Self-Assembled Peptide Nanofibers Encapsulated with Superfine

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Self-Assembled Peptide Nanofibers Encapsulated with Superfine Silver Nanoparticles via Ag+-Coordination Yuanyuan Hu, Wenlong Xu, Guihua Li, Lu Xu, Aixin Song*, and JingchengHao Key Laboratory of Colloid and Interface Chemistry & Key Laboratory of Special Aggregated Materials (Shandong University), Ministry of Education, Jinan 250100, China

* To whom correspondence should be addressed. E-mail: [email protected]; Tel: +86-531-88363532; Fax: +86-531-88364750 1

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ABSTRACT In this work, we demonstrated that a glutanthione-based oligopeptide, Fmoc-GCE, could self-assemble into nanofibers induced by Ag+ ions in NaOH solution. During the self-assembly process, the superfine silver nanoparticles were in situ produced on the nanofibers. Based on a series of characterizations, we proposed the possible mechanism of the self-assembly, for which the coordination interaction between Fmoc-GCE and Ag+ ions as well as the -stacking of fluorenyl groups were the main driving forces of the self-assembled nanofibers. At appropriate compositions, the three-dimensional networks of Fmoc-GCE/NaOH/Ag+ nanofibers could further form metallogel which was responsive to pyridine and melamine which could coordination with Ag+ ions. Moreover, the nanofibers encapsulated with superfine silver nanoparticles exhibited catalytic ability in degradation of the azo dye and the antibacterial properties to both gram-negative (E. coli) and gram-positive (S. aureus) bacteria.

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1. INTRODUCTION Among the numerous supramolecular structures which have potential applications in biomedicine,1 cell culture,2 and sensors,3,4 the self-assembly of amphiphiles based on peptides and amino acids show significant importance due to their designability and biocompatibility. With tunable numbers and sequences of amino acids, peptides are promising building blocks in molecular self-assembly which can be modulated by external conditions including temperature,5 ionic strength,6 enzymes,7 etc. The oligopeptides possessing fragments of conjugated aromatic components can easily self-organize

by

taking

advantage

of

-stacking.8

In

addition,

the

fluorenylmethoxycarbony (Fmoc-) group was generally used as a protecting group in the construction of peptide self-assembled structures. Therefore, due to the introduction of conjugated structure, the Fmoc-based peptides were easily to self-assemble into nanofibers.9,10 The existence of conjugated structures endows the self-assembled structures potential applications in optical and bioelectronic devices.7 When being introduced proper metal ions, the peptides or amino acids can also self-assemble to form metal-complexes through the metal-ligand coordination.11-14 The supramolecular materials in nanoscale formed by these complexes may have a range of fascinating properties such as fluorescence,15 catalysis,16 and color switch.17 Moreover, the fabrication of functional nanomaterials by self-assembly of peptide-based building blocks has also provided an avenue for synthesizing inorganic materials.18-21 The conventional method to obtain these materials is usually through the reducibility of hydroxyl,22 sodium borohydride,21 and photoreduction,23 etc. 3


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Abundant work of in situ synthesis of Au and Ag nanoparticles (AuNPs and AgNPs) via these methods has also been broadly reported. However, to our knowledge, the in situ synthesis of AgNPs by compounds containing thiol has not been reported because the thiol compounds were usually regarded as stabilizers for AgNPs.21,24-26 Herein, we designed a glutathione-like peptide, Fmoc-GCE-OH (simplified as Fmoc-GCE), containing glycine (G), cysteine (C) and glutamic (E) residues in molecular structure, as shown in Scheme 1. The N-terminus of the peptide is protected with fluorenylmethoxycarbony group (Fmoc-) which leads to a substantial increase in hydrophobicity and promotes self-assembly of the peptide by taking advantage of -stacking. The two hydrophilic COOH groups at C-terminus enhance the solubility of peptide in aqueous solution. Due to the presence of thiol-containing cysteine residue, Fmoc-GCE has strong affinity with some noble metals such as silver and gold. The peptide can self-assemble into nanofibers induced by coordination with Ag+ ions and the -stacking of fluorenyl groups. The Ag+-coordination leads Ag+ ions being fixed to the self-assembled structures which can be used as precursors for producing AgNPs. The AgNPs growing along the Fmoc-GCE nanofibers are monodisperse with rather small size of 1.6 ± 0.57 nm, exhibiting antibacterial properties to both gram-negative (E. coli) and gram-positive (S. aureus) bacteria and catalytic to the degradation of an azo dye, methyl orange.

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Scheme 1. The chemical structure of Fmoc-GCE.

2. EXPERIMENTAL SECTION 2.1. Chemicals and Materials. The peptide, Fmoc-GCE (98.6%), was synthesized and purified by China peptides Co., Ltd. (Shanghai, China). NaOH, methyl orange (MO), AgNO3 and NaBH4 were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Pyridine, melamine, agar, tryptone were obtained from J&K Chemical Company, Ltd. (China). All chemicals were used without further purification. The water used in the experiments was obtained using a UPH-IV ultrapure water apparatus (China) with a resistivity of 18.25 MΩ·cm. 2.2. Samples Preparation. Fmoc-GCE (2.65 mg) was weighed into tiny bottles, and 0.4 mL NaOH solution was added. The mixtures were stirred for 30 minutes to dissolve peptide completely. Then AgNO3 solutions (0.1 mL) with different concentrations were mixed with the Fmoc-GCE aqueous solution. The samples were covered by foils and incubated in a thermostat at 25.0 ±0.1 °C. 2.3. Transmission Electron Microscope (TEM) Observations. About 5 μL of sample solution was placed on carbon-coated copper grids (400 mesh) and then freeze-dried. The morphologies of samples were studied on a JEOL JEM-1400 TEM (acceleration voltage, 120 kV) with a Gatanmultiscan CCD for collecting images.

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2.4. Atomic Force Microscopy (AFM) Observation. A droplet of sample solution was placed on mica plate and the excess solution was blown away with nitrogen in order to obtain a thin film. Images were recorded using a digital instrument (NanoScope III) operating in tapping mode. 2.5. X-ray Photoelectron Spectroscopy (XPS) Measurements. A droplet of sample solution was placed on silicon wafer and freeze-dried at -55 °C. The XPS experiments were performed on ESCALAB 250 X-ray photoelectron spectrometer with an Mg Kα excitation source of 1.0 × 10-6 Pa and a resolution of 1.00 eV. 2.6. Fluorescence Emission Measurements. Fluorescence emission spectra were measured on a PerkinElmer LS55 fluorophotometer (U.K.). The excitation wavelength was 290 nm and the emission data were recorded within the range of 300 - 500 nm. 2.7. Fourier Transform Infrared (FT-IR) Measurements. FT-IR spectra were recorded on a Bruker Optics VERTEX-70/70v FT-IR spectrometer by taking 64 scans within the region of 400 cm−1- 4000 cm−1 with a resolution of 4 cm−1. 2.8. Ultraviolet and Visible (UV-Vis) Measurements. UV-Vis measurements were operated on a Cary 60 UV-Vis spectrometer (Agilent, America). 2.9. Circular Dichroism (CD) Measurements. CD spectra were measured on a JASCO J-810 spectropolarimeter. A quartz cuvette with 1 mm path length was used to obtain the spectra in steps of 0.5 nm from 330 to 210 nm.

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2.10. X-ray Diffraction (XRD) Measurements. The XRD patterns were recorded on a Rigaku D/Max 2200-PC diffractometer with Cu K radiation ( 0.15418 nm) and a graphite monochromator. The samples were tested within 1-10°. 2.11. Rheological Measurements. Rheological measurements were carried out on a HAAKE RS6000 rheometer with a cone-plate system (Ti, diameter, 35 mm; cone angle, 1°). To ensure the measurements were taken in the linear viscoelastic region, a stress sweep (at 1 Hz) was performed in oscillatory measurements. The frequency sweeps were carried out between 0.1 and 10 Hz. The experiments were performed at 25.0 ±0.1 °C with the help of a cyclic water bath. 2.12. Catalytic Reaction. To perform the catalytic reaction, MO (1 mL, 0.1mM) and freshly prepared NaBH4 aqueous solution (1 mL, 20 mM) were mixed in a quartz cuvette. The final concentration of MO and NaBH4 in the mixture was 0.05 mM and 10 mM, respectively. After the addition of Fmoc-GCE/Ag+ complexes with different concentrations, the reaction was monitored by UV-Vis spectroscopy at 464 nm. 2.13. Antibacterial Test. The bacterial suspensions (E. coli and S. aureus) used for tests were within 10-5-10-6 CFU/mL, for which the original optical density at 600 nm (OD600) was 0.1. The poor broth medium of bacteria suspensions contains 1% tryptone and 0.5% NaCl in PBS (pH = 7.5). The prepared Fmoc-GCE/Ag+ complexes (20 L) at different concentrations were added to 180 L bacteria suspensions in 96-well plate to confirm the final concentrations of complexes were 0, 0.05, 0.1, 0.4 and 0.8 mM, respectively. Then the mixed bacterial suspensions were incubated in a shaking incubator at 37 °C. The OD600 turbidity of the bacterial culture was monitored 7


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using ELX800 Universal Microplate Reader (Bio-Tek) in different time intervals. In addition, 200 L of the mixed bacterial suspension with Fmoc-GCE/Ag+ complexes (0.8 mM) was spread onto the agar plates and then the agar plates were inverted and incubated at 37 °C for 12 h.

3. RESULTS AND DISCUSSION 3.1. The Self-Assembled Structures. Fmoc-GCE was dissolved in NaOH aqueous solution firstly as its limited solubility in water. The self-assembly of Fmoc-GCE does not occur even at very high concentrations in NaOH solution, while can be triggered by the introduction of Ag+ ions. With the addition of Ag+ ions, the transparent solution becomes slightly turbid with an increasing viscosity, indicating the formation of aggregates. TEM and AFM images (Figure 1) show that the microstructures of the aggregates are three-dimensional (3D) networks of densely stacking nanofibers with the diameter between 10 and 20 nm and the length extending to several micrometers. The dynamic process of nanofibers formation displayed in Figure S1 indicates that the length and amount of the short segments of nanofibers gradually increase to form the 3D networks after 24 hours.

a

b

Figure 1. TEM (a) and AFM (b) images of self-assembled structures formed in 10 8


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mM Fmoc-GCE/20 mM NaOH/10 mM Ag+ solution. It was interesting to find that, without introducing any reducing agents or light (the samples were shaded by tinfoil), the superfine AgNPs with the average diameter of 1.6 ± 0.57 nm (Figure S2) were obtained along the nanofibers (Figure 2a). In Figure 2b, the signals at 368 eV and 374 eV with the interval of 6.0 eV respectively correspond to the binding energies of Ag 3d5/2 and Ag 3d3/2, confirming the existence of AgNPs in Fmoc-GCE/Ag+ complexes.26 Generally, AgNPs were obtained by adding reducing agents such as sodium borohydride or by light irradiation.3,21,23 However, in the present system, AgNPs can be prepared even in the freshly prepared samples only consisting of short segments of nanofibers, which demonstrates the self-assembly process and AgNPs formation are almost simultaneous (Figure S3). Thus, the nanofibers of Fmoc-GCE/Ag+ complexes can serve as templates for the in situ preparation of AgNPs. Ag 3d scan

b

a

~6 eV

Intencity

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368

364

Binding Energy / eV

Figure 2. TEM image (a) and X-ray photoelectron spectrum of AgNPs along nanofibers formed in10 mM Fmoc-GCE/20 mM NaOH/10 mM Ag+ solution. 3.2. Mechanism Explanation. As discussed above, the AgNPs were stably adhered to the nanofibers without diffusion in solution. When NaBH4 (2 mM) was added to 9


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the complex, the sample became light yellow with the AgNPs with average size of 3.0 ± 0.57 nm (Figure S4a) dispersing in solution rather than only distributing along the nanofibers (Figure 3a). When NaBH4 was excess (20 mM), the sample solution became dark brown and the originally formed nanofibers were destroyed, indicating the important role of Ag+ ions in the self-assembly process. The AgNPs with average size of 6.0 ± 0.37 nm (Figure S4b) were found to disperse in solution (Figure 3b) and to coagulate after several days (Figure S5). Thus, the AgNPs prepared along nanofibers are of much smaller size and more superior stability than those obtained through introducing NaBH4 as reducing agent. By adding NaBH4, more Ag+ ions were reduced, that broke the balance of different interactions which stabilized the self-assembled structures and gave rise to the disaggregation of nanofibers.

a

b

Figure 3. TEM images of AgNPs produced by adding (a) 2 mM and (b) 20 mM NaBH4 to10 mM Fmoc-GCE/20 mM NaOH/10 mM Ag+ solution. Fluorenyl is a fluorescent group whose spectroscopic feature is significantly altered with the aggregation state.9 According to previous reports, in most cases, no matter whether the fluorenyl group was in monomers or within aggregates, there was always a single peak of fluorenyl in the fluorescence spectrum only with a little shift between 10


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the two states.6,9,10,27 However, an exception occurred in the present system. The characteristic signal with the maximum emission at 320 nm (Figure S6a) was generated by monomeric fluorenyl.6 With the addition of Ag+ ions, the intensity of this excimer band decreased drastically and quenched completely when cAg+ was equal to the concentration of Fmoc-GCE. The microstructural change from short segments of nanofibers to the 3D networks was also observed (Figure S7), which demonstrated the increase in the Fmoc-GCE molecules in assembled form, and as a result, the number of monomeric Fmoc-GCE molecules decreased. We attribute the fluorescence quenching to the Ag+ ions doping in nanofibers, being like the quencher of pyrene derivatives whose fluorescent property is similar to fluorenyl derivatives.28 Another possible reason is that the fluorescence of fluorenyl is affected by AgNPs along nanofibers like the model of colloid-inducing fluorescence quenching through electronic plasma resonance reported.29 In addition, a relatively broad new peak appears around 420 nm (Figure S6a), implying the presence of an extensive J-aggregate in the self-assembled structures through -stacking between the fluorenyl groups.6,7,9 Circular dichroism (CD) spectrum in Figure S6b shows the positive Cotton effect at 224 nm (n-* transition), which is an indication of the superhelical arrangements of the amino acid residues in the peptide, while the positive adsorption within 250-305 nm (-* transition) corresponds to the stacking of fluorenyl moieties.6,27 In FT-IR spectra (Figure 4a), for Fmoc-GCE, the peaks at 1722 cm−1, 1658 cm−1 and 3308 cm−1 correspond to the stretching vibration of carboxyl, amide carbonyl and –N−H groups, respectively.25 While for Fmoc-GCE/Ag+ complex, 11


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the three peaks shift to 1700 cm−1, 1636 cm−1 and 3286 cm−1, respectively, indicating the formation of carboxylate and the hydrogen bonding, which may be formed between the –C=O and –N–H groups of two Fmoc-GCE molecules.30 In addition, the peaks at 1412 cm−1 and 1532 cm−1 of Fmoc-GCE respectively assigned to symmetric and antisymmetric stretching of carboxyl shift to 1368 cm−1 and 1542 cm−1, respectively, in Fmoc-GCE/Ag+ complex, denoting the presence of coordination between the carboxylate groups and Ag+ ions. The absence of the peak at 2550 cm−1 which is usually assigned to the SH stretching implies the existence of Ag-S interaction in Fmoc-GCE/Ag+ complex.12 In UV-Vis spectrum (Figure 4b), the peak at ∼370 nm of Fmoc-GCE/Ag+ complex is ascribed to the coupling low-energy ligand-to-metal charge-transfer band which is further demonstrated by the Ag-S interaction.12 The surface plasmon mediated circular dichroism responses was usually used to detect the orientation and the assembly of nanoparticles.31 In the present system, we consider that this peak is not caused by the surface plasmon resonance (SPR) absorption of AgNPs because no Cotton effect can be found at the same position, 370 nm, in CD spectrum (Figure S6b). According to the Bragg equation,32 n 2dsin, the peak at 2.93°in XRD spectrum (Figure S8) indicates the d value of 30 Å, which is correlated to the length of the ordered cyclic units in the arrangements of the self-assembled structure. As the length of Fmoc-GCE molecule and fluorenyl group are 19 Å and 7 Å, respectively, it can be deduced that two Fmoc-GCE molecules are in antiparallel arrangement with the overlap of fluorenyl groups (Figure S9). 12


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a Fmoc-GCE/Ag

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Fmoc-GCE

1542

1700

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Abs / a. u.

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1800

0.0 320

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Wavelength / nm

Wavenumber / cm-1

Figure 4. (a) FT-IR spectra of Fmoc-GCE and 10 mM Fmoc-GCE/20 mM NaOH/10 mM Ag+ complex; (b) UV-vis spectrum of 10 mM Fmoc-GCE/20 mM NaOH/10 mM Ag+ complex. On the basis of above measurements, we proposed the possible assembly mechanism of Fmoc-GCE induced by Ag+ ions. The carboxyl groups in Fmoc-GCE molecules were deprotonated to be negatively charged in NaOH solution. When Ag+ ions were introduced, the coordination between deprotonated Fmoc-GCE and Ag+ as well as the - stacking of fluorenyl groups are the main driving forces which link the molecules to assemble, which is shown in Figure 5. During the self-assembly process, AgNPs come into being perhaps due to the rich electrons of thiol groups for which the further study is needed because the accurate generating process is still undefined. The in situ simultaneously generated AgNPs during the peptide self-assembly link with thiol groups in Fmoc-GCE molecules, while the excessive Ag+ ions were absorbed by carboxylate groups through coordination interaction. Because of the combination of AgNPs with thiol groups, the AgNPs can be produced along the peptide nanofibers. Beyond that, some other interactions, such as hydrogen bonding, hydrophobic interaction, and van der Waals force may also participate to maintain the balance of 13


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various driving forces in the self-assembly process.1

Figure 5. The proposed self-assembly mechanism of Fmoc-GCE/Ag+ complexes. 3.3. Gelation Behavior of Fmoc-GCE/Ag+ Complexes. Being an important kind of soft materials, gels exhibit exciting applications in many areas such as tissue engineering and electronics.33 In this system, hydrogels can be formed by the Fmoc-GCE/Ag+ complexes at appropriate conditions. As Fmoc-GCE contains two carboxyl groups in glutamic residue, cNaOH affects the form of Fmoc-GCE molecules significantly. Figure S10 shows the samples formed by 10 mM Fmoc-GCE with 10 mM Ag+ in NaOH solutions of different concentrations. At low cNaOH, as a typical concentration such as 10 mM, suspensions were found because of the poor solubility of Fmoc-GCE. With the addition of NaOH, the precipitates of Fmoc-GCE were dissolved gradually and hydrogels were formed at cNaOH = 16 mM. With further 14


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increase in cNaOH, the hydrogels were destroyed to form transparent solution. During this process, the carboxyl groups of Fmoc-GCE were deprotonated to be ionic form with increasing cNaOH (Figure S11). This process induced the formation of nanofibers through coordination between Ag+ and the ionic Fmoc-GCE. At high NaOH proportion, i.e., cNaOH : cFmoc-GCE being near or above 2 : 1, the Fmoc-GCE molecules were almost completely deprotonated and the strong electrostatic repulsion between the negatively charged Fmoc-GCE molecules restricted their self-assembly for forming hydrogels. The mechanical strength, being of significant importance in the hydrogels applications,32,34 was obviously affected by the amounts of Ag+ ions. Figure 6a shows the elastic modulus (G') as a function of stress (). The yield stress (), at which G' decreases sharply because the shear stress is high enough to break the network structures of the hydrogels, can be obtained.32 For samples of 10 mM Fmoc-GCE/16 mM NaOH/Ag+ mixtures at cAg+ < 7 mM, only transparent solutions with very low viscoelasticity can be formed (not shown). When cAg+ increases from 8 mM to 10 mM,values increase from ~10 Pa to 600 Pa, indicating the significant effect of Ag+ on gelation. The nondestructive frequency sweep (Figure 6b) shows that both G' and the viscous modulus (G") are independent of frequency over the investigated oscillating frequency range. The G' values are approximately an order of magnitude higher than those of G", showing the elastic dominance. These rheological behaviors are characteristic of the solid-like gel materials.25

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Figure 6. Stress sweep (a) and frequency sweep (b) results of the hyrogels formed by 10 mM Fmoc-GCE/16 mM NaOH with different concentrations of Ag+ ions. Hydrogels produced through weak interactions were found to be sensitive to various external stimuli such as pH, heat, sonication, shearing force, irradiation, enzymes and suitable metal chelating agents which can coordinate with metal ions to replace the original ligands.11,23,34,35 Herein, the hydrogels from our system exhibited smart response to pyridine and melamine (Figure 7). The transition from gel to sol occurred when pyridine or melamine was added, which disturbed the coordination between Ag+ and Fmoc-GCE. The solution can be reversed to gel by adding AgNO3 to the solution. Thus, it can be concluded that the coordination between Fmoc-GCE and Ag+ plays an important role in the self-assembly process. This hydrogel system may be applied as a detector or sensor of the relevant substances responding to Ag+ ions.

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Figure 7. The reversible gel-sol transition induced by pyridine and melamine. 3.4. Catalytic Property and Antibacterial Performance of Fmoc-GCE/Ag+ Complexes. The catalytic activity and antibacterial efficacy of Fmoc-GCE/Ag+ complexes were evaluated in this section. Dyes are widely used in many industrial processes for which the azo dyes share about 50 % in all dye varieties.13 Here one kind of azo dye, methyl orange (MO),36 was selected as a model to be used for the evaluation of catalytic activity. In the presence of Fmoc-GCE/Ag+ complexes, the degradation of MO can be completely achieved within several minutes (Figure S12). As shown in Figure 8a, the reaction has a delay time at the beginning. During this process, oxides on the catalyst surface are assumed by the NaBH4 molecules to activate the catalyst. This may be caused by a better solubility of oxygen in presence of the carrier system.37 Thus, the degradation of MO occurs following the delay time. The effect of Fmoc-GCE/Ag+ complexes and NaBH4 on the degradation of MO was shown in Figure 8. One can note that the degradation rate is significantly influenced by the concentration of both Fmoc-GCE/Ag+ complexes and NaBH4. With appropriate concentration of NaBH4, the reaction can be completed within few minutes at the presence of very low concentrations of Fmoc-GCE/Ag+ complexes, indicating the 17


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good catalytic activity Fmoc-GCE/Ag+ complexes. 1.6

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Figure 8. The degradation of 0.05 mM MO at (a) 10 mM NaBH4 with different concentrations of Fmoc-GCE/Ag+ complexes and (b) 12.5 μM Fmoc-GCE/Ag+ complexes with different concentrations of NaBH4. The molar ratio of Fmoc-GCE to Ag+ in Fmoc-GCE/Ag+ complexes is 1:1. The typical gram-negative (E. coli) and gram-positive (S. aureus) bacteria in liquid medium were used to perform the antibacterial test. It can be found that after being shaken for 22 h at 37 °C, the bacterial suspension without Fmoc-GCE/Ag+ complexes become turbid while the bacteria suspension containing complexes remains nearly transparent. In addition, with the increasing addition of complexes, the bacterial suspension become more transparent, indicating the antibacterial abilities were enhanced with the increasing concentration of complexes, as shown in Figure 9. The minimum inhibitory concentration38 against both E. coli and S. aureus is 0.4 mM. The complexes show better antibacterial efficacy to E. coli than to S. aureus, which might be ascribed to the difference in the bacterial cellular structures.6 Subsequently, we plated the bacteria suspensions without and with Fmoc-GCE/Ag+ complexes whose concentration was larger than minimum inhibitory concentration onto the agar plates 18


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and incubated at 37 °C for 12 h. As shown in Figure S13, compared with the control agar plates, the results showed that the number of surviving bacteria was extremely low, indicating the quite effective antimicrobial activity. 0.6 +

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Figure 9. The dose-dependent growth inhibitions of (a) E. coli and (b) S. aureus bacteria in the presence of different concentrations of Fmoc-GCE/Ag+ complexes. The molar ratio of Fmoc-GCE to Ag+ in Fmoc-GCE/Ag+ complexes is 1:1.

4. CONCLUSIONS In conclusion, we have demonstrated that the 3D networks of nanofibers were formed by the self-assembly of Fmoc-GCE under the introduction of Ag+ ions. The self-assembly was proved mainly driven by the synergistic effect of metal coordination, - stacking of fluorenyl groups, and other weak interactions. Parts of Ag+ ions were found to be reduced to AgNPs along the nanofibers during the self-assembly process of Fmoc-GCE. This work may provide a method for the simultaneous occurrence of supramolecular self-assembly and the generation of inorganic materials. The hybrid materials possess catalytic ability for the reduction of MO and antibacterial properties for E. coli and S. aureus. At appropriate deprotonated degree of Fmoc-GCE, hydrogels with high mechanical strength were obtained and exhibited smart stimuli to the substances responding to Ag+ ions. We envisage that the 19


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self-assembled structures of Fmoc-GCE/Ag+ complexes incorporated with AgNPs may have applications in bioelectronics and biosensors in further study.

AUTHOR INFORMATION Corresponding Author *Tel: +86-531-88363532. Fax: +86-531-88564750. E-mail: [email protected]. Notes The authors declare no competing financial interest.

ACKNOWLEDGEMENTS We acknowledge the financial aids supported by the NSF for Distinguished Young Scholars of Shandong Province (JQ201303) and NSFC (21420102006 and 21173132).

ASSOCIATED CONTENT TEM images of nanofibers, AgNPs along nanofibers, and coagulated AgNPs; size distribution of AgNPs along nanofibers and formed in solution; emission spectra and CD spectrum of sample; small angle XRD spectra of complex; illustration of the arrangement between Fmoc-GCE molecules, photos of samples and colonies of E. coli and S. aureus; chemical structural transition of Fmoc-GCE with basicity; time-dependent absorption spectra of MO/NaBH4/Fmoc-GCE/Ag+ complex. The supporting information

is

available free

of charge via the

Internet

at

http://pubs.acs.org.

REFERENCES (1) Zhao, X.; Pan, F.; Xu, H.; Yaseen, M.; Shan, H.; Hauser, C. A.; Zhang, S.; Lu, J. 20


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Self-Assembled Peptide Nanofibers Encapsulated with Superfine

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