Gold Nanoparticle Assemblies through Hydrogen-Bonded

UniVersity of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands ... gold nanoparticle assemblies with multicomponent double rosette molecular bo...
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Langmuir 2007, 23, 8772-8777

Gold Nanoparticle Assemblies through Hydrogen-Bonded Supramolecular Mediators Sachin S. Kinge, Mercedes Crego-Calama,*,‡ and David N. Reinhoudt Laboratory of Supramolecular Chemistry and Technology, MESA+ Institute for Nanotechnology, UniVersity of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands ReceiVed February 21, 2007. In Final Form: May 29, 2007

The synthesis of spherical gold nanoparticle assemblies with multicomponent double rosette molecular boxes as mediators is presented. These nine-component hydrogen-bonded supramolecular structures held together by 36 hydrogen bonds induce gold nanoparticle assembly. The morphologies of the nanoparticle assemblies can be tuned easily by changing the quantity of the building block chemisorbed on the nanoparticle surface.

Introduction Applications of nanoparticle-based materials demand precise control over the morphological properties of the individual building blocks as well as the assembled nanoarchitectures.1 In this respect, size- and shape-selective synthesis of nanoparticles and their assemblies is of profound interest.2 For example, linear and nonlinear optical properties, hyperpolarizability, and electric field enhancement factors of nanoparticles strongly depend on parameters such as size, shape, and interparticle distances.3 These properties can be exploited for colorimetric, surface-enhanced Raman resonance (SERS) and surface plasmon resonance (SPR) bioassays,4 for applications such as drug and pregnancy test kits.5 A variety of strategies are applied to achieve multidimensional nanoparticle assemblies. Two approachessself-assembly and mediator-templatingsare particularly promising for assembling inorganic nanoparticles in solution. The self-assembly strategy is based on the use of noncovalent interactions to direct the assembly of the nanoparticles.6 This process relies on the recognition of complementary elements on the nanoparticle * To whom correspondence should be addressed. E-mail: [email protected]. Phone: +31(0)40 2774119. Fax: +31(0)40 2746400. ‡ Present address: Stichting IMEC Nederland, P.O. Box 8550, 5605 KN, Eindhoven, The Netherlands. (1) (a) El-Sayed, M. A. Acc. Chem. Res. 2001, 34, 257-264. (b) Daniel, M. C.; Astruc, D. Chem. ReV. 2004, 104, 293-346. (2) (a) Sau, T. K.; Murphy, C. J. J. Am. Chem. Soc. 2004, 126, 8648-8649. (b) Wei, Z. Q.; Mieszawska, A. J.; Zamborini, F. P. Langmuir 2004, 20, 43224326. (c) Chen, S. Langmuir 2001, 17, 6664-6668. (d) Milliron, D. J.; Hughes, S. M.; Cui, Y.; Manna, L.; Li, J. B.; Wang, L. W.; Alivisatos, A. P. Nature 2004, 430, 190-195. (e) Puntes, V. F.; Zanchet, D.; Erdonmez, C. K.; Alivisatos, A. P. J. Am. Chem. Soc. 2002, 124, 12874-12880. (f) Kim, F.; Connor, S.; Song, H.; Kuykendall, T.; Yang, P. Angew. Chem., Int. Ed. 2004, 43, 3673-3677. (g) Thomas, K. G.; Barazzouk, S.; Ipe, B. I.; Joseph, S. T. S.; Kamat, P. V. J. Phys. Chem. B 2004, 108, 13066-13068. (3) (a) Chumanov, G.; Sokalov, K.; Gregory, B. W.; Cotton, T. M. J. Phys. Chem. 1995, 99, 9466-9471. (b) Vance, F. W.; Lemon, B. I.; Hupp, J. T. J. Phys. Chem. 1998, 102, 10091-10093. (4) (a) Mirkin, C. A.; Letsinger, R. L.; Mucic, R. C.; Storhoff, J. J. Nature 1996, 382, 607-609. (b) He, L.; Musick, M. D.; Nicewarner, S. R.; Salinas, F. G.; Benkovic, S. J.; Natan, M. J.; Keating, C. D. J. Am. Chem. Soc. 2000, 122, 9071-9077. (c) Drechsler, U.; Erdogan, B.; Rotello, V. M. Chem. Eur. J. 2004, 10, 5570-5579. (5) (a) Liu, J.; Lu, Y. J. Am. Chem. Soc. 2003, 125, 6642-6643. (b) Glomm, W. R. J. Dispersion Sci. Technol. 2005, 26, 389-394. (6) (a) Special issue: Supramolecular Chemistry and Self-Assembly; Science 2002, 295, 2400-2421. (b) Steed, J. W.; Atwood, J. L. Supramolecular Chemistry; Wiley: Chichester, England, 2000. (c) Templating, Self-Assembly, and SelfOrganization. In ComprehensiVe Supramolecular Chemistry; Lehn, J.-M., Atwood, J. L., Davis, J. E. D., MacNicol, D. D., Voegtle, F., Eds.; Pergamon Press: Oxford, England, 1996; Vol. 9.

surfaces.7 For example, hydrogen bonding induces the nanoparticle assembly formation in the hybridization process of complementary DNA strands conjugated to gold nanoparticles.8 Other examples include non-DNA-like oligonucleotides such as deoxyguanosine,9 and polymer mediated recognition10 through hydrogen bonding between a diaminotriazine-functionalized polymer and thymine-functionalized colloids. In the mediatortemplate approach, stabilized nanoparticles are interconnected with bi- or multifunctional linkers (mediators) assembling the nanoparticles through place-exchanging of the stabilizing ligands on the nanoparticle surfaces.11 For example, gold nanoparticles self-assemble spherically through multidentate thioethers (Me4-nSi(CH2SMe)n),12 1,9 nonanedithiol,13a biphenyl dithiols12c (7) (a) Kumar, A.; Phadtare, S.; Pasricha, R.; Guga, P.; Ganesh, K. N.; Sastry, M. Curr. Sci. India 2003, 84, 71-74. (b) Aherne, D.; Rao, S. N.; Fitzmaurice, D. J. Phys. Chem. B 1999, 103, 1821-1825. (c) Kimura, M.; Kobayashi, S.; Kuroda, T.; Hanabusa, K.; Shirai, H. AdV. Mater. 2004, 16, 335-338. (c) Han, L.; Luo, J.; Kariuki, N. N.; Maye, M. M.; Jones, V. W.; Zhong, C. J. Chem. Mater. 2003, 15, 29-37. (8) (a) Mirkin, C. A.; Letsinger, R. L.; Mucic, R. C.; Storhoff, J. J. Nature 1996, 382, 607-609. (b) Elghanian, R.; Storhoff, J. J.; Mucic, R. C.; Letsinger, R. L.; Mirkin, C. A. Science 1997, 277, 1078-1081. (c) Taton, T. A.; Mucic, R. C.; Mirkin, C. A.; Letsinger, R. L. J. Am. Chem. Soc. 2000, 122, 6305-6306. (d) Wang, G.; Murray, R. W. Nano Lett. 2004, 4, 95-101. (e) Alivisatos, A. P.; Johnsson, K. P.; Peng, X. G.; Wilson, T. E.; Loweth, C. J.; Bruchez, M. P.; Schultz, P. G. Nature 1996, 382, 609-611. (f) Mbindyo, J. K. N.; Reiss, B. D.; Martin, B. R.; Keating, C. D.; Natan, M. J.; Mallouk, T. E. AdV. Mater. 2001, 13, 249-254. (9) Li, Z.; Mirkin, C. A. J. Am. Chem. Soc. 2005, 127, 11568-11569. (10) (a) Zheng, W. X.; Maye, M. M.; Leibowitz, F. L.; Zhong, C. J. Anal. Chem. 2000, 72, 2190-2199. (b) Boal, A. K.; Rotello, V. M. J. Am. Chem. Soc. 2000, 122, 734-735. (c) Boal, A. K.; Ilhan, F.; DeRouchey, J. E.; Thurn-Albrecht, T.; Russell, T. P.; Rotello, V. M. Nature 2000, 404, 746-748. (d) Boal, A. K.; Rotello, V. M. J. Am. Chem. Soc. 2002, 124, 5019-5024. (11) (a) Templeton, A. C.; Wuelfing, W. P.; Murray, R. W. Acc. Chem. Res. 2000, 33, 27-36. (b) Andres, R. P.; Bielefeld, J. D.; Henderson, J. I.; Janes, D. B.; Kolagunta, V. R.; Kubiak, C. P.; Mahoney, W. J.; Osifchin, R. G. Science 1996, 273, 1690-1693. (c) Freeman, R. G.; Garbar, K. C.; Allison, K. J.; Bright, R. M.; Davis, J. A.; Guthrie, A. P.; Hommer, M. B.; Jackson, M. A.; Smith, P. C.; Walter, D. G.; Natan, M. J. Science 1995, 267, 1629-1632. (d) Zamborini, F. P.; Hicks, J. F.; Murray, R. W. J. Am. Chem. Soc. 2000, 122, 4514-4515. (e) Brust, M.; Bethell, D.; Kiely, C. J.; Schiffrin, D. J. Langmuir 1998, 14, 54255429. (f) Bethell, D.; Brust, M.; Schiffrin, D. J.; Kiely, C. J. J. Electroanal. Chem. 1996, 409, 137-143. (g) Brust, M.; Kiely, C. J.; Bethell, D.; Schiffrin, D. J. J. Am. Chem. Soc. 1998, 120, 12367-12368. (h) Baum, T.; Bethell, D.; Brust, M.; Schiffrin, D. J. Langmuir 1985, 15, 866-871. (12) (a) Maye, M. M.; Chun, S. C.; Han, L.; Rabinovich, D.; Zhong, C. J. J. Am. Chem. Soc. 2002, 124, 4958-4959. (b) Maye, M. M.; Lim, I. S.; Luo, J.; Rab, Z.; Rabinovich, D.; Liu, T.; Zhong, C. J. J. Am. Chem. Soc. 2005, 127, 1519-1529. (c) Mayer, C. R.; Neveu, S.; Cabuil, V. AdV. Mater. 2002, 14, 595597. (13) (a) Hussain, I.; Wang, Z.; Cooper, A. I.; Brust, M. Langmuir 2006, 22, 2938-2941. (b) Liu, Y.; Zhao, Y.-L.; Chen, Y.; Wang, M. Macromol. Rapid Commun. 2005, 26, 401-406.

10.1021/la700514u CCC: $37.00 © 2007 American Chemical Society Published on Web 07/14/2007

Synthesis of Au Nanoparticle Assemblies

Langmuir, Vol. 23, No. 17, 2007 8773

chiral receptors,17 or fluorescent tags.18 To achieve the assembly of nanoparticles in solution using these multicomponent mediators, the thiol-functionalized barbituric acid 5-ethyl-5(10-mercaptodecyl) barbiturate (EMDB) was used as one of the double rosette building blocks. The addition of EMDB-functionalized gold nanoparticles to a solution of dimelamine 1 in toluene led to the formation of the gold nanoparticle assemblies (Figure 1c). The assembly process was monitored by dynamic light scattering (DLS) and ultraviolet-visible (UV-vis) analysis supported by simulations based on the Mie theory. Experimental Section

Figure 1. (a) Formation of the double rosette 13‚(EMDB)6. (b) Part of the 1H NMR of 13‚(EMDB)6 (300 MHz, 1 mM). The spectrum was recorded in [D8] toluene at 298 K. (c) Schematic representation of the nanoparticle assembly formation.

and thiocyclodextrin polymers13b as mediators. In the examples described so far in literature for both approaches, only one or two molecules take part in the nanoparticle assembly process; the self-assembly approach involves two complementary components, while the mediator approach involves only one multifunctional molecule that assembles the nanoparticles. To the best of our knowledge there are no examples in literature that use multicomponent mediators. If properly designed, the advantage of using such systems would be the broad functional group derivatization of the system. This would be particularly interesting for creating functional materials based on nanoparticle assemblies. Here, we report the first example of controlled nanoparticle assembly using multicomponent (nine building blocks), selfassembled double rosettes as mediators. These double rosette assemblies are molecular boxes that consist of two flat and circular self-assembled rosette motifs connected through three calix[4]arene moieties via the formation of 36 hydrogen bonds.14 Each circular motif (rosette)15 is formed by the complementary hydrogen bonding between three melamines (attached to the calix[4]arenes) and three barbituric acid derivatives (Figure 1a,b). These versatile molecular boxes can be precisely functionalized with many groups and functionalities such as metal atoms,16 (14) Prins, L. J.; Reinhoudt, D. N.; Timmerman, P. Angew. Chem., Int. Ed. 2001, 40, 2382-2426. (15) Seto, C. T.; Whitesides, G. M. J. Am. Chem. Soc. 1993, 115, 905-916. (16) Van Manen, H. -J.; Paraschiv, V.; Garc´ia-Lo´pez, J. J.; Scho¨nherr, H.; Zapotoczny, S.; Vansco, G. J.; Crego-Calama, M.; Reinhoudt, D. N. Nano Lett. 2004, 4, 441-446.

Materials and Methods. Octanethiol (Aldrich), methanol, and toluene were used as received (p.a. from Merck). Dimelamine 1 was synthesized according to a previous protocol.19 Water was purified by Millipore membrane units. 1H NMR spectra were recorded in CDCl3 on a Varian Unity 300 locked to the deuterated solvent at 300.1 MHz. Chemical shifts are given in parts per million relative to tetramethylsilane. Fast atom bombardment (FAB) mass spectra were recorded on a Finnigan MAT 90 spectrometer with mnitrobenzyl alcohol as the matrix. Matrix-assisted laser desorption ionization time-of-flight mass spectra were recorded on a VoyagerDE-RP mass spectrometer (Applied Biosystems/PerSeptive Biosystems, Inc., Framingham, MA) equipped with delayed extraction. A 337 nm UV nitrogen laser producing 3-ns pulses was used, and the mass spectra were obtained in the linear and reflectron modes. Samples for transmission electron microscopy (TEM) were prepared by deposition and evaporation of a drop of a solution in toluene onto amorphous graphite. TEM images were recorded with a Philips CM-30 Twin operating at 300 kV. The measured outer diameters of the observed features are averages of measurements obtained from randomly selected areas on different samples. UV-vis analyses were performed on an HP 8453 spectrophotometer. Spectra were collected over a 200-1000 nm range. The particle size and particlesize distribution were measured by DLS with the Zetasizer NanoSeries of Malvern instruments at room temperature. The instrument is equipped with a solid-state laser operating at 532 nm. Synthesis of 5-Ethyl-5(10-mercaptodecyl)pyrimidine-2,4,6(1H,3H)-trione.19 To 10 mL of methanol at 0 °C, acetyl chloride (1.0 mL) was added. After 10 min at 0 °C, 5-ethyl-5-(10thioacetyldecyl)-pyrimidine-2,4,6-(1H,3H,5H)-trione (0.10 g, 0.28 mmol) was added to this solution. The resulting mixture was stirred at 0 °C for 3 h, gradually warmed to room temperature, and stirred overnight. The reaction was stopped by the addition of 50 mL of degassed distilled water. The reaction mixture was then extracted with ethyl acetate. The organic extracts were washed with brine, dried over anhydrous MgSO4, filtered, and finally concentrated in vacuo. The residue was purified by flash chromatography (silica gel, 1:3 ethyl acetate/hexanes) to give 80 mg (88.8%, 0.25 mmol) of pure compound. 1H NMR (360 MHz), δ ) 0.88 (t, 3 H, J ) 7.4 Hz), 1.22 (m, 12 H), 1.31 (t, 1 H, J ) 7.8 Hz), 1.37 (m, 2 H), 1.59 (m, 2 H), 1.92 (m, 2 H), 2.04 (q, 2 H, J ) 7.4 Hz), 2.50 (dt, 2 H, J ) 7.4, 7.4 Hz), 8.86 (s, 2 H). HRMS-FAB: M+ calcd. for C16H28N2O3S, 329.1899; found, 329.16. Synthesis of Colloids 2, 3, and 4. A 15 mL aqueous solution of (30 mmol) hydrogen tetrachloroaurate was mixed with a 40 mL solution of (50 mmol) tetraoctylammonium bromide in toluene. The two-phase mixture was vigorously stirred until all the tetrachloroaurate was transferred into the organic layer, and EMDB (150 mg) was then added to the organic phase to prepare colloid 2 (for colloids 3 and 4, EMDB and octanethiol were added in 1:1 and 1:2 proportions, respectively). A freshly prepared aqueous solution of sodium borohydride (12 mL, 0.4 mol) was slowly added with vigorous stirring. After further stirring for 3 h, the organic phase was separated, (17) Ten Cate, M. G. J.; Omerovic´, M.; Oshovsky, G. V.; Crego-Calama, M.; Reinhoudt, D. N. Org. Biomol. Chem. 2005, 3, 3727-3733. (18) Arduini, M.; Crego-Calama, M.; Timmerman, P.; Reinhoudt, D. N. J. Org. Chem. 2003, 68, 1097-1106. (19) Motesharei, K.; Myles, D. C. J. Am. Chem. Soc. 1998, 29, 7328-7336.

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Kinge et al. with ethanol. The crude product was dissolved in 10 mL of toluene and again precipitated with 400 mL of ethanol. The specimens for examination by electron microscopy were prepared by evaporation of one or two drops of a toluene solution of the nanoparticles onto carbon films supported on standard copper grids. Synthesis of Colloidal Assemblies 5, 6, and 7. Gold colloid 2 (20 mg) was dispersed in 10 mL of [D8] toluene. In thiol-substituted gold colloids, the weight percent of the thiol is usually ∼15-20%.23 Therefore, 4 mg of calix[4]arene dimelamine 1 was added to the toluene solution. After additional stirring for an hour, the color of the red solution turns black. Also, precipitation of the colloid is observed, indicating nanoparticle assembly formation. A similar procedure was followed in the case of the other two colloids. The resulting assemblies were 5, 6, and 7 starting from colloids 2, 3, and 4, respectively.

Results and Discussion

Figure 2. TEM images of (a) colloid 2 (4.2 ( 0.5 nm), (b) 3 (3.4 ( 0.7 nm), and (c) 4 (2.6 ( 0.5 nm).

Figure 3. Part of the 1H NMR of (a) double rosette 13‚(EMDB)6, and nanoparticle assemblies (b) 5, (c) 6, and (d) 7 in [D8] toluene at 298 K. evaporated to 10 mL in a rotary evaporator, and mixed with 400 mL of ethanol to remove excess thiol. The mixture was kept for 4 h at -20 °C, and the dark brown precipitate was filtered off and washed

The synthesis of the thiol-substituted barbituric acid EMDB was carried out according to a reported procedure.19 In a preliminary experiment, the formation of double rosette assembly 13‚(EMDB)6 was confirmed (Figure 1a).20 This assembly is thermodynamically stable, even at a concentration of 5 µM.21 The formation of assembly 13‚(EMDB)6 was characterized by proton nuclear magnetic resonance (1H NMR).22 The imide proton signals corresponding to hydrogen-bonded EMDB appear at 13.4 and 14.1 ppm (Figure 1b). These signals are diagnostic for the formation of double rosettes.20 EMDB-stabilized gold nanoparticles were prepared according to a modified Brust method.23 In this method, an aqueous solution of hydrogen tetrachloroaurate (HAuCl4) was added to a toluene solution of tetraoctylammonium bromide (Oct4NBr). Phase transfer catalysis of HAuCl4 from the aqueous to organic phase occurs. Then the corresponding thiol was added in the separated organic phase. Subsequently, HAuCl4 was reduced with NaBH4 dissolved in water (see Supporting Information). Three different types of colloids (2-4) were prepared. Colloid 2 was stabilized by a 100% EMDB monolayer, while colloids 3 and 4 were stabilized with 1:1 and 1:2 ratios of EMDB/octanethiol monolayer, respectively. TEM analyses were carried out to determine the average particle size of the nanoparticles. The average diameters of the nanoparticles were 4.2 ( 0.5, 3.4 ( 0.7, and 2.6 ( 0.4 nm for colloids 2, 3, and 4, respectively (Figure 2). The differences in the sizes of nanoparticles are most probably due to the differences in the composition of their stabilizing layer. The TEM analysis showed the absence of nanoparticle agglomeration.24 This is an important observation as EMDB itself could lead to intermolecular H-bonding, causing agglomeration of the nanoparticles. This type of hydrogen bonding is probably not sufficient to stabilize larger nanoparticle aggregates. Further characterization of the particles was performed by UV-vis. UV-vis analyses of the three nanoparticle solutions showed plasmon resonance at 520 nm, which is characteristic of small (