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><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&#039;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 (&amp;ge;99.9%)</td><td>Sigma-Aldrich</td><td>34860-2L-R</td><td>new, &amp;ge;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 &amp;micro;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 &amp;micro;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 (HAuCl&lt;sub&gt;4&lt;/sub&gt;) (&amp;ge;99.9%)</td><td>Sigma-Aldrich</td><td>520918-1G</td><td>preferably new or never opened, &amp;ge;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 (&amp;ge;99.8%)</td><td>Sigma-Aldrich</td><td>244511-2L</td><td>new, anhydrous, &amp;ge;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 ...

Universidad de Cartagena UDEC

Research

JoVE Journal

Chemistry

14.3K 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

Gold Nanostar Synthesis with a Silver Seed Mediated Growth Method

The physical, chemical and optical properties of nano-scale colloids depend on their material composition, size and shape 1-5. There is a great interest in using nano-colloids for photo-thermal ablation, drug delivery and many other biomedical applications 6. Gold is particularly used because of its low toxicity 7-9. A property of metal nano-colloids is that they can have a strong surface plasmon resonance 10. The peak of the surface plasmon resonance mode depends on the structure and composition of the metal nano-colloids. Since the surface plasmon resonance mode is stimulated with light there is a need to have the peak absorbance in the near infrared where biological tissue transmissivity is maximal 11, 12.
We present a method to synthesize star shaped colloidal gold, also known as star shaped nanoparticles 13-15 or nanostars 16. This method is based on a solution containing silver seeds that are used as the nucleating agent for anisotropic growth of gold colloids 17-22. Scanning electron microscopy (SEM) analysis of the resulting gold colloid showed that 70 % of the nanostructures were nanostars. The other 30 % of the particles were amorphous clusters of decahedra and rhomboids. The absorbance peak of the nanostars was detected to be in the near infrared (840 nm). Thus, our method produces gold nanostars suitable for biomedical applications, particularly for photo-thermal ablation.

We synthesized star shaped gold nanostars using a silver seed mediated growth method. The diameter of the nanostars ranges from 200 to 300 nm and the number of tips vary from 7 to 10. The nanoparticles have a broad surface plasmon resonance mode centered in the near infrared.

The physical, chemical and optical properties of nano-scale colloids depend on their material composition, size and shape 1-5. There is a great interest ...

Bioengineering

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

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

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

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

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 ...

Fabrication of Periodic Gold Nanocup Arrays Using Colloidal Lithography

Within recent years, the field of plasmonics has exploded as researchers have demonstrated exciting applications related to chemical and optical sensing in combination with new nanofabrication techniques. A plasmon is a quantum of charge density oscillation that lends nanoscale metals such as gold and silver unique optical properties. In particular, gold and silver nanoparticles exhibit localized surface plasmon resonances-collective charge density oscillations on the surface of the nanoparticle-in the visible spectrum. Here, we focus on the fabrication of periodic arrays of anisotropic plasmonic nanostructures. These half-shell (or nanocup) structures can exhibit additional unique light-bending and polarization-dependent optical properties that simple isotropic nanostructures cannot. Researchers are interested in the fabrication of periodic arrays of nanocups for a wide variety of applications such as low-cost optical devices, surface-enhanced Raman scattering, and tamper indication. We present a scalable technique based on colloidal lithography in which it is possible to easily fabricate large periodic arrays of nanocups using spin-coating and self-assembled commercially available polymeric nanospheres. Electron microscopy and optical spectroscopy from the visible to near-infrared (near-IR) was performed to confirm successful nanocup fabrication. We conclude with a demonstration of the transfer of nanocups to a flexible, conformal adhesive film.

We demonstrate the fabrication of periodic gold nanocup arrays using colloidal lithographic techniques and discuss the importance of nanoplasmonic films.

Within recent years, the field of plasmonics has exploded as researchers have demonstrated exciting applications related to chemical and optical sensing ...

Engineering

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 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 ...

Large Area Substrate-Based Nanofabrication of Controllable and Customizable Gold Nanoparticles Via Capped Dewetting

Recent scientific advances in the utilization of metallic nanoparticle for enhanced energy conversion efficiency, improved optical device performance, and high-density data storage have demonstrated the potential benefit of their use in industrial applications. These applications require precise control over nanoparticle size, spacing, and sometimes shape. These requirements have resulted in the use of time and cost intensive processing steps to produce nanoparticles, thus making the transition to industrial application unrealistic. This protocol will resolve this issue by providing a scalable and affordable method for the large-area production of nanoparticle films with improved nanoparticle control compared to the current techniques. In this article, the process will be demonstrated with gold, but other metals can also be used.

This protocol details a novel nano-manufacturing technique that can be used to make controllable and customizable nanoparticle films over large areas based on the self-assembly of dewetting of capped metal films.

Recent scientific advances in the utilization of metallic nanoparticle for enhanced energy conversion efficiency, improved optical device performance, and ...

Synthesis of Functionalized 10-nm Polymer-coated Gold Particles for Endothelium Targeting and Drug Delivery

Gold nanoparticles (AuNPs) have been used extensively in medical research due to their size, biocompatibility, and modifiable surface. Specific targeting and drug delivery are some of the applications of these AuNPs, but endothelial extracellular matrices&#39; defensive properties hamper particle uptake. To address this issue, we describe a synthesis method for ultrasmall gold nanoparticles to improve vascular delivery, with customizable functional groups and polymer lengths for further adjustments. The protocol yields 2.5 nm AuNPs that are capped with tetrakis(hydroxymethyl)phosphonium chloride (THPC). The replacement of THPC with hetero-functional polyethylene glycol (PEG) on the surface of the AuNP increases the hydrodynamic radius to 10.5 nm while providing various functional groups on the surface. The last part of the protocol includes an optional addition of a fluorophore to allow the AuNPs to be visualized under fluorescence to track nanoparticle uptake. Dialysis and lyophilization were used to purify and isolate the AuNPs. These fluorescent nanoparticles can be visualized in both in vitro and in vivo experiments due to the biocompatible PEG coating and fluorescent probes. Additionally, the size range of these nanoparticles render them an ideal candidate for probing the glycocalyx without disrupting normal vasculature function, which may lead to improved delivery and therapeutics.

We describe a method of synthesizing biocompatible 10-nm gold nanoparticles, functionalized by coating poly-ethylene glycol onto the surface. These particles can be used in vitro and in vivo for delivering therapeutics to nanoscale cellular and extracellular spaces that are difficult to access with conventional nanoparticle sizes.

Gold nanoparticles (AuNPs) have been used extensively in medical research due to their size, biocompatibility, and modifiable surface. Specific targeting ...

Aqueous Synthesis of Plasmonic Gold-Tin Alloy Nanoparticles

This protocol describes the synthesis of Au nanoparticle seeds and the subsequent formation of Au-Sn bimetallic nanoparticles. These nanoparticles have potential applications in catalysis, optoelectronics, imaging, and drug delivery. Previously, methods for producing alloy nanoparticles have been time-consuming, require complex reaction conditions, and can have inconsistent results. The outlined protocol first describes the synthesis of approximately 13 nm Au nanoparticle seeds using the Turkevich method. The protocol next describes the reduction of Sn and its incorporation into the Au seeds to generate Au-Sn alloy nanoparticles. The optical and structural characterization of these nanoparticles is described. Optically, prominent localized surface plasmon resonances (LSPRs) are apparent using UV-visible spectroscopy. Structurally, powder X-ray diffraction (XRD) reflects all particles to be less than 20 nm and shows patterns for Au, Sn, and multiple Au-Sn intermetallic phases. Spherical morphology and size distribution are obtained from transmission electron microscopy (TEM) imaging. TEM reveals that after Sn incorporation, the nanoparticles grow to approximately 15 nm in diameter.

Author Spotlight: Designing Sustainable Nanomaterials for Advancing Synthesis and Element Mixing

Here, the synthesis of gold (Au) seeds is described using the Turkevich method. These seeds are then used to synthesize gold-tin alloy (Au-Sn) nanoparticles with tunable plasmonic properties.

This protocol describes the synthesis of Au nanoparticle seeds and the subsequent formation of Au-Sn bimetallic nanoparticles. These nanoparticles have ...

Gold Nanoparticle Synthesis

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

Hydroquinone Based Synthesis of Gold Nanorods

Fabrication of Periodic Gold Nanocup Arrays Using Colloidal Lithography

Rapid Nanoprobe Signal Enhancement by In Situ Gold Nanoparticle Synthesis

Synthesis and Characterization of Amphiphilic Gold Nanoparticles

Large Area Substrate-Based Nanofabrication of Controllable and Customizable Gold Nanoparticles Via Capped Dewetting

Synthesis of Functionalized 10-nm Polymer-coated Gold Particles for Endothelium Targeting and Drug Delivery

Aqueous Synthesis of Plasmonic Gold-Tin Alloy Nanoparticles