How to Produce Spherical Gold Nanoparticles?

Spherical gold nanoparticles are advanced nanomaterials with various applications, including biological imaging, targeted drug delivery, chemical catalysis, sensors, and radiotherapy.

Gold nanoparticles can be created using chemical techniques such as hydro-thermal reduction, aerosol-assisted chemical vapor deposition, and microemulsion. They can also be made through physical processes like plasma-assisted vacuum deposition, spray pyrolysis, laser ablation, and ion implantation.

This article details how spherical gold nanoparticles are made via the vacuum deposition technique, focussing on NL50, an exclusive deposition tool designed by Nikalyte.

Spherical gold nanoparticles generated in the Nikalyte NL50. Image Credit: Nikalyte Ltd

Vacuum Deposition Method

The vacuum deposition technique is an advanced, top-down physical deposition method used to create monodisperse and pure spherical gold nanoparticles. The base material is over 99.999% pure gold disk. The source material is placed into the chamber before atmospheric gases are expelled, creating a clean vacuum setting.

Icosahedral gold nanoparticles generated in the Nikalyte NL50. Image Credit: Nikalyte Ltd

The spherical gold nanoparticles are created through a magnetron sputtering process where ions of energized gas (plasma) knock individual atoms off from the high-purity source material. These individual atoms then start to stick to one another to form small groups that slowly combine and develop into spherical gold nanoparticles.

The in-depth morphologies of spherical gold nanoparticles can be explored using high-resolution transmission electron microscopy. Compared to nanorods and nanostars-shaped nanoparticles, spherical gold nanoparticles have the lowest cytotoxicity, rendering them ideal for life sciences applications.

The size of spherical gold nanoparticles can be altered by regulating the process parameters, for instance, the magnetron power and the gas flow rate. Upon generation, the nanoparticles are taken from the generation area into the sample chamber and placed onto the substrate surface. Their final morphology relies on their size and the ratio between their surface and bulk energies.

Gold nanoparticles smaller than 10 nm take a spherical shape, while those beyond 10 nm become icosahedral. Their size is important in establishing their optoelectronic properties. Gold nanoparticles measuring less than 30 nm look red, while those measuring more than 30 nm appear blue. The high surface-area-to-volume ratio of spherical gold nanoparticles also improves their detection sensitivity.

The NL50 offers the user total process control over vacuum deposition process parameters, allowing them to customize the nanoparticle size according to the target application effortlessly.

Advantages of Vacuum-Based Method over Chemical Synthesis

The conventional methods of creating gold nanoparticles include a bottom-up chemical synthesis method. The advantage of the vacuum deposition method is that it creates remarkably pure spherical gold nanoparticles with no ligands or hydrocarbons.

By comparison, the chemically synthesized spherical gold nanoparticles are contaminated by hydrocarbons and develop agglomerates in solution, meaning that they have weak colloidal stability. The interaction between ligands and solvent molecules in the reaction medium affects nanoparticle growth, and the chemical production process uses harmful reduction agents that can be dangerous as they form undesirable products. 

Another disadvantage of chemical synthesis is that its process procedure is not easily controllable. Factors such as concentration, pH, and temperature must be strictly monitored to attain the desired monodisperse gold nanoparticles. Vacuum deposition of gold nanoparticles avoids these disadvantages.

Image Credit: Nikalyte Ltd

The vacuum deposition method's line-of-sight deposition is a unique advantage that offers a consistent coating of planar and textured substrates with spherical gold nanoparticles. The evenly coated substrates enable unparalleled ppb-level detection sensitivity. These substrates can be employed in surface-enhanced Raman sensors (SERS).

The NL50 developed by Nikalyte is a unique, advanced nanoparticle deposition vacuum chamber where bare spherical gold nanoparticles can be deposited directly on various custom substrates.

The NL50 provides direct control over the density and size of nanoparticles. One layer of porous nanospheres can be deposited within just 30 minutes. Users can select any substrate, such as plastic, glass, or filter paper.

References

  1. Li et al. J. Wuhan Univ. Technol.-Mat. Sci. Edit. 29, 651–655 (2014). https://doi.org/10.1007/s11595-014-0973-9
  2. Bansal et al. Nanoscale Advances 2, 3764 (2020). https://doi.org/10.1039/D0NA00472C
  3. Rahimi, and M. Doostmohammadi, “Nanoparticle Synthesis, Applications, and Toxicity”, in Applications of Nanobiotechnology. London, United Kingdom: IntechOpen, (2019). https://www.intechopen.com/chapters/69099  DOI: 10.5772/intechopen.87973
  4. M. H. Hussain et al. Nanoscale Res Lett 15, 140 (2020). https://doi.org/10.11

This information has been sourced, reviewed and adapted from materials provided by Nikalyte Ltd.

For more information on this source, please visit Nikalyte Ltd.

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