A colorimetric and ratiometric fluorescent probe for mercury (II) in lysosome
Introduction
In a variety of heavy metal ions, mercury ion (Hg2+) is considered as one of the most prevalent toxic metal ions which widely exists in water and soil, especially those originated from chemical industries [1]. As it can cause severe damage to the central nervous system, the excessive exposure to Hg2+ can also lead to dysfunctions of the cells, kidney and stomach [2]. Therefore, developing an effective and sensitive method to selectively detect Hg2+ is of great significance not only in environmental science but also in biomedical science.
Compared with other detection techniques, small molecule probes based on fluorescent signal transduction have outstanding advantages such as rapid responsive time, high sensitivity, simple operation and easy visualization [3]. Particularly, the structures of the small molecule probes are convenient to be modified for specifically recognizing subcellular organelles such as lysosome, mitochondria, cell nucleus and cell membrane [4].
Over the past several years, Hg2+ fluorescent probes have attracted comprehensive attention based on various fluorophores such as rhodamine, coumarin, naphthalimide, and BODIPY etc. [5]. Usually, if Hg2+ fluorescent detection depends merely on the change of fluorescence intensity except from the shifts on excitation or emission wavelength, the measuring accuracy would suffer some influences from micro environment, probe localization, emission efficiency and so on [6]. To reduce the interference, developing ratiometric fluorescent probes for detecting Hg2+ is one of the most efficient strategies [5a]. In recent years, some ratiometric fluorescent Hg2+ probes have been reported and applied in bioimaging [7]. However, a few reports involved in the detection of Hg2+ in specific subcellular organelles. Lysosome contains acid hydrolase enzyme that can break down waste materials and cellular debris, therefore it is considered as an intracellular “enzyme warehouse” or “digestive powerhouse” [8]. Therefore, it is significant to develop the lysosome-targeting fluorescent probe to detect Hg2+ in this subcellular organelle.
In recent researches, the morpholine group has been confirmed by some groups that it possesses a capability of lysosome-targeting and can be used as a lysosomal localization groups [9]. Herein, we introduce the morpholine group to the NBD fluorophore, providing the NBD-based small molecule probe 1 (Scheme 1a), which can act as a colorimetric and ratiometric fluorescent probe for Hg2+ detection. Furthermore, we were fortunate enough to obtain the single crystal structures before and after coordination with Hg2+, which indicates the formation of a complex with a ratio of 2:2. Interestingly, morpholine moiety plays dual roles of serving as a lysosome-targeting group and acting as a ligand toward Hg2+. According to the optical properties, it displays high selectivity to Hg2+ in an aqueous solution and possesses a distinguished capability for lysosome-targeting detection of Hg2+ without interferences in living cells. The results suggest that Hg2+-selective probe can be used as an efficient tool for detecting cellular toxicological actions that are related to Hg2+. Moreover, it is worth mentioning that this probe possesses good water-solubility, biocompatibility and cell-penetrability.
Section snippets
Materials and instrumentation
All manipulations were carried out under an argon atmosphere using standard Schlenk techniques, unless otherwise stated. All chemicals were used as received without further purification. 1H and 13C NMR spectra were collected on Bruker 400 MHz spectrometer (Bruker, Bremen, Germany) in CDCl3-d1 with Me4Si as an internal reference. UV–vis absorption spectra were obtained using Hitachi U-3310 visible recording spectrophotometer. Fluorescence spectra were obtained using PerkinElmer-LS55. Mass spectra
Results and discussion
Probe 1 is synthesized according to the previous description outlined in Scheme 1b [10]. Probe 1 is obtained with a yield of 78% by treating 4-chloro-7-nitrobenzo-2,1,3-oxadiazole (NBD-Cl) and 4-(2-aminoethyl) morpholine in dioxane at room temperature and then fully characterized by 1H NMR, 13C NMR, mass spectra and single crystal.
To evaluate the selectivity of probe 1, numerous studies are carried out the use of probe 1 (10 μM) to detect metal cations (10 equiv.) such as Ca2+, Ni2+, Li+, Al3+, Cd
Conclusion
In conclusion, we discovered a small molecule fluorescent probe based on NBD fluorophore. In which, a dual-functional morpholine moiety plays a lysosome-targeting and ligand dual role. In the investigation of metal ion detection, this probe displays a highly selective colorimetric and ratiometric response to Hg2+ ions in an aqueous solution. Its good water-solubility, bio-compatibility and cell permeability facilitate it to be employed as an efficient biomarker to monitor the level of Hg2+ in
Acknowledgments
The authors acknowledge financial support from National Natural Science Foundation of China (21272088, 21472059, 21402057 and 81371684), the Scientific Research Foundation for the Returned Overseas Chinese Scholars, Ministry of Education and the self-determined research funds of CCNU from the colleges’basic research and operation of MOE (CCNU14A05009, CCNU14F01003).
YuFeng Zhang was born in Hunan province, PR China, in 1991. She received her bachelor degree in 2013 from Hunan Normal University. She joined the graduate school of department of chemistry at Central China Normal University as a master student in 2013.
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Cited by (0)
YuFeng Zhang was born in Hunan province, PR China, in 1991. She received her bachelor degree in 2013 from Hunan Normal University. She joined the graduate school of department of chemistry at Central China Normal University as a master student in 2013.
Haiyan Chen was born in Jiangsu Province, PR China, in 1982. She received her Ph.D. degree in 2009 from China Pharmaceutical University (CPU). Since then she began her research at department of biomedical engineering in CPU. She participated a visiting scholar program in Technical University of Munich in 2011. She is now an assistant professor at CPU with an h-index of 14. She is now learning in University of California, Riverside as a visiting scholar. Her research interests focus on the construction of multi-functional nano-medicine and its application in tumor imaging and combined tumor therapy.
Dan Chen was born in Jiangsu Province, PR China, in 1992. She received her bachelor degree in 2013 from China Pharmaceutical University (CPU). She is now a master's candidate of microbial and biochemical pharmacy at CPU. She has been doing research on metal nanoparticles (including gold nanocluster and gold nanorod) and its application on tumor imaging and tumor targeted therapy.
Di Wu was born in Hubei province, China, in 1988. He received his Ph.D. degree in 2007 from Central China Normal University (CCNU). He is presently working as a postdoctoral fellow in the group of Prof. Juyoung Yoon at Ewha Womans University.
Zhao Chen was born in Jiangxi Province, China, in 1989. He is now a Ph.D. candidate under the supervision of Prof. Shenghua Liu in the Central China Normal University.
Jing Zhang was born in Hubei Province, China, in 1988. She is now a PhD candidate under the supervision of Prof. Shenghua Liu in the Central China Normal University.
Xiaoqiang Chen was born in Hubei province, PR China, in 1981. He received Ph.D. degree in 2008 from Dalian University of Technology. He is now a professor at Nanjing University of Technology and has published over 24 papers. His research interests focus on supramolecular chemistry, chemical sensors and biosensors.
ShengHua Liu was born in Jiangxi province, PR China, in 1965. He received his master degree in 1994 and Ph.D. degree in 1999 from Wuhan University. He began his postdoctoral research at the Hong Kong University of Science and Technology (HKUST) from 1999 to 2002. He is now a professor at Central China Normal University and has published over 50 papers. His research interests focus on organic synthesis and metal organic chemistry.
Jun Yin was born in Hubei province, PR China, in 1981. He received his bachelor degree in 2002 and Ph.D. degree in 2007 from Central China Normal University (CCNU). He began his postdoctoral research at National University of Singapore before he joined the College of Chemistry, CCNU in 2010. He is now an associate professor at CCNU and has published over 110 papers. His research interests focus on functional supramolecular self-assembly, fluorescent sensors and biological functional materials.
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These authors contributed equally to this work.