Article pubs.acs.org/ac
Fluorescent Sulfur-Tagged Europium(III) Coordination Polymers for Monitoring Reactive Oxygen Species Huai-Song Wang,†,‡ Wen-Jing Bao,† Shi-Bin Ren,† Ming Chen,† Kang Wang,† and Xing-Hua Xia*,† †
State Key Laboratory of Analytical Chemistry for Life Science and Collaborative Innovation Center of Chemistry for Life Sciences, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China ‡ Department of Pharmaceutical Analysis, China Pharmaceutical University, Nanjing 210009, China S Supporting Information *
ABSTRACT: Oxidative stress caused by reactive oxygen species (ROS) is harmful to biological systems and implicated in various diseases. A variety of selective fluorescent probes have been developed for detecting ROS to uncover their biological functions. Generally, the preparation of the fluorescent probes usually undergoes multiple synthetic steps, and the successful fluorescent sensing usually relies on trial-and-error tests. Herein we present a simple way to prepare fluorescent ROS probes that can be used both in biological and environmental systems. The fluorescent europium(III) coordination polymers (CPs) are prepared by simply mixing the precursors [2,2′-thiodiacetic acid and Eu(NO3)3·6H2O] in ethanol. Interestingly, with the increase of reaction temperature, the product undergoes a morphological transformation from microcrystal to nanoparticle while the structure and fluorescent properties retain. The fluorescence of the sulfur-tagged europium(III) CPs can be selectively quenched by ROS, and thus, sensitive and selective monitoring of ROS in aerosols by the microcrystals and in live cells by the nanoparticles has been achieved. The results reveal that the sulfur-tagged europium(III) CPs provide a novel sensor for imaging ROS in biological and environmental systems.
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activation is mainly based on oxidation of the reduced nonfluorescent forms of the fluorophores to their oxidized fluorescent states.16 Recently, lanthanide-based fluorescent probes (Eu3+ or Tb3+ complexes) have shown them off as excellent alternatives for sensitive imaging detection of ROS, because of their long emission lifetime, sharp emission bands, and large Stokes shift.17−19 The red emission of Eu3+ complexes, originating from 4f−4f electron transitions, is of special interest for optical emission studies, and the emission spectra are very sensitive to structural details of the coordination environments.20,21 For example, the emission intensity of the “hypersensitive” lines (e.g., 5D0 → 7F2 of Eu3+) is strongly affected by local symmetry, even there are small deviations.22 Up to now, great efforts have been made toward the design and development of promising new lanthanide-based probes that are both biocompatible and bioresponsive.23,24 Herein, we for the first time report the preparation of a kind of europium(III) coordination polymer (CP) employing 2,2′thiodiacetic acid [S(CH2COO)22−, TDA] as bridging ligand for fluorescent detection of ROS. By simply mixing the precursors (TDA and Eu(NO 3 ) 3 ·6H 2 O) in ethanol, the product morphology can be transformed from microcrystals (CP-25) to nanoparticles (CP-150) upon increasing reaction temperature with retained structure and fluorescent properties (Figure
eactive oxygen species (ROS) have been considered to be one of the most important causes of human mortality and morbidity. The ROS (such as O2•−, OH·, RO·, H2O2, 1O2, etc.) are generated at low levels during the metabolic processes in living cells and play important roles in regulating the physiological functions, whereas excessive ROS expression can result in the phenomenon of oxidative stress, which causes cellular damages and various diseases including cardiovascular disease, cancer, and neurological disorders.1−3 Moreover, the presence of ROS in atmospheric aerosols or smoke can also bring to oxidative stress in the human lung.4,5 In order to understand the pathological processes, monitoring of ROS is definitely an important approach. A great number of approaches (including electrochemical, spectroscopic, and enzymatic techniques) for measuring ROS have been developed.6−9 About a half-century ago, the electron spin resonance (ESR) method was suggested to detect the free radicals that were considered as a typical kind of ROS.10,11 But the ESR spin trapping technique requires relatively expensive instruments and complex handling procedures for biological samples, which hampers its value for routine laboratory analysis. Thus, other methods for detecting ROS were proposed that make use of chromatography and chemiluminescence.12,13 Among them, fluorescence detection has been proven to be the most powerful one in terms of high sensitivity and experimental convenience. Fluorescent probes, such as dihydrorhodamine and dichlorofluorescein derivatives, have been successfully applied for direct ROS measurements within biological and environmental systems.14,15 The mechanism of fluorescence © XXXX American Chemical Society
Received: March 23, 2015 Accepted: June 2, 2015
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DOI: 10.1021/acs.analchem.5b01104 Anal. Chem. XXXX, XXX, XXX−XXX
Article
Analytical Chemistry 1). We use the fluorescent crystalline CP-25 and amorphous CP-150 for selective sensing of ROS. The sensing mechanism is
microscope (TEM, JEM-200CX, Japan) and scanning electron microscope (SEM, S-4800, Japan). Thermogravimetric analysis (TGA) curves were obtained on a STA 449C Jupiter thermoanalyzer (Germany). X-ray measurements of single crystals were collected on an AXS SMART APEX (Bruker, Germany) diffractometer. X-ray diffraction patterns were obtained on an X-ray powder diffractometer (XRD, X’TRA, Cu Kα radiation, Switzerland). The X-ray photoelectron spectra (XPS) were recorded on a PHI 5000 Versaprobe instrument (UlVAC-PHI, Japan). IR spectra were collected on a Nicolet 6700 FT-IR spectrometer (Thermo Scientific, U.S.A.). Thermogravimetric analyses (TGA) were performed on a thermal analyzer (PerkinElmer, U.S.A.). Fluorescence detection and microscopic investigations were performed using an inverted fluorescence microscope (Nikon, TiU, Japan) equipped with a mercury lamp with a UV excitation filter (
