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A Rapid and Facile Detection for Specific Small-Sized Amino Acids Based on Targets-Triggered Destruction of Metal Organic Frameworks Wei Li, Xue Qi, Chao-Yue Zhao, Xiu-Fang Xu, An-Na Tang, and De-Ming Kong ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b13998 • Publication Date (Web): 09 Dec 2016 Downloaded from http://pubs.acs.org on December 16, 2016

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ACS Applied Materials & Interfaces

A Rapid and Facile Detection for Specific Small-Sized Amino Acids Based on Targets-Triggered Destruction of Metal Organic Frameworks Wei Li,†Xue Qi,†Chao-Yue Zhao,‡Xiu-Fang Xu,‡An-Na Tang,*,† and De-Ming Kong*,† †

Tianjin Key Laboratory of Biosensing and Molecular Recognition, College of Chemistry,

Collaborative Innovation Center of Chemical Science and Engineering, Nankai University, 94 Weijin Road, Tianjin 300071, PR China

‡

Department of Chemistry, Key Laboratory of Advanced Energy Materials Chemistry

(Ministry of Education), Nankai University, 94 Weijin Road, Tianjin, 300071, PR China

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ABSTRACT

Most of the reported metal organic frameworks (MOFs)-based DNA sensors were developed by utilizing the different adsorption capacities of MOFs to different structural DNAs (for example single-stranded DNAs (ssDNAs) and double-stranded DNAs (dsDNAs)) or ssDNAs with different lengths. Herein, we introduced another strategy for the design of MOFs-based biosensing platforms. We found that specific small-sized amino acids (for example glycine and serine) could lead to the destruction of the MOFs formed

by

[Cu(mal)(bpy)]·2H2O]

thus

recovering

the

fluorescence

of

a

fluorophore-labeled ssDNA that had been quenched by MOFs. Corresponding working mechanism was discussed. Based on this finding, a mix-and-detect fluorescence method was designed for the turn-on detection of specific small-sized amino acids. The feasibility of its use in real serum samples was also demonstrated. Besides biosensing applications, the discovery of amino acids-triggered destruction of MOFs can also enrich the building blocks of molecular logic gate. As an example, a biomolecular logic gate that performs OR logic operation was constructed using glycine and a DNA strand as inputs.

KEYWORDS: metal organic frameworks; amino acids; fluorescence biosensors; mechanism; molecular logic gate

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1. INTRODUCTION As the building blocks of proteins and enzymes, amino acids play central roles in organisms.1 Most α-amino acids are widely distributed in the food, condiments and pharmaceutical preparations.2 For example, as a condiment, glycine (Gly) can cover the bitter taste of saccharine and enhance sweetness of food. However, eating too much glycine has side effects, which will break down the adsorption balance for amino acids and interfere with the absorption of other amino acids.3 Due to the analysis of amino acids playing an important role in biochemistry, protein chemistry, food science, clinical medicine and many other fields, developments of reliable methods for amino acid determination has attracted more and more attention.4-6 Nowadays, many amino acid detection methods, including UV-Vis spectrophotometry,7 high performance liquid chromatography (HPLC),8 cation-exchange chromatography,9 gas chromatography (GC)10 and capillary electrophoresis (CE),11 have been reported. Although sensitive, most of these methods have the limitations of high cost, low speed, complicated operation and requiring sophisticated instruments. Therefore, development of cost-effective and facile detection platforms for rapid and sensitive detection of amino acids is still urgently required. A good choice might be fluorescent spectrometry due to its advantages of high sensitivity, excellent selectivity, simple operation and inexpensive instruments.12-14 As a new class of crystalline coordination polymers,15 metal-organic frameworks (MOFs) have recently emerged as one kind of promising materials to develop novel catalysts,16-17 adsorbents,18-21 optical sensors22-25 and stationary phases in GC26-27 and HPLC28-30 because of their well-defined structure, accessible surface, flexible and uniform cavities can generate a high density of biomimic active centers and separation effects. In recent years, MOFs have been widely used in the development of DNA biosensors. The commonly used working mechanism is based on the different adsorption abilities of MOFs to different structural DNAs (for example single-stranded DNAs (ssDNAs) and double-stranded DNA (dsDNAs)) or ssDNAs with different lengths. That

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is, MOFs have strong adsorption capacity, it can effectively adsorb long fluorophore-labeled ssDNAs. As a result, the fluorescence of the fluorophore is quenched. Addition of complementary target DNAs or specific enzymes can covert long ssDNAs to dsDNAs or short length ssDNAs. Due to the reduced adsorption abilities of MOFs to dsDNAs and short length ssDNAs, fluorophore is desorbed from the surface of MOFs, thus resulting in the recovery of the quenched fluorescence.31-35 Herein, we synthesized the MOFs of [Cu(mal) (bpy)]·2H2O (Cu MOFs), and constructed one MOFs-based sensing platform using a new working mechanism. That is, MOFs can adsorb fluorophore-labeled DNAs, thus quench the fluorescence. In the presence of amino acids, MOFs will be dissolved, and such a destruction of MOFs is amino acid size-dependent. Accompanied by the destruction of MOFs, the quenched fluorescence is recovered. Based on this strategy, a rapid and facile sensing platform was developed for the detection of specific small-sized amino acid. To the best of our knowledge, no such applications of MOFs in biosensing based on target-mediated destruction of MOFs have been reported so far. Such a new working mechanism will enrich the design strategies of biosensors, thus further promoting the applications of MOFs in biosensing. Besides biosensing applications, the discovery of amino acids-triggered destruction of MOFs can also enrich the building blocks of molecular logic gate. As an example, a biomolecular logic gate that performs OR logic operation was constructed using glycine and a DNA strand as inputs. 2. EXPERIMENTAL 2.1. Materials and Methods All the amino acids were purchased from Sangon Biotech. Co. Ltd. (Shanghai, China). Cu(OAc)2 were obtained from Energy Chemical (Shanghai, China). D, L-malic acid, 4, 4′-bipyridyl were obtained from Tianjin Heowns Biochem LLC (Tianjin, China). Newborn bovine serum sample was purchased from Gibco. DNA oligonucleotides (24-mer: 5′-AGG CAG TAA CCA AGG CAG TAA CCA-FAM-3′; 24-mer-c: 5′-TGG

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TTA CTG CCT TGG TTA CTG CCT-3′) were synthesized and purified by Sangon Biotech. Co. Ltd. (Shanghai, China). The 3′-end of 24-mer is labeled with fluorescein (FAM). Double-distilled water, which was purified by a Nanopure II system (Barnstead, USA), was used in the whole experiment. A Perkin-Elmer 240C analyzer was used for Elemental analysis (C, H and N). A Tensor 27 OPUS (Bruker) FT-IR spectrometer with KBr pellets was used to measure IR spectra. Thermogravimetric (TG) analysis were performed on a Rigaku standard TG-DTA analyzer in the range of ambient temperature to 500 °C with a heating rate of 10 °C per minute, an empty Al2O3 crucible was selected as reference. A Rigaku D/Max-2500 diffractometer at 40 kV, 100 mA for a Cu-target tube and a graphite monochromator was used to record the powder X-ray diffraction spectra (PXRD). Simulation of the PXRD pattern was performed by the single-crystal data and diffraction-crystal module of the Mercury program version 3.0 and Diamond program 3. SEM was obtained from a Shimadzu SS-550 (Shimadzu, Japan). Microscope images were performed on a COIC microscope with 40×, NA=1.65, 160 mm and WD=0.17. All fluorescence data were measured by a SHIMADZU RF-5301PC spectrofluorimeter. A 40 µL micro quartz cell with 1 cm path-length (Starna Brand, England) was used. By setting the excitation wavelength at 480 nm, the emission spectra in the range of 500-650 nm were collected at room temperature. The slit widths of excitation and emission were both set at 10 nm. 2.2 Synthesis of [Cu(mal)(bpy)]·2H2O [Cu(mal)(bpy)]·2H2O (Cu MOFs) was prepared with a little modification according to the reported method.36 Cu(OAc)2 (0.0816 g, 0.15 mmol), DL-malic acid (0.1260 g, 0.3 mmol) and 4, 4′-bipyridyl (0.0702 g, 0.15 mmol) in 9 mL of water/methanol mixture (1:1, v/v), were sealed in a glass tube. The mixture was heated at 100oС for 24 h. Big dark blue square crystals were harvested and washed with methanol then vacuum dried at 70 oC for 3 h.

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2.3 Elemental and Thermogravimetric Analysis of Cu MOFs Elemental data of Cu MOFs were shown in Table S1. The as-synthesized Cu MOFs was in good agreement with the reported data. Thermogravimetric analysis data was shown in Figure S1. It can be found that solvent weight loss was about 8% (9% calculated for 2H2O). These results were similar to the literature report. 2.4 Fluorescence Quenching Property of Cu MOFs on FAM-Labeled DNA The FAM-labeled DNA (24-mer) was dissolved in phosphate-buffered saline (PBS). The solution was heated at 95 °C for 5 min, then cooled to room temperature gradually. Cu MOFs were added into the above solution. After the suspension was vortexed for 10 s at room temperature, the fluorescence signal at 518 nm was recorded (λex= 480 nm). 2.5 Assay of Specific Small-Sized Amino Acids For assay of specific small-sized amino acids, 50 nM 24-mer was dissolved in 10 mM PBS buffer (pH 7.4). The above solution was heated at 95 °C for 5 min and gradually cooled to ambient temperature. Then, different concentrations of amino acids were added and vortexed for 10 s. Finally, Cu MOFs was added to reach a final concentration of 0.50 mg mL-1. The total volume was 100 µL. Upon vortexing for 10 s at room temperature, the fluorescence intensity at 518 nm was measured (λex = 480 nm). 2.6 Assay of Specific Small-Sized Amino Acids in Newborn Bovine Serum The newborn bovine serum was melt in the refrigerator at 4 °C. Then the solution was heated at 95 °C for 15 min and cooled to ambient temperature gradually. The supernatant was taken out for further experiment. To demonstrate that the proposed method might be used for Gly and Ser quantitation in real samples, two concentrations of Gly (30 µg mL-1, 60 µg mL-1) or Ser (30 µg mL-1, 300 µg mL-1) were added into the newborn bovine serum sample. According to the obtained fluorescence intensities, the recovery values were calculated by utilizing the above-obtained calibration graph.

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2.7 Molecular Simulations of the Reaction between MOFs and Gly Geometry optimization and frequency analysis were performed using B3LYP functional37-39 and a mixed basis set of SDD40 for Cu and 6-31G(d) for other atoms. All reported Gibbs free energies involve thermal corrections to the Gibbs free energy at 373.15 K and solvation free energy corrections computed by single-point calculations, which were carried out on B3LYP-optimized geometries with the M06 functional,41 a mixed basis set of SDD for Cu and 6-311+G(d, p) for other atoms, and the SMD42solvation model with water as the solvent. All calculations were carried out with Gaussian 09.43 3. RESULTS AND DISCUSSION 3.1 Characterization of Cu MOFs Dark blue square crystals of Cu MOFs were harvested according to the literature with a little modification.36 Cu MOFs was obtained from water/methanol mixture with good yields (>80 %) and characterized by power X-ray diffraction (PXRD) (Figure 1B), scanning electron microscopy (SEM) (Figure 1C), FT-IR spectroscopy (Figure 1D), elemental (Table S1) and thermogravimetric analysis (Figure S1). The PXRD pattern of as-synthesized Cu MOFs was in good agreement with the reported data.36 The results of SEM showed the prepared Cu MOFs had a diameter of 40-50 µm. The FT-IR analysis of Cu MOFs showed that the absorption peaks for O-H and C-H stretching vibrational modes were at about 3282 cm-1 and 2935 cm-1. The peaks at 1608 cm-1 and 1344 cm-1 may be attributed to C-O bonding stretching vibrational modes. From the thermogravimetric analysis data, about 8% solvent weight loss (9% calculated for 2H2O) can be found. These results were similar to the reported literature. X-ray single-crystal diffraction data36 were simulated by the Mercury program version 3.0 and Diamond program 3 (Figure 1A). Asymmetric unit of Cu MOFs contains one Cu(II) cation, one malate anion and one 4, 4′-bipyridyl (bpy) linker. The Cu(II)

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cations coordinated three carboxylate oxygen atoms of three malate ligands. In turn, each malate anion was coordinated by three Cu(II) cations through carboxylate oxygen cations by µ3-O, O′, O″ mode. There were two nitrogen atoms of bpy ligands attached to the Cu(II) cations forming almost symmetrical tetragonal pyramidal coordination polyhedron (CN=5). The interatomic distances Cu-Obase (1.953,1.971 Å), Cu-Oapical (2.265 Å) and Cu-N (2.020 Å) were within normal coordination bonds, taking into account the distortion of Cu2+ ions due to Jahn-Teller effect. The copper atoms and malate anions formed a 2D layer structure. 3.2 Fluorescence Quenching of 24-mer by Cu MOFs We found that the Cu MOFs can be destroyed by specific small-sized amino acids (middle figure in Scheme 1A), for example Gly. Based on this finding, a specific small-sized amino acids sensor was developed. The design strategy was shown in Scheme 1. One fluorescent labeled ssDNA probe (24-mer) was employed in this proposed mix-and-detect method. The ssDNA could be absorbed by Cu MOFs effectively, resulting in fluorescence quenching of the fluorescein (FAM) labeled on it. When the target specific small-sized amino acids were added in the system, Cu MOFs was dissolved and the quenched fluorescence signal recovered. By recording the fluorescence change of the sensing system, the quantitation of target specific small-sized amino acids can be achieved. To demonstrate the proposed mechanism, the fluorescence emission spectra of 24-mer at different conditions were studied (Figure 2). Free 24-mer exhibited strong fluorescence emission. In the presence of Cu MOFs, however, the green fluorescence of 24-mer decreased with increasing Cu MOFs dosage from 0 to 0.50 mg mL-1, resulting in 91.4% quenching efficiency, which indicated that Cu MOFs could effectively quench the fluorescence of the ssDNA probe. Then, further increase of Cu MOFs concentration caused the increase of resonance peak of Cu MOFs, which would mask the fluorescence quenching to some degree. The fluorescence intensity change gave a Lineweaver-Burk

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plot (1/(F0-F)=1/F0 + KLB/(F0[Q])(RLB2 = 0.984, Figure S2A), F0 and F were the fluorescence intensity before and after Cu MOFs addition, KLB was the static quenching constant, and [Q] was the quencher concentration. While the Stern-Volmer plot (F0/F=1+KSV[Q], KSV was the quenching constant) displayed a poor correlation (RSV2 = 0.816, Figure S2B), thus indicating that the fluorescence quenching followed the static quenching mechanism rather than the dynamic one. The kinetic behavior of this quenching process was also investigated in detail. Figure S3 showed that the fluorescence intensity of 24-mer reduced quickly in the first 3 s after Cu MOFs addition, and then reached an equilibrium in 10 s. The fast fluorescence quenching of the probe by Cu MOFs ensures the high response rate of the present method. 3.3 Studies on Destruction Mechanism of MOFs by Specific Small-Sized Amino Acids Amino acids have both carboxyl and amino groups, which have strong coordination ability and might replace the ligands of Cu MOFs, thus resulting in the destruction of MOFs. Therefore, the adsorbed ssDNA desorbed from MOFs surface, then returned back into solution, accompanied by the recovery of the fluorescence signal. The recovered fluorescence intensity could reach 60.5% of the original free 24-mer. Correspondingly, before adding Cu MOFs, the solution of 24-mer was clear and transparent, and the solution became muddy after adding Cu MOFs, then solution became transparent blue after adding Gly (as shown by the middle figure in Scheme 1A). The abilities of 16 different amino acids to dissolve Cu MOFs and recovery the fluorescence of Cu MOFs/24-mer mixture were compared. As shown in Figure 3, except Gly, serine (Ser) and threonine (Thr), none of other tested amino acids could effectively prevent the fluorescence quenching of Cu MOFs to 24-mer. In the presence of these amino acids, 91.0-93.0% fluorescence quenching could still be observed with Cu MOFs, which is comparable to the 91.4% quenching efficiency of blank systems without amino acids. On the contrary, Gly, Ser and Thr show the ability to reduce the fluorescence quenching of 24-mer by MOFs, and the ability follows the order of Gly>Ser>Thr.

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Considering that these three amino acids have smaller volumes than others, the observed amino acids-triggered destruction of MOFs might be amino acid size dependent. The amino acids with smaller volume can enter into the pores of MOFs more easily, thus showing better destruction ability to MOFs. The pore sizes of MOFs were about 4.25Å × 9.95 Å. The small-sized Gly has a size of 3.20Å × 3.95 Å (Figure S4), which is much smaller than those of MOFs pore sizes. Therefore, Gly can easily enter into the pores of MOFs and replace the ligands of Cu MOFs. On the contrary, the amino acid with large size, for examples phenylalanine (Phe, 4.28Å × 8.60 Å) and tryptophane (Trp, 5.39 Å × 9.91 Å), cannot enter the pores of MOFs, thus showing no ability to destroy MOFs. The structure and size of 20 commonly used amino acids were shown in Figure S5. In order to observe the breakage process of MOFs, 0.5 mg mL-1 Cu MOFs mixing with 0.5 mg mL-1 Cys, Ser and Phe were observed under the microscope respectively. Figure S6A-C, G-I were Cu MOFs mixing with Cys and Phe, separately, varying over time from 0s to 60s (0s for without amino acids added). The morphology of MOFs was not changed obviously. Figure S6D-F were MOFs mixing with Ser varying over time from 0s to 10s. The morphology of MOFs was destroyed quickly. If the two amino acids have the similar size, such as Thr and Val (Valine), the amino acid with more hydroxyl groups will have the stronger ability to destroy MOFs. It is probably due to the strong coordination of hydroxyl group with Cu of MOFs. From Figure 3, we can find that the fluorescence signal was higher when Val was replaced by Thr. Ser and Cys also have the similar size with the difference in hydroxyl group and thiol group, the bigger-sized sulfur atom in Cys can impede the N and O to coordinate with Cu of MOFs. These results demonstrate that the proposed sensing platform has high response specificity to specific small-sized amino acids. To further explore the mechanism of specific small-sized amino acid-triggered destruction of MOFs, the reaction of MOFs and Gly was investigated through molecular

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simulations. Gibbs free energies were calculated to better understand the mode of ligand exchange reaction. The Gibbs free energy of several possible ligand exchange reactions were listed in Table S2. From the results, we could conclude that the reaction of one Cu(II) ion and two Gly anions most easily happened to form a bicyclic Cu complex (Scheme 1B). 3.4 Optimization of the Specific Small-Sized Amino Acids-Sensing Platform To obtain the best performance for specific small-sized amino acid analysis, several experimental conditions of the sensing system were optimized. Firstly, the influence of buffer solution acidity on the fluorescence quenching of 24-mer by Cu MOFs were examined (Figure S7). When increasing pH from 6.0 to 7.0, the quenching efficiency of Cu MOFs to 24-mer increased significantly and reached a maximum at pH 7.0. Then, further increasing pH almost had no effects on the quenching efficiency. Therefore, physiological pH (pH 7.4) was used in subsequent experiments. The effects of PBS buffer concentration were also investigated in the range of 5-40 mmol L-1 (Figure S8). With increasing concentration of PBS buffer, quenching efficiency gradually decreased. By compromising quenching efficiency and buffer capacity, 10 mmol L-1 PBS buffer was selected as the optimal condition. In the process of fluorescence recovering, the solution acidity and buffer concentration were the same with quenching condition. The kinetic behavior of fluorescence recovering process of the proposed sensing platform was investigated by monitoring the time-dependent changes of fluorescence intensity. With the addition of Gly, the fluorescence of 24-mer significantly increased, and about 60.5% recovering efficiency could be obtained immediately. As shown in Figure S9, the fluorescence intensity of 24-mer quickly increased with time within the first 3 s and reached a plateau in 10 s. Therefore, 10 s was chosen as the optimal incubation time. 3.5 The Calibration Curve and Linear Range

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Under the optimized conditions, calibration curve was constructed according to amino acid concentration-dependent fluorescence intensity change of the sensing system in the range of 0-2.00 mg mL-1 (Gly) or 0-0.80 mg mL-1 (Ser). With the increase of Gly concentration, fluorescence intensity increased quickly and reached a plateau after 0.80 mg mL-1 (Figure 4). A linear relationship (R2= 0.994) was observed between the fluorescence intensity and Gly concentration with the range from 0 to 100.00 µg mL-1 （0-1.3 mM）. The detection limit was 0.81 µg mL-1（10.8 µM）(S/N=3). Under the same conditions, Ser concentration-dependent fluorescence intensity increase was also observed, and the fluorescence intensity nearly reached a plateau when the Ser concentration was higher than 0.50 mg mL-1 (Figure S10). A linear relationship (R2 = 0.992) was obtained between the fluorescence intensity and Ser concentration with the range of 5.00-500.00 µg mL-1 (0.05-4.76 mM). The detection limit of Ser was calculated to be 1.51 µg mL-1 (14.4 µM) (S/N=3). Compared with the reported methods on the detection of amino acids, the proposed work has lower or comparable detection limits.44, 45

3.6 Biosensing Applications and Building Blocks of DNA Molecular Logic Gate To test the possibility of our approach for specific small-sized amino acids determination in real samples analysis, different amounts of amino acids were spiked into 1% newborn bovine serum samples, and corresponding recovery values were calculated by utilizing the above-obtained calibration curve. The good recoveries of amino acids added were ranging from 95.87 to106.60% (Table S3), thus demonstrating that the method is feasible to detect amino acids in real serum samples. Besides biosensing applications, the discovery of amino acids-triggered destruction of MOFs can also enrich the building blocks of DNA molecular logic gate. As an example, an OR logic gate was constructed using Gly and 24-mer-c, which is complementary with 24-mer, as the inputs, and the fluorescent signal at 518 nm is defined as the output. The presence of Gly and 24-mer-c is defined as “1”; their absence

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is defined as “0”. For the output, the fluorescence intensities of 24-mer higher or lower than 150 a.u. are defined as “1” and “0”. Without any inputs, the fluorescence of 24-mer was quenched by Cu MOFs, and an output of “0” was given. Addition of Gly or 24-mer-c or both could lead to increased fluorescence, and the output was changed to “1”. The fluorescence recovery in the presence of Gly was attributed to Gly-triggered destruction of MOFs, and the fluorescence recovery in the presence of 24-mer-c was caused by the release of 24-mer from MOFs surface due to the hybridization between 24-mer and 24-mer-c (Figure 5). Interestingly, the fluorescence recovery extent caused by Gly is much higher than that caused by 24-mer-c, thus suggesting our proposed sensing strategy might have better sensitivity than previously reported one. 4. CONCLUSIONS In summary, we found that the MOFs formed by [Cu(mal)(bpy)]·2H2O can be destroyed by specific small-sized amino acids. Based on this finding, a novel sensing platform was constructed for the facile and rapid quantitation of specific small-sized amino acids such as Gly and Ser with the detection limits of 0.81 µg mL-1 for Gly and 1.51 µg mL -1 for Ser. The discovery of this new sensing strategy not only will enlarge the horizon for the application of MOFs in biosensing systems, but also can enrich the building blocks of DNA molecular logic gate. As an example, an OR biomolecular logic gate was constructed. Since the destruction of MOFs is amino acid size-dependent, it is reasonable to speculate that different amino acid recognition abilities might be obtained by adjusting the pore size of MOFs.

ASSOCIATED CONTENT Supporting Information TG curves of Cu MOFs; Lineweaver-Burk plot andStern-Volmer plot of the quenching process for 24-mer by Cu MOFs; Fluorescence quenching efficiency (1-F/F0) change as a function of time after mixing 24-mer with Cu MOFs; The optimized

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geometries of MOFs, Gly, Phe and Trp; The structures and sizes of 20 commonly used amino acids; Microscope images of Cu MOFs mixing with Cys, Ser and Phe; pH-dependent fluorescence quenching efficiency of 24-mer by Cu MOFs; PBS buffer concentration-dependent fluorescence quenching efficiency of 24-mer by Cu MOFs; Time-dependent recovery of 24-mer fluorescence in the presence of Gly; Fluorescence spectra of the detection system with different concentrations of Ser; Elementary analysis of

Cu

MOFs;

B3LYP/SDD-6-311+G(d,p)/SMD(water)//B3LYP/SDD-6-31G(d)

calculated Gibbs free energy change (△rG) for the ligand exchange reactions; Analytical results for amino acids in 1% newborn bovine serum samples.

AUTHOR INFORMATION Correspondence: Dr. An-Na Tang and Dr. De-Ming Kong E-mail: [email protected], [email protected]

ACKNOWLEDGEMENTS Financial support from National Natural Science Foundation of China (21275081 and 21322507) and National Basic Research Program of China (2011CB707703) is gratefully acknowledged.

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Figure Captions Scheme 1(A) Specific small-sized amino acids sensing on the basis of destruction of MOFs. (B) Proposed mechanism of the destruction of MOFs by Gly. Figure 1Characterization of compound 1. (A) 3D framework of compound 1, down the crystallographic b axis. Hydrogen atoms are omitted for clarity. (B) PXRD patterns, (C) SEM image and (D) FT-IR spectrum of compound 1.

Figure 2 Compound 1 concentration-dependentfluorescence quenching of 24-mer. Inset: the fluorescence spectra of the 24-mer solution after addition of different amount of compound 1. F and F0 are the fluorescence intensities of 24-mer in the presence and absence of compound 1, respectively. [24-mer] =50 nM, λem= 518 nm.

Figure 3 Fluorescence response of the specific small-sized amino acids-sensing system to 16 different amino acids. Inset: the fluorescence spectra of the 24-mer solution after addition of compound 1 and different amino acids. [24-mer] = 50 nM, [compound 1] = 0.50 mg mL-1, [amino acids] = 0.050mg mL-1, λem = 518 nm.

Figure 4(A) Fluorescence spectra of the detection system in the presence of different concentrations of Gly. The concentrations of Gly are (arrow direction) 0, 0.005, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.20, 0.30, 0.40, 0.50, 0.60, 0.70, 0.80, 0.90, 1.00, 1.50, 2.00 mg mL-1. (B) Gly concentrations-dependent fluorescence intensity change at 518 nm. The insert shows the linear fluorescence response to Gly in the concentration range of 0-100 µg mL-1. [24-mer] = 50 nM, [compound 1] = 0.50 mg mL-1, all experiments were performed in triplicate.

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Figure 5 Construction of OR logic gate using Gly and 24-mer-c as inputs. (A) Fluorescence spectra of 24-mer in the presence of different inputs. (B) Fluorescence intensity of 24-mer at 518 nm in the presence of different inputs.(C) Scheme of the OR logic gate. (D) Truth table of the OR logic gate. [24-mer] = 50 nM, [compound 1] = 0.50 mg mL-1, [Gly] = 0.30 mg mL-1, [24-mer-c] = 90 nM, all experiments were performed in triplicate.

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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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Abstract Graphic 84x47mm (300 x 300 DPI)


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A Rapid and Facile Detection for Specific Small ... - ACS Publications

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