Name: synthesis of graphene nanofluids with controllable flake size distributions
Uploaded: 2019-07-17T13:00:00
Description: Watch this Scientific Journal Video about Synthesis of Graphene Nanofluids with Controllable Flake Size Distributions at JoVE.com

This work was supported by the National Nature Science Foundation of China (Grant&nbsp;No. 21776095), the Guangzhou Science and Technology Key Program (Grant&nbsp;No. 201804020048), and Guangdong Key Laboratory of Clean Energy Technology (Grant No. 2008A060301002). We thank LetPub (www.letpub.com) for its linguistic assistance during the preparation of this manuscript.

1. Exfoliation of graphite in a liquid phase
<ol>
	<li>Preparation of reagents
	<ol>
		<li>In a dry clean flat-bottom flask, add 20 g of polyvinyl alcohol (PVA), and then add 1,000 mL of distilled water. 
		NOTE: If the suspension was not processed to satisfaction, the step could be repeated to obtain an additional suspension.</li>
		<li>Gently swirl the flask until the PVA fully dissolves. 
		CAUTION: PVA is harmful to humans; thus, protective gloves and surgical&#160;masks should be used.</li>
		<li>Add 50 ...

<ol>
	<li>Sadeghinezhad, E., 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=A+comprehensive+review+on+graphene+nanofluids:+Recent+research,+development+and+applications.">A comprehensive review on graphene nanofluids: Recent research, development and applications.</a> Energy Conversion and Management. 111, 466-487 (2016).</li><li>Wang, W., 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=Highly+Efficient+Production+of+Graphene+by+an+Ultrasound+Coupled+with+a+Shear+Mixer+in+Supercritical+CO2.">Highly Efficient Production of Graphene by an Ultrasound Coupled with a Shear Mixer in Supercritical CO2.</a> Industrial &amp; Engineering Chemistry Research. 57 (49), 16701-16708 (2018).</li><li>Cao, H. Y., Guo, Z. X., Xiang, H., Gong, X. 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J., King, P. J., Wirtz, C., Duesberg, G. S., Coleman, J. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lateral+size+selection+of+surfactant-stabilised+graphene+flakes+using+size+exclusion+chromatography.">Lateral size selection of surfactant-stabilised graphene flakes using size exclusion chromatography.</a> Chemical Physics Letters. 531, 169-172 (2012).</li><li>Galvin, K. P., Pratten, S. J., Nicol, S. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dense+medium+separation+using+a+teetered+bed+separator.">Dense medium separation using a teetered bed separator.</a> Minerals Engineering. 12 (9), 1059-1081 (1999).</li><li>Cai, C. J., Sang, N. N., Shen, Z. G., Zhao, X. 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J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Controllable+size-selective+method+to+prepare+graphene+quantum+dots+from+graphene+oxide.">Controllable size-selective method to prepare graphene quantum dots from graphene oxide.</a> Nanoscale Research Letters. 10, 1-8 (2015).</li><li>Oikonomou, A., 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=Scalable+bottom-up+assembly+of+suspended+carbon+nanotube+and+graphene+devices+by+dielectrophoresis.">Scalable bottom-up assembly of suspended carbon nanotube and graphene devices by dielectrophoresis.</a> Physica Status Solidi-Rapid Research Letters. 9 (9), 539-543 (2015).</li><li>Liu, Y., Zhang, D., Pang, S. W., Liu, Y. Y., Shang, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Size+separation+of+graphene+oxide+using+preparative+free-flow+electrophoresis.">Size separation of graphene oxide using preparative free-flow electrophoresis.</a> Journal of Separation Science. 38 (1), 157-163 (2015).</li><li>Cui, C. N., Huang, J. T., Huang, J. H., Chen, G. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Size+separation+of+mechanically+exfoliated+graphene+sheets+by+electrophoresis.">Size separation of mechanically exfoliated graphene sheets by electrophoresis.</a> Electrochimica Acta. 258, 793-799 (2017).</li><li>Sun, Z. 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=High-yield+exfoliation+of+graphite+in+acrylate+polymers:+A+stable+few-layer+graphene+nanofluid+with+enhanced+thermal+conductivity.">High-yield exfoliation of graphite in acrylate polymers: A stable few-layer graphene nanofluid with enhanced thermal conductivity.</a> Carbon. 64, 288-294 (2013).</li><li>Sun, Z. 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=Amine-based+solvents+for+exfoliating+graphite+to+graphene+outperform+the+dispersing+capacity+of+N-methyl-pyrrolidone+and+surfactants.">Amine-based solvents for exfoliating graphite to graphene outperform the dispersing capacity of N-methyl-pyrrolidone and surfactants.</a> Chemical Communications. 50 (72), 10382-10385 (2014).</li><li>Du, B. L., Jian, Q. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Size+controllable+synthesis+of+graphene+water+nanofluid+with+enhanced+stability.">Size controllable synthesis of graphene water nanofluid with enhanced stability.</a> Fullerenes Nanotubes and Carbon Nanostructures. 27 (1), 87-96 (2019).</li><li>Tao, H. C., 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=Scalable+exfoliation+and+dispersion+of+two-dimensional+materials+-+an+update.">Scalable exfoliation and dispersion of two-dimensional materials - an update.</a> Physical Chemistry Chemical Physics. 19 (2), 921-960 (2017).</li><li>Phiri, J., Gane, P., Maloney, T. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-concentration+shear-exfoliated+colloidal+dispersion+of+surfactant-polymer-stabilized+few-layer+graphene+sheets.">High-concentration shear-exfoliated colloidal dispersion of surfactant-polymer-stabilized few-layer graphene sheets.</a> Journal of Materials Science. 52 (13), 8321-8337 (2017).</li></ol>

We have proposed a methodology for synthesizing graphene nanofluids with controllable flake size distributions. The method combines two procedures: exfoliation and centrifugation. Exfoliation controls the lower size limit of the nanoparticles, and centrifugation controls the upper size limit of the nanoparticles.
Although we employed liquid-phase exfoliation of graphite to produce graphene nanoparticles, the following modifications to the protocol should be considered. Additional exfoliation p...

Traditional methods used to synthesize graphene nanofluids often use sonication to disperse graphene powder1 in fluids, and sonication has been proven to change the size distribution of graphene nanoparticles2. Since the thermal conductivity of graphene depends on the flake length3,4, the synthesis of graphene nanofluids with controllable flake size distributions is vital to heat-transfer applications. Controlled centrifugation has been successfully applied to liquid exfoliated graphene dispersions to separate suspensions into fractions with different mean flake sizes5,6. Different terminal velocities used in centrifugation lead to different critical settling particle sizes7. The terminal velocity could be used to eliminate large graphene nanoparticles8.
Recently, size-controllable methods used to synthesize graphene via liquid-phase exfoliation have been introduced to overcome the fundamental problems encountered by conventional methods9,10,11,12,13. Liquid phase exfoliation of graphite has been proven to be an effective way to produce graphene suspensions14,15,16, and the underlying mechanism shows that the process parameters are related to the lower limits of the graphene nanoparticles size distributions. The graphene nanofluids were synthesized by the liquid exfoliation of the graphite with the help of surfactants17.While the lower limits of the graphene nanoparticle size distribution could be controlled by adjusting the parameters during the exfoliation, less attention is paid to the upper limits of the graphene nanoparticle size distribution.
The goal of this work is to develop a protocol that can be used to synthesize graphene nanofluids with controllable flake size distributions. Because exfoliation is responsible only for the lower size limit of the resulting graphene nanoflakes, additional centrifugation is introduced to control the upper size limit of the resulting graphene nanoflakes. However, the proposed method is not specific to graphene and could be appropriate for any other layered compounds that cannot be synthesized using traditional methods.

<table>
	<tbody>
		<tr>
			<td>Beaker</td>
			<td>China Jiangsu Mingtai Education Equipments Co., Ltd.</td>
			<td>500 mL</td>
			<td></td>
		</tr>
		<tr>
			<td>Beaker</td>
			<td>China Jiangsu Mingtai Education Equipments Co., Ltd.</td>
			<td>5000 mL</td>
			<td></td>
		</tr>
		<tr>
			<td>Deionized water</td>
			<td>Guangzhou Yafei Water Treatment Equipment Co., Ltd.</td>
			<td></td>
			<td>analytical grade</td>
		</tr>
		<tr>
			<td>Electronic balance</td>
			<td>Shanghai Puchun Co., Ltd.</td>
			<td>JEa10001</td>
			<td></td>
		</tr>
		<tr>
			<td>Filter membrane</td>
			<td>China Tianjin Jinteng Experiment Equipments Co., Ltd.</td>
			<td>0.2 micron</td>
			<td></td>
		</tr>
		<tr>
			<td>Graphite powder</td>
			<td>Tianjin Dengke chemical reagent Co., Ltd.</td>
			<td></td>
			<td>analytical grade</td>
		</tr>
		<tr>
			<td>Hand gloves</td>
			<td>China Jiangsu Mingtai Education Equipments Co., Ltd.</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Laboratory shear mixer</td>
			<td>Shanghai Specimen and Model Factory</td>
			<td>jrj-300</td>
			<td></td>
		</tr>
		<tr>
			<td>Long neck flat bottom flask</td>
			<td>China Jiangsu Mingtai Education Equipments Co., Ltd.</td>
			<td>1000 ml</td>
			<td></td>
		</tr>
		<tr>
			<td>Nanoparticle analyzer</td>
			<td>HORIBA, Ltd.</td>
			<td>SZ-100Z</td>
			<td></td>
		</tr>
		<tr>
			<td>PVA</td>
			<td>Shanghai Yingjia Industrial Development Co., Ltd.</td>
			<td>1788</td>
			<td>analytical grade</td>
		</tr>
		<tr>
			<td>Raman spectrophotometer</td>
			<td>HORIBA, Ltd.</td>
			<td>Horiba LabRam 2</td>
			<td></td>
		</tr>
		<tr>
			<td>Scanning electron microscope</td>
			<td>Zeiss Co., Ltd.</td>
			<td>LEO1530VP</td>
			<td>SEM</td>
		</tr>
		<tr>
			<td>Surgical mask</td>
			<td>China Jiangsu Mingtai Education Equipments Co., Ltd.</td>
			<td>for one-time use</td>
			<td></td>
		</tr>
		<tr>
			<td>Thermal Gravimetric Analyzer</td>
			<td>German NETZSCH Co., Ltd.</td>
			<td>NETZSCH TG 209 F1 Libra</td>
			<td>TGA analysis</td>
		</tr>
		<tr>
			<td>Transmission electron microscope</td>
			<td>Japan Electron Optics Laboratory Co., Ltd.</td>
			<td>JEM-1400plus</td>
			<td>TEM</td>
		</tr>
		<tr>
			<td>UV-Vis spectrophotometer</td>
			<td>Agilent Technologies, Inc.+BB2:B18</td>
			<td>Varian Cary 60</td>
			<td></td>
		</tr>
	</tbody>
</table>
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synthesis of graphene nanofluids with controllable flake size distributions

A method for synthesizing graphene nanofluids with controllable flake size distributions is presented. Graphene nanoflakes can be obtained by the exfoliation of graphite in the liquid phase, and the exfoliation time is used to control the lower limits of the graphene nanoflake size distributions. Centrifugation is successfully used to control the upper limits of the nanoparticle size distributions. The objective of this work is to combine exfoliation and centrifugation to control the graphene nanoflake size distributions in the resulting suspensions.

The existence of graphene nanosheets can be validated by various characteristic techniques. Figure 1 shows the results of the UV-Vis measurement for the various flake size distributions produced by the abovementioned protocol. The spectra absorbance peak obtained at a wavelength of 270 nm is evidence of the graphene flakes. Different absorbances correspond to different concentrations. The lowest absorbance observed corresponds to the highest centrifugation speed. The spectra strongly confirm...

Watch this Scientific Journal Video about Synthesis of Graphene Nanofluids with Controllable Flake Size Distributions at JoVE.com

Synthesis of Graphene Nanofluids with Controllable Flake Size Distributions

A method for synthesizing graphene nanofluids with controllable flake size distributions is presented.

A method for synthesizing graphene nanofluids with controllable flake size distributions is presented. Graphene nanoflakes can be obtained by the ...

The proposed method employs exfoliation process and centrifugation process to control the lower limits and the upper limits of size distributions of resulting graphinate suspension separately. The main advantage of the proposed method is that the final size distribution is controllable by adjusting the process parameters of the exfoliation step and the centrifugation step. In a dry, clean, flat bottom flask, add 20 grams of PVA, and then add 1000 milliliters of distilled water.Gently swirl the flask until the PVA fully dissolves. Then add 50 grams of graphite powder to the flat bottom flask and gently swirl the flask until the graphite powder fully disperses in the suspension. Transfer 500 milliliters of the resulting suspension to a 500-milliliter beaker.Place the beaker under a shear mixer, positioning the beaker near the center of the mixing vessel to prevent the formation of a vortex. Lower the mixing head to its lowest position, 30 millimeters from the base plane. Next, prepare a water bath by filling a 5000-milliliter beaker with room temperature water, and position the 500-milliliter beaker in the bath.Start the mixer, and increase the speed gradually to 4, 500 rpm. Mix at this speed for 120 minutes. Change the water every 30 minutes.Perform this exfoliation step five more times with different duration. The mixing time determines the lower lateral size limit of the graphene nanoflakes. Collect the 500-milliliter generated suspensions after each exfoliation step.Label each suspension with the exfolation time, and centrifuge the collected suspension at 140 times g for 45 minutes. To remove the unexfoliated graphite, use a pipette to collect the top 80%of the supernatant from each centrifuge tube for further centrifugation. Centrifuge the supernatant suspension from the last centrifugation step at 8, 951 times g for 45 minutes.Collect the upper 50%of the supernatant in the centrifuge tube, and label the sample with a number. Then, to recycle the sediment on the bottom of the centrifuge tube, add 50 milliliters of the previously prepared PVA water reagent to the sediment, and shake the tube vigorously by hand until the sediment is well-dispersed in the suspension. Centrifuge the suspension at 8, 951 times g for 45 minutes.Collect the upper 80%for further measurements. Repeat the centrifugation step for the pellet four more times with four different centrifugation speeds. The centrifugation speed determines the upper lateral size limit of the graphene nanoflakes.Now, prepare the ultraviolet visible spectroscopy. With the previously prepared PVA water solution in a dry, clean sample cell, calibrate the ultraviolet visible spectrometer, setting the PVA water concentrations to 0%Then, add the PVA water resuspension after centrifugation to a dry, clean sample cell, with a path length of 10 millimeters, and obtain a readout using the manufacturer's software. Click the Obtain button to get the measurement results graph, and save the results.Next, to determine the graphene weight, vacuum filter the sample suspension using a nylon membrane with a pore size of 0.2 microns. Obtain the membrane film, and wash with approximately 200 milliliters of water into a beaker. Repeat the wash three times, until all the solids are washed away from the membrane.Determine the washed water mass with a high-precision microbalance to obtain the weight of the solids. Again, vacuum filter the water suspensions using a nylon membrane with a pore size of 0.2 microns. Obtain the membrane, and dry it at room temperature for over 12 hours.Subsequently, rinse the film with 200 milliliters of deionized water into a beaker. If the desired concentration is less than the production rate at one milligram per milliliter, add the prepared PVA water solution to obtain the desired concentration. If the desired concentration is higher than 1%dry the deionized water under vacuum in the dryer for 24 hours to obtain the graphene nanosheets.In this protocol, the ultraviolet visible measurement of the various flake size distributions shows the spectra absorbance peak obtained at a wavelength of 270 nanometers, indicating the evidence of the graphene flakes. Suspension with different concentration has different 660-nanometer absorption. The D band and 2D band of the Raman spectroscopy determines the flake thickness of the graphene nanoflakes.The D band of the Raman spectrum, which is related to graphene sp3 carbon atoms, distinguishes between the initial graphite and the graphene nanoflakes. Low D band intensity indicates the defect-free graphene nanosheets. Distinctive size distribution was observed for the resulting suspension, prepared using different centrifugation speeds.Both the transmission electron microscopy and the scanning electron microscopy show that graphene was produced, and the exfoliation was successful. However, the centrifugation step only worked on nanoparticles with mean diameters larger than 1000 nanometers. The relationship between the upper limits of size distributions with centrifugation speed should be pre-determined.Since the size does not influence with the proposed method, the heat transfer efficiency is possible to be manipulated under conditions like some connectivity, convection, and transfer applications at the center. The PVA polymer is harmful to human. Face mask and gloves should be used to protect the operator.

synthesis-graphene-nanofluids-with-controllable-flake-size

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Chemistry

Template Directed Synthesis of Plasmonic Gold Nanotubes with Tunable IR Absorbance

A nearly parallel array of pores can be produced by anodizing aluminum foils in acidic environments1, 2. Applications of anodic aluminum oxide (AAO) membranes have been under development since the 1990's and have become a common method to template the synthesis of high aspect ratio nanostructures, mostly by electrochemical growth or pore-wetting. Recently, these membranes have become commercially available in a wide range of pore sizes and densities, leading to an extensive library of functional nanostructures being synthesized from AAO membranes. These include composite nanorods, nanowires and nanotubes made of metals, inorganic materials or polymers 3-10. Nanoporous membranes have been used to synthesize nanoparticle and nanotube arrays that perform well as refractive index sensors, plasmonic biosensors, or surface enhanced Raman spectroscopy (SERS) substrates 11-16, as well as a wide range of other fields such as photo-thermal heating 17, permselective transport 18, 19, catalysis 20, microfluidics 21, and electrochemical sensing 22, 23. Here, we report a novel procedure to prepare gold nanotubes in AAO membranes. Hollow nanostructures have potential application in plasmonic and SERS sensing, and we anticipate these gold nanotubes will allow for high sensitivity and strong plasmon signals, arising from decreased material dampening 15.

Solution-suspendable gold nanotubes with controlled dimensions can be synthesized by electrochemical deposition in porous anodic aluminum oxide (AAO) membranes using a hydrophobic polymer core. Gold nanotubes and nanotube arrays hold promise for applications in plasmonic biosensing, surface-enhanced Raman spectroscopy, photo-thermal heating, ionic and molecular transport, microfluidics, catalysis and electrochemical sensing.

A nearly parallel array of pores can be produced by anodizing aluminum foils in acidic environments1, 2. Applications of anodic aluminum oxide (AAO) ...

A Simple Method for the Size Controlled Synthesis of Stable Oligomeric Clusters of Gold Nanoparticles under Ambient Conditions

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We describe a simple method for producing highly stable oligomeric clusters of gold nanoparticles via the reduction of chloroauric acid (HAuCl4) with sodium thiocyanate (NaSCN). The oligoclusters have a narrow size distribution and can be produced with a wide range of sizes and surface coats.

Reducing dilute aqueous HAuCl4 with sodium thiocyanate (NaSCN) under alkaline conditions produces 2 to 3 nm diameter nanoparticles. Stable grape-like ...

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Here, we present a protocol to synthesize and characterize Fe-doped aluminosilicate nanotubes. The materials are obtained by either sol-gel synthesis upon addition of FeCl3&#8226;6H2O to the mixture containing the Si and Al precursors or by post-synthesis ionic exchange of preformed aluminosilicate nanotubes.

The goal of the protocol is to synthesize Fe-doped aluminosilicate nanotubes of the imogolite type with the formula (OH)3Al2-xFexO3SiOH. Doping with Fe ...

Chemical Precipitation Method for the Synthesis of Nb2O5 Modified Bulk Nickel Catalysts with High Specific Surface Area

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Chemical Precipitation Method for the Synthesis of Nb2O5 Modified Bulk Nickel Catalysts with High Specific Surface Area

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We demonstrate a method for the synthesis of NixNb1-xO catalysts with sponge-like and fold-like nanostructures. By varying the Nb:Ni ratio, a series of ...

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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 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 Structure Determination of &#181;-Conotoxin PIIIA Isomers with Different Disulfide Connectivities

Peptides with a high number of cysteines are usually influenced regarding the three-dimensional structure by their disulfide connectivity. It is thus highly important to avoid undesired disulfide bond formation during peptide synthesis, because it may result in a completely different peptide structure, and consequently altered bioactivity. However, the correct formation of multiple disulfide bonds in a peptide is difficult to obtain by using standard self-folding methods such as conventional buffer oxidation protocols, because several disulfide connectivities can be formed. This protocol represents an advanced strategy required for the targeted synthesis of multiple disulfide-bridged peptides which cannot be synthesized via buffer oxidation in high quality and quantity. The study demonstrates the application of a distinct protecting group strategy for the synthesis of all possible 3-disulfide-bonded peptide isomers of &#181;-conotoxin PIIIA in a targeted way. The peptides are prepared by Fmoc-based solid phase peptide synthesis using a protecting group strategy for defined disulfide bond formation. The respective pairs of cysteines are protected with trityl (Trt), acetamidomethyl (Acm), and tert-butyl (tBu) protecting groups to make sure that during every oxidation step only the required cysteines are deprotected and linked. In addition to the targeted synthesis, a combination of several analytical methods is used to clarify the correct folding and generation of the desired peptide structures. The comparison of the different 3-disulfide-bonded isomers indicates the importance of accurate determination and knowledge of the disulfide connectivity for the calculation of the three-dimensional structure and for interpretation of the biological activity of the peptide isomers. The analytical characterization includes the exact disulfide bond elucidation via tandem mass spectrometry (MS/MS) analysis which is performed with partially reduced and alkylated derivatives of the intact peptide isomer produced by an adapted protocol. Furthermore, the peptide structures are determined using 2D nuclear magnetic resonance (NMR) experiments and the knowledge obtained from MS/MS analysis.

Synthesis and Structure Determination of &amp;#181;-Conotoxin PIIIA Isomers with Different Disulfide Connectivities

Cysteine-rich peptides fold into distinct three-dimensional structures depending on their disulfide connectivity. Targeted synthesis of individual disulfide isomers is required when buffer oxidation does not lead to the desired disulfide connectivity. The protocol deals with the selective synthesis of 3-disulfide-bonded peptides and their structural analysis using NMR and MS/MS studies.

Peptides with a high number of cysteines are usually influenced regarding the three-dimensional structure by their disulfide connectivity. It is thus ...

Preparation of Graphene-Supported Microwell Liquid Cells for In Situ Transmission Electron Microscopy

The fabrication and preparation of graphene-supported microwell liquid cells (GSMLCs) for in situ electron microscopy is presented in a stepwise protocol. The versatility of the GSMLCs is demonstrated in the context of a study about etching and growth dynamics of gold nanostructures from a HAuCl4 precursor solution. GSMLCs combine the advantages of conventional silicon- and graphene-based liquid cells by offering reproducible well depths together with facile cell manufacturing and handling of the specimen under investigation. The GSMLCs are fabricated on a single silicon substrate which drastically reduces the complexity of the manufacturing process compared to two-wafer-based liquid cell designs. Here, no bonding or alignment process steps are required. Furthermore, the enclosed liquid volume can be tailored to the respective experimental requirements by simply adjusting the thickness of a silicon nitride layer. This enables a significant reduction of window bulging in the electron microscope vacuum. Finally, a state-of-the-art quantitative evaluation of single particle tracking and dendrite formation in liquid cell experiments using only open source software is presented.

Preparation of Graphene-Supported Microwell Liquid Cells for In Situ Transmission Electron Microscopy

A protocol for preparation of graphene-supported microwell liquid cells for in situ electron microscopy of gold nanocrystals from HAuCl4 precursor solution is presented. Furthermore, an analysis routine is presented to quantify observed etching and growth dynamics.

The fabrication and preparation of graphene-supported microwell liquid cells (GSMLCs) for in situ electron microscopy is presented in a stepwise protocol. ...

Application of Voltage in Dynamic Light Scattering Particle Size Analysis

Dynamic light scattering (DLS) is a common method for characterizing the size distribution of polymers, proteins, and other nano- and microparticles. Modern instrumentation permits measurement of particle size as a function of time and/or temperature, but currently there is no simple method for performing DLS particle size distribution measurements in the presence of applied voltage. The ability to perform such measurements would be useful in the development of electroactive, stimuli-responsive polymers for applications such as sensing, soft robotics, and energy storage. Here, a technique using applied voltage coupled with DLS and a temperature ramp to observe changes in aggregation and particle size in thermoresponsive polymers with and without electroactive monomers is presented. The changes in aggregation behavior observed in these experiments were only possible through the combined application of voltage and temperature control. To obtain these results, a potentiostat was connected to a modified cuvette in order to apply voltage to a solution. Changes in polymer particle size were monitored using DLS in the presence of constant voltage. Simultaneously, current data were produced, which could be compared with particle size data, to understand the relationship between current and particle behavior. The polymer poly(N-isopropylacrylamide) (pNIPAM) served as a test polymer for this technique, as pNIPAM's response to temperature is well-studied. Changes in the lower-critical solution temperature (LCST) aggregation behavior of pNIPAM and poly(N-isopropylacrylamide)-block-poly(ferrocenylmethyl methacrylate), an electrochemically active block-copolymer, in the presence of applied voltage are observed. Understanding the mechanisms behind such changes will be important when trying to achieve reversible polymer structures in the presence of applied voltage.

Here, a protocol to apply voltage to solution during dynamic light scattering particle size measurements with the intent to explore the effect of voltage and temperature changes on polymer aggregation is presented.

Dynamic light scattering (DLS) is a common method for characterizing the size distribution of polymers, proteins, and other nano- and microparticles. ...

Synthesis of Aptamer-PEI-g-PEG Modified Gold Nanoparticles Loaded with Doxorubicin for Targeted Drug Delivery

Due to drug resistance and toxicity in healthy cells, use of doxorubicin (DOX) has been limited in clinical cancer therapy. This protocol describes the designing of poly(ethylenimine) grafted with polyethylene glycol (PEI-g-PEG) copolymer functionalized gold nanoparticles (AuNPs) with loaded aptamer (AS1411) and DOX through amide reactions. AS1411 is specifically bonded with targeted nucleolin receptors on cancer cells so that DOX targets cancer cells instead of healthy cells. First, PEG is carboxylated, then grafted to branched PEI to obtain a PEI-g-PEG copolymer, which is confirmed by 1H NMR analysis. Next, PEI-g-PEG copolymer coated gold nanoparticles (PEI-g-PEG@AuNPs) are synthesized, and DOX and AS1411 are covalently bonded to AuNPs gradually via amide reactions. The diameter of the prepared AS1411-g-DOX-g-PEI-g-PEG@AuNPs is ~39.9 nm, with a zeta potential of -29.3 mV, indicating that the nanoparticles are stable in water and cell medium. Cell cytotoxicity assays show that the newly designed DOX loaded AuNPs are able to kill cancer cells (A549). This synthesis demonstrates the delicate arrangement of PEI-g-PEG copolymers, aptamers, and DOX on AuNPs that are achieved by sequential amide reactions. Such aptamer-PEI-g-PEG functionalized AuNPs provide a promising platform for targeted drug delivery in cancer therapy.

In this protocol, doxorubicin-loaded AS1411-g-PEI-g-PEG modified gold nanoparticles are synthesized via three-step amide reactions. Then, doxorubicin is loaded and delivered to target cancer cells for cancer therapy.

Due to drug resistance and toxicity in healthy cells, use of doxorubicin (DOX) has been limited in clinical cancer therapy. This protocol describes the ...