The authors would like to thank Frank Osterloh for assistance with nanoparticle synthesis methods. The authors would like to acknowledge financial support from the National Science Foundation (1807555 &#38; 203665) and the Semiconductor Research Corporation (2836).

<ol>
	<li>Sperling, R. A., Gil, P. R., Zhang, F., Zanella, M., Parak, W. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biological+applications+of+gold+nanoparticles.">Biological applications of gold nanoparticles.</a> Chemical Society Reviews. 37 (9), 1896-1908 (2008).</li><li>Dreaden, E. C., Alkilany, A. M., Huang, X., Murphy, C. J., El-Sayed, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+golden+age:+Gold+nanoparticles+for+biomedicine.">The golden age: Gold nanoparticles for biomedicine.</a> Chemical Society Reviews. 41 (7), 2740-2779 (2012).</li><li>Daniel, M. -. C., Astruc, D. <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:+Assembly,+Supramolecular+Chemistry,+Quantum-Size-Related+Properties,+and+Applications+toward+Biology,+Catalysis,+and+Nanotechnology.">Gold Nanoparticles: Assembly, Supramolecular Chemistry, Quantum-Size-Related Properties, and Applications toward Biology, Catalysis, and Nanotechnology.</a> Chemical Reviews. 104 (1), 293-346 (2004).</li><li>McCold, C. 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=Ligand+exchange+based+molecular+doping+in+2D+hybrid+molecule-nanoparticle+arrays:+length+determines+exchange+efficiency+and+conductance.">Ligand exchange based molecular doping in 2D hybrid molecule-nanoparticle arrays: length determines exchange efficiency and conductance.</a> Molecular Systems Design &amp; Engineering. 2 (4), 440-448 (2017).</li><li>Faraday, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Experimental+Relations+of+Gold+(and+other+Metals)+to+Light.">Experimental Relations of Gold (and other Metals) to Light.</a> Philosophical Transactions of the Royal Society of London. 147, 145-181 (1857).</li><li>Turkevich, J., Stevenson, P. C., Hillier, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+study+of+the+nucleation+and+growth+processes+in+the+synthesis+of+colloidal+gold.">A study of the nucleation and growth processes in the synthesis of colloidal gold.</a> Discussions of the Faraday Society. 11, 55-75 (1951).</li><li>Frens, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Controlled+Nucleation+for+the+Regulation+of+the+Particle+Size+in+Monodisperse+Gold+Suspensions.">Controlled Nucleation for the Regulation of the Particle Size in Monodisperse Gold Suspensions.</a> Nature Physical Science. 241 (105), 20-22 (1973).</li><li>Kimling, J., Maier, M., Okenve, B., Kotaidis, V., Ballot, H., Plech, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Turkevich+method+for+gold+nanoparticle+synthesis+revisited.">Turkevich method for gold nanoparticle synthesis revisited.</a> Journal of Physical Chemistry B. 110 (32), 15700-15707 (2006).</li><li>Wilcoxon, J. P., Williamson, R. L., Baughman, R. <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+gold+colloids+formed+in+inverse+micelles.">Optical properties of gold colloids formed in inverse micelles.</a> The Journal of Chemical Physics. 98 (12), 9933-9950 (1993).</li><li>Brust, M., Walker, M., Bethell, D., Schiffrin, D. J., Whyman, R. <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+thiol-derivatised+gold+nanoparticles+in+a+two-phase+liquid-liquid+system.">Synthesis of thiol-derivatised gold nanoparticles in a two-phase liquid-liquid system.</a> Journal of the Chemical Society, Chemical Communications. (7), 801-802 (1994).</li><li>Zhao, P., Li, N., Astruc, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=State+of+the+art+in+gold+nanoparticle+synthesis.">State of the art in gold nanoparticle synthesis.</a> Coordination Chemistry Reviews. 257 (3-4), 638-665 (2013).</li><li>Hiramatsu, H., Osterloh, F. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Simple+Large-Scale+Synthesis+of+Nearly+Monodisperse+Gold+and+Silver+Nanoparticles+with+Adjustable+Sizes+and+with+Exchangeable+Surfactants.">A Simple Large-Scale Synthesis of Nearly Monodisperse Gold and Silver Nanoparticles with Adjustable Sizes and with Exchangeable Surfactants.</a> Chemistry of Materials. 16 (13), 2509-2511 (2004).</li><li>Voorhees, P. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Theory+of+Ostwald+Ripening.">The Theory of Ostwald Ripening.</a> Journal of Statistical Physics. 38 (1-2), 231-252 (1985).</li><li>Lifshitz, I. M., Slyozov, V. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+kinetics+of+precipitation+from+supersaturated+solid+solutions.">The kinetics of precipitation from supersaturated solid solutions.</a> Journal of Physics and Chemistry of Solids. 19 (1-2), 35-50 (1961).</li><li>Haiss, W., Thanh, N. T. K., Aveyard, J., Fernig, D. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Determination+of+Size+and+Concentration+of+Gold+Nanoparticles+from+UV-Vis+Spectra.">Determination of Size and Concentration of Gold Nanoparticles from UV-Vis Spectra.</a> Analytical Chemistry. 79 (11), 4215-4221 (2007).</li><li>McCold, C. E., Fu, Q., Howe, J. Y., Hihath, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Conductance+based+characterization+of+structure+and+hopping+site+density+in+2D+molecule-nanoparticle+arrays.">Conductance based characterization of structure and hopping site density in 2D molecule-nanoparticle arrays.</a> Nanoscale. 7 (36), 14937-14945 (2015).</li><li>Hihath, S., McCold, C., March, K., Hihath, J. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+of+Ligand+Exchange+in+2D+Hybrid+Molecule-nanoparticle+Superlattices.">Characterization of Ligand Exchange in 2D Hybrid Molecule-nanoparticle Superlattices.</a> Microscopy and Microanalysis. 24 (1), 1722-1723 (2018).</li><li>McCold, C. 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=Molecular+Control+of+Charge+Carrier+and+Seebeck+Coefficient+in+Hybrid+Two-Dimensional+Nanoparticle+Superlattices.">Molecular Control of Charge Carrier and Seebeck Coefficient in Hybrid Two-Dimensional Nanoparticle Superlattices.</a> The Journal of Physical Chemistry C. 124 (1), 17-24 (2020).</li></ol>

The authors have nothing to disclose.

Performing the gold nanoparticle synthesis protocol as presented above should produce gold nanoparticles with ~12 nm diameter and fairly high monodispersity (&#177; 2 nm). However, there are some critical steps and process parameters that can be adjusted to potentially change the size/diameter and monodispersity/polydispersity of the gold nanoparticles. For example, after injecting the precursor solution into the reaction vessel and allowing the tetrachloroauric acid, oleylamine, and toluene solution to boil for two hour...

Gold nanoparticles are an interesting and useful class of nanomaterials that are the subject of many research studies and applications; such as biology1, medicine2, nanotechnology3, and electronic devices4. Scientific research on gold nanoparticles dates back to as early as 1857, when Michael Faraday performed foundational studies on the synthesis and properties of gold nanoparticles5. The two primary "bottom up" techniques for synthesizing gold nanoparticles are the citrate reduction method6,7,8 and the organic two-phase synthesis method9,10. The "Turkevich" citrate reduction method produces fairly monodisperse gold nanoparticles under 20 nm in diameter, but the polydispersity increases for gold nanoparticles above 20 nm in diameter; whereas the "Brust-Schiffrin" two-phase method uses sulfur/thiol ligand-stabilization to produce gold nanoparticles up to ~10 nm in diameter11. Gold nanoparticle solutions that are pre-synthesized using these methods are commercially available. For applications where large volumes, high monodispersity, and large diameters of gold nanoparticles are not necessary, it may be sufficient to purchase and use these pre-synthesized gold nanoparticles from suppliers. However, gold nanoparticles that are stored in solution, such as many of those that are commercially available, may degrade over time as nanoparticles begin to agglomerate and form clusters. Alternatively, for large-scale applications, long-term projects in which gold nanoparticles need to be used frequently or over a long period of time, or in which there are more stringent requirements for the monodispersity and size of the gold nanoparticles, it may be desirable to perform the gold nanoparticle synthesis oneself. By performing the gold nanoparticle synthesis process, one has the opportunity to potentially control various synthesis parameters such as the amount of gold nanoparticles that are produced, the diameter of the gold nanoparticles, the monodispersity of the gold nanoparticles, and the molecules used as the capping ligands. Furthermore, such gold nanoparticles can be stored as solid pellets in a dry environment, helping to preserve the gold nanoparticles so that they can be used at a later time, up to a year later, with minimal degradation in quality. There is also the potential for cost savings and the reduction of waste by fabricating gold nanoparticles in larger volumes and then storing them in a dry state so that they last longer. Overall, synthesizing gold nanoparticles oneself provides compelling advantages that may not be feasible with commercially available gold nanoparticles.
In order to realize the many advantages that are possible with gold nanoparticle synthesis, a process is presented herein for synthesizing gold nanoparticles. The gold nanoparticle synthesis process that is described is a modified version of a process that was developed by Hiramatsu and Osterloh12. Gold nanoparticles are typically synthesized with a diameter of ~12 nm using this synthesis process. The primary chemical reagents that are used to perform the gold nanoparticle synthesis process are tetrachloroauric acid (HAuCl4), oleylamine, and toluene. A nitrogen glovebox is used to provide an inert dry environment for the gold nanoparticle synthesis process, because tetrachloroauric acid is sensitive to water/humidity. The gold nanoparticles are encapsulated with oleylamine ligand molecules to prevent the gold nanoparticles from agglomerating in solution. At the end of the synthesis process, the gold nanoparticles are dried out in a vacuum environment so that they can be stored and preserved in a dry state for later use, up to one year later. When the gold nanoparticles are ready to be used, they can be resuspended into solution in organic solvents such as toluene.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>50 mL Conical Centrifuge Tubes with Plastic Caps (Quantity: 12)</td>
			<td>Ted Pella, Inc.</td>
			<td>12942</td>
			<td>used for cleaning/storing gold nanoparticle solution/precipitate (it&#39;s best to use 12 tubes, to allow the gold nanoparticles from the synthesis process to last up to one year (e.g., 1 tube per month))</td>
		</tr>
		<tr>
			<td>Acetone</td>
			<td>Sigma-Aldrich</td>
			<td>270725-2L</td>
			<td>solvent for cleaning glassware/tubes</td>
		</tr>
		<tr>
			<td>Acid Wet Bench</td>
			<td>N/A</td>
			<td>N/A</td>
			<td>for cleaning chemical reaction glassware/supplies with gold etchant solution (part of wet chemical lab facilities)</td>
		</tr>
		<tr>
			<td>Aluminum Foil</td>
			<td>Reynolds</td>
			<td>B08K3S7NG1</td>
			<td>for covering glassware after cleaning it to keep it clean</td>
		</tr>
		<tr>
			<td>Burette Clamps</td>
			<td>Fisher Scientific</td>
			<td>05-769-20</td>
			<td>for holding the condenser tube and reaction vessel during the synthesis process (located in the nitrogen glove box)</td>
		</tr>
		<tr>
			<td>Centrifuge (with 50 mL Conical Centrifuge Tube Rotor/Adapter)</td>
			<td>ELMI</td>
			<td>CM-7S</td>
			<td>for spinning the gold nanoparticles in solution and precipitating/collecting them at the bottom of the 50 mL conical centrifuge tubes</td>
		</tr>
		<tr>
			<td>DI Water</td>
			<td>Millipore</td>
			<td>Milli-Q Direct</td>
			<td>deionized water</td>
		</tr>
		<tr>
			<td>Fume Hood</td>
			<td>N/A</td>
			<td>N/A</td>
			<td>for cleaning laboratory glassware and supplies with solvents (part of wet chemical lab facilities)</td>
		</tr>
		<tr>
			<td>Glass Beaker (600 mL)</td>
			<td>Ted Pella, Inc.</td>
			<td>17327</td>
			<td>for holding reaction vessel, condenser tube, glass pipette, and magnetic stir bar during cleaning with gold etchant and then with water</td>
		</tr>
		<tr>
			<td>Glass Beakers (400 mL) (Quantity: 2)</td>
			<td>Ted Pella, Inc.</td>
			<td>17309</td>
			<td>for measuring toluene and gold etchant</td>
		</tr>
		<tr>
			<td>Glass Graduated Cylinder (5 mL)</td>
			<td>Fisher Scientific</td>
			<td>08-550A</td>
			<td>for measuring toluene and oleylamine for injection</td>
		</tr>
		<tr>
			<td>Glass Graduated Pipette (10 mL)</td>
			<td>Fisher Scientific</td>
			<td>13-690-126</td>
			<td>used with the rubber bulb with valves to inject the gold nanoparticle precursor solution into the reaction vessel</td>
		</tr>
		<tr>
			<td>Gold Etchant TFA</td>
			<td>Sigma-Aldrich</td>
			<td>651818-500ML</td>
			<td>(with potassium iodide) for cleaning reaction vessel, condenser tube, magnetic stir bar, glass pipette [alternatively, use Aqua Regia]</td>
		</tr>
		<tr>
			<td>Isopropanol</td>
			<td>Sigma-Aldrich</td>
			<td>34863-2L</td>
			<td>solvent for cleaning glassware/tubes</td>
		</tr>
		<tr>
			<td>Liebig Condenser Tube (~500 mm) (24/40)</td>
			<td>Fisher Scientific</td>
			<td>07-721C</td>
			<td>condenser tube, attaches to glass reaction vessel</td>
		</tr>
		<tr>
			<td>Magnetic Stirring Bar</td>
			<td>Fisher Scientific</td>
			<td>14-513-51</td>
			<td>for stirring reaction solution during the synthesis process</td>
		</tr>
		<tr>
			<td>Methanol (&#8805;99.9%)</td>
			<td>Sigma-Aldrich</td>
			<td>34860-2L-R</td>
			<td>new, &#8805;99.9% purity (for washing gold nanoparticles after synthesis)</td>
		</tr>
		<tr>
			<td>Microbalance (mg resolution)</td>
			<td>Accuris Instruments</td>
			<td>W3200-120</td>
			<td>for weighing tetrachloroauric acid powder (located in the nitrogen glove box)</td>
		</tr>
		<tr>
			<td>Micropipette (1000 &#181;L)</td>
			<td>Fisher Scientific</td>
			<td>FBE01000</td>
			<td>for measuring and dispensing liquid chemicals such as oleylamine and toluene (if using micropipette instead of graduated cylinder for measurement)</td>
		</tr>
		<tr>
			<td>Micropipette Tips (1000 &#181;L)</td>
			<td>USA Scientific</td>
			<td>1111-2831</td>
			<td>for measuring and dispensing liquid chemicals such as oleylamine and toluene (if using micropipette instead of graduated cylinder for measurement)</td>
		</tr>
		<tr>
			<td>Nitrile Gloves</td>
			<td>Ted Pella, Inc.</td>
			<td>81853</td>
			<td>personal protective equipment (PPE), for protection, and for keeping nitrogren glove box gloves clean</td>
		</tr>
		<tr>
			<td>Nitrogen Glove Box</td>
			<td>M. Braun</td>
			<td>LABstar pro</td>
			<td>for performing gold nanoparticle synthesis in a dry and inert environment</td>
		</tr>
		<tr>
			<td>Non-Aqueous 20 mL Glass Vials with PTFE-Lined Caps (Quantity: 2)</td>
			<td>Fisher Scientific</td>
			<td>03-375-25</td>
			<td>for weighing tetrachloroauric acid powder and mixing with oleylamine and toluene to make injection solution</td>
		</tr>
		<tr>
			<td>Oleylamine (Technical Grade, 70%)</td>
			<td>Sigma-Aldrich</td>
			<td>O7805-100G</td>
			<td>technical grade, 70%, preferably new, stored in the nitrogen glove box</td>
		</tr>
		<tr>
			<td>Parafilm M Sealing Film (2 in. x 250 ft)</td>
			<td>Sigma-Aldrich</td>
			<td>P7543</td>
			<td>for sealing the gold nanoparticles in the 50 mL centrifuge tubes after the synthesis process is over</td>
		</tr>
		<tr>
			<td>Round Bottom Flask (250 mL) (24/40)</td>
			<td>Wilmad-LabGlass</td>
			<td>LG-7291-234</td>
			<td>glass reaction vessel, attaches to condenser tube</td>
		</tr>
		<tr>
			<td>Rubber Bulb with Valves (Rubber Bulb-Type Safety Pipet Filler)</td>
			<td>Fisher Scientific</td>
			<td>13-681-50</td>
			<td>used with the long graduated glass pipette to inject the gold nanoparticle precursor solution into the reaction vessel</td>
		</tr>
		<tr>
			<td>Rubber Hoses (PVC Tubes) (Quantity: 2)</td>
			<td>Fisher Scientific</td>
			<td>14-169-7D</td>
			<td>for connecting the condenser tube to water inlet/outlet ports</td>
		</tr>
		<tr>
			<td>Stainless Steel Spatula</td>
			<td>Ted Pella, Inc.</td>
			<td>13590-1</td>
			<td>for scooping tetrachloroauric acid powder from small container</td>
		</tr>
		<tr>
			<td>Stand (Base with Rod)</td>
			<td>Fisher Scientific</td>
			<td>12-000-102</td>
			<td>for holding the condenser tube and reaction vessel during the synthesis process (located in the nitrogen glove box)</td>
		</tr>
		<tr>
			<td>Stirring Heating Mantle (250 mL)</td>
			<td>Fisher Scientific</td>
			<td>NC1089133</td>
			<td>for holding and supporting reaction vessel sphere, while heating with magnetic stirrer rotating the magnetic stirrer bar</td>
		</tr>
		<tr>
			<td>Tetrachloroauric(III) Acid (HAuCl4) (&#8805;99.9%)</td>
			<td>Sigma-Aldrich</td>
			<td>520918-1G</td>
			<td>preferably new or never opened, &#8805;99.9% purity, stored in fridge, then opened only in the nitrogen glove box, never exposed to air/water/humidity</td>
		</tr>
		<tr>
			<td>Texwipes / Kimwipes / Cleanroom Wipes</td>
			<td>Texwipe</td>
			<td>TX8939</td>
			<td>for miscellaneous cleaning and surface protection</td>
		</tr>
		<tr>
			<td>Toluene (&#8805;99.8%)</td>
			<td>Sigma-Aldrich</td>
			<td>244511-2L</td>
			<td>new, anhydrous, &#8805;99.8% purity</td>
		</tr>
		<tr>
			<td>Tweezers</td>
			<td>Ted Pella, Inc.</td>
			<td>5371-7TI</td>
			<td>for poking small holes in aluminum foil, and for removing Parafilm</td>
		</tr>
		<tr>
			<td>Vortexer</td>
			<td>Cole-Parmer</td>
			<td>EW-04750-51</td>
			<td>for vortexing the gold nanoparticles in toluene in 50 mL conical centrifuge tubes to resuspend the gold nanoparticles into the toluene solution</td>
		</tr>
	</tbody>
</table>

gold nanoparticle synthesis

Gold nanoparticles (Au nanoparticles) that are ~12 nm in diameter were synthesized by rapidly injecting a solution of 150 mg (0.15 mmol) of tetrachloroauric acid in 3.0 g (3.7 mmol, 3.6 mL) of oleylamine (technical grade) and 3.0 mL of toluene into a boiling solution of 5.1 g (6.4 mmol, 8.7 mL) of oleylamine in 147 mL of toluene. While boiling and mixing the reaction solution for 2 hours, the color of the reaction mixture changed from clear, to light yellow, to light pink, and then slowly to dark red. The heat was then turned off, and the solution was allowed to gradually cool down to room temperature for 1 hour. The gold nanoparticles were then collected and separated from the solution using a centrifuge and washed three times; by vortexing and dispersing the gold nanoparticles in 10 mL portions of toluene, and then precipitating the gold nanoparticles by adding 40 mL portions of methanol and spinning them in a centrifuge. The solution was then decanted to remove any remaining byproducts and unreacted starting materials. Drying the gold nanoparticles in a vacuum environment produced a solid black pellet; which could be stored for long periods of time (up to one year) for later use, and then redissolved in organic solvents such as toluene.

Figure 1&#160;shows how the gold nanoparticle synthesis chemical reaction mixture solution (tetrachloroauric acid, oleylamine, and toluene) should gradually change color over the course of several minutes as it initially boils in the reaction vessel; from clear, to light yellow (left image), to light pink (center image), to light red (right image). The changing color of the solution is an indication of the changing size of the gold nanoparticles as they begin to nucleate and grow larger over...

Watch this Scientific Journal Video about Gold Nanoparticle Synthesis at JoVE.com

Gold Nanoparticle Synthesis

A protocol for synthesizing ~12 nm diameter gold nanoparticles (Au nanoparticles) in an organic solvent is presented. The gold nanoparticles are capped with oleylamine ligands to prevent agglomeration. The gold nanoparticles are soluble in organic solvents such as toluene.

Gold nanoparticles (Au nanoparticles) that are ~12 nm in diameter were synthesized by rapidly injecting a solution of 150 mg (0.15 mmol) of ...

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14.1K Views.  University of California, Davis. A protocol for synthesizing ~12 nm diameter gold nanoparticles (Au nanoparticles) in an organic solvent is presented. The gold nanoparticles are capped with oleylamine ligands to prevent agglomeration. The gold nanoparticles are soluble in organic solvents such as toluene.

Video: Gold Nanoparticle Synthesis

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) ...

Synthesis and Catalytic Performance of Gold Intercalated in the Walls of Mesoporous Silica

As a promising catalytically active nano reactor, gold nanoparticles intercalated in mesoporous silica (GMS) were successfully synthesized and properties of the materials were investigated. We used a one pot sol-gel approach to intercalate gold nano particles in the walls of mesoporous silica. To start with the synthesis, P123 was used as template to form micelles. Then TESPTS was used as a surface modification agent to intercalate gold nano particles. Following this process, TEOS was added in as a silica source which underwent a polymerization process in acid environment. After hydrothermal processing and calcination, the final product was acquired. Several techniques were utilized to characterize the porosity, morphology and structure of the gold intercalated mesoporous silica. The results showed a stable structure of mesoporous silica after gold intercalation. Through the oxidation of benzyl alcohol as a benchmark reaction, the GMS materials showed high selectivity and recyclability.

Here, we present a protocol with a sol-gel process to synthesize gold intercalated in the walls of mesoporous materials (GMS), which is confirmed to possess a mesoporous matrix with gold intercalated in the walls imparting great stability and recyclability.

As a promising catalytically active nano reactor, gold nanoparticles intercalated in mesoporous silica (GMS) were successfully synthesized and properties ...

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

Reducing dilute aqueous HAuCl4 with sodium thiocyanate (NaSCN) under alkaline conditions produces 2 to 3 nm diameter nanoparticles. Stable grape-like oligomeric clusters of these yellow nanoparticles of narrow size distribution are synthesized under ambient conditions via two methods. The delay-time method controls the number of subunits in the oligoclusters by varying the time between the addition of HAuCl4 to alkaline solution and the subsequent addition of reducing agent, NaSCN. The yellow oligoclusters produced range in size from ~3 to ~25 nm. This size range can be further extended by an add-on method utilizing hydroxylated gold chloride (Na+[Au(OH4-x)Clx]-) to auto-catalytically increase the number of subunits in the as-synthesized oligocluster nanoparticles, providing a total range of 3 nm to 70 nm. The crude oligocluster preparations display narrow size distributions and do not require further fractionation for most purposes. The oligoclusters formed can be concentrated &#62;300 fold without aggregation and the crude reaction mixtures remain stable for weeks without further processing. Because these oligomeric clusters can be concentrated before derivatization they allow expensive derivatizing agents to be used economically. In addition, we present two models by which predictions of particle size can be made with great accuracy.

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 ...

Hydroquinone Based Synthesis of Gold Nanorods

Gold nanorods are an important kind of nanoparticles characterized by peculiar plasmonic properties. Despite their widespread use in nanotechnology, the synthetic methods for the preparation of gold nanorods are still not fully optimized. In this paper we describe a new, highly efficient, two-step protocol based on the use of hydroquinone as a mild reducing agent. Our approach allows the preparation of nanorods with a good control of size and aspect ratio (AR) simply by varying the amount of hexadecyl trimethylammonium bromide (CTAB) and silver ions (Ag+) present in the "growth solution". By using this method, it is possible to markedly reduce the amount of CTAB, an expensive and cytotoxic reagent, necessary to obtain the elongated shape. Gold nanorods with an aspect ratio of about 3 can be obtained in the presence of just 50 mM of CTAB (versus 100 mM used in the standard protocol based on the use of ascorbic acid), while shorter gold nanorods are obtained using a concentration as low as 10 mM.

This paper describes a protocol for the synthesis of gold nanorods, based on the use of hydroquinone as reducing agent, plus the different mechanisms for controlling their size and aspect ratio.

Gold nanorods are an important kind of nanoparticles characterized by peculiar plasmonic properties. Despite their widespread use in nanotechnology, the ...

Synthesis and Testing of Supported Pt-Cu Solid Solution Nanoparticle Catalysts for Propane Dehydrogenation

A convenient method for the synthesis of bimetallic Pt-Cu catalysts and performance tests for propane dehydrogenation and characterization are demonstrated here. The catalyst forms a substitutional solid solution structure, with a small and uniform particle size around 2 nm. This is realized by careful control over the impregnation, calcination, and reduction steps during catalyst preparation and is identified by advanced in situ synchrotron techniques. The catalyst propane dehydrogenation performance continuously improves with increasing Cu:Pt atomic ratio.

A convenient method for the synthesis of 2 nm supported bimetallic nanoparticle Pt-Cu catalysts for propane dehydrogenation is reported here. In situ synchrotron X-ray techniques allow for the determination of the catalyst structure, which is typically unobtainable using laboratory instruments.

A convenient method for the synthesis of bimetallic Pt-Cu catalysts and performance tests for propane dehydrogenation and characterization are ...

Liquid-cell Transmission Electron Microscopy for Tracking Self-assembly of Nanoparticles

Drying a nanoparticle dispersion is a versatile way to create self-assembled structures of nanoparticles, but the mechanism of this process is not fully understood. We have traced the trajectories of individual nanoparticles using liquid-cell transmission electron microscopy (TEM) to investigate the mechanism of the assembly process. Herein, we present the protocols used for liquid-cell TEM studies of the self-assembly mechanism. First, we introduce the detailed synthetic protocols used to produce uniformly sized platinum and lead selenide nanoparticles. Next, we present the microfabrication processes used to produce liquid cells with silicon nitride or silicon windows and then describe the loading and imaging procedures of the liquid-cell TEM technique. Several notes are included to provide helpful tips for the entire process, including how to manage the fragile cell windows. The individual motions of nanoparticles tracked by liquid-cell TEM revealed that changes in the solvent boundaries caused by evaporation affected the self-assembly process of nanoparticles. The solvent boundaries drove nanoparticles to primarily form amorphous aggregates, followed by flattening of the aggregates to produce a 2-dimensional (2D) self-assembled structure. These behaviors are also observed for different nanoparticle types and different liquid-cell compositions.

Here we introduce experimental protocols for the real-time observation of a self-assembly process using liquid-cell transmission electron microscopy.

Drying a nanoparticle dispersion is a versatile way to create self-assembled structures of nanoparticles, but the mechanism of this process is not fully ...

Rapid Nanoprobe Signal Enhancement by In Situ Gold Nanoparticle Synthesis

The use of nanoprobes such as gold, silver, silica or iron-oxide nanoparticles as detection reagents in bioanalytical assays can enable high sensitivity and convenient colorimetric readout. However, high densities of nanoparticles are typically needed for detection. The available synthesis-based enhancement protocols are either limited to gold and silver nanoparticles or rely on precise enzymatic control and optimization. Here, we present a protocol to enhance the colorimetric readout of gold, silver, silica, and iron oxide nanoprobes. It was observed that the colorimetric signal can be improved by up to a 10000-fold factor. The basis for such signal enhancement strategies is the chemical reduction of Au3+ to Au0. There are several chemical reactions that enable the reduction of Au3+ to Au0. In the protocol, Good&#39;s buffers and H2O2 are used and it is possible to favor the deposition of Au0 onto the surface of existing nanoprobes, in detriment of the formation of new gold nanoparticles. The protocol consists of the incubation of the microarray with a solution consisting of chloroauric acid and H2O2 in 2-(N-morpholino)ethanesulfonic acid pH 6 buffer following the nanoprobe-based detection assay. The enhancement solution can be applied to paper and glass-based sensors. Moreover, it can be used in commercially available immunoassays as demonstrated by the application of the method to a commercial allergen microarray. The signal development requires less than 5 min of incubation with the enhancement solution and the readout can be assessed by naked eye or low-end image acquisition devices such as a table-top scanner or a digital camera.

Rapid Nanoprobe Signal Enhancement by In Situ Gold Nanoparticle Synthesis

In this work, a protocol for signal enhancement of nanoprobe-based biosensing is presented. The protocol is based on the reduction of chloroauric acid onto the surface of existing nanoprobes that consist of gold, silver, silica or iron-oxide nanoparticles.

The use of nanoprobes such as gold, silver, silica or iron-oxide nanoparticles as detection reagents in bioanalytical assays can enable high sensitivity ...

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 ...

Gold Nanoparticle Modified Carbon Fiber Microelectrodes for Enhanced Neurochemical Detection

For over 30 years, carbon-fiber microelectrodes (CFMEs) have been the standard for neurotransmitter detection. Generally, carbon fibers are aspirated into glass capillaries, pulled to a fine taper, and then sealed using an epoxy to create electrode materials that are used for fast scan cyclic voltammetry testing. The use of bare CFMEs has several limitations, though. First and foremost, the carbon fiber contains mostly basal plane carbon, which has a relatively low surface area and yields lower sensitivities than other nanomaterials. Furthermore, the graphitic carbon is limited by its temporal resolution, and its relatively low conductivity. Lastly, neurochemicals and macromolecules have been known to foul at the surface of carbon electrodes where they form non-conductive polymers that block further neurotransmitter adsorption. For this study, we modify CFMEs with gold nanoparticles to enhance neurochemical testing with fast scan cyclic voltammetry. Au3+ was electrodeposited or dipcoated from a colloidal solution onto the surface of CFMEs. Since gold is a stable and relatively inert metal, it is an ideal electrode material for analytical measurements of neurochemicals. Gold nanoparticle modified (AuNP-CFMEs) had a stability to dopamine response for over 4 h. Moreover, AuNP-CFMEs exhibit an increased sensitivity (higher peak oxidative current of the cyclic voltammograms) and faster electron transfer kinetics (lower &#916;EP or peak separation) than bare unmodified CFMEs. The development of AuNP-CFMEs provides the creation of novel electrochemical sensors for detecting fast changes in dopamine concentration and other neurochemicals at lower limits of detection. This work has vast applications for the enhancement of neurochemical measurements. The generation of gold nanoparticle modified CFMEs will be vitally important for the development of novel electrode sensors to detect neurotransmitters in vivo in rodent and other models to study neurochemical effects of drug abuse, depression, stroke, ischemia, and other behavioral and disease states.

In this study, we modify carbon-fiber microelectrodes with gold nanoparticles to enhance the sensitivity of neurotransmitter detection.

For over 30 years, carbon-fiber microelectrodes (CFMEs) have been the standard for neurotransmitter detection. Generally, carbon fibers are aspirated into ...