Synthesis Methods of 5 nm Gold Nanoparticles: A Step-by-Step Approach

Learn step-by-step synthesis methods for 5 nm gold nanoparticles, including Turkevich, Brust-Schiffrin, and Seed-Mediated Growth

NNCrystal US Corporation NNCrystal US Corporation
Mar 19, 2025 - 09:47
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Synthesis Methods of 5 nm Gold Nanoparticles: A Step-by-Step Approach
5 nm gold nanoparticles

Gold nanoparticles (AuNPs) have gained significant attention in research due to their unique physical, chemical, and optical properties. Among them, 5 nm gold nanoparticles are widely used in biomedical, catalytic, and sensing applications. This article explores the most common synthesis methods, providing a step-by-step approach for obtaining high-quality 5 nm gold nanoparticles.

1. Turkevich Method (Citrate Reduction Method)

The Turkevich method is a widely used synthesis technique that employs citrate as both a reducing and stabilizing agent.

Materials Needed:

  • Gold(III) chloride trihydrate (HAuCl4·3H2O)

  • Trisodium citrate (Na3C6H5O7)

  • Deionized water

  • Glass beaker

  • Magnetic stirrer

  • Hot plate

Step-by-Step Procedure:

  1. Prepare the Gold Solution:

    • Dissolve 1 mM HAuCl4 in 100 mL of deionized water and heat the solution to 100°C while stirring continuously.

  2. Add Citrate Solution:

    • Quickly add 1% trisodium citrate solution (typically 10 mL) to the boiling gold solution.

  3. Observe Color Change:

    • The solution will turn from pale yellow to dark blue and finally to ruby red, indicating nanoparticle formation.

  4. Cool and Store:

    • Allow the solution to cool to room temperature and store it for further use.

2. Brust-Schiffrin Method (Organic Phase Synthesis)

This method is suitable for synthesizing monodisperse and stable gold nanoparticles in organic solvents.

Materials Needed:

  • Gold(III) chloride (HAuCl4)

  • Tetraoctylammonium bromide (TOAB)

  • Sodium borohydride (NaBH4)

  • Toluene

  • Deionized water

  • Magnetic stirrer

Step-by-Step Procedure:

  1. Phase Transfer of Gold Ions:

    • Dissolve HAuCl4 in water and add TOAB in toluene. Stir until the gold ions transfer to the organic phase.

  2. Reduce Gold Ions:

    • Slowly add NaBH4 solution while stirring. The solution turns dark, indicating nanoparticle formation.

  3. Purify and Store:

    • Wash the nanoparticles with ethanol and store them in an appropriate solvent for later use.

3. Seed-Mediated Growth Method

This method allows precise control over the size of 5 nm gold nanoparticles by growing them from preformed smaller seeds.

Materials Needed:

  • HAuCl4

  • Sodium citrate

  • Ascorbic acid

  • Gold seed solution (prepared separately)

  • Deionized water

  • Glass beaker

Step-by-Step Procedure:

  1. Prepare Gold Seeds:

    • Reduce HAuCl4 with sodium citrate to create small gold seeds (~2 nm).

  2. Growth Process:

    • Add HAuCl4 and ascorbic acid to the seed solution, allowing controlled growth to 5 nm size.

  3. Purification and Storage:

    • Wash and store nanoparticles for further applications.

Conclusion

Several synthesis methods are available for producing 5 nm gold nanoparticles, each offering advantages depending on the application. The Turkevich method is ideal for aqueous synthesis, the Brust-Schiffrin method is suited for organic-phase applications, and the Seed-Mediated Growth method provides precise size control. By following these step-by-step procedures, researchers can obtain high-quality gold nanoparticles for various scientific studies.