Lanthanide Coordination Polymer Nanoparticles as an Excellent

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A Lanthanide Coordination Polymer Nanoparticles as an Excellent Artificial Peroxidase for Hydrogen Peroxide Detection Hui-Hui Zeng, Wei-Bin Qiu, Li Zhang, Ru-Ping Liang, and Jian-Ding Qiu Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.6b00630 • Publication Date (Web): 25 May 2016 Downloaded from http://pubs.acs.org on May 26, 2016

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Analytical Chemistry

A Lanthanide Coordination Polymer Nanoparticles as an Excellent Artificial Peroxidase for Hydrogen Peroxide Detection Hui-Hui Zeng,1,2 Wei-Bin Qiu,1 Li Zhang,1 Ru-Ping Liang,1 Jian-Ding Qiu1,2* Department of Chemistry, Nanchang University, Nanchang 330031, China Department of Materials and Chemical Engineering, Pingxiang University, Pingxiang 337055, China * Corresponding author. Tel/Fax: +86 791 83969518.E-mail address: [email protected] (J.D. Qiu)

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ABSTRACT

Lanthanide coordination polymer nanoparticles (Ln-CPNs) have been recently demonstrated as excellent platforms for biomolecule detection. In this work, we synthesized a novel cerium coordination polymer nanoparticles ATP-Ce-Tris CPNs in a simple and quick way using ATP molecules as the biocompatible ligands to Ce3+ ions in Tris(hydroxymethyl)aminomethane hydrochloric (Tris-HCl) solution. In view of the excellent free radical scavenging property of cerium compounds, which is ascribed to the mixed valence state (Ce3+, Ce4+) and the reversible switch from Ce3+ to Ce4+, the synthesized ATP-Ce-Tris CPNs was used as artificial peroxidase to selectively and sensitively detect H2O2. The sensing mechanism depends on the oxidation of the fluorescent ATP-Ce(III)-Tris CPNs to non-fluorescent ATP-Ce(IV)-Tris CPNs by H2O2. Compared with those inorganic cerium oxide sensors, this kind of fluoresence ATP-Ce-Tris CPNs sensor needs no additional organic redox dye such as ABTS (2,20-azino-bis(3-ethylbenzthiazoline-6-sulfonic

acid),

TMB

(3,3,5,5-tetramethylbenzidine), or fluorescein as signal molecules. Moreover, such ATP-Ce-Tris CPNs sensor exhibited a more sensitive response to H2O2 with a detection limit down to 0.6 nM, which is two orders of magnitude lower than those of cerium oxide sensors. This sensing platform was further extended to the detection of glucose in combination with the specific catalytic effect of glucose oxidase (GOx) for the oxidation of glucose and formation of H2O2. 2


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INTRODUCTION

As a principal member of reactive oxygen species (ROS) and a by-product of the reactions catalyzed by a large number of oxidase enzymes, hydrogen peroxide (H2O2) plays vital roles in biological systems, pharmaceutical, industrial, and other fields.1-3 Therefore, efficient and reliable detection of H2O2 is of considerable significance and has become an important subject of current chemical research.4,5 In the past 30 years, a large number of elegant methods, including spectroscopic approaches, electrochemical strategies, enzymatic techniques, and so on, have been developed for H2O2 detection.6-11 Among them, enzymatic techniques detection has been proven to be the most powerful one for its high substrate specificity and efficiency. Nevertheless, the limited natural sources, time-consuming and high-cost purification processes, and inherent instability restrict their applications to some extent.12,13 To overcome these obstacles, increasing attention has been focused on the enzyme mimetics. Because of the large surface-to-volume ratio, nanomaterials are attractive to serve as artificial enzyme with a number of advantages such as low-cost, easy for mass-production, high stability, long-term storage, and tunable activity.14-17 To date, nanomaterials such as Fe3O4 magnetic nanoparticles,10,18,19 single-wall carbon nanotubes,20,21 and bimetallic alloy nanoparticles22-25 have been discovered with peroxidase-like activity. However, compared with natural enzymes, the efficiency of most nanozymes is still lower, especially the enzyme activity can be dramatically decreased by the additional coatings 3



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and bioconjugation. Therefore, the development of high performance nanozymes is still a research hotspot.15,17 The unique electronic shell structure endows lanthanide cerium many extraordinary photoelectric properties, especially its excellent catalytic and free radical scavenging properties.26,27 The mixed valence state (Ce3+, Ce4+) and the reversible switch from Ce3+ to Ce4+ renders the cerium compounds with efficient function of antioxidant.28-30 The antioxidant effects and the biological antioxidant mechanisms of nanoceria were examined by Sm3+ ions doping, and the research results confirmed that the Ce3+/Ce4+ redox reaction was responsible for its outstanding inoxidizability.2,31 Based on this special performance, a ceria colorimetric probe was developed for glucose detection with the color change of ceria as indicator signal.32 In addition, a series of cerium-based nanomaterials such as CeO2/nanotube-TiO2 nanocomposites,33 TiO2@CeOx core-shell nanoparticles,34 CePO4:Tb,Gd hollow nanospheres35 were also exploited as artificial peroxidase to detect H2O2. However, all these reported cerium-based nanozymes are inorganic

nanoparticles,

and

the

organic

redox

dye

such

as

TMB

(3,3,5,5-tetramethylbenzidine), ABTS (2,20-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid), and fluorescein are usually involved as signal molecules, which would limit their applications in biological field. Up to date, as far as we know, there was no report on the combination of the luminescence property of Ce3+ ions with its peroxidase mimic activity. Therefore, it is significant to develop multifunctional cerium-based nanoparticles as nanozymes. In the past decade, Ln-CPNs have been rapidly growing as a new kind of multifunctional materials for catalysis, chemical sensing and biomedical imaging because 4


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of their unique optical properties and intrinsic porosities, which enable them to take up guest substrates easier.36,37 Such Ln-CPNs are usually assembled from a large number of lanthanide ions (Ln3+) with organic ligands, and these organic ligands often serve as “antenna” to sensitize the luminescence of Ln3+. However, it is well known that the fluorescence of Ce3+ arises from the 4f-5d transition, although the inner 4f electrons of Ce3+ are well shielded by the outer 5s2 and 5p6 shells, their 5d orbitals are very sensitive to the ligand sphere. Many organic ligands have been discovered to quench Ce3+ luminescence upon complexation.38,39 Therefore, it is very important and significant to exploit appropriate organic ligand, especially the biocompatible organic ligands, to sensitize the luminescence of Ce3+ ions and obtain high performance cerium-based Ln-CPNs artificial peroxidase. Recently, the nucleotide base, deoxyguanosine monophosphate (dGMP) has been developed to coordinate with lanthanide terbium, and can greatly enhance the Tb3+ emission.40-42 As for adenosine triphosphate (ATP), the ubiquitous energy conversion for all living organisms, plays a critical role in the regulation and integration of cellular metabolism.43 Moreover, the biocompatible ATP molecule with multiple functional groups is also an outstanding ligand to many metal ions.44 In view of the high affinity of phosphate groups to lanthanides, the ATP molecule is expected to be an excellent ligand to lanthanide Ce3+ ions to synthesize cerium coordination polymer nanoparticles. Herein, we for the first time report the preparation of a kind of cerium(III) coordination polymer nanoparticles employing ATP molecule as bridging ligand by simply mixing the precursors (ATP and Ce(NO3)3·6H2O) in Tris-HCl buffer. The obtained nanoparticles can be used as an artificial peroxidase for selective sensing of H2O2 (Scheme 1). The sensing 5



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mechanism is explored as the oxidation of fluorescent ATP-Ce(III)-Tris CPNs to non-fluorescent ATP-Ce(IV)-Tris CPNs in the presence of H2O2. Combined with the specific catalytic effect of glucose oxidase for the oxidation of glucose and formation of H2O2, the ATP-Ce-Tris CPNs can also be exploited as the sensing platform for glucose detection. The ATP-Ce-Tris CPNs exhibited a more sensitive response to H2O2 with a detection limit down to 0.6nM, which was two orders of magnitude lower than those cerium oxide sensors of H2O2.2,32

Scheme 1. Schematic illustration of the synthesis of ATP-Ce-Tris CPNs and the detection of H2O2, glucose with the ATP-Ce-Tris CPNs as fluorescent probe.

EXPERIMENTAL SECTION Reagents and Chemicals. Adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP), guanosine triphosphate (GTP), cytidine triphosphate (CTP), thymidine triphosphate (TTP), uridine triphosphate (UTP), and glucose oxidase (GOx) were purchased from Sigma-Aldrich (USA). Other chemicals, such as glucose, Ce(NO3)3·6H2O (>99.99%), Tris(hydroxymethyl)aminomethane, 30 6


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wt % H2O2 solution, and metallic salts were bought from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China) and used without further purification. All solutions are prepared with ultrapure water of 18.2 MΩ cm-1. Human serum samples were supplied by Jiangxi Provincial People’s Hospital. After centrifugation at 1000 rpm for 5 min, the human serum were then collected and diluted to 1% with ultrapure water. Apparatus and Measurements. Quanta 200 scanning electron microscopy (SEM, USA) was used to characterize the size and morphology of the ATP-Ce-Tris CPNs. Fourier transform infrared (FT-IR) spectra were obtained using a Nicolet 5700 FT-IR spectrometer. X-ray photoelectron spectroscopy (XPS) characterizations were measured by a VG Multilab 2000X instrument (Thermal Electron, USA). Fluorescence spectra were performed on an F-7000 fluorescence spectrometer (Hitachi, Japan). The excitation wavelength, slit widths (including excitation and emission) and the photomultiplier tube (PMT) voltage were set at 310 nm, 5 nm and 700V, respectively. UV-vis absorption spectra were conducted on a UV-2450 spectrophotometer (Shimadzu, Japan). All experiments were carried out at room temperature. Preparation of ATP-Ce-Tris CPNs. The ATP-Ce-Tris CPNs were synthesized through ATP self-assembled with Ce3+ ions in Tris-HCl buffer aqueous solution. Typically, Ce(NO3)3 aqueous solution (8 mM, 1 mL) was added into pH 7.4 Tris-HCl buffer (50 mM, 1.6 mL) containing ATP (1.25 mM) to form a white flocculent suspension under stirring at room temperature. The obtained flocculent suspension was then purified by centrifugation and washed several times with ultrapure water, finally, the as-synthesized ATP-Ce-Tris CPNs were redisposed in 2 mL water to form ATP-Ce-Tris CPNs (4 mM) suspension which was stored at 4 °C prior to use. The analogous

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ADP-Ce-Tris CPNs, AMP-Ce-Tris CPNs, GTP-Ce-Tris CPNs, TTP-Ce-Tris CPNs, CTP-Ce-Tris CPNs and UTP-Ce-Tris CPNs were synthesized in the same way. H2O2 and Glucose Sensing. The ATP-Ce-Tris CPNs stock solution (4 mM, 20 µL) and H2O2 with different concentrations were orderly added into 40 µL Tris-HCl buffer (50 mM, pH 7.4), and the mixture was diluted with ultrapure water to a volume of 200 µL. After the solution was incubated for 25 min, fluorescence spectra were measured. Then the glucose sensing in buffer solution was performed. Typically, ATP-Ce-Tris CPNs stock solution (4 mM, 20µL), GOx solution (0.05 mg mL-1, 10 µL) and glucose with different concentrations were orderly added into 40 µL Tris-HCl buffer (50mM, pH 7.4), the mixture was diluted with ultrapure water to a volume of 200 µL and incubated at 37°C. The fluorescence spectra were subsequently measured. The same procedure was used to detect glucose from human serum. The ATP-Ce-Tris CPNs stock solution (4 mM, 20 µL), GOx solution (0.05 mg mL-1, 10 µL), 1% treated human serums (10 µL) and glucose solution with different concentrations were spiked into the 40 µL Tris-HCl buffer (50 mM, pH 7.4), the mixture was diluted with ultrapure water to a volume of 200 µL and incubated at 37°C, then the glucose detection was carried out.

RESULTS AND DISCUSSION Design, Synthesis and Characterization of the ATP-Ce-Tris CPNs. Given the hard-acid nature of Ln3+ ions, hard bases, such as carboxylic acids, amides, and pyridines, are often served as ligands in the design of lanthanide coordination polymer.45 As mentioned before, due to the high affinity of phosphate groups to metal ions, ATP molecule is an extremely good chelator, the N-7 in adenine moiety and the triphosphate chain of ATP molecule can coordinate to metal ions to form a macrochelate.44 As far as 8


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we know, there are almost no reports on synthesis of Ln-CPNs using ATP as ligand to self-assemble with Ln3+ ions. In the present experiment, different adenosine ligands such as AMP, ADP and ATP were selected to self-assemble with lanthanide cerium ions. The photoluminescence (PL) spectra of the as-synthesized Ln-CPNs are displayed in Figure 1A. The PL intensity of Ln-CPNs with different adenosine ligands increased gradually in order of AMP

Lanthanide Coordination Polymer Nanoparticles as an Excellent

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