Name: seeded synthesis of cdse/cds rod and tetrapod nanocrystals
Uploaded: 2013-12-11T13:15:00
Duration: 12 min 56 s
Description: Watch this Scientific Journal Video about Seeded Synthesis of CdSe/CdS Rod and Tetrapod Nanocrystals at JoVE.com

This work was supported by the Physical Chemistry of Inorganic Nanostructures Program, KC3103, Director, Office of Science, Office of Basic Energy Sciences, of the United States Department of Energy under contract DE-AC02-05CH11231. The Center for Nanoscale Materials at Argonne National Laboratory is supported by a U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences User Facility under Contract No. DE-AC02-06CH11357. K.M. and B.J.B. gratefully acknowledge the support of the Department of Energy Office of Science Graduate Fellowship Program (DOE SCGF), made possible in part by the American Recovery and Reinvestment Act of 2009 and administered by ORISE-ORAU under contract no. DE-AC05-06OR23100.

Please consult all relevant material safety data sheets (MSDS) before use. Several of the chemicals used in these syntheses are acutely toxic and carcinogenic. Nanomaterials may have additional hazards compared to their bulk counterpart. Please use all appropriate safety practices when performing a nanocrystal reaction including the use of engineering controls (fume hood, glovebox) and personal protective equipment (safety glasses, gloves, lab coat, full-length pants, closed-toe shoes). Portions of the following procedures involve standard air-free handling techniques15.
1. Preparation of Molecular Precursors
<ol>
	<li>Preparation of cadmium (II) myristate 
	Cadmium myristate can be synthesized in either an ex situ or in situ method, achieving similar results.
	<ol>
		<li>Ex situ preparation of cadmium myristate16
		<ol>
			<li>Dissolve 0.240 g sodium hydroxide and 1.370 g myristic acid in 240 ml&#160;methanol.</li>
			<li>Separately, dissolve 0.617 g cadmium nitrate tetrahydrate in 40 ml&#160;methanol.</li>
			<li>Add the cadmium nitrate solution drop-wise (~1 drop/sec) to the stirring (800 rpm) sodium myristate solution using an addition funnel.</li>
			<li>Filter the solution. Wash the resulting white precipitate with methanol three times. Dry the precipitate under vacuum overnight.</li>
		</ol>
		</li>
		<li>In situ preparation of cadmium myristate6
		<ol>
			<li>Combine 39 mg cadmium oxide (CdO) with 0.137 g myristic acid in 5 ml&#160;1-octadecene (ODE) in a 50 ml&#160;3-neck round bottom flask with a stir bar.</li>
			<li>Heat the solution to 250 &#176;C under inert gas while stirring (800 rpm) until the solution becomes a pale yellow color. Carefully swirl the solution as necessary to remove excess CdO from the sidewalls of the flask. Leaving this solution at elevated temperature beyond this point will cause it to become an undesired black color.</li>
			<li>Cool the solution to room temperature for use in subsequent reactions.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Preparation of TOP:Se precursor
	<ol>
		<li>Combine 58 mg selenium powder with 0.360 g tri-n-octylphosphine (TOP) under an inert atmosphere.</li>
		<li>Sonicate until the selenium powder is fully dissolved, yielding an optically clear solution. Alternatively, the solution can also be heated to 100 &#176;C in order to fully dissolve the selenium.&#160;Use proper glassware or a glove box to prevent exposure of the solution to air during sonication or heating.</li>
	</ol>
	</li>
	<li>Preparation of TOP:S precursor
	<ol>
		<li>Combine 0.160 g elemental sulfur with 1.853 g TOP.</li>
		<li>Heat to 50 &#176;C under an inert atmosphere until the solution is optically clear. Cool to room temperature for future use.</li>
	</ol>
	</li>
</ol>
2. Synthesis of CdSe Seeds
<ol>
	<li>Synthesis of wurtzite CdSe (w-CdSe) nanocrystals5
	<ol>
		<li>Combine 3.0 g trioctylphosphine oxide (TOPO), 280 mg n-octadecylphosphonic acid (ODPA), and 60 mg CdO with a stir bar in a 25 ml&#160;3-neck round bottom flask equipped with a thermocouple (inserted in a custom glass adapter or punctured through a rubber septum), a reflux condenser, and a rubber septum. Inspect all glassware for defects prior to use due to the high temperature of reaction and potential need for rapid cooling. Assemble all glass-to-glass joints with high temperature vacuum grease.</li>
		<li>Degas the mixture at 150 &#176;C under vacuum for 1 hr while stirring (800 rpm).</li>
		<li>Heat the solution to 300 &#176;C under inert gas to form an optically clear solution. Carefully swirl the solution to remove excess CdO from the sidewalls of the flask. Allow the solution to become optically clear again.</li>
		<li>Add 1.5 g TOP drop-wise to the solution and raise the temperature to 370 &#176;C.</li>
		<li>Rapidly inject TOP:Se solution using a syringe with a large diameter (14 G) needle. The rapid injection will create a sharp nucleation event, promoting a narrow size distribution.</li>
		<li>Let the reaction proceed for the desired duration, as the size of the w-CdSe nanocrystal can be tuned by adjusting the reaction time. Immediately cooling after the injection will yield nanocrystals of ~2-2.5 nm in diameter whereas reacting the solution for 3 and 5 min&#160;will yield ~3 nm and ~4 nm diameter nanocrystals, respectively.</li>
		<li>Remove the heating mantle and rapidly cool the flask using a stream of compressed air. Care should be taken when rapidly cooling a flask from elevated temperatures as the thermal shock may break the glassware. For this reason, the use of a water bath for rapid cooling is strongly discouraged.</li>
		<li>Add 10 ml&#160;of anhydrous methanol to the solution when the temperature is below 60 &#176;C to flocculate the nanocrystals. Transfer the solution to a vial under inert gas and centrifuge.</li>
		<li>Decant the solution. Discard the supernatant and redisperse the precipitate in anhydrous toluene. Add anhydrous methanol until the solution becomes turbid and centrifuge.</li>
		<li>Repeat a similar cleaning procedure (step 2.1.9) using a different solvent/nonsolvent pair: hexane/isopropanol. This helps prevent situations in which the nanocrystals and precursors precipitate simultaneously.</li>
		<li>Disperse the cleaned precipitate in a small volume (a few milliliters) of anhydrous toluene. The use of a small volume of solvent here will avoid the need to concentrate the particles as an additional step prior to their use in the seeded growth of CdS.</li>
		<li>Confirm the wurtzite crystal structure of the CdSe nanocrystals by X-ray diffraction. This step is strongly encouraged due to the polymorphism of CdSe and the strong dependence on the structure of the CdSe seed for the resulting heterostructures.</li>
		<li>Dilute a small aliquot of the w-CdSe stock solution by a known dilution factor and acquire a UV-Vis absorption spectrum.</li>
		<li>Determine the w-CdSe nanocrystal diameter and extinction coefficient based upon the first exciton absorbance according to the following formulas17: 
		D = (1.6122&#215;10-9)&#955;4&#160;- (2.6575&#215;10-6)&#955;3&#160;+ (1.6242&#215;10-3)&#955;2 - (0.4277)&#955; + 41.57 
		&#949;&#160;=&#160;5857(D)2.65 
		where D is the diameter (nm) of the w-CdSe nanocrystal, &#955;&#160;is the wavelength (nm) of the first excitonic absorption peak, and &#949; is the extinction coefficient (L/mol&#8226;cm)&#160;of nanocrystals at the first exciton.</li>
		<li>Determine the concentration of the w-CdSe nanocrystal stock solution using the absorbance at the first excitonic absorption peak in accordance with Beer-Lambert&#8217;s Law and the appropriate dilution factor.</li>
		<li>To prepare w-CdSe for the growth of seeded rods, combine 0.5 g TOP with a volume of the w-CdSe nanocrystal stock solution corresponding to 10-8 mol of w-CdSe nanocrystals. Sonicate briefly if needed to redisperse the w-CdSe nanocrystals in TOP. The use of a small volume of toluene for the w-CdSe stock solution in a prior step (2.1.11) should lead to only a small amount of toluene, on the order of microliters, in the seed solution used for the injection. The injection of larger volumes of volatile organic solvents, such as toluene, at temperatures substantially above their boiling point poses a safety hazard and will adversely affect the nanocrystal product due to large drops in reaction temperatures.</li>
	</ol>
	</li>
	<li>Synthesis of zinc-blende CdSe (zb-CdSe) nanocrystals16,18,19
	<ol>
		<li>Combine 0.17 g cadmium myristate and 37 ml&#160;ODE with a stir bar in a 50 ml&#160;3-neck round bottom flask equipped with a thermocouple (inserted in a custom glass adapter or punctured through a rubber septum), a reflux condenser, and a rubber septum. Inspect all glassware for defects prior to use due to the high temperature of reaction. Assemble all glass-to-glass joints with high temperature vacuum grease.</li>
		<li>Degas the solution under vacuum at 90 &#176;C for 1 hr while stirring (800 rpm). Subsequently, cool the solution to room temperature under inert gas.</li>
		<li>Briefly remove the rubber septum and add 33 mg selenium dioxide powder to the flask. Replace the septum. Degas the solution under vacuum at 50 &#176;C for 15 min.</li>
		<li>Heat to 240 &#176;C at a ramp rate of approximately 10 &#176;C/min under inert gas. As the temperature rises, the solution will begin to change color, progressing from yellow to red.</li>
		<li>Add a previously degassed solution of 1 ml&#160;oleic acid and 1 ml&#160;oleylamine in 4 ml&#160;ODE drop-wise when the solution reaches 240 &#176;C.</li>
		<li>React the solution for 30 min&#160;at 240 &#176;C. The size of the zb-CdSe nanocrystals can be tuned by modifying the reaction time. Take aliquots for absorption and photoluminescence spectra to monitor particle growth if desired.</li>
		<li>Remove the heating mantle and cool to room temperature. Transfer the crude solution to an inert atmosphere glove box and split the reaction mixture into 20 ml&#160;fractions in centrifuge vials.</li>
		<li>Add 10 ml&#160;anhydrous acetone to each vial and centrifuge solutions to isolate the nanocrystals.</li>
		<li>Pour off the supernatant and redisperse the precipitate in anhydrous toluene. Add acetone until the solution becomes turbid and centrifuge.</li>
		<li>Repeat a similar cleaning procedure (step 2.2.9) using a different solvent/nonsolvent pair: chloroform/methanol. This helps prevent situations in which the nanocrystals and precursors precipitate simultaneously.</li>
		<li>Disperse the cleaned precipitate in a small volume (a few milliliters) of anhydrous chloroform. The use of a small volume of solvent here will avoid the need to concentrate the particles as an additional step prior to their use in the seeded growth of CdS.</li>
		<li>After cleaning the particles, confirm the zinc-blende crystal structure of the CdSe nanocrystals by X-ray diffraction. This step is strongly encouraged due to the polymorphism of CdSe and the strong dependence on the structure of the CdSe seed for the resulting heterostructures.</li>
		<li>Dilute a small aliquot of the zb-CdSe stock solution by a known dilution factor and acquire a UV-Vis absorption spectrum.</li>
		<li>Determine the zb-CdSe nanocrystal diameter and extinction coefficient based upon the first exciton absorbance according to the following formulas20: 
		<img fo:content-width="2in" src="/files/ftp_upload/50731/50731eq1.jpg" width="240px" /> 
		&#949;&#160;=&#160;19300 (D)3 
		where D is the diameter (nm) of the zb-CdSe nanocrystal, Eg the band gap energy (eV) corresponding to the first excitonic absorption peak, and &#949; is the extinction coefficient (L/mol&#8226;cm)&#160;of nanocrystals at 340 nm.</li>
		<li>Determine the concentration of the zb-CdSe nanocrystal stock solution using the absorbance at 340 nm in accordance with&#160;Beer-Lambert&#8217;s Law and the appropriate dilution factor.</li>
		<li>Combine 0.5 g TOP with a volume of the zb-CdSe nanocrystal stock solution corresponding to 10-8 mol of zb-CdSe nanocrystals to prepare zb-CdSe injection for the growth of seeded tetrapods. Sonicate briefly if needed to redisperse the zb-CdSe nanocrystals in TOP. The use of a small volume of chloroform for the zb-CdSe stock solution in a prior step (2.2.11) should lead to only a small amount of chloroform, on the order of microliters, in the seed solution used for the injection. The injection of larger volumes of volatile organic solvents, such as chloroform, at temperatures substantially above their boiling point poses a safety hazard and will adversely affect the nanocrystal product due to large drops in reaction temperatures.</li>
	</ol>
	</li>
</ol>
3. Synthesis of CdSe/CdS Heterostructures
<ol>
	<li>Synthesis of CdSe/CdS seeded nanorods6
	<ol>
		<li>Combine 207 mg CdO, 1.08 g ODPA, 3.35 g TOPO, and 15 mg propylphosphonic acid (PPA) with a stir bar in a 25 ml&#160;3-neck round bottom flask equipped with a thermocouple (inserted in a custom glass adapter or punctured through a rubber septum), a reflux condenser, and a rubber septum. Inspect all glassware for defects prior to use due to the high temperature of reaction. Assemble all glass-to-glass joints with high temperature vacuum grease.</li>
		<li>Degas the solution under vacuum at 120 &#176;C for 30 min&#160;while stirring (800 rpm).</li>
		<li>Heat the solution to 320 &#176;C under inert gas to form an optically clear solution. Carefully swirl the solution to remove excess CdO from the sidewalls of the flask. Allow the solution to become optically clear again.</li>
		<li>Cool the solution to 120 &#176;C. Degas the solution under vacuum for 1 hr at 120 &#176;C.</li>
		<li>After degassing and complexing the reaction solution, heat the mixture to 340 &#176;C under inert gas. Inject 1.5 g TOP drop-wise and let the temperature recover to 340&#176;C.</li>
		<li>Rapidly inject 0.65 g TOP:S using a syringe with a large diameter (14 G) needle.</li>
		<li>20 seconds after the TOP:S injection, rapidly inject w-CdSe solution (10-8 mol w-CdSe nanocrystals in 0.5 g TOP) using a syringe with a large diameter (14 G) needle.</li>
		<li>Adjust the reaction temperature to 320 &#176;C. After 10 min&#160;at 320 &#176;C, remove the heating mantle and cool the solution.</li>
		<li>Add ~10 ml&#160;anhydrous toluene to the flask when the temperature is around 100 &#176;C to prevent solidification of the TOPO.</li>
		<li>Transfer the crude solution to a centrifuge vial. The purification of the crude solution of seeded rods can be performed in an inert atmosphere glovebox or ambient conditions, if desired, as the overgrowth of CdS enhances the environmental stability of the nanocrystals. Add an equal volume of anhydrous ethanol to flocculate the nanocrystals and centrifuge.</li>
		<li>Pour off the supernatant and redispersed the precipitate in hexane/octylamine (8:1 by volume). Add anhydrous ethanol until the solution appears turbid and centrifuge. Redisperse precipitate in anhydrous toluene.</li>
		<li>Occasionally, solutions of seeded rods will form a gel during the cleaning process. If this occurs, add a few drops of octylamine to dissolve the gel and continue the cleaning procedure. 
		Note: The length of the nanorods can be tuned by changing the concentration of injected CdSe seeds; higher seed&#160;concentrations lead to shorter rods. Adjusting the TOP:S concentration will vary the rod diameter and length; higher TOP:S concentration produces longer, thinner rods. See reference6 for further details.</li>
	</ol>
	</li>
	<li>Synthesis of CdSe/CdS seeded tetrapods6,17 
	<ol>
		<li>Combine 207&#160;mg CdO, 1.08 g ODPA, 3.35 g TOPO, and 50 mg PPA with a stir bar in a 25 ml&#160;3-neck round bottom flask equipped with a thermocouple (inserted in a custom glass adapter or punctured through a rubber septum), a reflux condenser, and a rubber septum. Inspect all glassware for defects prior to use due to the high temperature of reaction. Assemble all glass-to-glass joints with high temperature vacuum grease.</li>
		<li>Degas the solution under vacuum at 120 &#176;C for 1 hr while stirring (800 rpm).</li>
		<li>Heat the solution to 280 &#176;C under inert gas to form an optically clear solution. Carefully swirl the solution to remove excess CdO from the sidewalls of the flask. Allow the solution to become optically clear again.</li>
		<li>Cool the solution to 120 &#176;C. Degas the solution under vacuum for 1 hr at 120 &#176;C.</li>
		<li>After degassing and complexing the reaction solution, heat the mixture to 300 &#176;C under inert gas. Inject 1.5 g TOP drop-wise and let the temperature recover to its initial value.</li>
		<li>Rapidly inject 0.65 g TOP:S using a syringe with a large diameter (14 G) needle.</li>
		<li>40 seconds after the TOP:S injection, rapidly inject zb-CdSe solution (10-8 mol zb-CdSe nanocrystals in 0.5 g TOP) using a syringe with a large diameter (14 G) needle.</li>
		<li>Raise the reaction temperature to 315 &#176;C at a rate of 1 &#176;C/min. After 20 min&#160;at 315 &#176;C, remove the heating mantle and cool.</li>
		<li>Add anhydrous toluene to the flask when the temperature is around 100 &#176;C to prevent solidification of the TOPO.</li>
		<li>Transfer the crude solution to a centrifuge vial. The purification of the crude solution of seeded tetrapods can be performed in an inert atmosphere glovebox or ambient conditions, if desired, as the overgrowth of CdS enhances the environmental stability of the nanocrystals. Add anhydrous acetone until the solution becomes turbid and centrifuge.</li>
		<li>Pour off the supernatant and redisperse the precipitate in hexane/octylamine (8:1 by volume). Add anhydrous acetone until the solution becomes turbid and centrifuge.</li>
		<li>Repeat the purification of the tetrapods twice more using toluene and acetone as the solvent and nonsolvent, respectively. Store the tetrapods in toluene.</li>
		<li>Separate tetrapods from undesired nanorod byproducts by centrifuging toluene solutions at 12,000 x g for 30 min&#160;to develop a concentration gradient due to the mass difference between rods and tetrapods. Carefully remove and discard the upper layers, which contain mainly rods. Combine and dissolve the lower layers, which contain mostly tetrapods, in toluene. 
		Note: The length of the tetrapod arms can be tuned by changing the injection seed concentration; higher seed concentrations produce shorter arms. The growth time can be used to adjust the arm diameter; longer growth times increase the diameter of the arms. See reference6 for details. The yield of tetrapods can be varied by using different amounts of PPA in the initial reaction mixture. See reference19 for further details.</li>
	</ol>
	</li>
</ol>

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K., 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=Optical+Properties+of+Zincblende+Cadmium+Selenide+Quantum+Dots.">Optical Properties of Zincblende Cadmium Selenide Quantum Dots.</a> J. Phys. Chem. C. 114, 6371-6376 (2010).</li><li>Qu, L., Peng, X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Control+of+Photoluminescence+Properties+of+CdSe+Nanocrystals+in.">Control of Photoluminescence Properties of CdSe Nanocrystals in.</a> Growth. J. Am. Chem. Soc. 124, 2049-2055 (2002).</li><li>Manna, L., Scher, E. C., Alivisatos, A. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Shape+Control+of+Colloidal+Semiconductor+Nanocrystals.">Shape Control of Colloidal Semiconductor Nanocrystals.</a> J. Cluster Sci. 13, 521-532 (2002).</li><li>Sitt, A., Sala, F. D., Menagen, G., 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=Multiexciton+Engineering+in+Seeded+Core/Shell+Nanorods:+Transfer+from+Type-I+to+Quasi-type-II+Regimes.">Multiexciton Engineering in Seeded Core/Shell Nanorods: Transfer from Type-I to Quasi-type-II Regimes.</a> Nano Lett. 9, 3470-3476 (2009).</li></ol>

We have nothing to disclose.

The optical spectra for the w-CdSe and zb-CdSe seeds exhibit clear excitonic absorption (Figures 1a and&#160;1b) as the seeds are highly monodisperse; the energy of the first exciton corresponds to diameters of 3.3 nm and 3.6 nm for w-CdSe and zb-CdSe, respectively. The seeds also exhibit strong photoluminescence, with quantum yields ranging from approximately 3-30%, depending on the method of preparation of the sample; for instance, a greater number of cleaning steps tends to remove the surface ligands and lead to lower quantum yields6. The narrow full width at half-maximum of the PL peak (31 nm and 33 nm for the w-CdSe and zb-CdSe nanocrystals, respectively) is consistent with size distributions of 5-10%21.
The X-ray diffraction patterns collected for the seeds (Figures 1c and&#160;1d) confirm that they are of the desired phase. The wurtzite phase has clear reflections at 41.1&#176; and 53.8&#176; that are absent for the zinc-blende phase. The peak broadening arises from Scherrer broadening due to finite crystal size.
The differences in the crystal structure of the CdSe seeds lead to dramatically different morphologies of the final heterostructure (Figures 2a and 2b)6. w-CdS nucleates and grows from the (001) and (00<img fo:content-width="0.07in" src="/files/ftp_upload/50731/50731bar.jpg" />)&#160;facets of the w-CdSe, leading to a final rod-shaped particle since there is uniaxial growth. In contrast, w-CdS nucleates and grows off the {111} facets of zb-CdSe. Of the eight {111} facets, four exhibit lower coordinative saturation than the others; as a result, we observe more rapid growth of w-CdS off of these four facets, which leads to a tetrapod morphology22. The seeded rods and tetrapods display high crystallinity, corresponding to wurtzite CdS as confirmed by XRD (Figures 2c and&#160;2d).
Because the CdS portion of the heterostructures is much larger compared to the CdSe seed, the absorption due to the seeds is a small percentage of the overall absorption. As a result, the heterostructures absorb weakly at wavelengths longer than 500 nm, where the majority of absorption is due to the CdSe seed (Figures 2e and&#160;2f). At wavelengths shorter than 500 nm, absorption is dramatically enhanced since the larger bandgap CdS begins to absorb significantly. The extinction coefficients for the seeds are on the order of 105 M-1cm-1, while the rods and tetrapods have significantly enhanced extinction coefficients6 of 107 M-1cm-1 and 108 M-1cm-1, respectively. For both the rods and tetrapods, the first excitonic transition for the heterostructures is red-shifted compared to the bare seeds (Figures 2e and 2f) since the electrons and holes are spread out over a larger particle.
Depending on the particular size of the components of the heterostructure and the resulting band structure, the hole tends to be somewhat confined to the seed while the electron is more free to move throughout the entire particle23. As a result, recombination occurs away from the particle surface, leading to quantum yields for rods above 75% and for tetrapods between 35-70%, which are significantly higher than that of the bare CdSe seeds6. Furthermore, the inorganic passivation from the CdS on the CdSe seeds provides enhanced environmental stability.
We have demonstrated a method for controlling the final morphology of a nanoscale heterostructure via control over the crystal structure of the seed. This same seeded-growth approach has already been applied to a wide range of structures, and we expect that the types of heterostructures that can be synthesized by this approach will continue to expand.

The synthesis of multicomponent nanostructures has developed rapidly over recent years1. A range of II-VI semiconductor nanoheterostructures has been synthesized, including spherical core-shell particles2,3, seeded nanorods4,5, and seeded tetrapods6. These heterostructures allow for sophisticated manipulation of photons and carriers at the nanoscale and exhibit many interesting phenomena, including extremely high extinction coefficients, polarized emission4&#160;and high quantum yields2,7.
The synthesis of multicomponent nanostructures requires precise control over the composition, phase, shape, size, and connectivity of each component. Control over these various factors relies largely on the ability to independently modulate the rate of nucleation and growth8,9,10. One strategy to achieve independent control over nucleation and growth is to separate these two processes into separate synthetic steps. Here, we will show how small seeds of CdSe generated under reaction conditions optimized for nucleation and growth of spherical nanocrystals can then be transferred to a second flask where the growth of CdS occurs under reaction conditions optimized for anisotropic growth of rod-shaped arms6. By tuning the crystal structure of the CdSe seed from wurtzite to zinc-blende, we will demonstrate how the morphology of CdSe/CdS heterostructures grown under similar conditions can be changed from a nanorod to a tetrapod, highlighting the precise control over phase, shape, and size afforded by state-of-the-art nanoparticle synthesis methods. Nanostructures of the cadmium chalcogenides have served as a useful model-system for the development of new synthetic techniques, as this material system has been intensively explored; although the synthesis of a particular nanostructure is shown in this video protocol, the same techniques are applicable to the synthesis of numerous other nanostructures.
Small differences in the techniques and reagents employed in nanoparticle syntheses have been shown to create dramatic differences in the final product. For instance, the temperature ramp rate11 and impurities12-14 present during the synthesis have been shown to dramatically impact the size and shape of the nanocrystals. With identification of the specific factors to which the synthetic procedures are highly sensitive, the reproducibility of nanocrystal syntheses continues to improve. This detailed video protocol is intended to help new practitioners in the field avoid many common pitfalls associated with the synthesis of nanoparticles.

<table border="0" cellpadding="0" cellspacing="0" width="737">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:316px;">Sodium hydroxide, 98%</td>
			<td style="width:131px;">Fisher</td>
			<td style="width:137px;">BP359</td>
			<td style="width:155px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:316px;">Myristic acid, 99%</td>
			<td style="width:131px;">Sigma Aldrich</td>
			<td style="width:137px;">M3128</td>
			<td style="width:155px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:316px;">Methanol, 99.8%</td>
			<td style="width:131px;">Fisher</td>
			<td style="width:137px;">A412</td>
			<td style="width:155px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:316px;">Cadmium nitrate tetrahydrate, 99%</td>
			<td style="width:131px;">Sigma Aldrich</td>
			<td style="width:137px;">20911</td>
			<td style="width:155px;">Highly toxic</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:316px;">Cadmium oxide (CdO), 99.99%</td>
			<td style="width:131px;">Sigma Aldrich</td>
			<td style="width:137px;">202894</td>
			<td style="width:155px;">Highly toxic</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:316px;">1-Octadecene (ODE), 90%</td>
			<td style="width:131px;">Sigma Aldrich</td>
			<td style="width:137px;">O806</td>
			<td style="width:155px;">Technical grade</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:316px;">Selenium (Se), 100 mesh, 99.99%</td>
			<td style="width:131px;">Sigma Aldrich</td>
			<td style="width:137px;">229865</td>
			<td style="width:155px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:316px;">Tri-n-octylphosphine (TOP), 97%</td>
			<td style="width:131px;">Strem</td>
			<td style="width:137px;">15-6655</td>
			<td style="width:155px;">Air sensitive</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:316px;">Sulfur (S), 99.9995%</td>
			<td style="width:131px;">Alfa Aesar</td>
			<td style="width:137px;">10343</td>
			<td style="width:155px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:316px;">Trioctylphosphine oxide (TOPO), 99%</td>
			<td style="width:131px;">Strem</td>
			<td style="width:137px;">15-6661</td>
			<td style="width:155px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:316px;">N-Octadecylphosphonic acid (ODPA), 99%</td>
			<td style="width:131px;">PCI Synthesis</td>
			<td style="width:137px;">104224</td>
			<td style="width:155px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:316px;">Methanol, anhydrous, 99.8%</td>
			<td style="width:131px;">Sigma Aldrich</td>
			<td style="width:137px;">322415</td>
			<td style="width:155px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:316px;">Toluene, anhydrous, 99.8%</td>
			<td style="width:131px;">Sigma Aldrich</td>
			<td style="width:137px;">244511</td>
			<td style="width:155px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:316px;">Chloroform, anhydrous, 99%</td>
			<td style="width:131px;">Sigma Aldrich</td>
			<td style="width:137px;">288306</td>
			<td style="width:155px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:316px;">Acetone, 99.9%</td>
			<td style="width:131px;">Fisher</td>
			<td style="width:137px;">A949</td>
			<td style="width:155px;">Dried over 4&#197; sieves</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:316px;">Hexane, anhydrous, 95%</td>
			<td style="width:131px;">Sigma Aldrich</td>
			<td style="width:137px;">296090</td>
			<td style="width:155px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:316px;">2-Propanol, anhydrous, 99.5%</td>
			<td style="width:131px;">Sigma Aldrich</td>
			<td style="width:137px;">278475</td>
			<td style="width:155px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:316px;">Selenium dioxide, 99.999%</td>
			<td style="width:131px;">Sigma Aldrich</td>
			<td style="width:137px;">204315</td>
			<td style="width:155px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:316px;">Oleic acid, 90%</td>
			<td style="width:131px;">Sigma Aldrich</td>
			<td style="width:137px;">364525</td>
			<td style="width:155px;">Technical grade</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:316px;">Oleylamine, 70%</td>
			<td style="width:131px;">Sigma Aldrich</td>
			<td style="width:137px;">O7805</td>
			<td style="width:155px;">Technical grade</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:316px;">Propylphosphonic acid (PPA), 95%</td>
			<td style="width:131px;">Sigma Aldrich</td>
			<td style="width:137px;">305685</td>
			<td style="width:155px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:316px;">Ethanol, anhydrous, 99.5%</td>
			<td style="width:131px;">Sigma Aldrich</td>
			<td style="width:137px;">459836</td>
			<td style="width:155px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:316px;">Octylamine, 99%</td>
			<td style="width:131px;">Sigma Aldrich</td>
			<td style="width:137px;">O5802</td>
			<td style="width:155px;"></td>
		</tr>
	</tbody>
</table>

seeded synthesis of cdse/cds rod and tetrapod nanocrystals

We demonstrate a method for the synthesis of multicomponent nanostructures consisting of CdS and CdSe with rod and tetrapod morphologies. A seeded synthesis strategy is used in which spherical seeds of CdSe are prepared first using a hot-injection technique. By controlling the crystal structure of the seed to be either wurtzite or zinc-blende, the subsequent hot-injection growth of CdS off of the seed results in either a rod-shaped or tetrapod-shaped nanocrystal, respectively. The phase and morphology of the synthesized nanocrystals are confirmed using X-ray diffraction and transmission electron microscopy, demonstrating that the nanocrystals are phase-pure and have a consistent morphology. The extinction coefficient and quantum yield of the synthesized nanocrystals are calculated using UV-Vis absorption spectroscopy and photoluminescence spectroscopy. The rods and tetrapods exhibit extinction coefficients and quantum yields that are higher than that of the bare seeds. This synthesis demonstrates the precise arrangement of materials that can be achieved at the nanoscale by using a seeded synthetic approach.

Absorption spectra, photoluminescence (PL) spectra, X-ray diffraction (XRD) patterns, and transmission electron microscopy (TEM) images were collected for the seeds (Figure 1) and the final heterostructures (Figure 2). The absorption and PL spectra are used to calculate the extinction coefficient and quantum yield of the nanostructures. XRD and TEM are used to determine the phase and morphology of the nanostructures.
<img alt="Figure 1" fo:content-width="5in" fo:src="/files/ftp_upload/50731/50731fig1highres.jpg" src="/files/ftp_upload/50731/50731fig1.jpg" width="500px" /> 
Figure 1. CdSe nanocrystal seeds of wurtzite and zinc-blende crystal structures. (a, b) Absorption (black) and PL (red) spectra with inset of TEM images of wurtzite and zinc-blende&#160;CdSe nanocrystals, respectively. (c, d) X-ray diffraction patterns of wurtzite and zinc-blende CdSe nanocrystals with the line patterns of corresponding bulk materials provided for reference. <a href="https://www.jove.com/files/ftp_upload/50731/50731fig1highres.jpg" target="_blank">Click here to view larger image</a>.
<img alt="Figure 2" fo:content-width="5in" fo:src="/files/ftp_upload/50731/50731fig2highres.jpg" src="/files/ftp_upload/50731/50731fig2.jpg" width="500px" /> 
Figure 2. CdSe/CdS seeded heterostructures of rod and tetrapod morphologies. (a, b)&#160; TEM images of CdSe/CdS nanorods and CdSe/CdS tetrapods, respectively. (c, d) XRD patterns of CdSe/CdS nanorods and tetrapods. Only reflections from wurtzite CdS are apparent. (e, f) Absorption (black) and PL (red) spectra of CdSe/CdS nanorods and tetrapods. Green line shows magnified absorption spectra to highlight absorption due to the CdSe seed. <a href="https://www.jove.com/files/ftp_upload/50731/50731fig2highres.jpg" target="_blank">Click here to view larger image</a>.

Watch this Scientific Journal Video about Seeded Synthesis of CdSe/CdS Rod and Tetrapod Nanocrystals at JoVE.com

Seeded Synthesis of CdSe/CdS Rod and Tetrapod Nanocrystals

A protocol for the seeded synthesis of rod-shaped and tetrapod-shaped multicomponent nanostructures consisting of CdS and CdSe is presented.

We demonstrate a method for the synthesis of multicomponent nanostructures consisting of CdS and CdSe with rod and tetrapod morphologies. A seeded ...

seeded-synthesis-of-cdsecds-rod-and-tetrapod-nanocrystals

Research

JoVE Journal

Chemistry

Photochemical Oxidative Growth of Iridium Oxide Nanoparticles on CdSe@CdS Nanorods

We demonstrate a procedure for the photochemical oxidative growth of iridium oxide catalysts on the surface of seeded cadmium selenide-cadmium sulfide (CdSe@CdS) nanorod photocatalysts. Seeded rods are grown using a colloidal hot-injection method and then moved to an aqueous medium by ligand exchange. CdSe@CdS nanorods, an iridium precursor and other salts are mixed and illuminated. The deposition process is initiated by absorption of photons by the semiconductor particle, which results with formation of charge carriers that are used to promote redox reactions. To insure photochemical oxidative growth we used an electron scavenger. The photogenerated holes oxidize the iridium precursor, apparently in a mediated oxidative pathway. This results in the growth of high quality crystalline iridium oxide particles, ranging from 0.5 nm to about 3 nm, along the surface of the rod. Iridium oxide grown on CdSe@CdS heterostructures was studied by a variety of characterization methods, in order to evaluate its characteristics and quality. We explored means for control over particle size, crystallinity, deposition location on the CdS rod, and composition. Illumination time and excitation wavelength were found to be key parameters for such control. The influence of different growth conditions and the characterization of these heterostructures are described alongside a detailed description of their synthesis. Of significance is the fact that the addition of iridium oxide afforded the rods astounding photochemical stability under prolonged illumination in pure water (alleviating the requirement for hole scavengers).

A protocol for the photochemical oxidative growth of small crystalline iridium oxide nanoparticles on the surface of CdSe@CdS seeded rod nanoparticles is presented.

We demonstrate a procedure for the photochemical oxidative growth of iridium oxide catalysts on the surface of seeded cadmium selenide-cadmium sulfide ...

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 ...

Sediment Core Extrusion Method at Millimeter Resolution Using a Calibrated, Threaded-rod

Aquatic sediment core subsampling is commonly performed at cm or half-cm resolution. Depending on the sedimentation rate and depositional environment, this resolution provides records at the annual to decadal scale, at best. An extrusion method, using a calibrated, threaded-rod is presented here, which allows for millimeter-scale subsampling of aquatic sediment cores of varying diameters. Millimeter scale subsampling allows for sub-annual to monthly analysis of the sedimentary record, an order of magnitude higher than typical sampling schemes. The extruder consists of a 2 m aluminum frame and base, two core tube clamps, a threaded-rod, and a 1 m piston. The sediment core is placed above the piston and clamped to the frame. An acrylic sampling collar is affixed to the upper 5 cm of the core tube and provides a platform from which to extract sub-samples. The piston is rotated around the threaded-rod at calibrated intervals and gently pushes the sediment out the top of the core tube. The sediment is then isolated into the sampling collar and placed into an appropriate sampling vessel (e.g., jar or bag). This method also preserves the unconsolidated samples (i.e., high pore water content) at the surface, providing a consistent sampling volume. This mm scale extrusion method was applied to cores collected in the northern Gulf of Mexico following the Deepwater Horizon submarine oil release. Evidence suggests that it is necessary to sample at the mm scale to fully characterize events that occur on the monthly time-scale for continental slope sediments.

An extrusion method using a calibrated threaded-rod is presented, which allows for mm scale subsampling of aquatic sediment cores. Millimeter-scale sampling is necessary to fully characterize recent event stratigraphy in sediment records.

Aquatic sediment core subsampling is commonly performed at cm or half-cm resolution. Depending on the sedimentation rate and depositional environment, ...

Green and Low-cost Production of Thermally Stable and Carboxylated Cellulose Nanocrystals and Nanofibrils Using Highly Recyclable Dicarboxylic Acids

Here we demonstrate potentially low cost and green productions of high thermally stable and carboxylated cellulose nanocrystals (CNCs) and nanofibrils (CNF) from bleached eucalyptus pulp (BEP) and unbleached mixed hardwood kraft pulp (UMHP) fibers using highly recyclable dicarboxylic solid acids. Typical operating conditions were acid concentrations of 50 - 70 wt% at 100 &#176;C for 60 min and 120 &#176;C (no boiling at atmospheric pressure) for 120 min, for BEP and UMHP, respectively. The resultant CNCs have a higher thermal degradation temperature than their corresponding feed fibers and carboxylic acid group content from 0.2 - 0.4 mmol/g. The low strength (high pKa of 1.0 - 3.0) of organic acids also resulted in CNCs with both longer lengths of approximately 239 - 336 nm and higher crystallinity than CNCs produced using mineral acids. Cellulose loss to sugar was minimal. Fibrous cellulosic solid residue (FCSR) from the dicarboxylic acid hydrolysis was used to produce carboxylated CNFs through subsequent mechanical fibrillation with low energy input.

Here we demonstrate a novel method for green and sustainable productions of highly thermally stable and carboxylated cellulose nanocrystals (CNC) and nanofibrils (CNF) using highly recyclable solid dicarboxylic acids.

Here we demonstrate potentially low cost and green productions of high thermally stable and carboxylated cellulose nanocrystals (CNCs) and nanofibrils ...

Measurements of Long-range Electronic Correlations During Femtosecond Diffraction Experiments Performed on Nanocrystals of Buckminsterfullerene

The precise details of the interaction of intense X-ray pulses with matter are a topic of intense interest to researchers attempting to interpret the results of femtosecond X-ray free electron laser (XFEL) experiments. An increasing number of experimental observations have shown that although nuclear motion can be negligible, given a short enough incident pulse duration, electronic motion cannot be ignored. The current and widely accepted models assume that although electrons undergo dynamics driven by interaction with the pulse, their motion could largely be considered &#39;random&#39;. This would then allow the supposedly incoherent contribution from the electronic motion to be treated as a continuous background signal and thus ignored. The original aim of our experiment was to precisely measure the change in intensity of individual Bragg peaks, due to X-ray induced electronic damage in a model system, crystalline C60. Contrary to this expectation, we observed that at the highest X-ray intensities, the electron dynamics in C60 were in fact highly correlated, and over sufficiently long distances that the positions of the Bragg reflections are significantly altered. This paper describes in detail the methods and protocols used for these experiments, which were conducted both at the Linac Coherent Light Source (LCLS) and the Australian Synchrotron (AS) as well as the crystallographic approaches used to analyse the data.

We describe an experiment designed to probe the electronic damage induced in nanocrystals of Buckminsterfullerene (C60) by intense, femtosecond pulses of X-rays. The experiment found that, surprisingly, rather than being stochastic, the X-ray induced electron dynamics in C60 are highly correlated, extending over hundreds of unit cells within the crystals1.

The precise details of the interaction of intense X-ray pulses with matter are a topic of intense interest to researchers attempting to interpret the ...

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 ...

Synthesis and Mass Spectrometry Analysis of Oligo-peptoids

Peptoids are sequence-controlled peptide-mimicking oligomers consisting of N-alkylated glycine units. Among many potential applications, peptoids have been thought of as a type of molecular information storage. Mass spectrometry analysis has been considered the method of choice for sequencing peptoids. Peptoids can be synthesized via solid phase chemistry using a repeating two-step reaction cycle. Here we present a method to manually synthesize oligo-peptoids and to analyze the sequence of the peptoids using tandem mass spectrometry (MS/MS) techniques. The sample peptoid is a nonamer consisting of alternating N-(2-methyloxyethyl)glycine (Nme) and N-(2-phenylethyl)glycine (Npe), as well as an N-(2-aminoethyl)glycine (Nae) at the N-terminus. The sequence formula of the peptoid is Ac-Nae-(Npe-Nme)4-NH2, where Ac is the acetyl group. The synthesis takes place in a commercially available solid-phase reaction vessel. The rink amide resin is used as the solid support to yield the peptoid with an amide group at the C-terminus. The resulting peptoid product is subjected to sequence analysis using a triple-quadrupole mass spectrometer coupled to an electrospray ionization source. The MS/MS measurement produces a spectrum of fragment ions resulting from the dissociation of charged peptoid. The fragment ions are sorted out based on the values of their mass-to-charge ratio (m/z). The m/z values of the fragment ions are compared against the nominal masses of theoretically predicted fragment ions, according to the scheme of peptoid fragmentation. The analysis generates a fragmentation pattern of the charged peptoid. The fragmentation pattern is correlated to the monomer sequence of the neutral peptoid. In this regard, MS analysis reads out the sequence information of the peptoids.

A protocol is described for the manual synthesis of oligo-peptoids followed by sequence analysis by mass spectrometry.

Peptoids are sequence-controlled peptide-mimicking oligomers consisting of N-alkylated glycine units. Among many potential applications, peptoids have ...

Fabrication of Spherical and Worm-shaped Micellar Nanocrystals by Combining Electrospray, Self-assembly, and Solvent-based Structure Control

Micellar nanocrystals (micelles with encapsulated nanocrystals) have become an emerging major class of nanobiomaterials. We describe a method of fabricating micellar nanocrystals based on combining top-down electrospray, bottom-up self-assembly, and solvent-based structure control. This method involves first using electrospray to generate uniform ultrafine liquid droplets, each of which functions as a micro-reactor in which self-assembly reaction occurs forming micellar nanocrystals, with the structures (micelle shape and nanocrystal encapsulation) controlled by the organic solvent used. This method is largely continuous and produces high quality micellar nanocrystal products with an inexpensive structure control approach. By using a water-miscible organic solvent tetrahydrofuran (THF), worm-shaped micellar nanocrystals can be produced due to solvent-induced/facilitated micelle fusion. Compared with the common spherical micellar nanocrystals, worm-shaped micellar nanocrystals can offer minimized non-specific cellular uptake, thus enhancing biological targeting. By co-encapsulating multiple nanocrystals into each micelle, multifunctional or synergistic effects can be achieved. Current limitations of this fabrication method, which will be part of the future work, primarily include imperfect encapsulation in the micellar nanocrystal product and the incompletely continuous nature of the process.

The present work describes a method to fabricate micellar nanocrystals, an emerging major class of nanobiomaterials. This method combines top-down electrospray, bottom-up self-assembly, and solvent-based structure control. The fabrication method is largely continuous, can produce high quality products, and possesses an inexpensive means of structure control.

Micellar nanocrystals (micelles with encapsulated nanocrystals) have become an emerging major class of nanobiomaterials. We describe a method of ...

Synthesis of Substrate-Bound Au Nanowires Via an Active Surface Growth Mechanism

Advancing synthetic capabilities is important for the development of nanoscience and nanotechnology. The synthesis of nanowires has always been a challenge, as it requires asymmetric growth of symmetric crystals. Here, we report a distinctive synthesis of substrate-bound Au nanowires. This template-free synthesis employs thiolated ligands and substrate adsorption to achieve the continuous asymmetric deposition of Au in solution at ambient conditions. The thiolated ligand prevented the Au deposition on the exposed surface of the seeds, so the Au deposition only occurs at the interface between the Au seeds and the substrate. The side of the newly deposited Au nanowires is immediately covered with the thiolated ligand, while the bottom facing the substrate remains ligand-free and active for the next round of Au deposition. We further demonstrate that this Au nanowire growth can be induced on various substrates, and different thiolated ligands can be used to regulate the surface chemistry of the nanowires. The diameter of the nanowires can also be controlled with mixed ligands, in which another &#34;bad&#34; ligand could turn on the lateral growth. With the understanding of the mechanism, Au nanowire-based nanostructures can be designed and synthesized.

We report a solution-based method to synthesize substrate-bound Au nanowires. By tuning the molecular ligands used during the synthesis, the Au nanowires can be grown from various substrates with different surface properties. Au nanowire-based nanostructures can also be synthesized by adjusting the reaction parameters.

Advancing synthetic capabilities is important for the development of nanoscience and nanotechnology. The synthesis of nanowires has always been a ...

Synthesis and Characterization of Amphiphilic Gold Nanoparticles

Gold nanoparticles covered with a mixture of 1-octanethiol (OT) and 11-mercapto-1-undecane sulfonic acid (MUS) have been extensively studied because of their interactions with cell membranes, lipid bilayers, and viruses. The hydrophilic ligands make these particles colloidally stable in aqueous solutions and the combination with hydrophobic ligands creates an amphiphilic particle that can be loaded with hydrophobic drugs, fuse with the lipid membranes, and resist nonspecific protein adsorption. Many of these properties depend on nanoparticle size and the composition of the ligand shell. It is, therefore, crucial to have a reproducible synthetic method and reliable characterization techniques that allow the determination of nanoparticle properties and the ligand shell composition. Here, a one-phase chemical reduction, followed by a thorough purification to synthesize these nanoparticles with diameters below 5 nm, is presented. The ratio between the two ligands on the surface of the nanoparticle can be tuned through their stoichiometric ratio used during synthesis. We demonstrate how various routine techniques, such as transmission electron microscopy (TEM), nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA), and ultraviolet-visible (UV-Vis) spectrometry, are combined to comprehensively characterize the physicochemical parameters of the nanoparticles.

Amphiphilic gold nanoparticles can be used in many biological applications. A protocol to synthesize gold nanoparticles coated by a binary mixture of ligands and a detailed characterization of these particles is presented.

Gold nanoparticles covered with a mixture of 1-octanethiol (OT) and 11-mercapto-1-undecane sulfonic acid (MUS) have been extensively studied because of ...