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Gold Nanoparticle Synthesis

Published: July 10th, 2021



1Department of Electrical and Computer Engineering, University of California, Davis, 2Department of Computer Sciences and Electrical Engineering, Marshall University, 3Department of Materials Science and Engineering, 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.

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.

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

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Chemical Amounts:
​NOTE: To obtain the appropriate chemical amounts for the nanoparticle synthesis, take the initial amounts found on the "Nanoparticle Synthesis" sheet (on the 2nd page of the supporting information from the Osterloh research article12), and multiply the amount of all doses by 3, with some slight modifications. Table 1 shows the chemical amounts that are needed for the injection solution, boiling solution, washing/purification .......

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Figure 1 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.......

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Performing the gold nanoparticle synthesis protocol as presented above should produce gold nanoparticles with ~12 nm diameter and fairly high monodispersity (± 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.......

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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 & 203665) and the Semiconductor Research Corporation (2836).


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

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