NANO LETTERS
Thiolated Peptide Nanotube Assembly as Arrays on Patterned Au Substrates
2004 Vol. 4, No. 12 2437-2440
Ipsita A. Banerjee, Lingtao Yu, Robert I. MacCuspie, and Hiroshi Matsui* Department of Chemistry and Biochemistry at Hunter College and the Graduate Center, The City UniVersity of New York, New York, New York 10021 Received September 22, 2004; Revised Manuscript Received October 27, 2004
ABSTRACT A variety of nanotubes were addressed to particular directions by using external forces such as microfluidics, magnetic fields, electric fields, and the Langmuir−Blodgett technique. Recently in another approach, nanotubes were assembled by chemical interactions. For example, nanotubes coated by proteins were assembled onto the complimentary ligand-patterned substrates in solution. Molecular recognitions, hydrogen bonding, hydrophobic interactions, and charge interactions were also applied to locate nanotubes in the specific regions on substrates. In this report, we assembled thiolated peptide nanotubes by using one of the stronger chemical interactions, thiol−Au interaction. Due to the strong thiol−Au interaction, the nanotubes show a strong affinity toward Au substrates and the nanotubes were only addressed to Au regions on the substrates. Because of the strong affinity, the nanotube assembly could be scaled up to form nanotube arrays by patterning Au pads on the substrates with AFM-based nanolithography. This technique may lead to an alternative nontraditional fabrication method for electric circuits because the physical properties of aligned peptide nanotubes can be tuned after the targeted positioning with semiconductor/metal coatings on the nanotubes with simple chemical procedures.
The bottom-up approach has been gaining a significant momentum in the field of nanometer-sized device fabrication and it leads to develop a variety of smart nanoscale building blocks. Among various nanoscale building blocks, nanotubes and nanowires have been synthesized with desired physical properties to be incorporated in electronic and optical devices. Whereas the nanotube material syntheses have been explored extensively, the effort to address those nanotubes onto specific locations of the substrates for the device fabrications has just begun. Recently, nanotubes were addressed to particular directions by using external forces such as microfluidics, magnetic fields, electric fields, and the Langmuir-Blodgett technique.1-7 In another approach, nanotubes were addressed by chemical/biological interactions. For example, nanotubes coated by proteins were addressed onto the complimentary ligand-patterned substrates in solution.8-10 Molecular recognitions, hydrogen bonding, hydrophobic interactions, and charge interactions were also applied to locate nanotubes in the specific regions on substrates.11-16 In this report, we describe the assembly of thiolated peptide nanotubes by using a strong thiol-Au interaction. Due to the strong thiol-Au interaction as compared to biological, hydrophobic, and charge interactions, the peptide nanotubes, whose sidewalls were chemically modified to contain thiol groups, show a strong affinity toward Au substrates and the nanotubes were only addressed to Au regions on the substrates. Because of the strong affinity, the nanotube assembly could be scaled up to form nanotube arrays by patterning Au pads on the substrates with AFM-based 10.1021/nl0484503 CCC: $27.50 Published on Web 11/20/2004
© 2004 American Chemical Society
nanolithography (Figure 1).17-19 This technique may lead to an alternative nontraditional fabrication method for electric circuits because the physical properties of aligned peptide nanotubes can be tuned after the targeted positioning with semiconductor/metal coatings on the nanotubes with simple chemical procedures.20-24 In this study, the peptide nanotubes were used to examine the targeted immobilization because their sidewalls can be thiolated by simple procedures.9 Peptide nanotubes with average diameter of 200 nm were assembled on the patterned Au pads to demonstrate the proof-of-principle of our proposed scheme. The peptide nanotubes were formed from bolaamphiphile peptide monomers in NaOH/citric acid solution.25,26 While the nanotubes were self-assembled via intermolecular hydrogen bonding between amide and carboxylic acid groups of the bolaamphiphile peptide monomers, the free carboxylic acid groups on the nanotube sidewalls were converted to thiols in the following two steps. First, the carboxylic acid groups of the nanotubes were substituted with NHS esters by reacting with N-hydroxysuccinimide (NHS) and ethyl-3-[3-(dimethylamino)propyl]carbodiimide (EDAC).27,28 Because the NHS esters bind amine groups covalently, the addition of 2-mercaptoethylamine to the NHS ester-functionalized nanotubes introduced thiol groups covalently linked to the nanotube surfaces.29 The patterning of Au pads on substrates was achieved by AFM-based nanolithography (Nanoscope IIIa and MultiMode microscope, Digital Instruments). For this fabrication, 1-octadecanethiol was used as a mask to prevent the nonspecific
Figure 1. Schematic diagram of thiolated peptide nanotube assembly on the Au trench arrays. (a) Self-assembly of alkylthiols on Au substrates. (b) Shaving trenches on the alkylthiol SAM by using the AFM tip. (c) Location-specific immobilization of the thiolated peptide nanotube onto the patterned Au trenches.
nanotube attachment and it was first self-assembled on the flat Au substrate (Figure 2a). This step is shown in Figure 1a. Then, the octadecanethiol self-assembled monolayer (SAM) was shaved by a Si3N4 tip (Veeco Metrology) to expose Au regions (Figure 1b). The exposed Au trenches were patterned by using a customized Nanoscript software (Veeco Metrology). After the Au trenches were drawn, the substrate was washed sequentially first with ethanol and then with hexane. However, in some substrates, the detached alkylthiol molecules by the AFM tip were still partially piled and remained at the edges of trenches. After the octadecanethiol (0.01 mM) was self-assembled on a Au substrate in 99% ethanol at room temperature for 12 h, a Au trench (200 nm × 2 µm) was created by the AFM tip, as shown in Figure 2b. In this AFM image, the brighter region represents the octadecanethiol SAM and the Au trench is darker due to their height contrast. To attach the thiolated nanotubes to the patterned Au pads on the substrate, the nanotubes were incubated in solution containing the patterned substrate overnight at room temperature under nitrogen. After these substrates were washed thoroughly with ethanol/water solution, the thiolated nanotube was observed to attach selectively to the Au trench via the thiol-Au interaction, as shown in Figure 2c. This process corresponds to the step in Figure 1c. In this AFM image, the shaved region became higher as compared to the background due to the nanotube attachment because the 2438
Figure 2. AFM images of (a) the alkylthiol SAM on the Au substrate, scale bar ) 1 µm. (b) The trench (200 nm × 2 µm) shaved by the AFM tip, scale bar ) 1 µm. Inset: the AFM image in the height mode, scale bar ) 500 nm. (c) The thiolated peptide nanotube attached on the trench, scale bar ) 1 µm. Inset: the AFM image in the height mode, scale bar ) 500 nm. (d) The thiolated peptide nanotubes attached on the 200 nm-trench array, scale bar ) 2 µm.
nanotube diameter was larger than the height of octadecanethiol SAMs. This nanotube assembly on the patterned Au substrate could be scaled up with a larger number of nanotubes. When multiple Au trenches were shaved on the substrate and the nanotubes were incubated, most of the Au trenches were filled with the nanotubes, as shown in Figure 2d. Statistically, about 90% of the Au trenches were observed to have thiolated nanotubes in the AFM images. The thiolated peptide nanotubes in the diameter of 200 nm were assembled effectively onto Au trenches of comparable size. But the selective attachment of the nanotube to the larger Au trenches was not demonstrated yet. We produced a 1.5 µm × 3 µm Au trench by the same procedure and examined how the thiolated nanotubes recognize the larger Au trenches. When nanotubes were incubated in solution containing the patterned substrate overnight at room temperature under nitrogen, the multiple nanotubes with the diameter of 200 nm were attached in the 1.5 µm Au trench (Figure 3a). About 90% of nanotubes were aligned parallel in a close-packed manner, and the magnified AFM images in Figure 3b clearly show that eight nanotubes with average diameter of 200 nm were aligned inside the trench. Previously, multiple antibody-coated nanotubes were packed in the trenches functionalized by the complementary antigens in the same alignment as observed in this system.10 Carbon nanotubes were also aligned on the polar molecular patterns on Au.15 In both cases, the concentrations of nanotubes and the internanotube interactions seem to be important factors for alignment, and the thiolated peptide nanotube alignment in the larger trench likely occurred in the appropriate nanotube concentration. Further systematic alignment studies Nano Lett., Vol. 4, No. 12, 2004
NaOH to form a 10 mM solution. The pH of the solution was adjusted to 4.6 with 50 mM citric acid. The pH-adjusted solution was placed at room temperature and the peptide nanotubes appeared in the solution after two weeks. The resulting nanotubes were washed with deionized water and microcentrifuged (14500 rpm) for 10 min. Thiolization of the Peptide Nanotube. The peptide nanotubes in 200 µL aqueous solution were mixed with NHS (15 mM), and then 200 µL of EDAC (75 mM) was added to the solution and vortexed for 30 min. This procedure was followed by centrifuging the nanotube solution for 1 h and then washing with water. After nitrogen was bubbled through the nanotube solution for 30 min, the nanotube sample was treated with 0.1 mM solution of 2-mercaptoethylamine. The mixture was again vortexed for 1 h and the nanotubes were centrifuged. After the nanotube solution was left at 4 °C overnight, the nanotubes were centrifuged and washed immediately prior to the attachment to the patterned Au trenches. Preparation of the Alkylthiol SAM. Au substrates were purchased from Molecular Imaging. The substrate was washed thoroughly with 99% ethanol prior to the use. After 1-octadecanethiol (0.01 mM) was self-assembled on Au substrates in 99% ethanol at room temperature for 12 h, the substrate was washed in ethanol for AFM-based nanolithography.
Figure 3. AFM images of (a) the multiple thiolated peptide nanotubes attached inside the large Au trench (1.5 µm × 3 µm), scale bar ) 2.5 µm; (b) the magnified AFM image of (a), scale bar ) 700 nm. Inset: the AFM image in the height mode, scale bar ) 800 nm.
as a function of the nanotube concentration are necessary to understand the alignment mechanism of the thiolated peptide nanotubes. In summary, the peptide nanotubes whose sidewalls were thiolated could be assembled onto Au trenches patterned on alkylhiol SAMs. When the diameter of the nanotubes was comparable to the width of Au trench, about 90% of the trenches were attached by nanotubes. As the width of trench was increased, multiple nanotubes were observed to attach inside the large Au trench in the close-packed manner. While the peptide nanotubes in the diameter of 200 nm were used as a proof-of-principle to demonstrate that this approach may lead to an alternative nontraditional fabrication method in order to address nanometer-scale building blocks for device fabrications with simple chemical procedures, smaller nanotube assembly is desirable to be comparable to conventional photolithographic fabrications. We are currently assembling peptide nanotubes in the diameters of 10-30 nm on Au areas in various shapes and sizes systematically. Experimental Section. Synthesis of the Peptide Nanotube. The monomer for the self-assembled nanotubes, bis(N-Ramido-glycylglycine)-1,7-heptane dicarboxylate, was prepared as described elsewhere.25,26 To self-assemble the peptide nanotubes, the monomer was dissolved in 30 mM Nano Lett., Vol. 4, No. 12, 2004
Acknowledgment. This work was supported by the U.S. Department of Energy (DE-FG-02-01ER45935). References (1) Jin, S.; Whang, D. M.; McAlpine, M. C.; Friedman, R. S.; Wu, Y.; Lieber, C. M. Nano Lett. 2004, 4, 915-919. (2) Long, D. P.; Lazorcik, J. L.; Shashidhar, R. AdV. Mater. 2004, 16, 814-817. (3) Smith, P. A.; Nordquist, C. D.; Jackson, T. N.; Mayer, T. S.; Martin, B. R.; Mbindyo, J.; Mallouk, T. E. Appl. Phys. Lett. 2000, 77, 13991401. (4) Chung, J. Y.; Lee, K. H.; Lee, J. H.; Ruoff, R. S. Langmuir 2004, 20, 3011-3017. (5) Huang, Y.; Duan, X.; Cui, Y.; Lauhon, L. J.; Kim, K. H.; Lieber, C. M. Science 2001, 294, 1313-1317. (6) Lay, M. D.; Novak, J. P.; Snow, E. S. Nano Lett. 2004, 4, 603-606. (7) Huang, L.; Wind, S. J.; O’Brien, S. P. Nano Lett. 2003, 3, 299303. (8) Matsui, H.; Porrata, P.; Douberly, G. E. J. Nano Lett. 2001, 1, 461464. (9) Banerjee, I. A.; Yu, L.; Matsui, H. Nano Lett. 2003, 3, 283-287. (10) Nuraje, N.; Banerjee, I. A.; MacCuspie, R. I.; Yu, L.; Matsui, H. J. Am. Chem. Soc. 2004, 126, 8088-8089. (11) Mbindyo, J. K. N.; Reiss, B. D.; Martin, E. R.; Keating, C. D.; Natan, M. J.; Mallouk, T. E. AdV. Mater. 2001, 13, 249. (12) Banerjee, I. A.; Yu, L.; Matsui, H. J. Am. Chem. Soc. 2003, 125, 9542. (13) Braun, E.; Eichen, Y.; Sivan, U.; Ben-Yoseph, G. Nature 1998, 391, 775. (14) Matsui, H.; Gologan, B.; Pan, S.; Douberly, G. J. Eur. Phys. J. D 2001, 16, 403-406. (15) Rao, S. G.; Huang, L.; Setyawan, W.; Hong, S. H. Nature 2003, 425, 36-37. (16) Caswell, K. K.; Wilson, J. N.; Bunz, U. H. F.; Murphy, C. J. J. Am. Chem. Soc. 2003, 125, 13914-13915. (17) Wouters, D.; Schubert, U. S. Angew. Chem., Intl. Ed. Engl. 2004, 43, 2480-2495. (18) Liu, G.-Y.; Xu, S.; Qian, Y. Acc. Chem. Res. 2000, 33, 457-466. (19) Ginger, D. S.; Zhang, H.; Mirkin, C. A. Angew. Chem., Intl. Ed. Engl. 2004, 43, 30-45. 2439
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NL0484503
Nano Lett., Vol. 4, No. 12, 2004
