This material is based upon work supported by the National Science Foundation under CHE - 1352507.

1. Synthesis of Gold Nanoparticles
<ol>
	<li>Weigh the gold salt in the glove box and add to a vial previously cleaned with aqua regia before diluting with water in a volumetric flask. Prepare a 1 mM Gold (III) chloride trihydrate (393.83 g/mol) in 100 ml water for gold stock solution.</li>
	<li>Weigh out 3.2 g solid CTAC (320 g/mol) and heat, in 25 ml water, to approximately 60 &#176;C for dissolution. Cool to room temperature and dilute the mixture with to 50 ml with water in a volumetric flask to prepare a 0.2 M Cet...

<ol>
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E., Banin, U. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Colloidal+hybrid+nanostructures:+a+new+type+of+functional+materials.">Colloidal hybrid nanostructures: a new type of functional materials.</a> Angewandte Chemie International Edition. 49, 4878-4897 (2010).</li><li>Xu, X., 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=Near-Field+Enhanced+Plasmonic-Magnetic+Bifunctional+Nanotubes+for+Single+Cell+Bioanalysis.">Near-Field Enhanced Plasmonic-Magnetic Bifunctional Nanotubes for Single Cell Bioanalysis.</a> Advanced Functional Materials. 23, 4332-4338 (2013).</li><li>Zhang, J., Tang, Y., Lee, K., Ouyang, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nonepitaxial+growth+of+hybrid+core-shell+nanostructures+with+large+lattice+mismatches.">Nonepitaxial growth of hybrid core-shell nanostructures with large lattice mismatches.</a> Science. 327, 1634-1638 (2010).</li><li>Sun, H., 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=Investigating+the+Multiple+Roles+of+Polyvinylpyrrolidone+for+a+General+Methodology+of+Oxide+Encapsulation.">Investigating the Multiple Roles of Polyvinylpyrrolidone for a General Methodology of Oxide Encapsulation.</a> Journal of the American Chemical Society. 135, 9099-9110 (2013).</li><li>Khatua, S., 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=Resonant+Plasmonic+Enhancement+of+Single-Molecule+Fluorescence+by+Individual+Gold+Nanorods.">Resonant Plasmonic Enhancement of Single-Molecule Fluorescence by Individual Gold Nanorods.</a> ACS Nano. 8, 4440-4449 (2014).</li><li>Lakowicz, J. R., 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=Plasmon-controlled+fluorescence:+a+new+paradigm+in+fluorescence+spectroscopy.">Plasmon-controlled fluorescence: a new paradigm in fluorescence spectroscopy.</a> Analyst. 133, 1308-1346 (2008).</li><li>Tam, F., Goodrich, G. P., Johnson, B. R., Halas, N. 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V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantum+Dot+Solar+Cells.+Semiconductor+Nanocrystals+as+Light+Harvesters.">Quantum Dot Solar Cells. Semiconductor Nanocrystals as Light Harvesters.</a> The Journal of Physical Chemistry C. 112, 18737-18753 (2008).</li><li>Nagraj, N., 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=Selective+sensing+of+vapors+of+similar+dielectric+constants+using+peptide-capped+gold+nanoparticles+on+individual+multivariable+transducers.">Selective sensing of vapors of similar dielectric constants using peptide-capped gold nanoparticles on individual multivariable transducers.</a> Analyst. 138, 4334-4339 (2013).</li><li>Nossier, A. I., Eissa, S., Ismail, M. F., Hamdy, M. A., Azzazy, H. M. E. -. 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A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Plasmonic+enhancement+of+dye-sensitized+solar+cells+using+core-shell-shell+nanostructures.">Plasmonic enhancement of dye-sensitized solar cells using core-shell-shell nanostructures.</a> The Journal of Physical Chemistry C. 117, 927-934 (2013).</li><li>Ratchford, D., Shafiei, F., Kim, S., Gray, S. K., Li, X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Manipulating+Coupling+between+a+Single+Semiconductor+Quantum+Dot+and+Single+Gold+Nanoparticle.">Manipulating Coupling between a Single Semiconductor Quantum Dot and Single Gold Nanoparticle.</a> Nano Letters. 11, 1049-1054 (2011).</li><li>Sau, T. K., Murphy, C. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Self-Assembly+Patterns+Formed+upon+Solvent+Evaporation+of+Aqueous+Cetyltrimethylammonium+Bromide-Coated+Gold+Nanoparticles+of+Various+Shapes.">Self-Assembly Patterns Formed upon Solvent Evaporation of Aqueous Cetyltrimethylammonium Bromide-Coated Gold Nanoparticles of Various Shapes.</a> Langmuir. 21, 2923-2929 (2005).</li><li>Ma, Y., 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=Au@Ag+Core-Shell+Nanocubes+with+Finely+Tuned+and+Well-Controlled+Sizes,+Shell+Thicknesses,+and+Optical+Properties.">Au@Ag Core-Shell Nanocubes with Finely Tuned and Well-Controlled Sizes, Shell Thicknesses, and Optical Properties.</a> ACS Nano. 4, 6725-6734 (2010).</li><li>Park, G., Lee, C., Seo, D., Song, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Full-Color+Tuning+of+Surface+Plasmon+Resonance+by+Compositional+Variation+of+Au@Ag+Core-Shell+Nanocubes+with+Sulfides.">Full-Color Tuning of Surface Plasmon Resonance by Compositional Variation of Au@Ag Core-Shell Nanocubes with Sulfides.</a> Langmuir. 28, 9003-9009 (2012).</li><li>Germain, V., Li, J., Ingert, D., Wang, Z. L., Pileni, M. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stacking+Faults+in+Formation+of+Silver+Nanodisks.">Stacking Faults in Formation of Silver Nanodisks.</a> The Journal of Physical Chemistry B. 107, 8717-8720 (2003).</li><li>Reiss, P., Proti&#232;re, M., Li, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Core/Shell+Semiconductor+Nanocrystals.">Core/Shell Semiconductor Nanocrystals.</a> Small. 5, 154-168 (2009).</li><li>Vossmeyer, T., 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=CdS+nanoclusters:+synthesis,+characterization,+size+dependent+oscillator+strength,+temperature+shift+of+the+excitonic+transition+energy,+and+reversible+absorbance+shift.">CdS nanoclusters: synthesis, characterization, size dependent oscillator strength, temperature shift of the excitonic transition energy, and reversible absorbance shift.</a> The Journal of Physical Chemistry. 98, 7665-7673 (1994).</li><li>Shore, M. S., Wang, J., Johnston-Peck, A. C., Oldenburg, A. L., Tracy, J. 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Authors have nothing to disclose

Gold nanoparticles
In order to guarantee high quality core shell nanoparticles, a monodisperse sample of gold nanoparticles must first be synthesized as a template.28,29,30 We modified the gold nanoparticle synthesis to produce long-chain tertiary amines-capped nanoparticles instead of oleylamine-capped nanoparticles. Oleylamine-capped nanoparticles show a rather narrow plasmon resonance, indicative of monodisperse size range, but the particles synthesized via reduction using tert-b...

Gold and silver nanoparticles have potential for future technological advances in a variety of applications including photonics,1 photovoltaics,2 catalysis,3 chemical/biological sensing,4 biological imaging,5 and photodynamic therapy.6 Under visible excitation, the surface electrons can oscillate to form a resonance known as a localized surface Plasmon resonance (SPR), which can be utilized to concentrate incident radiation in the visible spectrum. Recently, noble metal nanoparticles have been combined with semiconductor or magnetic nanoparticles to produce hybrid nanoparticles with enhanced and tunable functionality.7,8 Recent literature, such as the study conducted by Ouyang et al.9 or Chen et al.10, has shown the possibility for the synthesis of these particles, but only limited control in the uniformity of the hybrid species is possible due to a distribution of gold nanoparticle sizes and compounded by the lack of optical characterization coupled with physical characterization at each stage of growth. Zamkov et al. showed similar uniformity in shell formation but only one shell thickness was utilized with different core sizes, with some shells not being fully formed around the nanoparticles. In order to effectively utilize these nanoparticles, the precise optical response must be known and characterized for a variety of shell thicknesses. Higher precision in shell thickness can be accomplished through the use of monodisperse, aqueous gold particles as the template, resulting in higher control over the final hybrid species. Interaction between the core and shell may show limited enhancement in absorption or emission rates due to the small amount of semiconductor material and the proximity to the gold core. Instead of interaction between the semiconductor found in the shell and the gold particle, the shell may be used as a spacer to limit the distance between an external chromophore.11 This will allow for higher control over the spatial separation between the plasmon while, negating the consequences of direct contact with the metal surface.
The extent of the electronic interaction between the surface plasmon resonance and exciton produced in the chromophore, is directly correlated to the distance between the metallic and semiconductor species, the surface environment and strength of the interaction.12 When the species are separated by distances greater than 25 nm, the two electronic states remain unperturbed and the optical response remains unchanged.13 The strong coupling regime is dominant when the particles have more intimate contact and can result in the quenching of any excitation energy via nonradiative rate enhancement or Forester Resonance Energy Transfer (FRET).14,15 Manipulation of the coupling strength, by tuning the spacing between the chromophore and metal nanoparticle, can result in positive effects as well. The nanoparticle extinction coefficient can be orders of magnitude larger than most chromophores, allowing the nanoparticles to concentrate the incident light much more effectively. Utilizing the increased excitation efficiency of the nanoparticle can result in higher excitation rates in the chromophore.12 Coupling of the excitation dipole can also increase the emission rate of the chromophore which, can result in increase in quantum yield if nonradiative rates are unaffected.12 These effects could lead to solar cells or films with increased absorbance, and photovoltaic efficiencies, facilitated by the increased absorption cross-section of the gold and the ease of charge extraction from the semiconductor layer due to the existence of localized surface states.12,16 This study will also provide useful information on the coupling strength of the plasmon as a function of distance.
Localized surface plasmons have widely been used in sensing17 and detection18 applications due to the sensitivity of the plasmon resonance to the local environment. Cronin et al., showed the catalytic efficiency of TiO2 films can be improved with addition of gold nanoparticles. Simulations showed that this increase in activity is due to coupling of the plasmon electric field with excitons created in the TiO2, which subsequently increases exciton generation rates.19 Schmuttenmaer et al., showed that the efficiency of Dye-sensitized (DSSC) solar cells could be improved with the incorporation of the Au/SiO2/TiO2 aggregates. The aggregates enhance the absorption through creation of broad localized surface plasmon modes which increase optical absorption over a broader range of frequencies.20 In other literature, Li et al. observed significant reduction in fluorescence lifetime as well as distance dependent enhancement in steady state fluorescence intensity was observed through direct coupling of a single CdSe/ZnS quantum dot and single gold nanoparticle.21 In order to take full advantage of this plasmonic enhancement, there is a need for physical coupling with a set distances between the two species.
Synthesis of Hybrid Nanoparticles
Jiatiao et al., described a method to coat semiconductor material onto gold nanoparticles via a cationic exchange in order to produce uniform and tunable shell thicknesses. The shells were uniform in thickness, but the gold templates were not very monodisperse. This will alter the semiconductor to gold ratio from particle to particle and therefore the coupling strength.9 An in-depth study on the optical properties of these core shell nanoparticles has been conducted, in order to develop a reproducible synthetic method. Previous methods rely on organic-based nanoparticle synthesis, which can produce samples with broad plasmon resonances due to inhomogeneity in the gold nanoparticle size. A modified aqueous synthesis of gold nanoparticles can provide a reproducible and monodisperse gold nanoparticle template with stability for long periods of time. The aqueous surfactant cetyl trimethyl ammonium chloride forms a double layer on the nanoparticle surface due to interaction between the long carbon chains of nearby cetyl trimethyl ammonium chloride molecules.22 This thick surface layer requires careful washing to remove excess surfactant and allow access to the nanoparticle surface, but can provide higher control over the nanoparticle size and shape.23 The aqueous addition of a silver shell can be controlled with high precision leading to a more intimate correlation between shell thickness and optical properties.23 A slower reduction via ascorbic acid is utilized to deposit the silver on the gold surface, requiring the addition of silver salt to be very precise in order to prevent formation of silver nanoparticles in the solution. The third step requires a large excess of sulfur to be added into an organic phase and a phase transfer of the aqueous nanoparticles must occur. With addition of oleylamine as an organic capping agent and oleic acid, which may act as both a capping agent and aid in phase transfer of the nanoparticles, a uniform, amorphous silver sulfide shell can be formed around the nanoparticles.9,24 The concentration of these molecules must be high enough to prevent aggregation of the nanoparticles in this step, but too much excess can make purification difficult. In the presence of tri butyl phosphine and a metal nitrate (Cd, Zn or Pb), a cationic exchange inside of the amorphous sulfide shell can be conducted. Reaction temperatures must be modified for the different reactivates of the metals9 and any excess sulfur must be eliminated to reduce the formation of individual quantum dots. Each step of the synthesis corresponds to a change in the surface environment of the nanoparticle, therefore, a change in plasmon should be observed due to the dependence of the plasmon frequency on surrounding dielectric field. A parallel study of optical absorption as a function of Transmission Electron Microscopy (TEM) characterization was used to characterize the nanoparticles. This synthetic procedure will provide us with well-controlled and uniform samples, providing better correlation from microscopy and spectroscopy data.
Coupling with Fluorophores
Applying a dielectric spacing layer between a plasmonic metal surface and a fluorophore can help to diminish losses due to nonradiative energy transfer of created excitons into the metal. This spacing layer can also aid in the study of distance dependence between the fluorophore and the plasmon resonance on the metal surface. We propose using the semiconductor shell of the hybrid nanoparticles as our dielectric spacing layer. The shell thickness can be tuned with nanometer precision with thicknesses ranging from 2 nm to 20 nm allowing precise distance correlation experiments to be conducted. The shell can also be tuned with Cd, Pb or Zn cations and S, Se and Te anions, allowing for control over not only the distance but also the dielectric constant, electronic band arrangement and even crystal lattice parameters.

<table border="0" cellpadding="0" cellspacing="0" width="927">
	<tbody>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">MilliQ Water</td>
			<td style="width:71px;">Millipore</td>
			<td style="width:119px;">Millipore water purification system</td>
			<td style="width:521px;">water with 18 mega ohm resistivity was utilized in all experiments</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Gold (II) chloride trihydrate</td>
			<td style="width:71px;">Sigma Aldrich</td>
			<td align="right">520918</td>
			<td>used as gold precursor for nanoparticle synthesis</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Cetyl trimethyl ammonium chloride(CTAC)</td>
			<td style="width:71px;">TCI America</td>
			<td style="width:119px;">H0082</td>
			<td>used as surfactant for gold nanoparticles</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Borane tert butyl amine</td>
			<td style="width:71px;">Sigma Aldrich</td>
			<td align="right" style="width:119px;">180211</td>
			<td>used as reducing agent for gold nanoparticles</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Silver nitrate</td>
			<td style="width:71px;">Sigma Aldrich</td>
			<td align="right" style="width:119px;">204390</td>
			<td>used as silver source for shell application</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Ascorbic acid</td>
			<td style="width:71px;">Sigma Aldrich</td>
			<td style="width:119px;">A0278</td>
			<td>used as reducing agent for silver shell application</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Sulfur powder</td>
			<td style="width:71px;">Acros</td>
			<td align="right" style="width:119px;">199930500</td>
			<td>used as sulfur source for silver sulfide shell conversion</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Oleylamine</td>
			<td style="width:71px;">Sigma Aldrich</td>
			<td style="width:119px;">O7805</td>
			<td>used as surfactant for silver sulfide shell conversion</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Oleylamine</td>
			<td style="width:71px;">Sigma Aldrich</td>
			<td align="right" style="width:119px;">364525</td>
			<td>used as surfactant for silver sulfide shell conversion</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">cadmium nitrate tetrahydrate</td>
			<td style="width:71px;">Sigma Aldrich</td>
			<td align="right" style="width:119px;">642405</td>
			<td>used as cadmium source for cation exchange</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">zinc nitrate hexahydrate</td>
			<td style="width:71px;">Fisher Scientific</td>
			<td style="width:119px;">Z45</td>
			<td>used as zinc source for cation exchange</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">11-Mercaptoundecanoic acid</td>
			<td style="width:71px;">Sigma Aldrich</td>
			<td align="right" style="width:119px;">450561</td>
			<td>used as water soluable ligand during ligand exchange</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">3,4 diaminobenzoic acid</td>
			<td style="width:71px;">Sigma Aldrich</td>
			<td style="width:119px;">D12600</td>
			<td>used as water soluable ligand during ligand exchange</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">UV-Vis absorption spectrophotometer</td>
			<td style="width:71px;">Cary</td>
			<td style="width:119px;">50 Bio</td>
			<td>used to monitor absorption spectrum of colloidal solutions</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">JEOL TEM 2100</td>
			<td style="width:71px;">JEOL</td>
			<td style="width:119px;">2100</td>
			<td>used to analyze size of synthesized nanoparticles. TEM grids were purchased from tedpella</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">FTIR spectrophotometer</td>
			<td style="width:71px;">Perkin Elmer</td>
			<td style="width:119px;">Spec 100</td>
			<td>used to monitor chemical compostion of nanoparticle surface after ligand exchange.&#160;</td>
		</tr>
	</tbody>
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synthesis, characterization, and functionalization of hybrid au/cds and au/zns core/shell nanoparticles

Plasmonic nanoparticles are an attractive material for light harvesting applications due to their easily modified surface, high surface area and large extinction coefficients which can be tuned across the visible spectrum. Research into the plasmonic enhancement of optical transitions has become popular, due to the possibility of altering and in some cases improving photo-absorption or emission properties of nearby chromophores such as molecular dyes or quantum dots. The electric field of the plasmon can couple with the excitation dipole of a chromophore, perturbing the electronic states involved in the transition and leading to increased absorption and emission rates. These enhancements can also be negated at close distances by energy transfer mechanism, making the spatial arrangement of the two species critical. Ultimately, enhancement of light harvesting efficiency in plasmonic solar cells could lead to thinner and, therefore, lower cost devices. The development of hybrid core/shell particles could offer a solution to this issue. The addition of a dielectric spacer between a gold nanoparticles and a chromophore is the proposed method to control the exciton plasmon coupling strength and thereby balance losses with the plasmonic gains. A detailed procedure for the coating of gold nanoparticles with CdS and ZnS semiconductor shells is presented. The nanoparticles show high uniformity with size control in both the core gold particles and shell species allowing for a more accurate investigation into the plasmonic enhancement of external chromophores.

Normalized absorbance spectra of gold nanoparticles with three different surfactants are shown in Figure 1. The surfactants utilized are oleylamine, tetradecyl trimethyl ammonium chloride (TTAC), and cetyl trimetyl ammonium chloride. CTAC and TTAC surfactants show narrower plasmon resonance absorption band.
The amount of reducing agent not only affects the FWHM but the peak position of the resulting nanoparticle...

Watch this Scientific Journal Video about Synthesis, Characterization, and Functionalization of Hybrid Au/CdS and Au/ZnS Core/Shell Nanoparticles at JoVE.com

Synthesis, Characterization, and Functionalization of Hybrid Au/CdS and Au/ZnS Core/Shell Nanoparticles

The synthesis of uniform gold nanoparticles coated with semiconductor shells of CdS or ZnS is performed. The semiconductor coating is conducted by first depositing a silver sulfide shell and exchanging the silver cations for zinc or cadmium cations.

Plasmonic nanoparticles are an attractive material for light harvesting applications due to their easily modified surface, high surface area and large ...

The overall goal of this procedure is to prepare gold nanoparticles that are overcoated with a wide bandgap semiconductor shell. The shell material can be either cadmium or zinc sulfide, and the thickness should be tunable. This technique overcomes the large lattice mismatch between core and shell by using a four-step cation exchange technique to form the shells.The main advantage of this technique is the ability to produce highly monodisperse gold core shell nanoparticles with excellent control of the shell thickness. The nanoparticles produced with this technique could be used as plasmonic elements that couple with absorbers in opto-electronic systems because the wide bandgap shell enables precise tuning of interaction distances. Tuning interactions in this way enables us to limit losses and maximize absorption or emission gains and provide insight into the potential of exciton plasmon coupling for a range of applications.To begin synthesis of gold nanoparticles, work in a glove box to weigh gold salt in a vial previously cleaned with aqua regia before diluting with 100 milliliters of water in a volumetric flask. Then add 3.2 grams of solid cetyltrimethylammonium chloride, or CTAC, and heat in 25 milliliters of water to approximately 60 degrees Celsius for dissolution. Cool the mixture to room temperature and dilute to 50 milliliters with water in a volumetric flask to prepare a 0.2 molar CTAC solution.Mix 20 milliliters of one millimolar gold solution and 20 milliliters of 0.2 molar CTAC solution inside a round-bottom boiling flask. Allow to mix in an oil bath set to 60 degrees Celsius for ten minutes. Next add 1.7 milligrams of solid borane tert-butylamine to the gold CTAC solution, and let the mixture stir for 30 minutes.The solution should turn deep red. The resulting solution has a gold particle concentration of about 5 micromolar, and can be stored for months at a time or used immediately for the next phase of the reaction. Then, add the silver solution dropwise to the gold and ascorbic acid solution and allow the reaction to stir for two hours.In a 70 degree Celsius oil bath, mix 10 milliliters of stock gold nanoparticles with ascorbic acid to make a 20 millimolar solution. Next, prepare a 4.0 millimolar silver nitrate solution in five milliliters of water. The reaction will turn light orange to dark orage depending on the shell thickness over the course of the reaction.Centrifuge the nanoparticles at 21, 130 gs for ten minutes, and then re-disperse into clean water. Decant the supernatant from pelleted nanoparticles to aid in removal of bare gold nanoparticles or silver nanoparticles, which may have been formed. Weigh elemental sulfur in a 200 to one molar ratio to the silver used in the previous stage of the experiment.For ten milliliters of gold silver core shell particles and a five nanometer shell, into ten milliliters of toluene, dissolve 1.5 milliliters of oleic acid and three milliliters of oleylamine. Once dissolved, the solution should be a light yellow. Residual water can disrupt the solubility of both the nanoparticles and the free surfactive molecules, possibly leading to irreversible aggregation of the gold naonparticles.To ensure the removal of water during the next purification step concentrate the silver colloids via cetrifugation at 21, 130 gs for ten minutes. Disperse the silver colloids in one milliliter of water. This helps increase the efficiency of the extraction from the aqueous layer to the organic layer upon formation of the silver shell.Add the colloids dropwise to the sulfur solution under stirring for one hour. The solution will turn dark blue for thinner shells, to purple for thicker shells, as the sulfurization goes to completion. Add the same volume of 70 percent ethanol before centrifuging.Centrifuge the colloidal solution at 4, 000 gs for 10 minutes, after the reaction has stirred for two hours, to remove the water and unreacted sulfur from the solution. Excess oleylamine or oleic acid may fall out of solution and can be removed after this step by decanting the solution from the white solid. If necessary re-disperse the nanoparticles by sonicating in a bath sonicator for 30 seconds to one minute in order to disperse into the toluene.Make the metal precursor by dissolving the metal nitrate into one milliliter of methanol to make a 0.2 molar solution of cadmium nitrate or zinc nitrate. Mix the metal solution with the silver-sulfide-shelled naonparticles in a one to one molar ratio with the silver. Heat to 50 degrees Celsius for cadmium shell, and 65 degree Celsius for zinc shells, under a nitrogen atmosphere.Next, add tributylphosphine in a 500 to one molar ratio to the metal precursor. Purify via centrifugation at 21, 130 gs for ten minutes in order to remove any isolated cadmium sulfide or zinc sulfide nanoparticles which may have been formed. Disperse the pelleted nanoparticles into a clean, nonpolar solvent, such as hexane, toluene, or chloroform.Shown here are transmission electron microscopy, or TEM images of gold nanoparticles synthesized with CTAC as the surfactant. The nanoparticles were single crystalline with a 16 nanometer diameter and a standard deviation of 0.4 nanometers. The thickness of the silver shell can be monitored through ultraviolet visible absorption spectroscopy.In this figure silver thickness increases from black to light blue. The surface plasmon of gold nanoparticles shifts to higher energies as the thickness of the silver shell increases. TEM images of gold nanoparticles with silver shells are shown here.Silver is grown onto the gold core to provide a template for the subsequent semiconductor shell. The shells are tuned from three to seven nanometers in radius. In the next step the silver coated nanoparticles are treated with sulfur to form a silver sulfide shell.The resulting shells tend to be slightly larger than the previous silver shells, but uniform in distribution. Finally cadmium, in this example, or zinc can be used to replace the silver ions and produce a semiconductor shell of cadmium sulfide or zinc sulfide. The resulting shell is single crystalline with a radius corresponding to the silver radius in the first coating step.Once mastered, this technique can be done in seven to eight hours if performed properly. While attempting this procedure, it is important to properly clean all glassware with aqua regia before use. After watching the video you should be able to coat aqueous gold nanoparticles with cadmium or zinc sulfide.The gold nanoparticles are coated with silver, which is transformed to silver sulfide. Finally, the silver is exchanged with cadmium or zinc.

synthesis-characterization-functionalization-hybrid-aucds-auzns

Research

JoVE Journal

Chemistry

18.1K visualizações.  University of North Carolina at Charlotte. The overall goal of this procedure is to prepare gold nanoparticles that are overcoated with a wide bandgap semiconductor shell. The shell material can be either cadmium or zinc sulfide, and the thickness should be tunable. This technique overcomes the large lattice mismatch between core and shell by using a four-step cation exchange technique to form the shells.The main advantage of this technique is the ability to produce highly monodisperse gold core shell nanoparticles with excelle...