The Modern Applications of Gold Nanoparticles

The use of gold nanoparticles dates back centuries due to the vibrant colors they produce while interacting with natural light. Progress in science and technology has uncovered their outstanding qualities and multifunctionality and expanded the range of high-end technologies to which they can be applied.

Silver (left), copper (middle) and gold (right) nanoparticles deposited on filter paper using the Nikalyte NL50 nanoparticle deposition system. Image Credit: Nikalyte Ltd.

This article briefly describes the main characteristics and current uses of gold nanoparticles.

Key Properties

Optoelectronic Properties

The multifunctionality of gold nanoparticles results from the superior blend of their optical and electronic properties governed by their shape, size, morphology, and surface chemistry. 

Surface plasmons are resonant oscillations produced when the free electrons in gold nanoparticles interact with the oscillating electronic field of light rays. Gold nanoparticles as small as 30 nm result in surface plasmons that reflect red light, giving the gold nanoparticles a red appearance.

When the particle size increases, the absorption wavelength related to surface plasmons shifts to longer wavelengths, absorbing red light and making gold nanoparticles appear blue due to blue light being reflected.

Chemical Properties

The surface-to-volume ratio of gold nanoparticles is high, so their surface has more free bonds to bind to target analytes. Raman spectroscopy takes advantage of this enhanced detection sensitivity of spherical gold nanoparticles.

Unlike chemical production, vacuum deposition techniques yield pure gold nanoparticles devoid of ligands and hydrocarbons. Gold nanoparticles created chemically, however, are clumped together in a solution and polluted with hydrocarbons.

Gold nanoparticles are chemically benign and have excellent biocompatibility, minimal toxicity, and good oxidation resistance. They also undergo surface modification by forming stable chemical bonds with S- and N-containing groups and attaching them to a range of organic ligands.

Physical Properties

Gold atoms have a high atomic number, so gold nanoparticles have a high X-Ray absorption coefficient. They also have localized surface plasmon resonance (LSPR), which means that they are helpful when it comes to detecting and treating tumors while limiting X-Ray exposure to healthy tissues.

Gold nanoparticles also have a high molar absorption coefficient, so they can accurately detect nanomole levels in calorimetric analysis, surpassing traditional calorimetric methods. They contain more radioactive atoms with the potential to produce β-particles. The high energy linked to β-emission can destroy tumor tissues and cells.

Applications

The following are some of the primary uses for gold nanoparticles:

Biomedical and Lifesciences

Gold nanoparticles cater to several biomedical applications, including cancer therapy and diagnosis. Chemiresistor sensors based on functionalized gold nanoparticles are employed for the cost-effective and non-invasive diagnosis of biomarkers in lung cancer.

Gold nanoparticles are also utilized as photothermal therapeutic agents for targeted photodynamic therapy. In particular, gold nanostructures combine with antibodies and peptides that specifically target cells, effectively converting near-infrared radiation into heat that destroys malignant tissues.

Gold nanoparticles’ radioactivity makes them suitable for radionuclide imaging and treatment.

Comparison of Raman Spectrum for 1ppm aqueous caffeine solution, measured in vial and using Nikalyte's SERS substrate. Image Credit: Nikalyte Ltd.

Sensors

Gold nanoparticles boost Raman signals and are used as substrates in surface-enhanced Raman spectroscopy to identify several biological and chemical species, such as chemical pollutants and narcotics, and analyze pesticides and contamination in food products. 

SERS uses the plasmonic properties of gold nanoparticles to increase the measurement sensitivity to detect minuscule concentrations within ppb and ppm levels.

Miniature Electronics

Gold nanoparticles are employed in electronic chips for connecting resistors and conductors. They are also used to fabricate electrochemical sensors by being placed on electrode surfaces to increase effective area and mass transfer due to greater interstitial space between spherical particles.

Microscopy Probes

Gold nanoparticles are frequently used in biological imaging because they scatter light and produce a colored spectrum in dark-field microscopy. They are also used in transmission electron microscopy probes due to their distinctively high density.

Chemical Catalysis

Gold nanoparticles can be used as catalysts for selective oxidation as they are active even in ambient settings. As they are durable and chemically resistant to poison, gold nanoparticles are also used to control pollution, e.g., to purify hydrogen streams in fuel cells.

References

  1. Peng et al. Nature Nanotechnology 4, 669–673 (2009). https://doi.org/10.1038/nnano.2009.235
  2. Y-C. Yeh et al. Nanoscale 4(6), 1871-80 (2012). doi:10.1039/c1nr11188d
  3. https://www.sigmaaldrich.com/DE/de/technical-documents/technical-article/materials-science-and-engineering/biosensors-and-imaging/gold-nanoparticles
  4. Stuchinskaya et al. Photochem. Photobiol. Sci. 10, 822-831 (2011). https://doi.org/10.1039/C1PP05014A
  5. Bai et al. International Journal of Molecular Sciences 21, 2480 (2020). https://doi.org/10.3390/ijms21072480

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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