For centuries gold has captivated mankind and has been considered as a precious metal. Reports state that colloidal gold nanoparticles have been utilized for centuries by artists for their vibrant colors, which are produced by their interaction with visible light. However, only in the 1850s scientists began studying their properties in more detail.
Gold is a Block D, Period 6 element. It is a soft metal that is often alloyed to give it more strength. It is a good conductor of heat and electricity. It is a good reflector of infrared and is chemically inert.
The versatile surface chemistry of gold nanoparticles allows them to be coated with small molecules, polymers, and biological recognition molecules, thereby extending their range of application. The morphology of gold nanoparticles is spherical, and they appear as a brown powder.
The chemical properties of gold nanoparticles are outlined in the following table.
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The physical properties of gold nanoparticles are given in the following table.
The thermal properties of gold nanoparticles are provided in the table below.
Gold nanoparticles are commonly produced in a liquid by reducing chloroauric acid. After dissolving the acid, the solution is rapidly mixed along with a reducing agent. This process then causes Au3+ ions to be reduced to neutral gold atoms.
As more of these gold atoms are generated, the solution becomes supersaturated. Gold then begins to precipitate in the form of sub-nanometer particles. If the solution is mixed in a vigorous manner, the particles tend to be uniform in size.
A stabilizing agent is sometimes added to prevent the particles from aggregating.
Gold nanoparticles are versatile materials with a broad range of applications in a variety of fields. Researchers have coated gold particles with DNA and injected them into plant embryos or plant cells. This will ensure that some genetic material will enter the cells and transform them. This method enhances plant plastids.
The July 2007 issue of Analytical Chemistry reported that scientists from Purdue University were able to use gold nanoparticles to detect breast cancer. Later it was also discovered that the nanoparticles could detect toxins and pathogens.
The optical-electronics properties of gold nanoparticles are being explored widely for use in high technology applications such as sensory probes, electronic conductors, therapeutic agents, organic photovoltaics, drug delivery in biological and medical applications, and catalysis.
Other applications of gold nanoparticles are listed below:
- As an anti-biotic, anti-fungal, and anti-microbial agent when added in plastics, coatings, nanofibers and textiles
- In nanowires and catalyst applications
- In therapeutic agent delivery
- To connect resistors, conductors, and other elements of an electronic chip
- In photodynamic therapy - When light is applied to a tumor containing gold nanoparticles, the particles rapidly heat up, killing tumor cells
- In various sensors, e.g. colorimetric sensor with gold nanoparticles can identify if foods are suitable for consumption
- As substrates to enable the measurement of vibrational energies of chemical bonds in surface enhanced Raman spectroscopy
- The scattered colors of gold nanoparticles are currently used for biological imaging applications
- Gold nanoparticles are quite dense, thus allowing them to be used as probes for transmission electron microscopy
- To detect biomarkers in the diagnosis of cancers, heart diseases, and infectious agents
- As catalysts in a number of chemical reactions
- For fuel cell applications