One-Step Fabrication of Self-Assembled Peptide Thin Films with

Dec 9, 2013 - Fabrication of organic thin films with highly dispersed inorganic nanoparticles is a very challenging topic. In this work, a new approac...
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One-Step Fabrication of Self-Assembled Peptide Thin Films with Highly Dispersed Noble Metal Nanoparticles Jinmao Yan,† Yunxiang Pan,† Andrew G. Cheetham,‡ Yi-An Lin,‡ Wei Wang,† Honggang Cui,*,‡ and Chang-Jun Liu*,† †

Collaborative Innovation Center of Chemical Science and Engineering, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China ‡ Department of Chemical and Biomolecular Engineering and Institute for NanoBioTechnology, The Johns Hopkins University, Baltimore, Maryland 21218, United States S Supporting Information *

ABSTRACT: Fabrication of organic thin films with highly dispersed inorganic nanoparticles is a very challenging topic. In this work, a new approach that combines electron-induced molecular self-assembly with simultaneous nanoparticle formation by room temperature electron reduction was developed to prepare peptide thin films with highly dispersed noble metal nanoparticles. Argon glow discharge was employed as the resource of electrons. The peptide motif KLVFF (Aβ16−20) self-assembled into two-dimensional membranes under the influence of hydrated electrons, while the metal ions in solution can be simultaneously reduced by electrons to form nanoparticles. Our TEM imaging reveals that metal nanoparticles were well-distributed in the resulting peptide thin films. Our results also suggest that the size of metal nanoparticles can be tuned by varying the initial concentration of the metal ion. This simple approach can be viewed as a promising strategy to create hybrid thin films that integrate functional inorganics into biomolecule scaffolds.

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abundance of appropriate functional groups on the fibrillar surface,20−22 with a few cases on the use of two-dimensional (2D) templates.23 This is simply because creation of a 2D template using molecular assembly strategy is still a very challenging task.24,25 There are only a few very remarkable examples in the literature that reported the organization of inorganic nanoparticles at interfaces in a 2D fashion.26−28 Other methods of obtaining 2D nanoparticle arrays typically involve the use of solid substrates such as glass, silicon, and metals. Recently, our group reported an effective, simple, and environmentally-friendly method to construct peptide-based films at room temperature using argon glow discharge.29 Glow discharge is well-known as a conventional cold plasma and contains high-energy electrons. Formation of the peptide thin films was proposed to be mediated by the hydrated electrons provided by the argon glow discharge that led to enhanced interactions among peptide fibrils. Since glow discharge can also be utilized as an effective and convenient means to reduce ionic metals into metallic nanoparticles,30,3132 we report here the use of glow discharge as a source of hydrated electrons both to produce the peptide thin films and to reduce metal ions into highly dispersed nanoparticles.

INTRODUCTION Over the past several decades, biologic and inorganic nanocomposites have aroused significant interest because of their unique combination of various properties, allowing for potential applications in catalytic, optical, and electronic devices and in biodiagnostics.1−7 Since many of these devices have now been miniaturized to the nanoscale, biomolecules have found extensive uses due to their multifunctional properties and welldefined intermolecular interactions.4,6−8 Peptides and polypeptides, in particular, have been extensively studied because of their ability to self-assemble into well-ordered one-, two-, and three-dimensional structures under appropriate conditions.9−13 For instance, the diphenylalanine (FF) structural motif and its derivatives have been found to self-assemble into highly stable nanoarchitectures such as nanofibrils,14,15 nanotubes,16 nanobelts,17 and even well-organized films formed from nanotubes.18 Obviously, the self-assembling potential of peptides provides a powerful approach for fabricating integrated nanoscale devices. Indeed, peptide-based nanostructures have been used as scaffolds to organize and mediate assembly of inorganic nanoparticles into linear, monolayer, and multilayer structures.19−23 Such an approach attempts to take advantage of the multifunctional properties of peptides and the unique physicochemical and electronic properties of inorganic materials. Among various nanoarchitectures known, nanofibrils have been used most frequently as the biomolecular template for organizing small inorganic metal nanoparticles based on the © 2013 American Chemical Society

Received: September 23, 2013 Revised: November 24, 2013 Published: December 9, 2013 16051

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Figure 1. Visualizing the evolution of film formation. AFM images of C-Aβ16−20 after 24 h incubation (a) showing fibril formation only (inset) and PAβ16−20 after 24 (b), 72 (c), and 120 h (d) incubation, indicating the time-dependent formation of intact films.

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RESULTS AND DISCUSSION The peptide KLVFF (Aβ16−20) used in the study is well-known to self-assemble into one-dimensional nanostructures rich in βsheets.33−36 In particular, we showed recently that the KLVFF nanofibrils can be induced to form a thin film in aqueous solution upon exposure to argon glow discharge.29 After 24 h of incubation at 37 °C, C-Aβ16−20 was observed to form short fibrous structures by AFM (Figure 1a). This is consistent with previous studies of the Aβ16−20 peptide, which have shown that aqueous solutions will self-assemble into 1D nanostructures under appropriate conditions.35,36 The CD spectrum obtained for the C-Aβ16−20 sample after 120 h incubation (Figure S1a in the Supporting Information) shows a negative maximum at about 230 nm and a positive maximum at 198 nm. The former peak can be associated with the stacking of aromatic amino acids due to peptide aggregation,37 and the latter peak at 198 nm is associated with the amide π−π* transition. However, the CD spectrum of C-Aβ16−20 is not that expected for a β-sheet structure, which typically shows a negative maximum at 216 nm. This may be due to slow assembly kinetics of Aβ16−20 under these conditions. In stark contrast to C-Aβ16−20, 24 h incubation of P-Aβ16−20 leads to the formation of both short fibrils and larger aggregate structures (Figure 1b). It is evident that the fibrils aggregate along the direction perpendicular to their long axis, leading to formation of some small imperfect films. After incubating for 72 h (Figure 1c), larger and better films can be observed to have developed, though some growth defects are still apparent within the structure. Further increasing the incubation time allows these defects to gradually close up and after 120 h intact films can be observed by AFM imaging (Figure 1d). Compared with the C-Aβ16−20 samples, many more fibrils are formed and aggregate together. As the concentration of the Aβ16−20 solution increases to 500 μM, white hyaline films were clearly observed in the quartz boat during the discharge process (Figure 4e). This demonstrates that the Aβ16−20 can self-assemble into films under exposure to the glow discharge plasma. The CD spectrum for P-Aβ16−20 (Figure S1a) shows a maximum ellipticity band at about 196 nm and a minimum ellipticity band at about 220 nm. Such a spectrum type is often ascribed to the β-sheet secondary structure and indicates that the glow discharge plasma can induce and promote the assembly of the Aβ16−20 peptide through β-sheet formation.29 To gain further structural information on C-Aβ16−20 and PAβ16−20, we studied dried films of each using the FTIR transmission mode (Figure S1b). The FTIR spectra of the CAβ 16−20 and P-Aβ 16−20 samples present many similar absorbance peaks at 1139, 1204, 1433, 1633, 1674, 2875, 2933, 2962, and 3089 cm−1. The peak at 1633 cm−1 contains the −NH3+ antisymmetric deformation and amide I bands, the

Aβ16−20 was purchased from Shanghai Science Peptide Biological Technology Co. Ltd., China, 98%. The C-Aβ16−20 samples were prepared by direct incubation of an Aβ16−20 solution in a temperatureconstant incubator at 37 °C. The P-Aβ16−20 or P-M/Aβ16−20 (M = Au, Pt, and Pd) samples were prepared by placing the Aβ16−20 solution or the Aβ16−20 and metal salt (HAuCl4, H2PtCl6, or PdCl2) hybrid aqueous solution into the discharge chamber to interact with the argon glow discharge for 8 min and then incubated in a temperature-constant incubator at 37 °C. The electron-induced self-assembly behavior of Aβ16−20 was established by the study of aqueous solutions that were either left untreated (C-Aβ16−20) or were exposed to the glow discharge plasma (P-Aβ16−20). The resulting nanostructures were then characterized by atomic force microscopy (AFM), circular dichroism (CD), and Fourier-transform infrared spectroscopy (FT-IR). AFM samples were prepared at 100 μM, while CD samples were prepared at 500 μM. Samples for AFM analysis were prepared by loading 40 μL of the hybrid solution on a freshly peeled mica substrate and left to dry overnight under ambient conditions before imaging. AFM images were recorded on a Multimode SPM and Nanoscope V controller (Veeco Instruments) in the tapping mode with a silicon cantilever. The spring constant and resonant frequency of the cantilever were 30 N m−1 and 240 kHz, respectively. CD spectra were measured on a JASCO J-810 spectropolarimeter (Jasco International Co., Tokyo, Japan) at room temperature, with 1.0 mm path length quartz cuvettes. Spectra were obtained from 190 to 260 nm with a 1 nm step, 1 nm bandwidth, and 1 s collection time per step. FTIR spectra were recorded on a Bruker Tensor-27 FTIR spectrometer with a resolution of 4 cm−1. Samples for FTIR analyses were prepared on Si wafers, using a clean Si wafer without any sample as the reference. Transmission electron microscopy (TEM) analyses were performed using a FEI Tecnai 12 TWIN system equipped with SIS Megaview III wide-angle camera. The samples for TEM analyses were prepared by loading 5 μL of suspension solutions onto copper grids with carbon film (Electron Microscopy Sciences, CF400-Cu). The high-resolution TEM images were recorded on a Philips Tecnai G2 F20 system operated at 200 kV. UV−vis absorption spectra of the samples were recorded on a Beckman DU-8B UV−vis spectrophotometer. Liquid chromatography mass spectrometry (LC-MS) was performed using a HPLC system (Agilent 1200) equipped with a 4.6 × 250 mm Zorbax SB-C18 column (Agilent). The column was equilibrated with 100% solvent A (0.1% TFA in water) in the first 2 min, followed by a 20 min linear gradient from 26% to 46% solvent B (0.1% TFA in acetonitrile). The sample was detected at 220 nm with a flow rate of 1 mL min−1. The effluent was fed to an Agilent 6310 ion trap mass spectrometer operating in the positive ion mode. Measurements were obtained for m/z (mass/ charge) values of 200−2200 Da. X-ray powder diffraction (XRD) analysis was conducted on a Rigaku D/Max-2500 diffractometer with a Cu Kα1 radiation source (λ = 0.154 056 nm) at a scanning speed of 5° min−1. Crystalline phases were identified by reference to the JCPDS data files. 16052

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Figure 2. Self-assembly of Aβ16−20-based Au monolayer films. Typical TEM micrographs of P−Au/Aβ16−20 films prepared using 100 μM Aβ16−20 and 5 μM HAuCl4 hybrid aqueous solutions (a, b). Inset (a) depicts the corresponding size distribution of Au particles, and inset (b) shows highresolution TEM micrographs of the Au nanoparticles. (c) Representative TEM image of the sample that was prepared by applying argon glow discharge on the peptide solution with gold nanoparticles that were prepared using 5 μM gold ions in the absence of peptide. (d) Representative TEM image of the sample that was prepared by applying argon glow discharge on the HAuCl4 aqueous solution in the presence of assembled peptide thin films. In all panels, P refers to treatment with glow discharge plasma.

Figure 3. (a) X-ray diffraction patterns for dried P−Au/Aβ16−20 sample. (b) UV−vis absorbance spectra for P-HAuCl4 (HAuCl4 aqueous solution after plasma), Aβ16−20, P-Aβ16−20, and P−Au/Aβ16−20 aqueous solution samples.

latter of which is associated with β-sheet structures, while the peak at 1674 cm−1 is often associated with the antiparallel βsheet conformation.38,39 The FTIR results therefore indicate a β-sheet structure is present in the dried films of C-Aβ16−20 and P-Aβ16−20. An additional peak is located in the amide A band at 3274 cm−1 for C-Aβ16−20, corresponding to the ν(N−H) stretch

of the NH2 group.40 However, a broad band centered at 3236 cm−1 is observed for P-Aβ16−20. The shift of this ν(N−H) band may be due to the different intermolecular interactions required to form a film. LC-MS analysis of P-Aβ16−20 (Figure S2) shows that no noticeable chemical changes occur to the peptide after the glow discharge processing, suggesting that the assembly 16053

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Figure 4. Representative TEM images of the P−Au/Aβ16−20 films prepared using (a) 100 μM HAuCl4 with 100 μM Aβ16−20 aqueous solutions (100 Au + 100 Aβ16−20), (b) 200 Au + 100 Aβ16−20, (c) 500 Au + 100 Aβ16−20, and (d) 100 Au + 500 Aβ16−20. (e−g) Photograph of P-Aβ16−20 (e) and P− Au/Aβ16−20 (f) in the quartz boat after the glow discharge treatment (P−Au/Aβ16−20 sample using 100 μM Aβ16−20 and 500 μM HAuCl4 hybrid aqueous solutions) and representative TEM micrographs of the film formed (g).

from fibrils to films is driven by a change in the arrangement of the β-sheets rather than by alterations in the chemical structure. Having demonstrated that the glow discharge processing is an effective method for preparing Aβ16−20 peptide films, we next sought to test this approach in the creation of peptide-based Au nanoparticle films (P−Au/Aβ16−20). In this experiment, a mixture of Aβ16−20 (100 μM) and HAuCl4 (5 μM) in aqueous solution was used to prepare a P−Au/Aβ16−20 film. Imaging of a P−Au/Aβ16−20 sample incubated for 24 h by TEM (Figure 2a,b) and AFM (Figure S3) indicates that in the presence of the Au salt, Aβ16−20 monomers assemble into films that are similar to the P-Aβ16−20 sample but differ in that they contain a number of spherical objects throughout the films. Since our previous study showed that Au3+ ions of HAuCl4 can be reduced to Au nanoparticles under glow discharge conditions,32 these highly dispersed spheres should be the Au nanoparticles. Compared with the P-Aβ16−20 sample, less time was required for Aβ16−20 monomers to form a relatively intact film in the presence of HAuCl4. These Au nanoparticles were found to have a diameter of 2.5 ± 0.6 nm (Figure 2a inset). Using high-resolution TEM, we were able to visualize the atomic planes of Au nanoparticles (Figure 2b inset), observing lattice fringes with a d spacing of 0.235 nm that correlates to the (111) plane of Au. XRD analysis (Figure 3a) of the dried P−Au/Aβ16−20 sample (prepared using 100 μM Aβ16−20 and 500 μM HAuCl4 solution) shows the characteristic diffraction peaks of Au(0) at 38°, 44°, 64°, 77°, and 82°, which are associated with the Au (111), (200), (220), (311), and (222) planes, respectively. This observation is consistent with the TEM analysis, with both techniques revealing the highly crystalline nature of the

obtained Au nanoparticles. The thickness of the P−Au/ Aβ16−20 film was shown to be approximately 1 nm by AFM imaging (Figure S3 inset). Comparing the size of the Au nanoparticles to the height of the bright dots, it suggests that the Au nanoparticles are embedded in the peptide films. In order to understand the formation mechanism of the composite films, we performed two control experiments. In the first set of experiments, we first used the glow discharge to reduce gold ions into nanoparticles in the absence of the peptide, and the unassembled peptide was then introduced into the metal nanoparticles solution. Argon glow discharge was initiated again to promote the assembly of peptides into thin films. Our TEM imaging (Figure 2c) shows no evidence for formation of peptide thin film but random aggregates of gold nanoparticles. In the second set of experiments, we first prepared the peptide film in the absence of gold ions, and then added the metal ions into the peptide film solution, followed by reduction using the argon glow discharge. TEM imaging again shows random aggregates of gold nanoparticles that were not uniformly incorporated into the peptide thin films (Figure 2d). These two experiments clearly demonstrate that the assembly of peptide into thin films and the reduction of gold ions into nanoparticles must occur simultaneously in order to form peptide/Au NP hybrid thin films with the nanoparticles uniformly distributed. To further confirm the nature of the Au nanoparticles and to verify that embedding into the peptide film does not affect their physical properties, we performed UV−vis absorbance analysis of Aβ16−20, P-Aβ16−20, and P−Au/Aβ16−20 (Figure 3b). The P− Au/Aβ16−20 sample displays a broad band centered at 528 nm, 16054

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Figure 5. (a) TEM micrographs of P−Pt/Aβ16−20 films (using a 100 μM Aβ16−20 and 100 μM H2PtCl6 hybrid solution). (b) TEM micrographs of P−Pd/Aβ16−20 films (using a 300 μM Aβ16−20 and 100 μM Pd(NO3)2 hybrid solution).

symmetrical peaks are apparent and can be ascribed to Pd0 32 (Figure S4). Accordingly, the room temperature electron reduction is excellent for the preparation of highly dispersed metal nanoparticles on the thermal sensitive substrates, like peptides.30 Those metal ions with positive standard electrode potentials (this means they can easily catch electrons) can be easily reduced by this electron reduction (with non-hydrogen glow discharge as the resource of electrons).30,32 In this way, we can easily extend the present method to prepare other metal/ peptide monolayer films (like silver (Ag), rhodium (Rh), or iridium (Ir)/peptide monolayer films). Because the room temperature electron reduction possesses characteristics of fast nucleation and slow crystal growth,30 this makes it excellent for the size control. This is the reason that highly dispersed monolayers can be achieved by room temperature electron reduction. On the basis of the results and discussions above, we propose the following mechanism for the formation of peptide-based metal nanoparticle monolayer films (Figure 6), using the formation of Au monolayer films as an example. First, the Aβ16−20 monomers interact with the AuCl4− ions through electrostatic interactions with the positively charged lysine residues, giving well-distributed Au ions. Second, the hybrid solution interacts with the glow discharge plasma, during which

whereas Aβ16−20 and P-Aβ16−20 do not. This same peak is also present in a discharge-affected solution of HAuCl4 only (PHAuCl4) and is associated with the typical plasmon peak of Au nanoparticles (2−10 nm).41 This result suggests that the embedding of the Au nanoparticles into the Aβ16−20 peptide film does not affect their surface plasmon resonance properties. To investigate the effect of gold ion concentration on the particle size and shape, we performed experiments by varying concentrations of the gold ion while fixing the peptide concentration. As shown in Figure 4, as the concentration of HAuCl4 was increased from 100 μM to 200 μM and then to 500 μM, the average size of the resulting Au particles increased from 3.2 nm to 4.7 nm and 19.4 nm, respectively. This demonstrates clearly the potential of tuning the size of Au nanoparticles embedded within the peptide films. However, we did notice that at 500 μM the resulting nanoparticles started to overlap among each other, leading to some nonuniform distribution of the particles within the film. We also performed experiment using a higher concentration of the Aβ16−20 peptide (500 μM). Figure 4d shows a representative TEM image of the resulting film with sparsely distributed Au particles, in contrast to the dense film (Figure 4a) obtained at 100 μM peptide solution with the same HAuCl4 concentration (100 μM). There was no significant change in Au particle size, indicating that it is the concentration of HAuCl4 that primarily determines the particle size. The P−Au/Aβ16−20 films obtained at higher concentrations of both peptides and Au ions become visually observable, forming dark purple thin films in the quartz boat after interaction with the glow discharge (Figure 4f). The majority of the observed films presents as centimeter-scale long and millimeter-scale wide ribbons. The color of the films is caused by the Au nanoparticles, as the pure Aβ16−20 films are transparent (Figure 4e). TEM imaging (Figure 4g) shows that the P−Au/Aβ16−20 sample formed at high concentration can produce a well-distributed thin film as well. In addition to Au, we also examined the potential for the formation of monolayer films of platinum (Pt) and palladium (Pd). Figure 5 presents TEM images of well-distributed monolayer Pt and Pd films. The lattice fringes with a d spacing of 0.226 nm of Pt (111) can be observed in TEM imaging (Fugure 5a). XPS analyses also confirm the metallic status of the obtained monolayer films. Figure S4 presents the XPS spectrum of Pd 3d of the sample P−Pd/Aβ16−20. Two

Figure 6. Process of peptide-based Au monolayer film self-assembly: (a) peptide monomers interact with AuCl4− ions through the positive charge on the K residue; (b) Au ions are reduced to Au nanoparticles by glow discharge plasma, while the peptide monomers self-assemble into fibrils; (c) Au nanoparticles and peptide fibrils assemble into welldistributed films. 16055

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the Aβ16−20 monomers assemble into antiparallel β-sheet fibrils through hydrogen bonding and the AuCl4− ions are reduced into Au nanoparticles. Finally, the β-sheet fibrils aggregate in the direction perpendicular to their long axes through C−C and N−N interactions, leading to the formation of monolayer films. Based on the previous study about the possible formation mechanism for the films, some hydrated electrons may be replaced by Au nanoparticles within the film, retaining the electric charge in order to stabilize the film during its formation. This retained negative charge will also lead to repulsion between Au nanoparticles, resulting in the stable distribution of Au monolayer films in the aqueous solution.

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ASSOCIATED CONTENT

(5) Sarikaya, M.; Tamerler, C.; Jen, A. K. Y.; Schulten, K.; Baneyx, F. Molecular biomimetics: nanotechnology through biology. Nat. Mater. 2003, 2 (9), 577−585. (6) Warner, M. G.; Hutchison, J. E. Linear assemblies of nanoparticles electrostatically organized on DNA scaffolds. Nat. Mater. 2003, 2 (4), 272−277. (7) Tkachenko, A. G.; Xie, H.; Coleman, D.; Glomm, W.; Ryan, J.; Anderson, M. F.; Franzen, S.; Feldheim, D. L. Multifunctional gold nanoparticle-peptide complexes for nuclear targeting. J. Am. Chem. Soc. 2003, 125 (16), 4700−4701. (8) Cha, J. N.; Stucky, G. D.; Morse, D. E.; Deming, T. J. Biomimetic synthesis of ordered silica structures mediated by block copolypeptides. Nature 2000, 403 (6767), 289−292. (9) Bellomo, E. G.; Wyrsta, M. D.; Pakstis, L.; Pochan, D. J.; Deming, T. J. Stimuli-responsive polypeptide vesicles by conformation-specific assembly. Nat. Mater. 2004, 3 (4), 244−248. (10) Black, M.; Trent, A.; Kostenko, Y.; Lee, J. S.; Olive, C.; Tirrell, M. Self-assembled peptide amphiphile micelles containing a cytotoxic T-cell epitope promote a protective immune response in vivo. Adv. Mater. 2012, 24 (28), 3845−3849. (11) Cui, H. G.; Webber, M. J.; Stupp, S. I. Self-assembly of peptide amphiphiles: from molecules to nanostructures to biomaterials. Biopolymers 2010, 94 (1), 1−18. (12) Petka, W. A.; Harden, J. L.; McGrath, K. P.; Wirtz, D.; Tirrell, D. A. Reversible hydrogels from self-assembling artificial proteins. Science 1998, 281 (5375), 389−392. (13) Sun, J.; Zuckermann, R. N. Peptoid polymers: A highly designable bioinspired material. ACS Nano 2013, 7 (6), 4715−4732. (14) Liang, G. L.; Yang, Z. M.; Zhang, R. J.; Li, L. H.; Fan, Y. J.; Kuang, Y.; Gao, Y.; Wang, T.; Lu, W. W.; Xu, B. Supramolecular hydrogel of a D-amino acid dipeptide for controlled drug release in vivo. Langmuir 2009, 25 (15), 8419−8422. (15) Huang, R. L.; Su, R. X.; Qi, W.; Zhao, J.; He, Z. M. Hierarchical, interface-induced self-assembly of diphenylalanine: formation of peptide nanofibers and microvesicles. Nanotechnology 2011, 22 (24), 245609. (16) Hendler, N.; Sidelman, N.; Reches, M.; Gazit, E.; Rosenberg, Y.; Richter, S. Formation of well-organized self-assembled films from peptide nanotubes. Adv. Mater. 2007, 19 (11), 1485−1488. (17) Smith, A. M.; Williams, R. J.; Tang, C.; Coppo, P.; Collins, R. F.; Turner, M. L.; Saiani, A.; Ulijn, R. V. Fmoc-Diphenylalanine self assembles to a hydrogel via a novel architecture based on π-π interlocked beta-sheets. Adv. Mater. 2008, 20 (1), 37−41. (18) Adler-Abramovich, L.; Aronov, D.; Beker, P.; Yevnin, M.; Stempler, S.; Buzhansky, L.; Rosenman, G.; Gazit, E. Self-assembled arrays of peptide nanotubes by vapour deposition. Nat. Nanotechnol. 2009, 4 (12), 849−854. (19) Fu, X. Y.; Wang, Y.; Huang, L. X.; Sha, Y. L.; Gui, L. L.; Lai, L. H.; Tang, Y. Q. Assemblies of metal nanoparticles and self-assembled peptide fibrils - Formation of double helical and single-chain arrays of metal nanoparticles. Adv. Mater. 2003, 15 (11), 902−906. (20) Li, L. S.; Stupp, S. I. One-dimensional assembly of lipophilic inorganic nanoparticles templated by peptide-based nanofibers with binding functionalities. Angew. Chem., Int. Ed. 2005, 44 (12), 1833− 1836. (21) Acar, H.; Garifullin, R.; Guler, M. O. Self-assembled templatedirected synthesis of one-dimensional silica and titania nanostructures. Langmuir 2011, 27 (3), 1079−1084. (22) Yuwono, V. M.; Hartgerink, J. D. Peptide amphiphile nanofibers template and catalyze silica nanotube formation. Langmuir 2007, 23 (9), 5033−5038. (23) Lamm, M. S.; Sharma, N.; Rajagopal, K.; Beyer, F. L.; Schneider, J. P.; Pochan, D. J. Laterally spaced linear nanoparticle arrays templated by laminated beta-sheet fibrils. Adv. Mater. 2008, 20 (3), 447−451. (24) Nam, K. T.; Shelby, S. A.; Choi, P. H.; Marciel, A. B.; Chen, R.; Tan, L.; Chu, T. K.; Mesch, R. A.; Lee, B. C.; Connolly, M. D.; Kisielowski, C.; Zuckermann, R. N. Free-floating ultrathin two-

In conclusion, a well-distributed peptide-based Au monolayer film has been formed directly via self-assembly of Aβ16−20 peptides and inorganic Au nanoparticles under the influence of electrons from glow discharge plasma at room temperature. The noble metal ions are reduced by the plasma electrons to give nanoparticles that simultaneously embed within the growing peptide films, resulting in the formation of giant peptide-based metal nanoparticle monolayer films. The size of Au nanoparticles can be tuned in the nanometer range by changing the initial HAuCl4 concentration. This method for constructing the peptide-based metal monolayer films is simple, effective, and environmentally friendly. Moreover, it not only is a promising way to synthesize thin metal (Au, Pt, Ag, and Pd) films but also provides a new type of biomolecular scaffold for assembling more complicated functional thin films. S Supporting Information *

CD and FTIR spectra, photographs and LC-MS analysis of the peptide films, AFM imaging of the peptide-based Au monolayer films, and XPS spectrum. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail [email protected] (H.C.). *E-mail [email protected] (C.-J.L.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (#20990223).

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REFERENCES

(1) Rosi, N. L.; Mirkin, C. A. Nanostructures in biodiagnostics. Chem. Rev. 2005, 105 (4), 1547−1562. (2) Lee, J. S.; Han, M. S.; Mirkin, C. A. Colorimetric detection of mercuric ion (Hg2+) in aqueous media using DNA-functionalized gold nanoparticles. Angew. Chem., Int. Ed. 2007, 46 (22), 4093−4096. (3) Levy, R.; Thanh, N. T. K.; Doty, R. C.; Hussain, I.; Nichols, R. J.; Schiffrin, D. J.; Brust, M.; Fernig, D. G. Rational and combinatorial design of peptide capping Ligands for gold nanoparticles. J. Am. Chem. Soc. 2004, 126 (32), 10076−10084. (4) Macfarlane, R. J.; Lee, B.; Jones, M. R.; Harris, N.; Schatz, G. C.; Mirkin, C. A. Nanoparticle superlattice engineering with DNA. Science 2011, 334 (6053), 204−208. 16056

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dimensional crystals from sequence-specific peptoid polymers. Nat. Mater. 2010, 9 (5), 454−460. (25) Cui, H.; Muraoka, T.; Cheetham, A. G.; Stupp, S. I. Selfassembly of giant peptide nanobelts. Nano Lett. 2009, 9 (3), 945−951. (26) Tang, Z. Y.; Zhang, Z. L.; Wang, Y.; Glotzer, S. C.; Kotov, N. A. Self-assembly of CdTe nanocrystals into free-floating sheets. Science 2006, 314 (5797), 274−278. (27) Xu, L. G.; Ma, W.; Wang, L. B.; Xu, C. L.; Kuang, H.; Kotov, N. A. Nanoparticle assemblies: dimensional transformation of nanomaterials and scalability. Chem. Soc. Rev. 2013, 42 (7), 3114−3126. (28) Kinge, S.; Crego-Calama, M.; Reinhoudt, D. N. Self-assembling nanoparticles at surfaces and interfaces. ChemPhysChem 2008, 9 (1), 20−42. (29) Pan, Y. X.; Liu, C. J.; Zhang, S.; Yu, Y.; Dong, M. D. 2Doriented self-assembly of peptides induced by hydrated electrons. Chem.Eur. J. 2012, 18 (46), 14614−14617. (30) Liu, C.-J.; Zhao, Y.; Li, Y. Z.; Zhang, D.-S.; Chang, Z.; Bu, X.-H. Perspectives on electron assisted reduction for the preparation of highly dispersed noble metal catalysts. ACS Sustainable Chem. Eng. http://dx.doi.org/10.1021/sc400376m. (31) Zhou, Y.; Xiang, Z. H.; Cao, D. P.; Liu, C. J. Covalent organic polymer supported palladium catalysts for CO oxidation. Chem. Commun. 2013, 49 (50), 5633−5635. (32) Wang, Z. J.; Xie, Y. B.; Liu, C. J. Synthesis and characterization of noble metal (Pd, Pt, Au, Ag) nanostructured materials confined in the channels of mesoporous SBA-15. J. Phys. Chem. C 2008, 112 (50), 19818−19824. (33) Lu, K.; Guo, L.; Mehta, A. K.; Childers, W. S.; Dublin, S. N.; Skanthakumar, S.; Conticello, V. P.; Thiyagarajan, P.; Apkarian, R. P.; Lynn, D. G. Macroscale assembly of peptide nanotubes. Chem. Commun. 2007, 26, 2729−2731. (34) Tjernberg, L. O.; Naslund, J.; Lindqvist, F.; Johansson, J.; Karlstrom, A. R.; Thyberg, J.; Terenius, L.; Nordstedt, C. Arrest of beta-amyloid fibril formation by a pentapeptide ligand. J. Biol. Chem. 1996, 271 (15), 8545−8548. (35) Krysmann, M. J.; Castelletto, V.; Kelarakis, A.; Hamley, I. W.; Hule, R. A.; Pochan, D. J. Self-assembly and hydrogelation of an amyloid peptide fragment. Biochemistry 2008, 47 (16), 4597−4605. (36) Castelletto, V.; Hamley, I. W.; Hule, R. A.; Pochan, D. HelicalRibbon formation by a beta-amino acid modified Amyloid betapeptide fragment. Angew. Chem., Int. Ed. 2009, 48 (13), 2317−2320. (37) Castelletto, V.; Hamley, I. W.; Harris, P. J. F.; Olsson, U.; Spencer, N. Influence of the solvent on the self-assembly of a modified Amyloid beta peptide fragment. I. Morphological investigation. J. Phys. Chem. B 2009, 113 (29), 9978−9987. (38) Bicudo, T. C.; Forato, L. A.; Batista, L. A. R.; Colnago, L. A. Study of the conformation of gamma-zeins in purified maize protein bodies by FTIR and NMR spectroscopy. Anal. Bioanal. Chem. 2005, 383 (2), 291−296. (39) Jiang, H. Z.; Guler, M. O.; Stupp, S. I. The internal structure of self-assembled peptide amphiphiles nanofibers. Soft Matter 2007, 3 (4), 454−462. (40) Ryu, J.; Park, C. B. Solid-phase growth of nanostructures from amorphous peptide thin film: Effect of water activity and temperature. Chem. Mater. 2008, 20 (13), 4284−4290. (41) Garcia-Martinez, J. C.; Crooks, R. M. Extraction of Au nanoparticles having narrow size distributions from within dendrimer templates. J. Am. Chem. Soc. 2004, 126 (49), 16170−16178.

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dx.doi.org/10.1021/la4036908 | Langmuir 2013, 29, 16051−16057