised form 17 May 2018; Accepted 28 May 2018 Available online 29 May 2018 0925-4005/ © 2018 Elsevier B.V. All rights reserved.
Sensors & Actuators: B. Chemical 272 (2018) 146–150
J. Wang et al.
Scheme 1. Schematic illustration for one-pot synthesized DNAzyme-CdTe QDs for highly sensitive detection of Mg2+.
2.2. Apparatus
3. Results and discussion
UV–vis absorption spectroscopy and fluorescence spectrum measurements were recorded on a UV-2550 (Shimadzu, Kyoto, Japan) and F-7000 (Hitachi, Tokyo, Japan). Transmission electron microscopic (TEM) was obtained by a HT7700 transmission electron microscope (Hitachi, Tokyo, Japan). FTIR spectral analysis was recorded by a Nicolet iS10 spectrometer (Thermo Fisher Scientific Co., Madison, WI).
3.1. Synthesis and characterization of the DNAzyme – CdTe QDs The synthesis conditions of DNAzyme – CdTe QDs, including the reaction time, pH, the concentration of DNA and the number of ps, were discussed as shown in Fig. 1. The optimum parameters were chosen as follows: the reaction time was 2 h, pH value was 9.0, concentration of DNA1 was 0.03 nM and ps modified G number was five. The distinct exciton absorption peak of DNAzyme – CdTe QDs appeared at 545 nm and a strong fluorescence emission peak was at 607 nm as Fig. 2A shown. The emission spectrum of CdTe QDs would share a broad overlapping with the absorbance of Cy5, because the absorption position peak of Cy5 was about 650 nm as shown in Fig. 2B. The CdTe QDs and Cy5 could be as the donor-acceptor pairs to promise an efficient FRET happened. According to the Peng’s empirical formula [13], we could calculate that the size of CdTe QDs was about 3.1 nm. TEM analysis of as-synthesis QDs also indicated that these QDs had spherical shapes and the average size was about 3.1 nm as shown in Fig. 2C, which was consistent with the calculation of above empirical equation. FT-IR was investigated as shown in Fig. 2D. The functional groups belong to DNAzyme sequence appeared including the stretching vibrations of C]O (1560 cm−1) and eOH (3436 cm−1), the PeO stretches of the main chain (880 cm−1), the eNH2 feature (1620 cm−1), the out of phase symmetrical stretches (1040 cm−1), and the asymmetric stretching vibrations of the PO2−(1380 cm−1). The results confirmed that the DNAzyme strand as ligand agent had participated in the synthesis and had successfully coordinated on the surface of CdTe QDs.
2.3. Preparation of DNAzyme – templated CdTe QDs CdCl2 (0.0183 g), MPA (0.0106 g) and deionized water (50 mL) were loaded in flask together. The mixture solution agitated and pH value was adjusted to 9.0. Then, Na2TeO3 (0.0056 g) and NaBH4 (0.0189 g) were added to provide a Cd2+ to MPA to TeO32− molar ratio of 1:1:0.25 solution. 10 μL DNAzyme (10 μM) was added in 1 mL above mixture solution and heated to 90 °C. The crude DNAzyme-CdTe QDs samples were washed by deionized water and alcohol three times.
2.4. Establishment of the sensing system for Mg2+ 160 μL DNAzyme – CdTe QDs (about 50 μM) and 160 μL S-DNA-Cy5 with some concentration complementary strand were successively added into 0.5 mL calibrated test tube. Then the solution was diluted to 400 μL with Tris-HCl (pH 8.0, 0.1 mol/L) followed by the shaking and incubating for some time at 37 °C. Then, 20 μL Mg2+ (0, 1, 5, 10, 20, 40, 100, 500 nM) was added and shaked for 60 min. The PL intensity was investigated by fluorescence spectrum (λex = 485 nm). 147
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Fig. 1. Optimization of parameter for the synthesis of DNAzyme – CdTe QDs, (A) the reaction time, (B) pH, (C) the concentration of DNA and (D)the number of ps.
Fig. 2. (A) UV-vis and fluorescent emission spectra of DNAzyme-CdTe QDs. (B) Fluorescence emission of DNAzyme – CdTe QDs and UV-vis spectrum of Cy5 solution. The excitation wavelength was set to 485 nm (C)TEM image of DNAzyme-CdTe QDs (D) The FT-IR spectra of DNA1-CdTe QDs. 148
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Fig. 3. (A) Fluorescence emission spectra of DNAzyme – CdTe QDs and S-DNA- Cy5 solution upon the addition of different concentration of Mg2+ (respectively 0, 1, 5, 10, 20, 40, 100, 500 nM). (B) The linear plots of IDye/IQDs versus the Mg2+ concentration in the range of 0–20 nM. Measurement in Tris-HCl (pH 8.0, 0.1 mol/L).
Appendix A. Supplementary data
3.2. The fabrication of DNAzyme-CdTe QDs sensing system for detecting Mg2+
Supplementary data associated with this article can be found, in the online version, at https://doi.org/10.1016/j.snb.2018.05.162.
After S-DNA had hybridized with DNAzyme, the fluorescence intensity of CdTe QDs, whose peak was at 607 nm, decreased gradually with the increase of Cy5, which was 664 nm 10 μM and 3 h were chosen as the best hybridization conditions, after were discussed in Fig. S1A and Fig. S1B. To investigate the influence of Mg2+ on fluorescence intensity, Mg2+ with various concentration (0, 1, 5, 10, 20, 40, 100, 500 nM) was added in the above hybridization system. IDye/IQDs evolved with Mg2+ concentration, which showed a good linear relationship. IDye/IQD = 4.14 + 0.145C (IDye and IQDs was the fluorescence intensity of QDs and Cy5 solution, respectively; C is the concentration of Mg2+, (nM)). The corresponding coefficient is 0.9664. The line ranges from 0 to 20 nM and the detection limit was 0.3 nM (S/ N = 3) (Fig. 3). The reproducibility of sensor was evaluated by DNAzyme – CdTe with 40, 70, 100, μM (DNAzyme – CdTe QDs: S-DNA-Cy5 was about 1:2). The relative standard deviation (RSD) of these batches were 8.0%, 6.4% and 5.2%, respectively. To investigate the stability of sensor, the hybridization mixture solution of DNAzyme – CdTe QDs and S-DNACy5 were stored in the refrigerator at 4 °C. The fluorescence biosensor retained 94% of its original response to Mg2+ after a month storage. To test selectivity, different metal cations were examined. Mg2+ indicated an obvious change in IDye/IQDs, while other metal ions were almost no change (Fig. S1C). The sensor exhibited good selectivity. This sensing system was also applied to the detecting Mg2+ in real water samples from bottled drinking water with the standard addition method. The water samples were spiked with different concentrations of Mg2+. The average recovery was 99–102% as shown in Table S1, which demonstrated that this sensor would meet the requirements for trace analysis of Mg2+ owing to its good precision.
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4. Conclusions DNAzyme- templated CdTe QDs were successfully synthesized via a facile one-step route. The obtained QDs were used to fabricate ratiometric magnesium sensor, which showed a wide range of linear response (0–20 nM), low detection limit (0.3 nM, (S/N = 3)), good reproducibility stability and selectivity. This one-step synthesis of DNAzyme- CdTe QDs and the novel construction of ratiometric magnesium sensor would provide a promising and common approach in the nanomaterials synthesis and metal ions detection.
Xiaoyu Wang received his bachelor's degree in chemical engineering and technology in 2015 at school of environmental and chemical engineering, Yanshan University, China. He is currently studying as a graduate student at Yanshan University. His research interests are the synthesis of semiconductor nanomaterials and their applications in electrochemical biosensor.
Acknowledgments
Hengshan Tang received his master's degree in chemical engineering in 2017 at school of environmental and chemical engineering, Yanshan University, China. He is currently working as a patent agent at Guangzhou huajin joint patent trademark agency co. LTD. His current research interests focus on the patent writing.
This research was supported by the Natural Science Foundation of Hebei Province (H2015203231), Youth Foundation Project supported by the Hebei Education Department of China (QN2014004), the Key Research and Development Program of Qin Huangdao (201602A110), Doctoral Fund of Yanshan University (B821).
Shengquan He received his bachelor's degree in chemical engineering and technology in 2016 at school of light industry department, Hubei University of Technology, China. He is currently studying as a graduate student at Yanshan University. His research interests are focus on antineoplastic drugs.
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Yue Zheng received master's degree in Hebei Medical University, China. He is currently working as a professor at the First Hospital in Qinhuangdao Affiliated to Hebei Medical University, China. Her research interests are fabrication of biosensor and the detection of tumor mark and trace metal ions.
Zehua Gao received his bachelor's degree in chemical engineering and technology in 2016 at Institute of Petrochemical Technology from Changzhou University, China. He is currently studying as a graduate student at Yanshan University. His current research interests focus on biosensors.
Shumin Han received his Ph.D. in chemical engineering and technology from Yanshan University, China. He is currently working as a professor at Yanshan University. His current research interests focus on the synthesis of functional semiconductor and polymer materials.
Ruixu Niu received her bachelor's degree in Liren College of Yanshan University in 2016. She is currently studying as a graduate student at Yanshan University. Her research interests are cell microscopic imaging.
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