Name: synthesis, characterization, and functionalization of hybrid au/cds and au/zns core/shell nanoparticles
Uploaded: 2016-03-02T13:00:00
Description: Watch this Scientific Journal Video about Synthesis, Characterization, and Functionalization of Hybrid Au/CdS and Au/ZnS Core/Shell Nanoparticles at JoVE.com

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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J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Important+Role+of+Hydroxyl+on+Oxidation+Catalysis+by+Gold+Nanoparticles.">The Important Role of Hydroxyl on Oxidation Catalysis by Gold Nanoparticles.</a> Accounts of chemical research. , (2013).</li><li>Saha, K., Agasti, S. S., Kim, C., Li, X., Rotello, V. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gold+Nanoparticles+in+Chemical+and+Biological+Sensing.">Gold Nanoparticles in Chemical and Biological Sensing.</a> Chemical Reviews. 112, 2739-2779 (2012).</li><li>Wang, 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=Computed+tomography+imaging+of+cancer+cells+using+acetylated+dendrimer-entrapped+gold+nanoparticles.">Computed tomography imaging of cancer cells using acetylated dendrimer-entrapped gold nanoparticles.</a> Biomaterials. 32, 2979-2988 (2011).</li><li>Huang, X., Jain, P. K., El-Sayed, I. H., El-Sayed, M. 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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. J. <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+molecular+fluorescence.">Plasmonic enhancement of molecular fluorescence.</a> Nano Letters. 7, 496-501 (2007).</li><li>Achermann, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Exciton-Plasmon+Interactions+in+Metal-Semiconductor+Nanostructures.">Exciton-Plasmon Interactions in Metal-Semiconductor Nanostructures.</a> The Journal of Physical Chemistry Letters. 1, 2837-2843 (2010).</li><li>Zhang, 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=Experimental+and+Theoretical+Investigation+of+the+Distance+Dependence+of+Localized+Surface+Plasmon+Coupled+F&#246;rster+Resonance+Energy+Transfer.">Experimental and Theoretical Investigation of the Distance Dependence of Localized Surface Plasmon Coupled F&#246;rster Resonance Energy Transfer.</a> ACS Nano. 8, 1273-1283 (2014).</li><li>Kamat, P. 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. -. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Direct+detection+of+hyaluronidase+in+urine+using+cationic+gold+nanoparticles:+A+potential+diagnostic+test+for+bladder+cancer.">Direct detection of hyaluronidase in urine using cationic gold nanoparticles: A potential diagnostic test for bladder cancer.</a> Biosensors and Bioelectronics. 54, 7-14 (2014).</li><li>Hou, W., Liu, Z., Pavaskar, P., Hung, W. H., Cronin, S. B. <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+photocatalytic+decomposition+of+methyl+orange+under+visible+light.">Plasmonic enhancement of photocatalytic decomposition of methyl orange under visible light.</a> Journal of Catalysis. 277, 149-153 (2011).</li><li>Sheehan, S. W., Noh, H., Brudvig, G. W., Cao, H., Schmuttenmaer, C. 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. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis+of+Au+(Core)/Ag+(Shell)+nanoparticles+and+their+conversion+to+AuAg+alloy+nanoparticles.">Synthesis of Au (Core)/Ag (Shell) nanoparticles and their conversion to AuAg alloy nanoparticles.</a> Small. 7, 230-234 (2011).</li><li>Liu, X., Atwater, M., Wang, J., Huo, Q. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Extinction+coefficient+of+gold+nanoparticles+with+different+sizes+and+different+capping+ligands.">Extinction coefficient of gold nanoparticles with different sizes and different capping ligands.</a> Colloids and Surfaces B: Biointerfaces. 58, 3-7 (2007).</li><li>Lambright, 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=Enhanced+Lifetime+of+Excitons+in+Nonepitaxial+Au/CdS+Core/Shell+Nanocrystals.">Enhanced Lifetime of Excitons in Nonepitaxial Au/CdS Core/Shell Nanocrystals.</a> ACS Nano. 8, 352-361 (2014).</li><li>Srnov&#225;-&#352;loufov&#225;, I., Lednick&#253;, F., Gemperle, A., Gemperlov&#225;, J. <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+(Ag)+Au+bimetallic+nanoparticles:+analysis+of+transmission+electron+microscopy+images.">Core-shell (Ag) Au bimetallic nanoparticles: analysis of transmission electron microscopy images.</a> Langmuir. 16, 9928-9935 (2000).</li></ol>

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>
</table>

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

Split-and-pool Synthesis and Characterization of Peptide Tertiary Amide Library

Peptidomimetics are great sources of protein ligands. The oligomeric nature of these compounds enables us to access large synthetic libraries on solid phase by using combinatorial chemistry. One of the most well studied classes of peptidomimetics is peptoids. Peptoids are easy to synthesize and have been shown to be proteolysis-resistant and cell-permeable. Over the past decade, many useful protein ligands have been identified through screening of peptoid libraries. However, most of the ligands identified from peptoid libraries do not display high affinity, with rare exceptions. This may be due, in part, to the lack of chiral centers and conformational constraints in peptoid molecules. Recently, we described a new synthetic route to access peptide tertiary amides (PTAs). PTAs are a superfamily of peptidomimetics that include but are not limited to peptides, peptoids and N-methylated peptides. With side chains on both &#945;-carbon and main chain nitrogen atoms, the conformation of these molecules are greatly constrained by sterical hindrance and allylic 1,3 strain. (Figure 1) Our study suggests that these PTA molecules are highly structured in solution and can be used to identify protein ligands. We believe that these molecules can be a future source of high-affinity protein ligands. Here we describe the synthetic method combining the power of both split-and-pool and sub-monomer strategies to synthesize a sample one-bead one-compound (OBOC) library of PTAs.

Peptide tertiary amides (PTAs) are a superfamily of peptidomimetics that include but are not limited to peptides, peptoids and N-methylated peptides. Here we describe a synthetic method which combines&#160;both split-and-pool and sub-monomer strategies to synthesize a one-bead one-compound library of PTAs.

Peptidomimetics are great sources of protein ligands. The oligomeric nature of these compounds enables us to access large synthetic libraries on solid ...

Synthesis and Characterization of Functionalized Metal-organic Frameworks

Metal-organic frameworks have attracted extraordinary amounts of research attention, as they are attractive candidates for numerous industrial and technological applications. Their signature property is their ultrahigh porosity, which however imparts a series of challenges when it comes to both constructing them and working with them. Securing desired MOF chemical and physical functionality by linker/node assembly into a highly porous framework of choice can pose difficulties, as less porous and more thermodynamically stable congeners (e.g., other crystalline polymorphs, catenated analogues) are often preferentially obtained by conventional synthesis methods. Once the desired product is obtained, its characterization often requires specialized techniques that address complications potentially arising from, for example, guest-molecule loss or preferential orientation of microcrystallites. Finally, accessing the large voids inside the MOFs for use in applications that involve gases can be problematic, as frameworks may be subject to collapse during removal of solvent molecules (remnants of solvothermal synthesis). In this paper, we describe synthesis and characterization methods routinely utilized in our lab either to solve or circumvent these issues. The methods include solvent-assisted linker exchange, powder X-ray diffraction in capillaries, and materials activation (cavity evacuation) by supercritical CO2 drying. Finally, we provide a protocol for determining a suitable pressure region for applying the Brunauer-Emmett-Teller analysis to nitrogen isotherms, so as to estimate surface area of MOFs with good accuracy.

Synthesis, activation, and characterization of intentionally designed metal-organic framework materials is challenging, especially when building blocks are incompatible or unwanted polymorphs are thermodynamically favored over desired forms. We describe how applications of solvent-assisted linker exchange, powder X-ray diffraction in capillaries and activation via supercritical CO2 drying, can address some of these challenges.

Metal-organic frameworks have attracted extraordinary amounts of research attention, as they are attractive candidates for numerous industrial and ...

Preparation and Characterization of SDF-1&#945;-Chitosan-Dextran Sulfate Nanoparticles

Chitosan (CS) and dextran sulfate (DS) are charged polysaccharides (glycans), which form polyelectrolyte complex-based nanoparticles when mixed under appropriate conditions. The glycan nanoparticles are useful carriers for protein factors, which facilitate the in vivo delivery of the proteins and sustain their retention in the targeted tissue. The glycan polyelectrolyte complexes are also ideal for protein delivery, as the incorporation is carried out in aqueous solution, which reduces the likelihood of inactivation of the proteins. Proteins with a heparin-binding site adhere to dextran sulfate readily, and are, in turn, stabilized by the binding. These particles are also less inflammatory and toxic when delivered in vivo. In the protocol described below, SDF-1&#945; (Stromal cell-derived factor-1&#945;), a stem cell homing factor, is first mixed and incubated with dextran sulfate. Chitosan is added to the mixture to form polyelectrolyte complexes, followed by zinc sulfate to stabilize the complexes with zinc bridges. The resultant SDF-1&#945;-DS-CS particles are measured for size (diameter) and surface charge (zeta potential). The amount of the incorporated SDF-1&#945; is determined, followed by measurements of its in vitro release rate and its chemotactic activity in a particle-bound form.

Preparation and Characterization of SDF-1&amp;#945;-Chitosan-Dextran Sulfate Nanoparticles

The objective of this protocol is to incorporate SDF-1&#945;, a stem cell homing factor, into dextran sulfate-chitosan nanoparticles. The resultant particles are measured for their size and zeta potential, as well as the content, activity, and in vitro release rate of SDF-1&#945; from the nanoparticles.

Chitosan (CS) and dextran sulfate (DS) are charged polysaccharides (glycans), which form polyelectrolyte complex-based nanoparticles when mixed under ...

Reverse Microemulsion-mediated Synthesis of Monometallic and Bimetallic Early Transition Metal Carbide and Nitride Nanoparticles

A reverse microemulsion is used to encapsulate monometallic or bimetallic early transition metal oxide nanoparticles in microporous silica shells. The silica-encapsulated metal oxide nanoparticles are then carburized in a methane/hydrogen atmosphere at temperatures over 800 &#176;C to form silica-encapsulated early transition metal carbide nanoparticles. During the carburization process, the silica shells prevent the sintering of adjacent carbide nanoparticles while also preventing the deposition of excess surface carbon. Alternatively, the silica-encapsulated metal oxide nanoparticles can be nitridized in an ammonia atmosphere at temperatures over 800 &#176;C to form silica-encapsulated early transition metal nitride nanoparticles. By adjusting the reverse microemulsion parameters, the thickness of the silica shells, and the carburization/nitridation conditions, the transition metal carbide or nitride nanoparticles can be tuned to various sizes, compositions, and crystal phases. After carburization or nitridation, the silica shells are then removed using either a room-temperature aqueous ammonium bifluoride solution or a 0.1 to 0.5 M NaOH solution at 40-60 &#176;C. While the silica shells are dissolving, a high surface area support, such as carbon black, can be added to these solutions to obtain supported early transition metal carbide or nitride nanoparticles. If no high surface area support is added, then the nanoparticles can be stored as a nanodispersion or centrifuged to obtain a nanopowder.

A &#8220;removable ceramic coating method&#8221; is presented in visual format for the synthesis of non-sintered and metal-terminated monometallic and bimetallic early transition metal carbide and nitride nanoparticles with tunable sizes and crystal structures.

A reverse microemulsion is used to encapsulate monometallic or bimetallic early transition metal oxide nanoparticles in microporous silica shells. The ...

Synthesis and Characterization of Supramolecular Colloids

Control over colloidal assembly is of utmost importance for the development of functional colloidal materials with tailored structural and mechanical properties for applications in photonics, drug delivery and coating technology. Here we present a new family of colloidal building blocks, coined supramolecular colloids, whose self-assembly is controlled through surface-functionalization with a benzene-1,3,5-tricarboxamide (BTA) derived supramolecular moiety. Such BTAs interact via directional, strong, yet reversible hydrogen-bonds with other identical BTAs. Herein, a protocol is presented that describes how to couple these BTAs to colloids and how to quantify the number of coupling sites, which determines the multivalency of the supramolecular colloids. Light scattering measurements show that the refractive index of the colloids is almost matched with that of the solvent, which strongly reduces the van der Waals forces between the colloids. Before photo-activation, the colloids remain well dispersed, as the BTAs are equipped with a photo-labile group that blocks the formation of hydrogen-bonds. Controlled deprotection with UV-light activates the short-range hydrogen-bonds between the BTAs, which triggers the colloidal self-assembly. The evolution from the dispersed state to the clustered state is monitored by confocal microscopy. These results are further quantified by image analysis with simple routines using ImageJ and Matlab. This merger of supramolecular chemistry and colloidal science offers a direct route towards light- and thermo-responsive colloidal assembly encoded in the surface-grafted monolayer.

A protocol for the synthesis and characterization of colloids coated with supramolecular moieties is described. These supramolecular colloids undergo self-assembly upon the activation of the hydrogen-bonds between the surface-anchored molecules by UV-light.

Control over colloidal assembly is of utmost importance for the development of functional colloidal materials with tailored structural and mechanical ...

Synthesis of Ligand-free CdS Nanoparticles within a Sulfur Copolymer Matrix

Aliphatic ligands are typically used during the synthesis of nanoparticles to help mediate their growth in addition to operating as high-temperature solvents. These coordinating ligands help solubilize and stabilize the nanoparticles while in solution, and can influence the resulting size and reactivity of the nanoparticles during their formation. Despite the ubiquity of using ligands during synthesis, the presence of aliphatic ligands on the nanoparticle surface can result in a number of problems during the end use of the nanoparticles, necessitating further ligand stripping or ligand exchange procedures. We have developed a way to synthesize cadmium sulfide (CdS) nanoparticles using a unique sulfur copolymer. This sulfur copolymer is primarily composed of elemental sulfur, which is a cheap and abundant material. The sulfur copolymer has the advantages of operating both as a high temperature solvent and as a sulfur source, which can react with a cadmium precursor during nanoparticle synthesis, resulting in the generation of ligand free CdS. During the reaction, only some of the copolymer is consumed to produce CdS, while the rest remains in the polymeric state, thereby producing a nanocomposite material. Once the reaction is finished, the copolymer stabilizes the nanoparticles within a solid polymeric matrix. The copolymer can then be removed before the nanoparticles are used, which produces nanoparticles that do not have organic coordinating ligands. This nascent synthesis technique presents a method to produce metal-sulfide nanoparticles for a wide variety of applications where the presence of organic ligands is not desired.

Herein we present a method to synthesize ligand-free cadmium sulfide (CdS) nanoparticles based on a unique sulfur copolymer. The sulfur copolymer operates as a high temperature solvent and a sulfur source during the nanoparticle synthesis and stabilizes the nanoparticles after the reaction.

Aliphatic ligands are typically used during the synthesis of nanoparticles to help mediate their growth in addition to operating as high-temperature ...

Synthesis of Core-shell Lanthanide-doped Upconversion Nanocrystals for Cellular Applications

Lanthanide-doped upconversion nanocrystals (UCNs) have attracted much attention in recent years based on their promising and controllable optical properties, which allow for the absorption of near-infrared (NIR) light and can subsequently convert it into multiplexed emissions that span over a broad range of regions from the UV to the visible to the NIR. This article presents detailed experimental procedures for high-temperature co-precipitation synthesis of core-shell UCNs that incorporate different lanthanide ions into nanocrystals for efficiently converting deep-tissue penetrable NIR excitation (808 nm) into a strong blue emission at 480 nm. By controlling the surface modification with biocompatible polymer (polyacrylic acid, PAA), the as-prepared UCNs acquires great solubility in buffer solutions. The hydrophilic nanocrystals are further functionalized with specific ligands (dibenzyl cyclooctyne, DBCO) for localization on the cell membrane. Upon NIR light (808 nm) irradiation, the upconverted blue emission can effectively activate the light-gated channel protein on the cell membrane and specifically regulate the cation (e.g., Ca2+) influx in the cytoplasm. This protocol provides a feasible methodology for the synthesis of core-shell lanthanide-doped UCNs and subsequent biocompatible surface modification for further cellular applications.

A protocol is presented for the synthesis of core-shell lanthanide-doped upconversion nanocrystals (UCNs) and their cellular applications for channel protein regulation upon near-infrared (NIR) light illumination.

Lanthanide-doped upconversion nanocrystals (UCNs) have attracted much attention in recent years based on their promising and controllable optical ...

Preparation and Characterization of C60/Graphene Hybrid Nanostructures

Physical thermal deposition in a high vacuum environment is a clean and controllable method for fabricating novel molecular nanostructures on graphene. We present methods for depositing and passively manipulating C60 molecules on rippled graphene that advance the pursuit of realizing applications involving 1D C60/graphene hybrid structures. The techniques applied in this exposition are geared towards high vacuum systems with preparation areas capable of supporting molecular deposition as well as thermal annealing of the samples. We focus on C60 deposition at low pressure using a homemade Knudsen cell connected to a scanning tunneling microscopy (STM) system. The number of molecules deposited is regulated by controlling the temperature of the Knudsen cell and the deposition time. One-dimensional (1D) C60 chain structures with widths of two to three molecules can be prepared via tuning of the experimental conditions. The surface mobility of the C60 molecules increases with annealing temperature allowing them to move within the periodic potential of the rippled graphene. Using this mechanism, it is possible to control the transition of 1D C60 chain structures to a hexagonal close packed quasi-1D stripe structure.

Preparation and Characterization of C60/Graphene Hybrid Nanostructures

Here we present a protocol for the fabrication of C60/graphene hybrid nanostructures by physical thermal evaporation. Particularly, the proper manipulation of deposition and annealing conditions allow the control over the creation of 1D and quasi 1D C60 structures on rippled graphene.

Physical thermal deposition in a high vacuum environment is a clean and controllable method for fabricating novel molecular nanostructures on graphene. We ...

Synthesis and Characterization of 1,2-Dithiolane Modified Self-Assembling Peptides

This report focuses on the synthesis of an N-terminus 1,2-dithiolane modified self-assembling peptide and the characterization of the resulting self-assembled supramolecular structures. The synthetic route takes advantage of solid-phase peptide synthesis with the on-resin coupling of the dithiolane precursor molecule, 3-(acetylthio)-2-(acetylthiomethyl)propanoic acid, and the microwave-assisted thioacetate deprotection of the peptide N-terminus before final cleavage from the resin to yield the 1,2-dithiolane modified peptide. After the high-performance liquid chromatography (HPLC) purification of the 1,2-dithiolane peptide, derived from the nucleating core of the A&#946; peptide associated with Alzheimer&#39;s disease, the peptide is shown to self-assemble into cross-&#946; amyloid fibers. Protocols to characterize the amyloid fibers by Fourier-transform infrared spectroscopy (FT-IR), circular dichroism spectroscopy (CD) and transmission electron microscopy (TEM) are presented. The methods of N-terminal modification with a 1,2-dithiolane moiety to well-characterized self-assembling peptides can now be explored as model systems to develop post-assembly modification strategies and explore dynamic covalent chemistry on supramolecular peptide nanofiber surfaces.

A protocol for the synthesis of a 1,2-dithiolane modified peptide and the characterization of the supramolecular structures resulting from the peptide self-assembly.

This report focuses on the synthesis of an N-terminus 1,2-dithiolane modified self-assembling peptide and the characterization of the resulting ...

High Resolution Physical Characterization of Single Metallic Nanoparticles

Individual molecules can be detected and characterized by measuring the degree by which they reduce the ionic current flowing through a single nanometer-scale pore. The signal is characteristic of the molecule&#39;s physicochemical properties and its interactions with the pore. We demonstrate that the nanopore formed by the bacterial protein exotoxin Staphylococcus aureus alpha hemolysin (&#945;HL) can detect polyoxometalates (POMs, anionic metal oxygen clusters), at the single molecule limit. Moreover, multiple degradation products of 12-phosphotungstic acid POM (PTA, H3PW12O40) in solution are simultaneously measured. The single molecule sensitivity of the nanopore method allows for POMs to be characterized at significantly lower concentrations than required for nuclear magnetic resonance (NMR) spectroscopy. This technique could serve as a new tool for chemists to study the molecular properties of polyoxometalates or other metallic clusters, to better understand POM synthetic processes, and possibly improve their yield. Hypothetically, the location of a given atom, or the rotation of a fragment in the molecule, and the metal oxidation state could be investigated with this method. In addition, this new technique has the advantage of allowing the real-time monitoring of molecules in solution.&#160;

Here, we present a protocol to detect discrete metal oxygen clusters, polyoxometalates (POMs), at the single molecule limit using a biological nanopore-based electronic platform. The method provides a complementary approach to traditional analytical chemistry tools used in the study of these molecules.