Nitrogen-Doped Carbon Nanoparticles Derived from Silkworm Excrement as On–Off–On Fluorescent Sensors to Detect Fe(III) and Biothiols
<p>A schematic illustration of the formation of nitrogen-doped CNPs (N-CNPs) from silkworm excrement, and the fluorescence “on–off–on” detection of Fe(III) and biothiols.</p> "> Figure 2
<p>Transmission electron microscopy (TEM) image (<b>a</b>); the particle size distribution histogram (<b>b</b>); X-ray diffraction (XRD) pattern (<b>c</b>); and fourier transform infrared (FT-IR) spectrum (<b>d</b>) of N-CNPs.</p> "> Figure 3
<p>X-ray photoelectron spectroscopy (XPS) full survey (<b>a</b>); C 1s (<b>b</b>); N 1s (<b>c</b>) and O 1s (<b>d</b>) spectra of N-CNPs. Black line: raw, navy line: background, other lines: fitting.</p> "> Figure 4
<p>Ultraviolet-visible (UV-vis) absorption spectrum (<b>a</b>) and photoluminescent (PL) emission spectra at different excitation wavelengths (<b>b</b>) of N-CNPs. Inset: photographs of N-CNPs in water under daylight and UV irradiation.</p> "> Figure 5
<p>(<b>a</b>) Selectivity of N-CNPs with different ions at the same concentration (500 μM); (<b>b</b>) The linear relationship between F<sub>0</sub>/F and Fe(III) concentration. F and F<sub>0</sub> were the PL intensities (424 nm) of N-CNPs at 340 nm excitation in the presence and absence of ions, respectively.</p> "> Figure 6
<p>(<b>a</b>) Selectivity of N-CNPs/Fe(III) to different biological molecules at the same concentration (1 mM); (<b>b</b>) The linear relationship between (F’/F’<sub>0</sub>) and the square root of glutathione (GSH) concentration. F’ and F’<sub>0</sub> were the PL intensities (424 nm) of N-CNPs/Fe(III) at 340 nm excitation in the absence and presence of biological molecules, respectively.</p> ">
Abstract
:1. Introduction
2. Materials and Methods
2.1. Materials and Chemicals
2.2. Characterization
2.3. Preparation and Purification of Nitrogen-Doped CNPs (N-CNPs)
2.4. Selectivity and Quantitative Measurements for Fe(III) and Biothiols
2.5. The Detection of Glutathione (GSH) in Fetal Calf Serum Samples
2.6. Quantum Yield (QY) Measurement
3. Results and Discussion
4. Conclusions
Supplementary Materials
Author Contributions
Funding
Conflicts of Interest
References
- Chen, W.; Luo, H.; Liu, X.; Foley, J.W.; Song, X. Broadly Applicable Strategy for the Fluorescence Based Detection and Differentiation of Glutathione and Cysteine/Homocysteine: Demonstration in Vitro and in Vivo. Anal. Chem. 2016, 88, 3638–3646. [Google Scholar] [CrossRef] [PubMed]
- Yin, J.; Kwon, Y.; Kim, D.; Lee, D.; Kim, G.; Hu, Y.; Ryu, J.-H.; Yoon, J. Cyanine-Based Fluorescent Probe for Highly Selective Detection of Glutathione in Cell Cultures and Live Mouse Tissues. J. Am. Chem. Soc. 2014, 136, 5351–5358. [Google Scholar] [CrossRef] [PubMed]
- Labib, M.; Sargent, E.H.; Kelley, S.O. Electrochemical Methods for the Analysis of Clinically Relevant Biomolecules. Chem. Rev. 2016, 116, 9001–9090. [Google Scholar] [CrossRef] [PubMed]
- Gupta, A.; Verma, N.C.; Khan, S.; Nandi, C.K. Carbon dots for naked eye colorimetric ultrasensitive arsenic and glutathione detection. Biosens. Bioelectron. 2016, 81, 465–472. [Google Scholar] [CrossRef] [PubMed]
- Wu, Y.; Liu, X.; Wu, Q.; Yi, J.; Zhang, G. Carbon Nanodots-Based Fluorescent Turn-On Sensor Array for Biothiols. Anal. Chem. 2017, 89, 7084–7089. [Google Scholar] [CrossRef] [PubMed]
- Li, Z.; Zhang, J.; Li, Y.; Zhao, S.; Zhang, P.; Zhang, Y.; Bi, J.; Liu, G.; Yue, Z. Carbon dots based photoelectrochemical sensors for ultrasensitive detection of glutathione and its applications in probing of myocardial infarction. Biosens. Bioelectron. 2018, 99, 251–258. [Google Scholar] [CrossRef] [PubMed]
- Zhou, X.; Zhao, G.; Chen, M.; Gao, W.; Zhou, X.; Xie, X.; Yang, L.; Du, G. Facile and Green Approach to Prepare Nanostructured Au@MnO2 and Its Applications for Catalysis and Fluorescence Sensing of Glutathione in Human Blood. ACS Sustain. Chem. Eng. 2018, 6, 3948–3956. [Google Scholar] [CrossRef]
- Niu, L.-Y.; Guan, Y.-S.; Chen, Y.-Z.; Wu, L.-Z.; Tung, C.-H.; Yang, Q.-Z. BODIPY-Based Ratiometric Fluorescent Sensor for Highly Selective Detection of Glutathione over Cysteine and Homocysteine. J. Am. Chem. Soc. 2012, 134, 18928–18931. [Google Scholar] [CrossRef] [PubMed]
- Pan, J.; Zheng, Z.; Yang, J.; Wu, Y.; Lu, F.; Chen, Y.; Gao, W. A novel and sensitive fluorescence sensor for glutathione detection by controlling the surface passivation degree of carbon quantum dots. Talanta 2017, 166, 1–7. [Google Scholar] [CrossRef] [PubMed]
- Durocher, S.; Rezaee, A.; Hamm, C.; Rangan, C.; Mittler, S.; Mutus, B. Disulfide-Linked, Gold Nanoparticle Based Reagent for Detecting Small Molecular Weight Thiols. J. Am. Chem. Soc. 2009, 131, 2475–2477. [Google Scholar] [CrossRef] [PubMed]
- Janeš, L.; Lisjak, K.; Vanzo, A. Determination of glutathione content in grape juice and wine by high-performance liquid chromatography with fluorescence detection. Anal. Chim. Acta 2010, 674, 239–242. [Google Scholar] [CrossRef] [PubMed]
- Safavi, A.; Maleki, N.; Farjami, E.; Mahyari, F.A. Simultaneous Electrochemical Determination of Glutathione and Glutathione Disulfide at a Nanoscale Copper Hydroxide Composite Carbon Ionic Liquid Electrode. Anal. Chem. 2009, 81, 7538–7543. [Google Scholar] [CrossRef] [PubMed]
- Saha, A.; Jana, N.R. Detection of Cellular Glutathione and Oxidized Glutathione Using Magnetic–Plasmonic Nanocomposite-Based “Turn-Off” Surface Enhanced Raman Scattering. Anal. Chem. 2013, 85, 9221–9228. [Google Scholar] [CrossRef] [PubMed]
- Achadu, O.J.; Nyokong, T. Graphene quantum dots decorated with maleimide and zinc tetramaleimido-phthalocyanine: Application in the design of “OFF-ON” fluorescence sensors for biothiols. Talanta 2017, 166, 15–26. [Google Scholar] [CrossRef] [PubMed]
- Yang, C.; Deng, W.; Liu, H.; Ge, S.; Yan, M. Turn-on fluorescence sensor for glutathione in aqueous solutions using carbon dots–MnO2 nanocomposites. Sens. Actuators B Chem. 2015, 216, 286–292. [Google Scholar] [CrossRef]
- Xu, S.; Liu, Y.; Yang, H.; Zhao, K.; Li, J.; Deng, A. Fluorescent nitrogen and sulfur co-doped carbon dots from casein and their applications for sensitive detection of Hg2+ and biothiols and cellular imaging. Anal. Chim. Acta 2017, 964, 150–160. [Google Scholar] [CrossRef] [PubMed]
- Huang, H.; Weng, Y.; Zheng, L.; Yao, B.; Weng, W.; Lin, X. Nitrogen-doped carbon quantum dots as fluorescent probe for “off-on” detection of mercury ions, l-cysteine and iodide ions. J. Colloid Interface Sci. 2017, 506, 373–378. [Google Scholar] [CrossRef] [PubMed]
- Iqbal, A.; Iqbal, K.; Xu, L.; Li, B.; Gong, D.; Liu, X.; Guo, Y.; Liu, W.; Qin, W.; Guo, H. Heterogeneous synthesis of nitrogen-doped carbon dots prepared via anhydrous citric acid and melamine for selective and sensitive turn on-off-on detection of Hg(II), glutathione and its cellular imaging. Sens. Actuators B Chem. 2018, 255, 1130–1138. [Google Scholar] [CrossRef]
- Ju, J.; Zhang, R.; He, S.; Chen, W. Nitrogen-doped graphene quantum dots-based fluorescent probe for the sensitive turn-on detection of glutathione and its cellular imaging. RSC Adv. 2014, 4, 52583–52589. [Google Scholar] [CrossRef]
- Borse, V.; Thakur, M.; Sengupta, S.; Srivastava, R. N-doped multi-fluorescent carbon dots for ‘turn off-on’ silver-biothiol dual sensing and mammalian cell imaging application. Sens. Actuators B Chem. 2017, 248, 481–492. [Google Scholar] [CrossRef]
- Wang, Y.; Xu, J.; Lei, L.; Wang, F.; Xu, Z.; Zhang, W. Multi-functional carbon dots-based nanoprobe for ratiometric enzyme reaction monitoring and biothiol analysis. Sens. Actuators B Chem. 2018, 264, 296–303. [Google Scholar] [CrossRef]
- Yang, R.; Guo, X.; Jia, L.; Zhang, Y. A fluorescent “on-off-on” assay for selective recognition of Cu(II) and glutathione based on modified carbon nanodots, and its application to cellular imaging. Microchim. Acta 2017, 184, 1143–1150. [Google Scholar] [CrossRef]
- Guo, Y.; Yang, L.; Li, W.; Wang, X.; Shang, Y.; Li, B. Carbon dots doped with nitrogen and sulfur and loaded with copper(II) as a “turn-on” fluorescent probe for cystein, glutathione and homocysteine. Microchim. Acta 2016, 183, 1409–1416. [Google Scholar] [CrossRef]
- Gu, J.; Hu, D.; Wang, W.; Zhang, Q.; Meng, Z.; Jia, X.; Xi, K. Carbon dot cluster as an efficient “off–on” fluorescent probe to detect Au(III) and glutathione. Biosens. Bioelectron. 2015, 68, 27–33. [Google Scholar] [CrossRef] [PubMed]
- Shangguan, J.; Huang, J.; He, D.; He, X.; Wang, K.; Ye, R.; Yang, X.; Qing, T.; Tang, J. Highly Fe3+-Selective Fluorescent Nanoprobe Based on Ultrabright N/P Codoped Carbon Dots and Its Application in Biological Samples. Anal. Chem. 2017, 89, 7477–7484. [Google Scholar] [CrossRef] [PubMed]
- Li, S.; Li, Y.; Cao, J.; Zhu, J.; Fan, L.; Li, X. Sulfur-doped graphene quantum dots as a novel fluorescent probe for highly selective and sensitive detection of Fe3+. Anal. Chem. 2014, 86, 10201–10207. [Google Scholar] [CrossRef] [PubMed]
- Atchudan, R.; Edison, T.N.J.I.; Aseer, K.R.; Perumal, S.; Karthik, N.; Lee, Y.R. Highly fluorescent nitrogen-doped carbon dots derived from Phyllanthus acidus utilized as a fluorescent probe for label-free selective detection of Fe3+ ions, live cell imaging and fluorescent ink. Biosens. Bioelectron. 2018, 99, 303–311. [Google Scholar] [CrossRef] [PubMed]
- Paulo, S.; Palomares, E.; Martinez-Ferrero, E. Graphene and Carbon Quantum Dot-Based Materials in Photovoltaic Devices: From Synthesis to Applications. Nanomaterials 2016, 6, 157. [Google Scholar] [CrossRef] [PubMed]
- Baker, S.N.; Baker, G.A. Luminescent Carbon Nanodots: Emergent Nanolights. Angew. Chem. Int. Ed. 2010, 49, 6726–6744. [Google Scholar] [CrossRef] [PubMed]
- Ding, C.; Zhu, A.; Tian, Y. Functional Surface Engineering of C-Dots for Fluorescent Biosensing and in Vivo Bioimaging. Acc. Chem. Res. 2014, 47, 20–30. [Google Scholar] [CrossRef] [PubMed]
- Georgakilas, V.; Perman, J.A.; Tucek, J.; Zboril, R. Broad Family of Carbon Nanoallotropes: Classification, Chemistry, and Applications of Fullerenes, Carbon Dots, Nanotubes, Graphene, Nanodiamonds, and Combined Superstructures. Chem. Rev. 2015, 115, 4744–4822. [Google Scholar] [CrossRef] [PubMed]
- Lim, S.Y.; Shen, W.; Gao, Z. Carbon quantum dots and their applications. Chem. Soc. Rev. 2015, 44, 362–381. [Google Scholar] [CrossRef] [PubMed]
- Sun, Y.-P.; Zhou, B.; Lin, Y.; Wang, W.; Fernando, K.A.S.; Pathak, P.; Meziani, M.J.; Harruff, B.A.; Wang, X.; Wang, H.; et al. Quantum-Sized Carbon Dots for Bright and Colorful Photoluminescence. J. Am. Chem. Soc. 2006, 128, 7756–7757. [Google Scholar] [CrossRef] [PubMed]
- Luo, Z.; Qi, G.; Chen, K.; Zou, M.; Yuwen, L.; Zhang, X.; Huang, W.; Wang, L. Microwave-Assisted Preparation of White Fluorescent Graphene Quantum Dots as a Novel Phosphor for Enhanced White-Light-Emitting Diodes. Adv. Funct. Mater. 2016, 26, 2739–2744. [Google Scholar] [CrossRef]
- Ting, Z.X.; Arundithi, A.; Qian, L.K.; Peng, C. Glowing Graphene Quantum Dots and Carbon Dots: Properties, Syntheses, and Biological Applications. Small 2015, 11, 1620–1636. [Google Scholar]
- Tao, H.; Yang, K.; Ma, Z.; Wan, J.; Zhang, Y.; Kang, Z.; Liu, Z. In Vivo NIR Fluorescence Imaging, Biodistribution, and Toxicology of Photoluminescent Carbon Dots Produced from Carbon Nanotubes and Graphite. Small 2012, 8, 281–290. [Google Scholar] [CrossRef] [PubMed]
- Ye, R.; Xiang, C.; Lin, J.; Peng, Z.; Huang, K.; Yan, Z.; Cook, N.P.; Samuel, E.L.G.; Hwang, C.-C.; Ruan, G.; et al. Coal as an abundant source of graphene quantum dots. Nat. Commun. 2013, 4, 2943. [Google Scholar] [CrossRef] [PubMed] [Green Version]
- Han, S.; Chang, T.; Zhao, H.; Du, H.; Liu, S.; Wu, B.; Qin, S. Cultivating Fluorescent Flowers with Highly Luminescent Carbon Dots Fabricated by a Double Passivation Method. Nanomaterials 2017, 7, 176. [Google Scholar] [CrossRef] [PubMed]
- Zhu, S.; Meng, Q.; Wang, L.; Zhang, J.; Song, Y.; Jin, H.; Zhang, K.; Sun, H.; Wang, H.; Yang, B. Highly Photoluminescent Carbon Dots for Multicolor Patterning, Sensors, and Bioimaging. Angew. Chem. Int. Ed. 2013, 52, 3953–3957. [Google Scholar] [CrossRef] [PubMed]
- Shi, B.; Su, Y.; Zhang, L.; Huang, M.; Liu, R.; Zhao, S. Nitrogen and Phosphorus Co-Doped Carbon Nanodots as a Novel Fluorescent Probe for Highly Sensitive Detection of Fe3+ in Human Serum and Living Cells. ACS Appl. Mater. Interfaces 2016, 8, 10717–10725. [Google Scholar] [CrossRef] [PubMed]
- Jiang, K.; Sun, S.; Zhang, L.; Lu, Y.; Wu, A.; Cai, C.; Lin, H. Red, Green, and Blue Luminescence by Carbon Dots: Full-Color Emission Tuning and Multicolor Cellular Imaging. Angew. Chem. Int. Ed. 2015, 54, 5360–5363. [Google Scholar] [CrossRef] [PubMed]
- Jiang, K.; Zhang, L.; Lu, J.; Xu, C.; Cai, C.; Lin, H. Triple-Mode Emission of Carbon Dots: Applications for Advanced Anti-Counterfeiting. Angew. Chem. Int. Ed. 2016, 55, 7231–7235. [Google Scholar] [CrossRef] [PubMed]
- Gu, J.; Hu, D.; Huang, J.; Huang, X.; Zhang, Q.; Jia, X.; Xi, K. One-pot synthesis and control of aqueous soluble and organic soluble carbon dots from a designable waterborne polyurethane emulsion. Nanoscale 2016, 8, 3973–3981. [Google Scholar] [CrossRef] [PubMed]
- Hsu, P.-C.; Shih, Z.-Y.; Lee, C.-H.; Chang, H.-T. Synthesis and analytical applications of photoluminescent carbon nanodots. Green Chem. 2012, 14, 917–920. [Google Scholar] [CrossRef]
- Zhang, J.; Yuan, Y.; Liang, G.; Yu, S.-H. Scale-Up Synthesis of Fragrant Nitrogen-Doped Carbon Dots from Bee Pollens for Bioimaging and Catalysis. Adv. Sci. 2015, 2, 1500002. [Google Scholar] [CrossRef] [PubMed] [Green Version]
- Yao, Y.-Y.; Gedda, G.; Girma, W.M.; Yen, C.-L.; Ling, Y.-C.; Chang, J.-Y. Magnetofluorescent Carbon Dots Derived from Crab Shell for Targeted Dual-Modality Bioimaging and Drug Delivery. ACS Appl. Mater. Interfaces 2017, 9, 13887–13899. [Google Scholar] [CrossRef] [PubMed]
- Hu, Y.; Zhang, L.; Li, X.; Liu, R.; Lin, L.; Zhao, S. Green Preparation of S and N Co-Doped Carbon Dots from Water Chestnut and Onion as Well as Their Use as an Off–On Fluorescent Probe for the Quantification and Imaging of Coenzyme, A. ACS Sustain. Chem. Eng. 2017, 5, 4992–5000. [Google Scholar] [CrossRef]
- Lei, S.; Chen, L.; Zhou, W.; Deng, P.; Liu, Y.; Fei, L.; Lu, W.; Xiao, Y.; Cheng, B. Tetra-heteroatom self-doped carbon nanosheets derived from silkworm excrement for high-performance supercapacitors. J. Power Sources 2018, 379, 74–83. [Google Scholar] [CrossRef]
- Wei, Y.; Wu, Y.; Chang, Q.; Xie, M.; Wang, X.; Mo, J.; He, X.; Zhao, Z.; Zhao, Z. Ultrasonic-assisted modification of a novel silkworm-excrement-based porous carbon with various Lewis acid metal ions for the sustained release of the pesticide thiamethoxam. RSC Adv. 2017, 7, 30020–30031. [Google Scholar] [CrossRef] [Green Version]
- Yuan, Y.; Jiang, J.; Liu, S.; Yang, J.; Zhang, H.; Yan, J.; Hu, X. Fluorescent carbon dots for glyphosate determination based on fluorescence resonance energy transfer and logic gate operation. Sens. Actuators B Chem. 2017, 242, 545–553. [Google Scholar] [CrossRef]
- Fang, B.; Wang, P.; Zhu, Y.; Wang, C.; Zhang, G.; Zheng, X.; Ding, C.; Gu, J.; Cao, F. Basophilic green fluorescent carbon nanoparticles derived from benzoxazine for the detection of Cr(vi) in a strongly alkaline environment. RSC Adv. 2018, 8, 7377–7382. [Google Scholar] [CrossRef] [Green Version]
- Shen, C.; Sun, Y.; Wang, J.; Lu, Y. Facile route to highly photoluminescent carbon nanodots for ion detection, pH sensors and bioimaging. Nanoscale 2014, 6, 9139–9147. [Google Scholar] [CrossRef] [PubMed]
- Holá, K.; Sudolská, M.; Kalytchuk, S.; Nachtigallová, D.; Rogach, A.L.; Otyepka, M.; Zbořil, R. Graphitic Nitrogen Triggers Red Fluorescence in Carbon Dots. ACS Nano 2017, 11, 12402–12410. [Google Scholar] [CrossRef] [PubMed]
- Li, F.; Li, T.; Sun, C.; Xia, J.; Jiao, Y.; Xu, H. Selenium-Doped Carbon Quantum Dots for Free-Radical Scavenging. Angew. Chem. Int. Ed. 2017, 56, 9910–9914. [Google Scholar] [CrossRef] [PubMed]
- Wang, H.; Reiva, R.; Wang, K.; Kant, R.J.; Mu, Q.; Gai, Z.; Hong, K.; Zhang, M. Paramagnetic Properties of Metal-Free Boron-Doped Graphene Quantum Dots and Their Application for Safe Magnetic Resonance Imaging. Adv. Mater. 2017, 29, 1605416. [Google Scholar] [CrossRef] [PubMed]
- Arcudi, F.; Đorđević, L.; Prato, M. Synthesis, Separation, and Characterization of Small and Highly Fluorescent Nitrogen-Doped Carbon NanoDots. Angew. Chem. Int. Ed. 2016, 55, 2107–2112. [Google Scholar] [CrossRef] [PubMed] [Green Version]
- Rao, L.; Tang, Y.; Li, Z.; Ding, X.; Liang, G.; Lu, H.; Yan, C.; Tang, K.; Yu, B. Efficient synthesis of highly fluorescent carbon dots by microreactor method and their application in Fe3+ ion detection. Mater. Sci. Eng. C 2017, 81, 213–223. [Google Scholar] [CrossRef] [PubMed]
- Shrivastava, A.; Gupta, V.B. Methods for the determination of limit of detection and limit of quantitation of the analytical methods. Chron. Young Sci. 2011, 2, 21–25. [Google Scholar] [CrossRef]
- Chin, S.-F.; Tan, S.-C.; Pang, S.-C.; Ng, S.-M. Nitrogen doped carbon nanodots as fluorescent probes for selective detection and quantification of Ferric(III) ions. Opt. Mater. 2017, 73, 77–82. [Google Scholar] [CrossRef]
- Dong, Y.; Su, M.; Chen, P.; Sun, H. Chemiluminescence of carbon dots induced by diperiodato-nicklate(IV) in alkaline solution and its application to a quenchometric flow-injection assays of paracetamol, l-cysteine and glutathione. Microchim. Acta 2015, 182, 1071–1077. [Google Scholar] [CrossRef]
- Gao, G.; Jiang, Y.-W.; Jia, H.-R.; Yang, J.; Wu, F.-G. On-off-on fluorescent nanosensor for Fe3+ detection and cancer/normal cell differentiation via silicon-doped carbon quantum dots. Carbon 2018, 134, 232–243. [Google Scholar] [CrossRef]
Added GSH (μM) | Found GSH (μM) | Recovery (%) | RSD (%) |
---|---|---|---|
4 | 4.35 | 108.7 | 1.50 |
50 | 51.96 | 103.9 | 2.14 |
100 | 102.4 | 102.4 | 2.43 |
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Lu, X.; Liu, C.; Wang, Z.; Yang, J.; Xu, M.; Dong, J.; Wang, P.; Gu, J.; Cao, F. Nitrogen-Doped Carbon Nanoparticles Derived from Silkworm Excrement as On–Off–On Fluorescent Sensors to Detect Fe(III) and Biothiols. Nanomaterials 2018, 8, 443. https://doi.org/10.3390/nano8060443
Lu X, Liu C, Wang Z, Yang J, Xu M, Dong J, Wang P, Gu J, Cao F. Nitrogen-Doped Carbon Nanoparticles Derived from Silkworm Excrement as On–Off–On Fluorescent Sensors to Detect Fe(III) and Biothiols. Nanomaterials. 2018; 8(6):443. https://doi.org/10.3390/nano8060443
Chicago/Turabian StyleLu, Xingchang, Chen Liu, Zhimin Wang, Junyi Yang, Mengjing Xu, Jun Dong, Ping Wang, Jiangjiang Gu, and Feifei Cao. 2018. "Nitrogen-Doped Carbon Nanoparticles Derived from Silkworm Excrement as On–Off–On Fluorescent Sensors to Detect Fe(III) and Biothiols" Nanomaterials 8, no. 6: 443. https://doi.org/10.3390/nano8060443