Real-Time Monitoring of Dissolved Oxygen with Inherent Oxygen

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Real-Time Monitoring of Dissolved Oxygen with Inherent Oxygen-Sensitive Centers in Metal-Organic Frameworks Jian Yang, Zhe Wang, Yongsheng Li, Qixin Zhuang, and Jinlou Gu Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.6b00016 • Publication Date (Web): 03 Apr 2016 Downloaded from http://pubs.acs.org on April 7, 2016

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Real-Time Monitoring of Dissolved Oxygen with Inherent Oxygen-Sensitive Centers in Metal-Organic Frameworks Jian Yang,† Zhe Wang,† Yongsheng Li,† Qixin Zhuang,† and Jinlou Gu*,†

†

Key Laboratory for Ultrafine Materials of Ministry of Education, School of Materials Science

and Engineering, East China University of Science and Technology, Shanghai 200237, China

Fax: +86-21-64250740; Tel: +86-21-64252599


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ABSTRACT Despite they are regarded as the ideal sensory platform, there are still no report on luminescent metal-organic frameworks (LMOFs) for dissolved oxygen (DO) measurement. Here we reported the rational construction of a platinum(II) porphyrinic LMOF, PCN-224(Pt), as an novel porous matrix for the phosphorescent DO sensing with commercially available Pt(II) meso-tetra(4carboxyphenyl)porphyrin as the bridging struts, oxygen-sensitive centers and luminescent reporters. The newly developed probe featured excellent tolerance to harsh chemical environments, excellent photostability as well as pH-independent luminescence, rationalizing its suitability for DO sensing. Thanks to the homogenous and well-isolated arrangement of the oxygen-accessible sites in porous network, PCN-224(Pt) exhibited reversible phosphorescent response and excellent linear Stern-Volmer quenching behavior toward DO. A real-time analysis of DO during the process of enzyme-catalytic reaction exemplified its potentials in industrial and biological applications with oxygen involved.


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1. INTRODUCTION Monitoring of dissolved oxygen (DO) is of great significance in many fields because it is related to water quality, food freshness, cell respiration and other biological processes.1-4 Although several strategies have been developed for the measurement of DO, a simple and effective technique such as optical sensing is more preferred due to the high demand of continuous monitoring, noninvasive measurement, in situ and in vivo analyses of DO in complex system.5-9 Luminescent metal-organic frameworks (LMOFs) are highly ordered and permanent porous crystals with unique luminescent properties, which could offer an ideal platform for chemical sensing.10-26 Their infinite combination of organic linkers and metal clusters allows structural diversity and tunable luminescent property with favorable implications on oxygen sensing. 27-34 Despite that, the current thrust of applied MOFs was mainly focused on their luminescent properties, and significant advances have been documented in the sensing of gas-phase oxygen. By comparison, the sensing of DO in aqueous solution and biological sample, in spite of its great importance in industrial setting and life system, remains largely unexplored in the field of MOFs. Therefore, an urgent need exists to exploit the water-resistant LMOF that exhibits excellent sensing property and practical application for tracking the informative marker of DO. Consensus has been achieved that platinum(II) porphyrin and its derivatives are ideal oxygensensitive phosphorescent dyes.35,36 Their long triplet state lifetime offers sufficient energy transfer from these complexes to oxygen molecules. This accompanies with an obvious phosphorescence quenching and a shortening of phosphorescent lifetime in correlation with DO level. Unfortunately, as highly conjugated macrocycle compounds, most of artificial porphyrinic species are hydrophobic and subject to aggregate in aqueous media, limiting their practical applications for


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DO measurement.37 Keeping these pros and cons in mind, we intend to construct a heterogeneous DO sensor to inherit both merits of LMOFs and the long lifetime oxygen-sensitive dyes. Scheme 1. Pictural illustration for the synthesis of LMOFs of PCN-224(Pt), and the schematic description of oxygen quenching process with platinum(II) porphyrinic TCPP(Pt) as the inherent bridging struts, oxygen-sensitive centers and luminescent reporters.

It has been verified that porphyrin-based MOFs of PCN-224 present exceptional chemical stability and water-resistant feature due to the strong interaction between Zr−O clusters and carboxylates in tetrakis(4-carboxyphenyl)porphyrin (TCPP) ligands.38,39 This strongly motivates us to propose that PCN-224(Pt) could hopefully provide a new platform to fabricate a long wavelength phosphorescent sensor for the detection of DO provides that the isostructural platinum(II) TCPP (TCPP(Pt)) molecules are utilized as organic ligands to construct the 3D MOF structure (Scheme 1) in place of TCPP. Compared to other traditional solid-state matrices,40-43 the advantages of such porous heterogenous sensor are obvious. Firstly, TCPP(Pt) is well-isolated by inorganic nodes of Zr-O clusters, which can effectively restrain π–π interactions between dye molecules and diminish the aggregation-induced quenching effect in aqueous solution. Secondly, each individual TCPP(Pt) unit could fully work as oxygen-accessible sites thanks to its homogeneous arrangement in the highly ordered architectures. Finally, TCPP(Pt) is an inherent


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component as the organic struts for the construction of PCN-224(Pt), so that the multi-step procedures for the introduction of the oxygen-sensitive molecules could be effectively avoided, and the pore space of developed LMOFs remains unblocked although abundant dye molecules are integrated.42,44 As expected, the red phosphorescence of PCN-224(Pt) could be reversibly switched upon its exposure to DO and dissolved nitrogen with a linear Stern-Volmer quenching behavior toward DO. This prefigures the great potentials of the current elaborated sensor for DO monitoring in a variety of biological reaction processes with oxygen involved. As a proof of principle, its primary practical application for the real-time and rapid tracking of DO in enzyme-catalytic reaction was exemplified.

2. EXPERIMENTAL DETAILS Chemicals and Materials. TCPP(Pt) was purchased from J&K Scientific Ltd., Beijing, China. Zirconyl chloride octahydrate (ZrOCl2·8H2O), acetic acid and N,N-Dimethylformamide (DMF) were purchased from Sigma-aldrich. β-D-glucose was supplied by TCI. Glucose oxidase (GOx 216 U·mg−1) was purchased from Yuanye Bio-Technology Co., Ltd, Shanghai, China. All other chemicals were obtained from Sinopharm Chemical Reagent Co., Ltd, China. All reagents were of analytical grade and used as received without additional purification. The applied water (18.1 MΩ·cm-1) in the experiments was purified from a NW Ultra-pure Water System (Heal Force, China). Synthesis of PCN-224(Pt). As a typical synthesis, ZrOCl2·8H2O (156.25 mg) was dissolved in 125 mL of DMF, and the mixture was sonicated for about 30 min. Then, TCPP(Pt) (31.25 mg) and acetic acid (31.25 mL) were added to the above solution. After further ultrasonic treatment for 10 min, the solution was placed in a 250 mL vial and heated at 65°C for 3 to 5 days. After cooling to


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room temperature, the red solid was collected by centrifugation and washed with DMF (5×100 mL). The DMF was then replaced with acetone (5×200 mL) at 65 °C over a 5 day period. Finally, the PCN-224(Pt) powder was activated at 120 °C in vacuo for 24 h. Photostability Study. Air-saturated PCN-224(Pt) aqueous suspension and free TCPP(Pt) in water/ethanol solution were continuously irradiated by a hand-held UV-lamp with excitation wavelength at 365 nm over a period of 6 h. The phosphorescent emmision at 655 nm was recorded with an interval of 30 min. Meanwhile, air-saturated PCN-224(Pt) aqueous suspension was irradiated at 512 nm every 1 s in the RF-5301PC spectro-fluorophotometer for a period of 3 h. Spectral Determination of DO with PCN-224(Pt). The PCN-224(Pt) probe was prepared by dispersing PCN-224(Pt) samples in 100 mL of ultrapure water under ultrasonic condition for 10 min. The concentration of PCN-224(Pt) suspension was set at 50 mg/L. To prepare a range of DO concentration for oxygen sensing investigation, the PCN-224(Pt) suspension was bubbled with varitional oxygen and nitrogen. The DO concentration was measured by a YSI model 550A DO electrode. The phosphorescent spectra were recorded with excitation at 512 nm, and phosphorescence lifetime decay spectra were monitored at 655 nm with excitation at 512 nm. Reversible Luminescence Response to DO. 3 mL of PCN-224(Pt) suspension was placed into a quartz cuvette with cuvette cap. Emission measurements were taken every 4 s at the maximum emission peak of 655 nm with an excitation wavelength of 512 nm. To modulate the concentration of DO in water, flowmeter was used to control gas flow through a tube and needle to bubble the PCN-224(Pt) suspension. Oxygen and nitrogen flow rates were set at 0.2 L·min-1. In the reversible test, the suspension was first saturated with oxygen and the phosphorescent intensity was measured. Following that, nitrogen was introduced into the suspension to reach N2-saturated state and


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repeated the phosphorescent measurement. The recycle experiments were conducted by swithching oxygen and nitrogen in PCN-224(Pt) suspension for 5 times. Real-Time Monitoring of DO in the Enzyme-Catalytic Process. β-D-glucose was added to PCN224(Pt) (50 mg·L-1) suspension, and the concentration of β-D-glucose was set at 0.25 M. Then, 3 mL of PCN-224(Pt) suspension containing β-D-glucose was placed into a quartz cuvette with cuvette cap. To initiate the reaction, 14, 28 or 56 μL of GOx solution (1 mg·mL-1; 216 U·mL-1) was added to the test solutions, respectively. The reaction was conducted at room temperature. Emission measurements were taken every 4 s at the maximum emission peak of 655 nm with excitation wavelength of 512 nm. A control experiment was conducted in a 25 mL vial in which DO electrode was equipped to determine the oxygen consumption in the enzyme-catalytic process. Instruments and Methods. Phosphorescent spectra were recorded with a RF-5301PC spectrofluorophotometer (Shimadzu), and UV-vis absorption spectra were measured with a UV-3600 spectrophotometer (Shimadzu). The powder X-Ray diffraction (XRD) patterns were obtained on a Bruker D8 instrument using Cu Kα radiation (40 kV, 40 mA). N2 sorption isotherms were recorded with a surface area and pore sizeanalyzer (Micromeritics Tristar 3020). All of the samples were degassed under vacuum for 12 h before measurements. The specific surface area was calculated by the Brunauer−Emmett−Teller (BET) method using adsorption data at a relative pressure lower than 0.15. ICP-AES was recorded in a Thermo Elemental IRIS 1000 instrument. Field emission scanning electron microscopy (FESEM) and energy dispersive spectroscopy (EDS) were conducted on a JEOL JSM6700F electron microscope. Oxygen concentration was calibrated with a YSI 550A hand-held dissolved oxygen electrode. The time-resolved phosphorescence decay data were recorded with a FLS 980 spectrometer (Edinburgh Instruments Ltd. UK) using a 512


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nm flashlamp (µF2) as the excitation source. The lifetime was calculated using the instrument software (FAST).

3. RESULTS AND DISCUSSION

Figure 1. Powder XRD patterns of (a) the simulated PCN-224 structure, (b) the as-synthesized samples of PCN-224(Pt), and PCN-224(Pt) upon the treatments in (c) water, (d) acidic and (e) basic solutions for the test of the chemical stability. Characterization of PCN-224(Pt) MOFs. The platinum(II) porphyrinic LMOF was prepared through the moderate solvothermal reaction between zirconium precursor and TCPP(Pt). To optimize the synthesis conditions, the XRD and N2 sorption techniques were employed to track the structural evolvement of the synthesized LMOFs under various reaction times from 3 to 5 days (Figures S1 and S2, Supporting Information). It is found that the longer reaction time (5 days) benefits to the production of high-quality crystal with high surface area. The powder XRD pattern of the as-synthesized LMOFs is essentially similar to that of parent PCN-224 (Figure 1, a and b) with the main diffraction peaks presenting at 3.2o, 4.6o, 5.6o, 6.5o, 7.9o and 9.2o. Such platinum(II) porphyrinic LMOFs thus adopts a PCN-224-type topology that is assembled with six-connected


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Zr6 octahedral clusters and TCPP(Pt) bridging struts (Scheme 1).39 To further confirm the 6coordinated Zr6 clusters in the porous structure, ICP-AES was conducted to determine the molar ratio of Zr/Pt (Table S1, Supporting Information). The ratio of Zr6 cluster to TCPP(Pt) in PCN224(Pt) is close to 2 : 3, coinciding with the fact that each Zr6 cluster is linked by six carboxyl groups in different TCPP(Pt) ligands. Additionally, PCN-224(Pt) features high chemical stability and retains good crystal structure upon the treatments in water, acidic (pH = 1) and basic (pH = 11) solutions (Figure 1, c-e). The good tolerance to water and harsh chemical environments meets the prerequisite as heterogeneous sensing platform for DO measurement in aqueous solutions.

Figure 2. SEM image of the as-synthesized PCN-224(Pt) particles. SEM images were taken to investigate the morphology of the synthesized PCN-224(Pt) particles. It can be observed that PCN-224(Pt) displays well-dispersive cubic microcrystals with uniform particle size of ca. 1 μm3 (Figure 2). The obtained material not only maintains the regular shape but also preserves the good dispersion upon the treatments in water, acidic (pH = 1) and basic (pH = 11) solutions (Figure S3, Supporting Information). The simultaneous EDS (Figure S4 and Table S2, Supporting Information) produces strong Pt and Zr signals with a molar ratio of approximate 2.67 to 0.67 in agreement with the deduction from ICP-AES measurements. The


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permanent porosity of activated PCN-224(Pt) was measured by N2 sorption measurement at 77 K (Figure S2c, Supporting Information). Type I isotherm is obtained for PCN-224(Pt), exhibiting a high surface area of around 1725 m2/g as well as an open framework structure with channels of 1.85 nm in diameter. The high surface area and large channel size make the oxygen-sensitive centers of platinum(II) porphyrin more accessible and benefit to the free diffusion of DO molecules, consequently favouring the design of the DO sensor. Spectroscopic Properties of PCN-224(Pt). The UV-visible absorption spectra of the free TCPP(Pt) in water/ethanol solution and PCN-224(Pt) in water were compared in Figure 3A. Free TCPP(Pt) displays a Soret band at 400 nm and two Q-bands at 508 and 538 nm. The peak positions of PCN224(Pt) are similar to those of the free TCPP(Pt) with a Soret band at 401 nm and two Q-bands at 512 and 538 nm. This similarity indicates that TCPP(Pt) ligands is well-isolated in a highly ordered MOF architecture.45 The existence of porous coordination network could greatly reduce the aggregation of TCPP(Pt) and significantly diminish the aggregation-induced quenching effect in aqueous solution. It is worth noting that free TCPP(Pt) is almost insoluble in water, which is problematic for the direct DO detection in aqueous-solution. The phosphorescence of PCN-224(Pt) sensitively responds to the variation of DO level as evidenced by monitoring the luminescent signal of PCN-224(Pt) suspension upon excitation at 512 nm. The sensitivity of oxygen probe could be evaluated by the luminescent quenching percentage in the saturated N2 and O2 solutions ((IN2-IO2)/IN2, IN2 and IO2 denote the phosphorescent intensities of sensor in saturated nitrogen and oxygen solutions, respectively).46 Based on this, an approximate 88% signal decay is quantified with the introduction of pure O2 gas to saturated N2 solution (Figure 3B). This datum for the developed probe is relatively high among the reported optical DO sensors (Table S3, Supporting Information), and rationalizes its suitability for DO monitoring.


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Additionally, the phosphorescent intensity of PCN-224(Pt) gradually weakens in saturated N2, air and O2 solutions, demonstrating that the current sensor not only exhibits excellent sensitivity but also a wide response range to DO.

Figure 3. (A) UV−vis absorption spectra (solid line) and phosphorescent spectra (dot line) of the free TCPP(Pt) in water/ethanol solution (v:v =1:1) and PCN-224(Pt) suspension in water at 25 oC (λex = 512 nm). (B) Phosphorescent spectra of PCN-224(Pt) suspension in saturated N2, air and O2 solutions upon excitation at 512 nm at 25 oC. (C) Photostabilities of the free TCPP(Pt) and PCN224(Pt) suspension in air-saturated aqueous media with 6 h of continuous exposure to a hand-held UV-lamp (irradiation at 365 nm). (D) pH-independent phosphorescence of PCN-224(Pt) in N2saturated aqueous solutions with pH ranging from 1 to 11. (λex = 512 nm, λem = 655 nm, T = 25 o

C).


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The photostability of probe is of great importance for DO monitoring. As shown in Figure 3C, the phosphorescent intensities of PCN-224(Pt) and free TCPP(Pt) keep stable after 6 h of continuous exposure to a hand-held UV-lamp with irradiation wavelength of 365 nm. The same phenomenon is also observed after the PCN-224(Pt) suspension is irradiated by the light of 512 nm for 3 h (Figure S5, Supporting Information). These illustrate that the developed sensor meets the need for a continuous DO monitoring. Additionally, the pH has almost no effect on the phosphorescence of PCN-224(Pt) over a wide pH range from 1 to 11 (Figure 3D). It is ascribed to the coordination of platinum(II) into the porphyrin, preventing the protonation or deprotonation of the pyrrole rings under acidic and basic conditions. Taking together, these merits, such as obvious phosphorescent response to DO, excellent photostability as well as pH-independent phosphorescence, offer the critical prerequisites for PCN-224(Pt) as an ideal platform for DO sensing. Measurement of DO with PCN-224(Pt) Probe. To investigate the oxygen-sensitive properties in detail, oxygen and nitrogen gases were circularly bubbled to tune DO concentration in PCN-224(Pt) suspension. As shown in Figure 4A, phosphorescent intensity of PCN-224(Pt) suspension gradually decreases with an increase of the DO level. Furthermore, the phosphorescence quenching process could be described by the linear Stern−Volmer equation.47 The Stern-Volmer plot (I0/I vs [DO]) exhibits a good linear correlation (R2 = 0.99) in the DO concentration range from nitrogen-saturated to oxygen-saturated solutions (Figure 4B), indicating that each TCPP(Pt) units are equally accessible and homogenously distributed in the microenvironment of porous PCN-224(Pt). This exciting discovery should benefit from the open network of MOFs in which the inorganic Zr-O clusters separate the platinum(II) porphyrin regularly and make them efficiently interact with the DO. Interestingly, even when the excitation wavelengths were varied, the PCN-


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224(Pt) probe could still work as an ideal sensory probe for the DO measurement. Two wavelengths at Soret-band (401 nm) and Q-band (512 nm) of PCN-224(Pt), and commonly available excitation wavelength of 365 nm in hand-held UV lamp were chosen for comparison. It is found that the phosphorescence of PCN-224(Pt) is not only obviously quenched by DO but also strictly obeys an excellent linear Stern-Volmer quenching behavior for all of the selected excitation wavelengths (Figures S6 and S7, Supporting Information). Actually, under the illumination of hand-held UV-lamp (λex = 365 nm), the naked eye visible red emission of PCN-224(Pt) suspension obviously becomes weakened in the presence of DO, directly confirming that the sensor could work in this wavelength (inset in Figure 4B). The detailed KSV values are listed in Table 1, and only slightly smaller variation of KSV is deduced upon increasing the excitation wavelength from 365 to 512 nm in agreement with the reported work.2 512 nm was selected in this work due to the strongest phosphorescent emission upon excitation with this wavelength.

Figure 4. (A) Evolvement of the phosphorescent spectra of PCN-224(Pt) (50 mg L−1) suspension with DO level increasing. (B) The corresponding Stern-Volmer plot of the phosphorescent intensity of PCN-224(Pt) suspension as a function of DO concentration. The inset: the digital


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pictures of the PCN-224(Pt) suspension in N2-saturated and O2-saturated aqueous solutions illuminated by hand-held UV lamp with an irradiation wavelength of 365 nm. To probe the quenching mechanism, phosphorescence lifetime decay of PCN-224(Pt) suspension in aqueous solution was measured at 25 oC. As shown in Figure S8, the data could be well fitted by single exponential lifetime decay under different DO concentrations, which indicates that abundant TCPP(Pt) luminophores are well isolated and distributed in a homogeneous microenvironment.48 The lifetime τ0 (24.0 μs) in a deoxygenated solution (oxygen concentration: 0 μΜ) steadily decreases with the increasing of DO concentration, and reduces to 2.9 μs in an oxygen-saturated solution (oxygen concentration: 728 μM, Table S4, Supporting Information). The phosphorescent lifetimes could be well fitted to the linear Stern-Volmer equation with KSV = 0.0099 μM-1, which is comparable to the result deduced from the phosphorescence intensity measurement (KSV = 0.0101 μM-1) (Figure 4). This coincides with a dynamic quenching process. Thanks to the slow emission from the triplet state of PCN-224(Pt) in the scale of microsecond (a forbidden process), the excited platinum(II) porphyrin molecules in PCN-224(Pt) can undergo a photochemical process of collisional quenching through interaction with molecular oxygen.8 Generally, phosphorescent molecules with long emission lifetimes are ideal for optical DO measurement. On the other hand, the phosphorescence of probe might be quenched too much in a very low level of DO if the lifetime is too long. Obviously, the current PCN-224(Pt) probe with appropriate lifetime maintains a balance between the sensitivity and the detection range for DO sensing. Table 1. Response of PCN-224(Pt) Probe to DO under Various Excitation Wavelengths and Temperatures


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Temperatures (oC)

Excitation Wavelengths (nm)

KSV (μM-1) Correlation (R2)

365

401

512

20

25

30

35

40

0.0118

0.0113

0.0101

0.0095

0.0101

0.0111

0.0116

0.0124

0.99

0.99

0.99

0.99

0.99

0.99

0.99

0.99

To further investigate the mechanism of dynamic quenching, the DO sensing properties of PCN-224(Pt) were also studied under different temperatures. As expected, high temperature decreases the phosphorescent intensity of PCN-224(Pt) but increases the DO quenching efficiency (Figures S9-12, Supporting Information). This is common in a dynamic quenching process since higher temperature is associated with the higher collisional frequency between platinum(II) porphyrin phosphors and O2 molecules.49 Again, good linear response can be observed from the Stern-Volmer plots of PCN-224(Pt) probe under various selected temperatures (Table 1), suggesting that the current sensor could work in a wide temperature range.

Figure 5. (A) Reversible phosphorescent response of PCN-224(Pt) suspension upon alternating exposure to N2 and O2 saturated aqueous solutions, and (B) the partial enlarged curve in Figure A (λex = 512 nm, λem = 655 nm, T = 25 oC).


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The kinetic phosphorescent spectra of PCN-224(Pt) suspension by alternating cycles of saturated O2 and saturated N2 solutions indicate that PCN-224(Pt) exhibits reversible oxygen quenching and nitrogen recovering properties (Figure 5A). It takes about 68 and 392 s, respectively, to accomplish 95% of total phosphorescent intensity variation from saturated N2 solution to saturated O2 solution and vice versa (Figure 5B). Given the oxygen dissolution/removal rate in water, this value essentially represents the conversion time between saturated O2 and saturated N2 solutions through bubbling method. This implies that the response time of PCN-224(Pt) probe toward oxygen might be much faster thanks to their highly ordered and open structure. To further explore the potential biological applications of the elaborated sensory platform, the PCN-224(Pt) probe was employed for the real-time monitoring of DO in enzyme-catalytic process.50-51 It is well known that GOx can catalyze the oxidation of β-D-glucose to gluconic acid and hydrogen peroxide by utilizing molecular oxygen as an electron acceptor.52 As phosphorescent kinetics illustrated in Figure 6A, the phosphorescent intensities of PCN-224(Pt) probe rapidly increase with the addition of GOx into β-D-glucose solutions, corresponding to a high catalytic reaction efficiency and rapid consumption of DO in water. The more rapid phosphorescent enhancement was observed when the higher concentration of GOx was introduced into β-Dglucose solutions, matching well with the fact that DO is more rapidly consumed with GOx increasing. Through the luminescent quantification method, the phosphorescent intensity is transferred to DO concentration (Figure 6B). The results confirm that the consumption rate of DO is positively correlated with the amount of GOx. The full removals of DO are achieved in 20 s for 4 U·mL−1 GOx, and 45 s and 90 s for 2 U·mL−1 and 1 U·mL−1 GOx, respectively. The DO electrode is also used to detect DO concentration in the process of enzyme-catalytic reaction. The data reading out from DO electrode and PCN-224(Pt) probe match well with each other (Figure S13,


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Supporting Information). This suggests that the newly developed PCN-224(Pt) probe is applicable to the real-time analysis of DO.

Figure 6. (A) Time-dependent phosphorescent emission from PCN-224(Pt) probe (50 mg L-1 in aqueous solution) for the monitoring of the oxygen consumption in the process of the enzymatic catalysis oxidation of β-D-glucose. The concentration of β-D-glucose is 0.25 M and the concentrations of GOx are set as 1, 2, 4 U·mL−1. (λex = 512 nm, λem = 655 nm, T = 25 oC.) (B) The corresponding DO concentrations after different times in the process of enzymatic catalytic oxidation of β-D-glucose.

4. CONCLUSIONS In summary, platinum(II) porphyrinic LMOFs have been successfully constructed and designed for the DO measurement. Thanks to the homogenous and well-isolated arrangement of oxygenaccessible sites in porous network, PCN-224(Pt) probe exhibits reversible phosphorescent response and excellent linear Stern-Volmer quenching behavior over the whole range of DO concentrations. A real-time analysis of DO during the process of GOx catalytic reaction exemplifies its potentials in industrial and biological applications. It is believed that this may be a


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facile strategy to fabricate novel optical oxygen-sensitive MOFs and further expand their applications for a wide variety of bioanalytical tasks.

ASSOCIATED CONTENT Supporting Information XRD patterns, N2 sorption isotherms, SEM images, EDS, Tables S1-4, photostability test, phosphorescent spectra of PCN-224(Pt) measured at different temperatures and excited at different wavelengths, phosphorescent lifetime spectra under different DO concentrations and their corresponding Stern-Volmer plot, comparison of DO level detected by oxygen electrode and PCN224(Pt) probe. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author E-mail: [email protected]; (J. L. Gu) Fax: +86-21-64250740; Tel: +86-21-64252599 Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT This work was financially supported by the Natural Science Foundation of China (Grants 51072053 and 51372084), the Innovation Program of Shanghai Municipal Education Commission (13zz040), the Nano-Special Foundation for Shanghai Committee of Science and Technology (12nm0502600) and the 111 Project (Grant B14018).


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TOC Figure for Publication


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Real-Time Monitoring of Dissolved Oxygen with Inherent Oxygen

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