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Multiporous Terbium Phosphonate Coordination Polymers Microspheres as Fluorescent Probe for Trace Anthrax Biomarker Detection Yongquan Luo, Lei Zhang, Lingyi Zhang, Bohao Yu, Yajie Wang, and Weibing Zhang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b01123 • Publication Date (Web): 05 Apr 2019 Downloaded from http://pubs.acs.org on April 7, 2019

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Multiporous Terbium Phosphonate Coordination Polymers Microspheres as Fluorescent Probe for Trace Anthrax Biomarker Detection Yongquan Luo, † Lei zhang, *,† Lingyi Zhang, † Bohao Yu, †Yajie Wang, ‡ and Weibing Zhang *,† †

Shanghai Key Laboratory of Functional Materials Chemistry, School of Chemistry &

Molecular Engineering, East China University of Science and Technology, Shanghai 200237, China. ‡

Department of Pharmacy, Anhui Medical College, Hefei, 230601, China

KEYWORDS: Coordination Polymers, Terbium Phosphonate, Fluorescent Probe, Dipicolinate Acid, Biomarker Abbreviation Index: LnCPs, Lanthanide Coordination Polymers; TbP-CPs, Terbium Phosphonate Coordination Polymers Microspheres; DPA, Dipicolinate Acid; RSD, Relative Standard Deviations; PCRs, Polymerase Chain Reactions; MIPs, Molecularly Imprinted Polymers; Eu-GQD, Eu-Graphene Quantum Dots; EBT, Eriochrome Black T; CTAB, cetyltrimethylammonium bromide; EDTMP, ethylene diamine tetra (methylene phosphonic acid). ABSTRACT: Lanthanide coordination polymers (LnCPs) have recently regarded as the attractive sensing materials because of its selectivity, high sensitivity and rapid response ability. In this research, the multiporous terbium phosphonate coordination polymers microspheres (TbP-CPs) were prepared as the novel fluorescent probe, which showed a fluorescence turn-on response capability for the detection of trace anthrax biomarker, dipicolinate acid (DPA). The morphology and chemical composition of as-prepared TbP-CPs were detailedly characterized. The TbP-CPs have the vegetable-flower-like structure and microporous surface. In addition, the as-prepared TbP-CPs not only possess the merits of convenience and simple preparation with high yield, but also have the excellent characters as fluorescent probe such as high stability, good selectivity and rapid detection ability within 30 seconds. This proposed sensor could detect DPA

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with a linear relationship in the concentrations range from 0 to 8.0 µM and a high detection sensitivity of 5.0 nM. Furthermore, the successful applications of DPA detection in urine and bovine serum were demonstrated. As a result, the recovery ranged from 93.93-101.6 % and the relative standard deviations (RSD) were less than 5 %. 1. INTRODUCTION Anthrax that mainly exists in the form of spore is an acute communicable disease caused by Bacillus anthracis 1. The spore exists everywhere in the world because of its stability in soil for decades. An inhalation of Bacillus anthracis spores more than 104 can lead to death in the absence of effective medical treatment within 24-28 h2,3. Consequently, Bacillus anthracis can be adopted as a potential bioterrorism agent. The dipicolinate acid (DPA), a main chemical constituent of bacillus anthracis, was regarded as a unique biomarker of Bacillus anthracis spores or anthracis disease4-6. Thus, numbers of attempts have been made to explore efficient and fast detection methods. Recently, several techniques for DPA detection have been developed such as gas chromatography/mass spectrometry7, Surface-Enhanced Raman Scattering (SERS)8-10 electrochemical detection1,11, molecular imprinting12-14, fluorescence spectroscopy15,16, and so on17-19. Traditional detection methods such as gas chromatography/mass spectrometry usually require complicated and time-consuming sample preparation processes, and relatively expensive instruments. The techniques of immunoassays18 and polymerase chain reactions (PCRs)19 alway need expensive chemicals, time-consuming processes and well-trained operation. Molecularly imprinted polymers (MIPs) technique has the advantages of specific recognition ability with high binding affinity, high selectivity, but it usually needs the complex and expensive production procedures and harsh conditions. Among those developed technologies, fluorescence spectroscopy is considered as a promising analytical method due to its advantages of excellent selectivity, low detection limit, low cost and rapid response ability. To develop a competitive and actually available fluorescence spectroscopy-based detection method, the crucial impact factor is the fluorescent probe. Nowadays, several kinds of fluorescent probes such as Quantum Dots20-25, traditional organic dyes26,27, transition metal complex28 and lanthanide-based coordination polymers29-33 have been designed and prepared. However, the traditional organic dyes are sometimes difficult to

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dissolve in water and easily bleached by light34,35. Several fluorescent probes are easily affected by background noise, which seriously influenced the detection results36. Among those fluorescent probes, lanthanide coordination polymers (LnCPs) are more attractive than others owing to the abundant active sites for chelating various lanthanide (Ln3+) ions. Benefit from the f–f electronic transition effect, the LnCPs have several unique characteristics,37-39 including large Stokes shift, sharply spiked emission, and long fluorescence lifetimes. Therefore, several LnCPs as fluorescent probes have been prepared for DPA detection. For example, Zhang reported the dual lanthanide-doped complexes (Tb/DPA@SiO2-Eu/GMP) as the time-resolved ratiometric fluorescent probe for DPA detection40. The analytical method was established for detecting Bacillus anthracis spores with the modification of europium ions on graphene quantum dots (Eu-GQD) as a ratiometric fluorescent probe41. The fluorescent probe of eriochrome Black T (EBT)-Eu3+ binary complex was designed and prepared for the selective and sensitive detection of DPA though both colorimetric and fluorescent spectra42. Phosphate is an important and popular ligand for chelating the lanthanide elements. Metal phosphate hybrid materials have received great attentions in catalysis, adsorption and biological applications due to the bridging structure of inorganic metal centers and organophosphates. Herein, we report the multiporous terbium phosphonate coordination polymers (TbP-CPs) based on Terbium (III) coordinated with ethylene diamine tetra (methylene phosphonic acid) in the surfactant cetyltrimethylammonium bromide (CTAB) solution. The asprepared TbP-CPs act as the anthrax sensor have the following unique characters. (1) The preparation process was simple to practice high yield without using poisonous and noxious reagents which were harmful to environment and human body such as EBT. (2) The obtained TbP-CPs possessed the vegetable-flower-like porous structure for efficient detection of DPA. This uniform structure could provide high surface area to enhance the interactions between DPA and Terbium (III) ions, as illustrated in Scheme 1. (3) The lanthanide phosphonates TbP-CPs have excellent stability. The fluorescence intensity of TbP-CPs in ultra-pure water was stable more than 15 days almost without change. (4) Compared with other fluorescence spectroscopy-based DPA detection methods, TbP-CPs sensor showed low detection limit (5.0 nM), high selectivity, rapid response ability (30 seconds), and it was accurate and credible for real sample detection such as urine and bovine serum.

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2. EXPERIMENTAL SECTION 2.1 Reagents and Chemicals. Cetyltrimethylammonium bromide (CTAB) and ethylene diamine tetra (methylene phosphonic acid) (EDTMP) were received from Aladdin Chemical Reagent Co., Ltd. Terbium (III) trichloride (TbCl3), p-phthalic acid, phthalic acid, benzoic acid, citric acid, Lglutathione, DL-proline, L-cysteine, L-histidine and Homocystine were obtained from J&K. Sodium acetate (NaAc), Acetic acid (HAc), Na2SO4, Na2SO3, NaNO2, Na2CO3 and NaCl were purchased from Sinopharm Chemical Reagent Co., Ltd. 2.2 Preparation of TbP-CPs. TbP-CPs were prepared using a hydrothermal method according to the previous reported procedure43. Briefly, 5 mL TbCl3 auqeous solution (0.747 g) was added to 25 mL aqueous soultuion containing EDTMP (0.436 g) and CTAB (1.09 g). Simultaneously, the pH value was regulated to 6.0 by using NaOH and HCl through the entire experiment. The suspension was stirred for about 2 h at room temperature, then sequentially reacted in an autoclave for 24 h at 120 °C. After the reaction was stoped, the autoclave was cooled down to 25 °C. The product was centrifugally collected at 10000 rpm for 10 min, cleaned with water and drying at 120 °C overnight. Finally, the obtained white solid (1.0 g) was washed with the mixed soulution containing concentrated HCl (4 mL) and ethanol (200 mL) for three times for 24 h per operation. 2.3 Fluorescence Detection of DPA Using TbP-CPs as Fluorescence Probe. In a typical process, various concentrations of DPA solution were prepared by serial dilution from the stock solution with a concentration of 1.0 mM. Then, 400 μL of 1.5 mg mL-1 TbP-CPs was added into DPA solutions with a serial different concentrations (0-20 μM). Then, the mixed suspension solution was diluted to 2 mL with NaAc-HAc buffer (200 mM, pH 5.0) and shocked for 15 seconds. Finally, the mixture was taken to a quartz optical cell for detection. All the fluorescence spectra shown in this research were obtained with exciting wavelength at 270 nm. The relative standard deviations were calculated by three measurements for one sample unless specified. 2.4 Selectivity and Interference tests. For determining the selectivity of TbP-CPs, the fluorescence intensity of 0.15 mg mL-1 of TbP-CPs with different amino acids such as Lglutathione, DL-proline, L-cysteine, L-histidine and Homocystine were measured. For investigating the interference factor of possible aromatic ligands and anion ions in DPA

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detection, the following compounds and sodium or potassium salts (5.0 μM) were used: pphthalic acid, phthalic acid, benzoic acid, citric acid, SO42-, SO32-, Cl-, NO2- and CO32-. 3. RESULTS AND DISCUSSIONS 3.1 Preparation and Characterization of TbP-CPs. TbP-CPs were prepared from CTAB, EDTMP and Terbium trichloride via a solvothermal reaction process. SEM and TEM were adopted for observing the structural morphology of TbP-CPs (Fig. 1). SEM images showed that the terbium phosphonate coordination polymers microspheres were uniform and well dispersed, the average diameter was measured to about 2.5 μm (Fig. 1 a, b). Meanwhile, the microspheres displayed the vegetable-flower-like structure (Fig. 1b), which enhanced the adsorption capability of the analytes. As shown in TEM images (Fig. 1c, d), the microspheres have abundant pores on the outer surface. The results illustrate that the as-prepared TbP-CPs were multiparous microspheres. The element composition and content of TbP-CPs were characterized by EDS spectrum (Fig. S1, Supporting Information). From the analytical result (Fig. S1), six main elements of C, N, O, P, Cl and Tb were clearly detected in TbP-CPs, and the corresponding contents were measured to 9.08 wt %, 2.67 wt %, 17.23 wt %, 16.63 wt %, 4.08 wt % and 50.31 wt %, respectively. It displayed that the TbP-CPs consisted of inorganic Tb3+ ions and organic phosphonate components. The chemical states of the TbP-CPs were investigated by XPS spectrum, the characteristic peaks of Tb3d (1241.76 eV), O1s (530.02 eV), N1s (400.09 eV), P2p (32.09 eV) and C1s (285.20 eV) were clearly observed (Fig. 2, and Fig. S2). The results were consistent with the EDS analysis result (Fig. S1). The spectrum of O1s was decomposed to two symmetrical components at 531.56 eV (O1) and 530.78 eV (O2). The main peak at 530.78 eV (O2) was associated with the O-P-O bonding, and the observed peak at 531.56 eV (O1) was assigned to the Tb-O bonds44. The spectrum of N1s was decomposed to two components at about 399.35 eV and 402.10 eV, which both were assigned to the bridging N in the TbP-CPs. The symmetric peak in P2p XPS spectrum at binding energy of 132.90 eV was assigned to the P moieties of phosphonate ligand in the TbP-CPs. The Tb3d XPS spectrum was split into two spinorbits as 3d5/2 (1242.55 eV) and 3d3/2 (1277.30 eV) with a binding energy difference of 34.75 eV. The result showed that the Tb3+ state was in the terbium phosphonate material45. What’s more, as the XPS analysis data shown in Fig. S3, after the addition of DPA, the binding energies of N1s

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and O1s were decreased to lower binding energies at 401.43, 398.73 and 530.33 eV, respectively. The binding energies of Tb 3d3/2 and Tb 3d5/2 were increased to higher binding energies at 1280.52 and 1244.70 eV, respectively. It suggested that the strong interactions between O element of carboxylate, N element of aromatic ring and Tb3+ ions. Thus, the strong interactions between TbP-CPs and DPA is beneficial to enhance the fluorescence intensity. The chemical composition of the TbP-CPs was further studied by FT-IR spectrum (Fig. 3). In the FT-IR spectrum of EDTMP (Fig. 3a), according to a previous report46, the characteristic peaks (broad bands) at 1437 and 1464 cm-1 were belonged to the C-H bending and P-C stretching vibrations in the EDTMP. The observed peaks at 1005 and 956 cm−1 were assigned to the P-OH group with asymmetric and symmetric stretching vibrations. The broad band at 2636 and 2305 cm-1 could be ascribed to characteristic stretching vibrations of association P-OH. However, they could not be obviously observed in the FT-IR spectrum of the TbP-CPs (Fig. 3 b). The strong band at 1096 cm-1 could be ascribed to the stretching vibrations of P-O-Tb, which revealed that phosphate group has coordinated with Tb3+ ions. Two characteristic peaks with strong intensities at 3351 and 1675 cm-1 were attributed to the mode of OH group with stretching vibrations and bending vibrations of water molecules, respectively. In order to study the interactions between DPA and TbP-CPs, the FT-IR spectrum of TbP-CPs with DPA was further analysis and shown in Fig. 3c. Compared with the FT-IR spectrum of TbP-CPs, the sharp band at 3420 cm-1 could be attributed to characteristic OH group with stretching vibrations, which was ascribed to the carboxyl of DPA. These analysis results demonstrate that DPA molecules could be adsorbed on the surface of TbP-CPs. The organic-inorganic hybrid structure of TbP-CPs was confirmed by TGA analysis. In Fig. 4 a, the weight loss was caused by the existent organic components. The organic component of asprepared microspheres was measured to about 28 wt %, and the residues were the terbium and their oxides. The multiporous property of as-prepared TbP-CPs hybrids was further investigated by N2 sorption analysis (Fig. 4 b, c). The BET specific surface area and total pore volume of the obtained TbP-CPs were determined to be 20.5 m2 g-1 and 0.032 cm3 g-1, respectively. According to the BJH model, the pore size analysis result revealed a uniform distribution with an average value of ca. 4.3 nm (Fig. 4 c). It also indicates that the as-synthesized organic-inorganic hybrid materials were multiporous polymers microspheres.

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3.2 Fluorescence properties. For better understanding the interactions between TbP-CPs and DPA, the fluorescence lifetime of TbP-CPs was measured with and without of DPA. As presented in Fig. S4, the fluorescence lifetime of TbP-CPs was increased from 4.210 ns to 4.346 ns after the addition of DPA. This result was consistent with the situation that the long fluorescence lifetime of Tb3+ could be decreased by non-radiative deactivation through O–H vibration of water molecules47. The slight increasing of fluorescence lifetime illustrated that the water molecules coordinated with Tb3+ ions were replaced by DPA and produced an efficient energy transfer from the DPA molecules to Tb3+ ions48. 3.3 Optimization of experimental parameters. To gain the optimal parameters for DPA detection, the experimental conditions such as excitation and emission, pH value, reaction time, and the stability of TbP-CPs were optimized. Excitation and emission spectra of TbP-CPs dispersed in aqueous solutions were presented in Fig. 5. In the excitation spectra of TbP-CPs solution, it showed a strong excitation peak at 270 nm, and four emission peaks at 480, 544, 584, and 626 nm, which were the characteristic peaks of Tb3+ ions. The fluorescence intensity of TbPCPs solution was increased about six times at the peak of 544 nm in the presence of DPA with a concentration of 2.0 μM. The fluorescence intensity showed a significant enhancement so that the difference could be distinguished clearly by naked eyes with the help of UV light lamp at a wavelength of 254 nm (inset in Fig. 5). The pH value of the solution was one of the impact factors for fluorescence detection. Therefore, several different pH values of reaction solution were prepared at the range of 2.6 to 8.0. As shown in Fig. S5, the fluorescence intensity of TbPCPs solution was declined slightly when the pH value higher than 6.0. However, the fluorescence intensity was enhanced with the raising of pH value at concentrations of 2.6-5.0 and then slightly decreased from 5.0 to 8.0 with the addition of 2.0 μM of DPA. Consequently, pH value at 5.0 was the best optimal choice for the detection of DPA. The relationship between reaction time and fluorescent probe of TbP-CPs and DPA was investigated in Fig. S6. The result revealed that the combination time between TbP-CPs and DPA was very rapid with the fluorescence enhancing equilibrium less than 0.5 min. The rapid response ability might result from the vegetable-flower-like structure and abundant microporous pores on the surface of TbPCPs, which favor fast mass transfer. Furthermore, the fluorescence intensity of TbP-CPs in ultrapure water was very stable when TbP-CPs solution was measured after 15 days (Fig. S7). The related analysis results were shown in Electronic Supporting Information. After the systematic

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study, the optimal parameters were determined as: (a) excitation peak at 270 nm (b) pH value of 5.0; (c) combination time of 0.5 min. 3.4 Selectivity and Interference of DPA detection. The fluorescence response ability of the TbP-CPs under this circumstance of interference amino acids, aromatic chemicals and anion ions was studied to evaluate the specific detection ability of DPA. The obtained analysis results were shown in Fig. 6. The amino acids, aromatic chemicals and anion ions can be detected, revealing that the fluorescent TbP-CPs material has good specific detection ability towards DPA. This prominent selectivity might be based on the strong interactions between O element of carboxylate, N element of aromatic ring and Tb3+ ions to completely substitute water molecules adsorbed in the center of Tb3+ ions. These analysis results display the promising application of as-prepared TbP-CPs for DPA detection in actual specimens. Thus, a new and effective method based on the fluorescent spectrum was demonstrated for the detection of DPA on the basis of multiporous terbium phosphonate coordination polymers microspheres. 3.5 Analytical performance and applications. According to the previously optimized experimental parameters, the calibration curves were adopted for the detection of DPA. As presented in Fig. 7, the turn-on fluorescence response was exhibited between intensity of solution and DPA concentrations from 0.05 to 20.0 μM. It showed a strong emission peak at 544 nm and corresponding excitation peak at 270 nm, which was caused by the electron transition of terbium ion from 5D0 to 7F2. With the addition of DPA into the TbP-CPs, this process can be enhanced by the energy transition from DPA molecules to Tb ion3+49. As expected, the fluorescence intensity of TbP-CPs solution increased gradually about 20 times with the raising of concentrations of DPA from 0 to 8.0 μM. The regression equation was determined as I/I0=2.3384C + 0.9297, with a correlation conefficient (R2) of 0.9986 during the concentration range of 0, 0.05, 0.10, 0.50, 0.75, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 8.0 μM. The detection limit of DPA with TbP-CPs as the fluorescence probe was 5.0 nM, which was lower than 60 μM of infectious concentration of Bacillus anthracis spores for animals and human being. The RSD of the developed detection method was 1.83 % (c=0.50 μM, n=7). A detailed comparison of this developed method and other previously reported detection method was shown in Table S1, our proposed method has an excellent detection sensitivity.

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For further confirming the detection practicability of the proposed method, urine and bovine serum as the real samples were adopted for DPA fluorescence detection with TbP-CPs as fluorescent probe. The urine and bovine serum samples were diluted to 100 and 1000 folds with NaAc-HAc buffer, respectively. For the urine and bovine serum, the recoveries of DPA were determined to 94.00-101.6 % (Table 1). These results suggest the satisfactory recoveries for low concentration of analytes. 4. CONCLUSIONS In this work, a kind of lanthanide phosphonate coordination polymer (TbP-CPs) was prepared by a simple hydrothermal method with high yield. The as-prepared TbP-CPs exhibited the vegetable-flower-like structure and microporous surface. In addition, the as-prepared TbP-CPs not only possess the merits of convenience and simple preparation, but also have the excellent characters as the fluorescent probe such as high stability, good selectivity and rapid detection ability within 30 seconds. The practical applications of TbP-CPs as fluorescence probe were successfully exploited for DPA detection in urine and bovine serum. These results demonstrated the significant strategy for expanding the application fields of lanthanide phosphonate coordination polymer. We anticipate that the TbP-CPs with good biocompatibility could be applied for further applications of cell microscopic imaging, medical diagnostics and chemical sensing. 

ASSOCIATED CONTENT

S: Supporting Information The Supporting Information is available free of charge on the ACS Publications websit at DOI:10.1021/acsami.xxxx. Material characterization, EDS spectrum, XPS spectra, fluorescent emission decay curves, detection limit, effects of pH values and interaction time on fluorescence intensity as noted in the text. 

AUTHOR INFORMATION

Corresponding Authors

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*E-mail: [email protected]. Tel: +86-21-64252942. Fax: +86-21-64252947. *E-mail: [email protected] Tel: +86-21-64252145. Fax: +86-021-64233161. Notes The authors declare no competing financial interest. 

ACKNOWLEDGEMENTS

This work was financially supported by the National Natural Science Foundation of China (21707034), Science and Technology Commission of Shanghai Municipality (No. 18142202500) Industry-University-Research Practice Program (No. YJ0130533) and Fundamental Research Funds for the Central Universities (No. 222201814020). REFERENCES (1) Zhou, Y.; Yu, B.; Levon, K. Potentiometric Sensor for Dipicolinic Acid. Biosens. Bioelectron. 2005, 20, 1851-1855. (2) Enserink, M. Bioterrorism - This Time it was Real: Knowledge of Anthrax Put to the Test. Science 2001, 294, 490-491. (3) King, D.; Luna, V.; Cannons, A.; Cattani, J.; Amuso, P. Performance Assessment of Three Commercial Assays for Direct Detection of Bacillus Anthracis Spores. J. Clin. Microbiol. 2003, 41, 3454-3455. (4) Cable, M. L.; Kirby, J. P.; Sorasaenee, K.; Gray, H. B.; Ponce, A. Bacterial Spore Detection by [Tb3+(macrocycle)(dipicolinate)] Luminescence. J. Am. Chem. Soc. 2007, 129, 1474-1475. (5) D. R. Walt, D. R. F. Peer Reviewed: Biological Warfare Detection. Anal. Chem. 2000, 72, 738–746. (6) Bhatta, D.; Christie, G.; Blyth, J.; Lowe, C. Development of a Holographic Sensor for the Detection of Calcium Dipicolinate—A Sensitive Biomarker for Bacterial Spores. Sens. Actuators. B 2008, 134, 356–359. (7) Li, D.; Truong, T. V.; Bills, T. M.; Holt, B. C.; VanDerwerken, D. N.; Williams, J. R.; Acharya, A.; Robison, R. A.; Tolley, H. D.; Lee, M. L. GC/MS Method for Positive Detection of Bacillus Anthracis Endospores. Anal. Chem. 2012, 84, 1637-1644. (8) Cheng, H. W.; Huan, S. Y.; Yu, R. Q. Nanoparticle-Based Substrates for Surface-Enhanced Raman Scattering Detection of Bacterial Spores. Analyst 2012, 137, 3601-3608. (9) Zhang, X.; Young, M. A.; Lyandres, O.; Van Duyne, R. P. Rapid Detection of an Anthrax Biomarker by Surface-Enhanced Raman Spectroscopy. J. Am. Chem. Soc. 2005, 127, 44844489.

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(10) Zhang, X.; Zhao, J.; Whitney, A. V.; Elam, J. W.; Van Duyne, R. P. Ultrastable Substrates for Surface-Enhanced Raman Spectroscopy: Al2O3 Overlayers Fabricated by Atomic Layer Deposition Yield Improved Anthrax Biomarker Detection. J. Am. Chem. Soc. 2006, 128, 1030410309. (11) Han, Y.; Zhou, S.; Wang, L.; Guan, X. Nanopore Back Titration Analysis of Dipicolinic Acid. Electrophoresis 2015, 36, 467-470. (12) Gültekin, A.; Ersöz, A.; Sarıözlü, N. Y.; Denizli, A.; Say, R. Nanosensors Having Dipicolinic Acid Imprinted Nanoshell for Bacillus Cereus Spores Detection. J Nanopart Res 2009, 12, 2069-2079. (13) Smith, C. B.; Anderson, J. E.; Edwards, J. D.; Kam, K. C. In Situ Surface-etched Bacterial Spore Detection using Dipicolinic Acid-europium-silica Nanoparticle Bioreporters. Appl Spectrosc 2011, 65, 866-875. (14) Nezammahalleh, H.; Mousavizadeh, S. H.; Babaeipour, V. New Potentiometric Sensor Based on Molecularly Imprinted Polymer for Dipicolinic Acid Detection in Aqueous Media. IEEE Sensors Journal 2018, 18, 7520-7528. (15) Xue, S. F.; Zhang, J. F.; Chen, Z. H.; Han, X. Y.; Zhang, M.; Shi, G. Multifunctional Fluorescent Sensing of Chemical and Physical Stimuli Using Smart Riboflavin-5'phosphate/Eu3+ Coordination Polymers. Anal. Chim. Acta. 2018, 1012, 74-81. (16) Cai, K.; Zeng, M.; Liu, F.; Liu, N.; Huang, Z.; Song, Y.; Wang, L. BSA-AuNPs@Tb-AMP Metal-Organic Frameworks for Ratiometric Fluorescence Detection of DPA and Hg2+. Luminescence 2017, 32, 1277-1282. (17) Tan, C.; Wang, Q.; Zhang, C. C. Optical and Electrochemical Responses of an Anthrax Biomarker Based on Single-walled Carbon Nanotubes Covalently Loaded with Terbium Complexes. Chem. Commun. 2011, 47, 12521-12523. (18) King, D.; Luna, V.; Cannons, A.; Cattani, J.; Amuso, P. J. Performance Assessment of Three Commercial Assays for Direct Detection of Bacillus Anthracis Spores. J. Clin. Microbiol. 2003, 41, 3454-3455. (19) Kim, J.; Yoon, M. Y. Recent Advances in Rapid and Ultrasensitive Biosensors for Infectious Agents: Lesson from Bacillus Anthracis Diagnostic Sensors. Analyst 2010, 135, 11821190. (20) Zhu, F.; Zhu, J.; Zhang, Z. Selective Detection of Glufosinate Using CuInS2 Quantum Dots as a Fluorescence Probe. RSC Adv. 2017, 7, 48077-48082. (21) Wei, F.; Lin, Y.; Wu, Y.; Sun, X.; Liu, L.; Zhou, P.; Hu, Q. Double Shell CdTe/CdS/ZnS Quantum Dots as a Fluorescence Probe for Quetiapine Determination in Fumarate Quetiapine Tablets. Anal. Methods 2014, 6, 482-489. (22) Wu, W. T.; Zhan, L. Y.; Fan, W. Y.; Song, J. Z.; Li, X. M.; Li, Z. T.; Wang, R. Q.; Zhang, J. Q.; Zheng, J. T.; Wu, M. B.; Zeng, H. B. Cu–N Dopants Boost Electron Transfer and Photooxidation Reactions of Carbon Dots. Angew. Chem. Int. Ed. 2015, 54, 6540-6544.

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(23) Wu, W. T.; Zhang, Q. G.; Wang, R. Q.; Zhao, Y. F.; Li, Z. T.; Ning, H.; Zhao, Q. S.; Wiederrecht, G. P.; Qiu, J. S.; Wu, M. B. Synergies between Unsaturated Zn/Cu Doping Sites in Carbon Dots Provide New Pathways for Photocatalytic Oxidation. ACS Catal. 2018, 8, 747-753. (24) Zhang, Q. Q.; Xu, W. M.; Han, C. C.; Wang, X. K.; Wang, Y. X.; Li, Z. T.; Wu, W. T.; Wu, M. B. Graphene Structure Boosts Electron Transfer of Dual-metal Doped Carbon Dots in Photooxidation. Carbon 2018, 126, 128-134. (25) Li, J. P.; Yang, S. W.; Deng, Y.; Chai, P. W.; Yang, Y. C.; He, X. Y.; Xie, X. M.; Kang, Z. H.; Ding, G. Q.; Zhou, H. F.; Fan, X. Q. Emancipating Target - Functionalized Carbon Dots from Autophagy Vesicles for a Novel Visualized Tumor Therapy. Adv. Funct. Mater. 2018, 28, 1800881. (26) Bhowmick, R.; Islam, A. S. M.; Giri, A.; Katarkar, A.; Ali, M. A Rhodamine Based Turn-on Chemosensor for Fe3+ in Aqueous Medium and Interactions of its Fe3+ Complex with HSA. New J. Chem. 2017, 41, 11661-11671. (27) Ogasawara, H.; Grzybowski, M.; Hosokawa, R.; Sato, Y.; Taki, M.; Yamaguchi, S. A Farred Fluorescent Probe Based on a Phospha-fluorescein Scaffold for Cytosolic Calcium Imaging. Chem. Commun. 2018, 54, 299-302. (28) Wang, P.; Li, Z.; Lv, G.-C.; Zhou, H.-P.; Hou, C.; Sun, W.-Y.; Tian, Y.-P. Zinc(II) Complex with Teirpyridine Derivative Ligand as “on–off” Type Fluorescent Probe for Cobalt(II) and Nickel(II) ions. Inorg. Chem. Commun. 2012, 18, 87-91. (29) Shi, N.; Zhang, Y.; Xu, D.; Song, C.; Jin, X.; Liu, D.; Xie, L.; Huang, W. π-System Based Coordination Polymer Hollow Nanospheres for the Selective Sensing of Aromatic Nitro Explosive Compounds. New J. Chem. 2015, 39, 9275-9280. (30) Wang, H.-M.; Liu, H.-P.; Chu, T.-S.; Yang, Y.-Y.; Hu, Y.-S.; Liu, W.-T.; Ng, S. W. A Luminescent Terbium Coordination Polymer for Sensing Methanol. RSC Adv. 2014, 4, 1403514041. (31) Shi, X.; Fan, Y.; Xu, J.; Qi, H.; Chai, J.; Sun, J.; Jin, H.; Chen, X.; Zhang, P.; Wang, L. Layer-structured Lanthanide Coordination Polymers Constructed from 3,5-bis(3,5dicarboxylphenyl)-pyridine Ligand as Fluorescent Probe for Nitroaromatics and Metal Ions. Inorg. Chim. Acta 2018, 483, 473-479. (32) Zhang, Z.; Wang, L.; Li, G.; Ye, B. Lanthanide Coordination Polymer Nanoparticles as a Turn-on Fluorescence Sensing Platform for Simultaneous Detection of Histidine and Cysteine. Analyst 2017, 142, 1821-1826. (33) Abdallah, A.; Freslon, S.; Fan, X.; Rojo, A.; Daiguebonne, C.; Suffren, Y.; Bernot, K.; Calvez, G.; Roisnel, T.; Guillou, O. Lanthanide-Based Coordination Polymers With 1,4Carboxyphenylboronic Ligand: Multiemissive Compounds for Multisensitive Luminescent Thermometric Probes. Inorg. Chem. 2019, 58, 462-475. (34) Wu, X.; Zhu, W. Stability Enhancement of Fluorophores for Lighting up Practical Application in Bioimaging. Chem. Soc. Rev. 2015, 44, 4179-4184.

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(35) Zheng, Q.; Juette, M. F.; Jockusch, S.; Wasserman, M. R.; Zhou, Z.; Altman, R. B.; Blanchard, S. C. Ultra-stable Organic Fluorophores for Single-molecule Research. Chem. Soc. Rev. 2014, 43, 1044-1056. (36) Nunnally, B. K.; He, H.; Li, L. C.; Tucker, S. A.; McGown, L. B. Characterization of Visible Dyes for Four-decay Fluorescence Detection in DNA Sequencing. Anal. Chem. 1997, 69, 2392-2397. (37) Zhang, M.; Qu, Z. B.; Ma, H. Y.; Zhou, T.; Shi, G. DNA-based Sensitization of Tb3+ Luminescence Regulated by Ag+ and Cysteine: Use as a Logic Gate and a H2O2 Sensor. Chem. Commun. 2014, 50, 4677-4679. (38) Li, H. Y.; Wei, Y. L.; Dong, X. Y.; Zang, S. Q.; Mak, T. C. W. Novel Tb-MOF Embedded with Viologen Species for Multi-Photofunctionality: Photochromism, Photomodulated Fluorescence, and Luminescent pH Sensing. Chem. Mater. 2015, 27, 1327-1331. (39) Bünzli, Jean-Claude, G. On the Design of Highly Luminescent Lanthanide Complexes. Coord. Chem. Rev. 2015, 293-294, 19-47. (40) Wang, Q. X.; Xue, S. F.; Chen, Z. H.; Ma, S. H.; Zhang, S.; Shi, G.; Zhang, M. Dual Lanthanide-doped Complexes: the Development of a Time-resolved Ratiometric Fluorescent Probe for Anthrax Biomarker and a Paper-based Visual Sensor. Biosens. Bioelectron. 2017, 94, 388-393. (41) Ryu, J.; Lee, E.; Lee, K.; Jang, J. A Graphene Quantum Dots Based Fluorescent Sensor for Anthrax Biomarker Detection and its Size Dependence. J. Mater. Chem. B 2015, 3, 4865-4870. (42) Yilmaz, M. D.; Oktem, H. A. Eriochrome Black T–Eu3+ Complex as a Ratiometric Colorimetric and Fluorescent Probe for the Detection of Dipicolinic Acid, a Biomarker of Bacterial Spores. Anal. Chem. 2018, 90, 4221-4225. (43) Zhu, Y. P.; Ma, T. Y.; Ren, T. Z.; Yuan, Z. Y. Mesoporous Cerium Phosphonate Nanostructured Hybrid Spheres as Label-free Hg2+ Fluorescent Probes. ACS Appl. Mater. Interfaces 2014, 6, 16344-16351. (44) Ramesh, B.; Dillip, G. R.; Rambabu, B.; Joo, S. W.; Raju, B. D. P. Structural Studies of a Green-emitting Terbium Doped Calcium Zinc Phosphate Phosphor. J. Mol. Struct. 2018, 1155, 568-572. (45) Ramesh, B.; Dillip, G. R.; Raju, B. D. P.; Somasundaram, K.; Peddi, S. P.; de Carvalho dos Anjos, V.; Joo, S. W. Facile one-pot Synthesis of Hexagons of NaSrB5O9:Tb3+ Phosphor for Solid-state Lighting. Mater. Res. Express 2017, 4, 046201. (46) Guo, B.; Lin, X.; Liu, P.; Zeng, Y.; Fan, H. Template-free Synthesis of High-yield Phosphonated Tin Oxides with High Specific Surface Area. Mater. Lett. 2019, 236, 85-88. (47) Fu, P. K. L.; Turro, C. Energy Transfer from Nucleic Acids to Tb(III): Selective Emission Enhancement by Single DNA Mismatches. J. Am. Chem. Soc. 1999, 121, 1-7. (48) Liu, M. L.; Chen, B. B.; He, J. H.; Li, C. M.; Li, Y. F.; Huang, C. Z. Anthrax Biomarker: An Ultrasensitive Fluorescent Ratiometry of Dipicolinic Acid by Using Terbium(III)-modified Carbon Dots. Talanta 2019, 191, 443-448.

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(49) Chen, H.; Xie, Y.; Kirillov, A. M.; Liu, L.; Yu, M.; Liu, W.; Tang, Y. A Ratiometric Fluorescent Nanoprobe Based on Terbium Functionalized Carbon Dots for highly Sensitive Detection of an Anthrax Biomarker. Chem. Commun. 2015, 51, 5036-5039.

Figure captions Scheme 1. Schematic description of DPA detection using multiporous terbium phosphonate coordination polymers microspheres (TbP-CPs) as fluorescent probe. Figure 1. SEM (a, b) and TEM (c, d) images of TbP-CPs. Figure 2. XPS spectra of O element (a), P element (b), N element (c) and Tb element (d) of TbPCPs. Figure 3. FT-IR spectra of EDTMP (a), TbP-CPs (b) and TbP-CPs with DPA (c). Figure 4. TGA curve of TbP-CPs (a), N2 sorption/desorption isotherms (b) and the corresponding pore size distribution curves (c) of TbP-CPs. Figure 5. Excitation spectra of TbP-CPs solution (green curve), emission spectra of TbP-CPs solution in the absence (black curve) and presence (red curve) of DPA (2.0 μM). (Inset: TbP-CPs solution in the presence (Left) and absence (Right) of 5.0 µM DPA under the 254 nm UV light lamp). Figure 6. Effects of various chemicals (5.0 μM) on fluorescence intensity of TbP-CPs with (red region) and without 5.0 μM DPA (black region) at 544 nm in NaAc-HAc buffer (200 mM, pH 5.0). Figure 7. The emission spectra of TbP-CPs solution with DPA of different concentration: 0, 0.05, 0.1, 0.5, 0.75, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 8.0 μM (Monitored and excited at 544 nm and 270 nm, respectively) (a). Fluorescence responses of TbP-CPs solution to various DPA concentrations (b). Inset: Linear relationship of fluorescence intensity at 544 nm as the response of DPA concentration in NaAc-HAc buffer (200 mM, pH 5.0). Table 1. Analysis result of DPA in serum and urine samples.

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Scheme 1.

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Figure 1.

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Figure 2.

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Figure 3.

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Figure 4.

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Figure 5.

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Figure 6.

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Figure 7.

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Table 1

Sample Urine (1%)

Bovine Serum (0.1%)

Add DPA (μM) Found (μM) Recovery (%)

RSD (%)

0

Not detected

/

/

0.70

0.660

94.29%

3.29%

2.00

2.010

100.5%

0.93%

3.00

2.996

99.87%

1.43%

5.00

4.700

94.00%

1.61%

0

Not detected

/

/

0.70

0.698

99.75%

4.14%

2.00

1.969

98.43%

1.78%

3.00

2.907

96.89%

1.35%

5.00

5.081

101.6%

0.45%

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The novel multiporous terbium phosphonate coordination polymers microspheres (TbP-CPs) with vegetable-flower-like structure and microporous surface were prepared as turn-on response fluorescent probe for dipicolinate acid (DPA) detection with high stability, good selectivity and rapid respond ability.

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Scheme 1. Schematic description of DPA detection using multiporous terbium phosphonate coordination polymers microspheres (TbP-CPs) as fluorescent probe. 194x70mm (300 x 300 DPI)

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Figure 1. SEM (a, b) and TEM (c, d) images of TbP-CPs.

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Figure 2. XPS spectra of O element (a), P element (b), N element (c) and Tb element (d) of TbP-CPs. 288x200mm (300 x 300 DPI)

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Figure 3. FT-IR spectra of EDTMP (a), TbP-CPs (b) and TbP-CPs with DPA (c). 181x184mm (300 x 300 DPI)

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Figure 4. TGA curve of TbP-CPs (a), N2 sorption/desorption isotherms (b) and the corresponding pore size distribution curves (c) of TbP-CPs. 286x201mm (300 x 300 DPI)

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Figure 5. Excitation spectra of TbP-CPs solution (green curve), emission spectra of TbP-CPs solution in the absence (black curve) and presence (red curve) of DPA (2.0 μM). (Inset: TbP-CPs solution in the presence (Left) and absence (Right) of 5.0 µM DPA under the 254 nm UV light lamp). 279x193mm (96 x 96 DPI)

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Figure 6. Effects of various chemicals (5.0 μM) on fluorescence intensity of TbP-CPs with (red region) and without 5.0 μM DPA (black region) at 544 nm in NaAc-HAc buffer (200 mM, pH 5.0). 288x200mm (300 x 300 DPI)

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Figure 7. The emission spectra of TbP-CPs solution with DPA of different concentration: 0, 0.05, 0.1, 0.5, 0.75, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 8.0 μM (Monitored and excited at 544 nm and 270 nm, respectively) (a). Fluorescence responses of TbP-CPs solution to various DPA concentrations (b). Inset: Linear relationship of fluorescence intensity at 544 nm as the response of DPA concentration in NaAc-HAc buffer (200 mM, pH 5.0). 288x200mm (300 x 300 DPI)

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Table 1. Analysis result of DPA in serum and urine samples. 200x127mm (300 x 300 DPI)

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