Langmuir 2007, 23, 9069-9075
9069
Site-Specific Functionalization on Individual Colloids: Size Control, Stability, and Multilayers Allison M. Yake, Charles E. Snyder, and Darrell Velegol* Department of Chemical Engineering, The PennsylVania State UniVersity, UniVersity Park, PennsylVania 16802 ReceiVed April 17, 2007 Individual colloidal particles are locally functionalized with nanoscale control. Here we use the particle lithography technique to mask one region of a silica or polystyrene particle (size 3.0 µm down to 170 nm), while the remaining 95% or more of the particle is coated with various sized nanocolloids. The images and data show precise and predictable control over the size of the region, with fine-tuned patch size control obtainable by changing the ionic strength of the solution. The coating on the particles remains stable even when subjected to sonication for 5 min. Both single regions and multilayer annuluses are readily formed. Particle lithography provides a general, reliable, stable, controllable, and scalable method for placing site-specific functionalizations on individual particles, opening the way to more complex particle patterning and the bottom-up assembly of more complex structures.
Introduction The bottom-up assembly of colloidal particles is becoming important in the fabrication of electronic,1,2 drug delivery,3 and photonic4 devices, and even in the fabrication of colloidal machines.5-8 The patterning of individual particles9 is also playing a key role in devices and in other purposes, like improved Pickering surfactants.10 Recently, our research group patterned single site-specific regions on individual colloidal particles, and these enabled us to fabricate colloidal doublets using bottom-up assembly.11 We used the “particle lithography” technique to create these site-specific regions. A number of techniques have been used to pattern individual particles. Janus particles have half the particle with one chemistry and the other half with a different chemistry.12,13 Such particles have been created by microfluidic synthesis14 or using PDMS stamping technique.15 Nanowire particles can be patterned directly from their synthesis. The nanowire16 particles are grown in templates to include different lengths of various metals or semiconductors and, thus, have circumferential stripes along the * To whom correspondence should be addressed. Address: 108 Fenske Laboratory, The Pennsylvania State University, University Park, Pennsylvania 16802. Phone (814) 895-8739. Fax: (814) 865-7846. E-mail: velegol@ psu.edu. (1) Patolsky, F.; Zheng, G.; Lieber, C. M. Nanomedicine 2006, 1 (1), 51-65. (2) Li, Y.; Qian, F.; Xiang, J.; Lieber, C. M. Mater. Today 2006, 9 (10), 10-27. (3) Langer, R.; Tirrell, D. A. Nature 2004, 428, 487-492. (4) Barrelet, C. J.; Bao, J.; Loncar, M.; Park, H.-G.; Capasso, F.; Lieber, C. M. Nano Lett. 2006, 6 (1), 11-15. (5) Terray, A.; Oakey, J.; Marr, D. W. M. Science 2002, 296, 1841-1844. (6) Kline, T. R.; Paxton, W. F.; Wang, Y.; Velegol, D.; Mallouk, T. E.; Sen, A. J. Am. Chem. Soc. 2005, 127, 17150-17151. (7) Whitesides, G. M. Small 2005, 1 (2), 172-179. (8) Comiskey, B.; Albert, J. D.; Yoshizawa, H.; Jacobson, J. Nature 1998, 394, 253-255. (9) Fialkowski, M.; Bitner, A.; Gryzybowski, B. A. Nat. Mater. 2005, 4, 9397. (10) Binks, B. P. Curr. Opin. Colloid Interface Sci. 2002, 7, 21-41. (11) Snyder, C. E.; Yake, A. M.; Feick, J. D.; Velegol, D. Langmuir 2005, 21, 4813-4815. (12) Perro, A.; Reculusa, S.; Ravaine, S.; Bourgeat-Lami, E.; Duguet, E. J. Mater. Chem. 2005, 15, 3745-3760. (13) Hong, L.; Cacciuto, A.; Luijten, E.; Granick, S. Nano Lett. 2006, 6 (11), 2510-2514. (14) Nie, Z.; Li, W.; Seo, M.; Xu, S.; Kumacheva, E. J. Am. Chem. Soc. 2006, 128, 9408-9412. (15) Cayer, O.; Paunov, V. N.; Velev, O. D. J. Mater. Chem. 2003, 13, 24452450.
length. Particles adhered in a plane have been bifunctionalized through micro contact printing the nonadsorbed side or by electroless deposition.15,17 Masking techniques have also been used to pattern particles. This includes adhering silica particles onto silica templates and coating the exposed surface to gold18 as well as adhering silica particles onto a template, covering with PDMS, and then removing the PDMS film so that the exposed cap can be functionalized.19 Polystyrene latex particles have also been formed into a colloidal crystal, and the particle contact points were masked from a gold vapor, giving multiple gold nanodots on each sphere in the array.20,21 Raspberry-like particles with uneven surfaces were formed by a self-assembled heterocoagulation of nanometer sized particles on larger polymer particle surfaces via a charge compensation mechanism.22 Small colloidal particles have been adsorbed onto larger colloidal particles of opposite surface charge to pattern the particle surface.23,24 Another example of patterning smaller particles onto larger ones, including the creation of more sophisticated patterning, has been achieved with bidisperse colloidal materials (different materials and size ratios) through an inverted water-in-oil emulsion technique.25 More sophisticated patterning of larger particles (∼100 µm) has been demonstrated by starting with liquid prepolymers9 and even showing national flags on the particles. For the various techniques listed here, issues arise with the flexibility of the techniques to accommodate a variety of materials, the ability to control the technique in a predictive manner, or the ability to scale-up the technique to larger quantities of production. (16) Nicewarner-Pena, S. R.; Freeman, R. G.; Reiss, B. D.; He, L.; Pena, D. J.; Walton, I. D.; Cromer, R.; Keating, C. D.; Natan, M. J. Science 2001, 294, 137. (17) Cui, J.-W.; Kretzschmar, I. Langmuir 2006, in press. (18) Love, J. C.; Gates, B. D.; Wolfe, D. B.; Paul, K. E.; Whitesides, G. M. Nano Lett. 2002, 2 (8), 891-894. (19) Charnay, C.; Lee, A.; Man, S.-Q.; Moran, C. E.; Radloff, C.; Bradley, R. K.; Halas, N. J. J. Phys. Chem. B 2003, 107, 7327-7333. (20) Zhang, G.; Wang, D.; Mohwald, H. Nano Lett. 2005, 5 (1), 143-146. (21) Zhang, G.; Wang, D.; Mohwald, H. Angew. Chem., Int. Ed. 2005, 44, 1-5. (22) Li, G.; Yang, X.; Bai, F.; Huang, W. J. Colloid Interface Sci. 2006, 297, 705-710. (23) Harley, S.; Thompson, D. W.; Vincent, B. Colloids Surf. 1992, 62, 153162. (24) Vincent, B.; Young, C. A.; Tadros, T. F. J. Chem. Soc. Faraday I 1980, 76, 665-673. (25) Cho, Y.-S.; Yi, G.-R.; Lim, J.-M.; Kim, S.-H.; Manoharan, V. N.; Pine, D. J.; Yang, S.-M. J. Am. Chem. Soc. 2005, 127, 15968-15975.
10.1021/la7011292 CCC: $37.00 © 2007 American Chemical Society Published on Web 07/13/2007
9070 Langmuir, Vol. 23, No. 17, 2007
In this paper, we analyze the “particle lithography” technique for patterning individual particles site-specifically. Particle lithography is a simple, general patterning and assembly technique that does not rely on conventional top-down lithographic techniques. In the present work, we (1) demonstrate precise and predictable size control over patterning single regions, (2) show quantitatively the stability of the coating layer and as a result the whole particle lithography process, (3) pattern an annulus region using the particle lithography technique, (4) show that the particle lithography technique works on particles down to at least 170 nm in diameter, and (5) identify causes for certain types of defects resulting from the technique. These advances enable the patterning of particles with rather general chemistries, either for direct use or for use in bottom-up assembly.11 The images and data in this work demonstrate that the technique is relatively simple, quite reproducible, and controllable and requires relatively inexpensive material requirements. Experimental Section Materials. Monodisperse, surfactant-free amidine and sulfatefunctionalized polystyrene latex (PSL) microspheres were purchased from Interfacial Dynamics Corporation (Portland, OR). Specifically, 20 nm (batch no: 1973), 43 nm (batch no: 2012,1), and 84 nm (batch no: 124,1) sulfate-functionalized PSL nanoparticles and 520 nm (batch no: 892,1), 1.5 µm (batch no: 1321,1), 2.1 µm (batch no: 1091,1), and 3.3 µm (batch no: 1414,1) amidine-functionalized PSL microspheres were used in the experiments described in this manuscript. Monodisperse, uniform 150 nm (lot no: 7660), 170 nm (lot no: 6594), 0.9 µm (lot no: 4949), and 1.54 µm (lot no: 5252) plain silica and 0.97 µm (lot no: 6497) amine-functionalized silica microspheres were purchased from Bang’s Laboratory (Fishers, IN). Monodisperse, 3.0 µm silica microspheres (lot no: F300) were purchased from the Corpuscular Company (Mahopac, NY). Potassium chloride (KCl, MW 74.5), poly(sodium 4-styrenesulfonate) (PSS, MW 70 000), and poly(allylamine hydrochloride) (PAH, MW 70 000) were purchased from Sigma-Aldrich Chemicals, USA. The deionized (DI) water that was used for all experiments and washing steps (Millipore Corp. Milli-Q system) had a specific resistance greater than 1 MΩ·cm (i.e., “equilibrium water”). Silicon wafers with an orientation of and resistivity values of 1-10 Ω-cm used as the substrate for FESEM imaging were purchased from Silicon Quest International (lot no. IMV3P0110PRM). Instrumentation. The Ultrasonicator was from VWR International (model 550T). The particle zeta potentials were measured on a Brookhaven Instrument PALS (Phase Analysis Light Scattering) zeta potential analyzer. The optical microscopy images were obtained on a Nikon Eclipse TE2000-U inverted optical microscope. The electron microscopy images were obtained on a ZeissSMT 1530 field emission scanning electron microscope (FESEM) at the Penn State Nanofabrication Facility. The pressurized heat treatments took place in a standard steam autoclave at 120 °C. FESEM Preparation. Approximately 2 µL of particle samples (10 µm particles which act as “flat” surfaces). In addition, we are working to create more complex patterns and assemblies by using surfaces more intricate than simple glass plates (e.g., V-blocks or other templates, including other particles), which will lead to more sophisticated bottom-up assemblies. Acknowledgment. The authors thank the National Science Foundation (NIRT Grant CCR-0303976, CBET Grant # 0651611) and the Petroleum Research Fund (Grant PRF 43453-AC10) for funding. We also thank the Penn State Materials Research Institute for funding the FESEM images taken at the Penn State Nanofabrication Facility, part of the NNIN. LA7011292
