This work was supported with funding provided from the Office of Naval Research.&#160;J. Fontana acknowledges the National Research Council for a postdoctoral associateship.

1. Self-assembled Ligand-nanoparticle Monolayers
As an illustrative example of the self-assembly technique, macroscopic, thiol-alkane capped gold nanosphere monolayer films are produced as follows:
<ol>
	<li>Concentrate 15&#160;nm gold nanospheres (commercially available at a number density: 1012 particles/ml) to ~1013 particles/ml&#160;in water.
	<ol>
		<li>Place 15 ml of the dilute nanosphere water suspension into an ultra centrifugal filter (100&#160;K nominal molecu...

<ol>
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M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Yellow-light+negative-index+metamaterials.">Yellow-light negative-index metamaterials.</a> Optics Letters. 34, 3478-3480 (2009).</li><li>Fang, N., Lee, H., Sun, C., Zhang, X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sub-diffraction-limited+optical+imaging+with+a+silver+superlens.">Sub-diffraction-limited optical imaging with a silver superlens.</a> Science. 308, (2005).</li><li>Liu, Z. W., Lee, H., Xiong, Y., Sun, C., Zhang, X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Far-field+optical+hyperlens+magnifying+sub-diffraction-limited+objects.">Far-field optical hyperlens magnifying sub-diffraction-limited objects.</a> Science. 315, 1686-1686 (2007).</li><li>Valentine, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Three-dimensional+optical+metamaterial+with+a+negative+refractive+index.">Three-dimensional optical metamaterial with a negative refractive index.</a> Nature. 455, (2008).</li><li>Law, M., Greene, L. E., Johnson, J. C., Saykally, R., Yang, P. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanowire+dye-sensitized+solar+cells.">Nanowire dye-sensitized solar cells.</a> Nature Materials. 4, 455-459 (2005).</li><li>Frens, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Controlled+Nucleation+for+Regulation+of+Particle-Size+in+Monodisperse+Gold+Suspensions.">Controlled Nucleation for Regulation of Particle-Size in Monodisperse Gold Suspensions.</a> Nature-Phys Sci. 241, 20-22 (1973).</li><li>Ye, X., Chen, J., Diroll, B. T., Murray, C. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tunable+Plasmonic+Coupling+in+Self-Assembled+Binary+Nanocrystal+Superlattices+Studied+by+Correlated+Optical+Microspectrophotometry+and+Electron+Microscopy.">Tunable Plasmonic Coupling in Self-Assembled Binary Nanocrystal Superlattices Studied by Correlated Optical Microspectrophotometry and Electron Microscopy.</a> Nano Letters. 13, 1291-1297 (2013).</li><li>Bigioni, T. P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Kinetically+driven+self-assembly+of+highly+ordered+nanoparticle+monolayers.">Kinetically driven self-assembly of highly ordered nanoparticle monolayers.</a> Nature Materials. 5, (2006).</li><li>Ng, K. 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This protocol describes a single &#8216;one-pot&#8217; self-assembly technique to create macroscopic nanoparticle-ligand monolayer films using phase transfer, phase separation and surface tension gradients.&#160; The advantage of this technique is that it combines three self-assembly processes into a single, low-cost process; by quickly and efficiently phase transferring the nanoparticles, assembling the particles into monolayers at the air-fluid interface and transporting the monolayer films onto template-free substrate...

The self-assembly of macroscopic nanoparticle films has attracted great attention for their unique properties determined from the geometry and composition of the elements5 and may lead to of a wide range of optical, electronic and chemical applications6-14. To self-assemble such films metallic nanoparticles capped with ligands must be packed into high density, monolayers. However several assembly issues need to be addressed to advance the development of such materials.
First, surfactant stabilized metallic nanoparticles are typically synthesized by wet-chemistry methods in dilute suspensions15. To prevent aggregation and to control the interparticle spacing of the nanoparticles in the films, the nanoparticles need to be capped with ligand shells. After the nanoparticles have been functionalized with ligands the nanoparticles typically remain in relatively dilute suspensions.&#160;A technique is then needed to self-assemble the nanoparticles into macroscopic, high-density, monolayer films16,17.
Cheng et al.18 phase transferred gold nanorods using thiolated polystyrene in a water-tetrahydrofuran suspension.&#160; The nanorods where then re-suspended in chloroform and a drop was placed at an air-water interface and evaporated slowly, forming monolayer films. Bigioni et al.17 created macroscopic monolayers of dodecanethiol capped gold nanospheres using excess ligand and rapid solvent evaporation, but the nanospheres needed to be phase transferred prior to self-assembling.&#160;
Once the monolayer films are formed they typically need to be transported onto a substrate.&#160; Mayya et al.3 confined nanospheres at a water-toluene interface and transferred them onto template-free substrates using surface tension gradients. Similarly, Johnson et al.4&#160;suspended silver nanospheres in excess ligand and then translated the nanoparticles up the walls of the vial using surface tension gradients from two immiscible fluids. While assembly techniques exist to address each of these issues the need for more efficient techniques is needed to aid in the development of large-scale nanoparticle film production.
Here we demonstrate a straightforward and robust technique that combines the three self-assembly issues described above in to a single &#8216;one-pot&#8217; technique, shown in Figure 1. A water miscible organic solvent (e.g. tetrahydrofuran, dimeythl sulfoxide), is used to first quickly and efficiently functionalize thiol-ligands (e.g. thiol-alkane, thiol-ene, thiol-phenol) onto the nanoparticles (e.g. gold nanospheres, nanorods, etc.). The mixture then drives&#160;self-assembly of the nanoparticles into macroscopic, high-density, monolayer films at the air-fluid interface using phase separation.&#160; Finally, monolayer films of nanoparticles form onto template-free substrates using surface tension gradients from the water/organic solvent mixture, Figure 2 and Figure 3.

<table border="0" cellpadding="0" cellspacing="0" width="628">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:224px;">1-6 hexanedithiol</td>
			<td style="width:97px;">Sigma</td>
			<td style="width:140px;">H12005-5G</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:224px;">1-dodecanethiol</td>
			<td style="width:97px;">Sigma</td>
			<td style="width:140px;">471364-100ML</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:224px;">20 ml liquid scintillation vials</td>
			<td style="width:97px;">Sigma</td>
			<td style="width:140px;">Z253081-1PAK</td>
			<td></td>
		</tr>
		<tr height="24">
			<td height="24" style="height:25px;width:224px;">acetone</td>
			<td style="width:97px;">Sigma</td>
			<td>650501-1L</td>
			<td></td>
		</tr>
		<tr height="24">
			<td height="24" style="height:24px;width:224px;">amicon ultra-15 centrifugal filter&#160;</td>
			<td style="width:97px;">Millipore</td>
			<td style="width:140px;">100K</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:224px;">centrifuge</td>
			<td style="width:97px;">Sorvall&#160;</td>
			<td style="width:140px;">RC5B</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:224px;">centrifuge&#160;</td>
			<td style="width:97px;">Eppendorf</td>
			<td style="width:140px;">5810R</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:224px;">deionized water&#160;</td>
			<td style="width:97px;">in-house&#39;</td>
			<td style="width:140px;">N/A</td>
			<td></td>
		</tr>
		<tr height="24">
			<td height="24" style="height:25px;width:224px;">glass slides</td>
			<td style="width:97px;">Sigma</td>
			<td style="width:140px;">CLS294875X25-72EA</td>
			<td></td>
		</tr>
		<tr height="24">
			<td height="24" style="height:24px;width:224px;">15 nm gold nanospheres</td>
			<td style="width:97px;">Ted Pella, Inc</td>
			<td style="width:140px;">15703-1</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:224px;">hexamethyldisilazane</td>
			<td style="width:97px;">Sigma</td>
			<td style="width:140px;">52619-50ML</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:224px;">hydrogen peroxide (30%)</td>
			<td style="width:97px;">Sigma</td>
			<td style="width:140px;">216763-100ML</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:224px;">scanning electron microscope</td>
			<td style="width:97px;">Carl Zeiss</td>
			<td style="width:140px;">Model 55</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:224px;">polished silicon wafer</td>
			<td style="width:97px;">Sun Edison</td>
			<td style="width:140px;">N/A</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:224px;">spectrometer</td>
			<td style="width:97px;">OceanOptics</td>
			<td style="width:140px;">USB4000-VIS-NIR</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:224px;">sulfuric acid</td>
			<td style="width:97px;">Fisher</td>
			<td style="width:140px;">A300-212</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:224px;">tetrahydrofuran</td>
			<td style="width:97px;">Sigma</td>
			<td style="width:140px;">401757-100ML</td>
			<td></td>
		</tr>
	</tbody>
</table>

a technique to functionalize and self-assemble macroscopic nanoparticle-ligand monolayer films onto template-free substrates

This protocol describes a self-assembly technique to create macroscopic monolayer films composed of ligand-coated nanoparticles1,2. The simple, robust and scalable technique efficiently functionalizes metallic nanoparticles with thiol-ligands in a miscible water/organic solvent mixture allowing for rapid grafting of thiol groups onto the gold nanoparticle surface. The hydrophobic ligands on the nanoparticles then quickly phase separate the nanoparticles from the aqueous based suspension and confine them to the air-fluid interface. This drives the ligand-capped nanoparticles to form monolayer domains at the air-fluid interface.&#160; The use of water-miscible organic solvents is important as it enables the transport of the nanoparticles from the interface onto template-free substrates.&#160; The flow is mediated by a surface tension gradient3,4 and creates macroscopic, high-density, monolayer nanoparticle-ligand films.&#160; This self-assembly technique may be generalized to include the use of particles of different compositions, size, and shape and may lead to an efficient assembly method to produce low-cost, macroscopic, high-density, monolayer nanoparticle films for wide-spread applications.

Figure 1(a) shows a suspension of gold nanospheres, thiol-alkane ligands, tetrahydrofuran and water in a glass vial immediately after mixing. A schematic of the three main self-assembly stages, phase transfer, phase separation, and surface tension gradient mediated film transport&#160;is shown in Figure 1(b) as an expanded view at the air-fluid interface near the side of the vial.
The thiol groups on the ligands rapidly bond to the gold nanospheres after mixin...

Watch this Scientific Journal Video about A Technique to Functionalize and Self-assemble Macroscopic Nanoparticle-ligand Monolayer Films onto Template-free Substrates at JoVE.com

A Technique to Functionalize and Self-assemble Macroscopic Nanoparticle-ligand Monolayer Films onto Template-free Substrates

A simple, robust and scalable technique to functionalize and self-assemble macroscopic nanoparticle-ligand monolayer films onto template-free substrates is described in this protocol.

This protocol describes a self-assembly technique to create macroscopic monolayer films composed of ligand-coated nanoparticles1,2. The simple, robust and ...

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Chemistry

10.7K vues.  Naval Research Laboratory.  Une technique simple, robuste et évolutive pour fonctionnaliser et s'auto-assembler macroscopiques monocouche films de nanoparticules sur des substrats ligand libre-modèle est décrit dans le présent protocole. 