LYCURGUS & AMBROSIA
Colloidal Gold nanoparticles have been utilized for centuries by artists due to the vibrant colors produced by their interaction with visible light. The most famous example of which is the Lycurgus Cup from the 4th Century that depicts Ambrosia destroying Lycurgus. The glass in the cup changes from red to green depending on the direction of the light.
More recently, these unique optoelectronic properties have been researched and utilized in high technology applications such as organic photovoltaics, sensory probes, therapeutic agents, drug delivery in biological and medical applications, electronic conductors and catalysis. The optical and electronic properties of gold nanoparticles are dependent on the size and shape of the particles.
ELECTRONICS
Gold nanoparticles are designed for use as conductors from printable inks to electronic chips. As the world of electronics become smaller, nanoparticles are important components in the chip design. Nanoscale gold nanoparticles are being used to connect resistors, conductors, and other elements of an electronic chip.
PHOTODYNAMIC THERAPY
Near-IR absorbing gold nanoparticles (including gold nanoshells and nanorods) produce heat when excited by light at wavelengths from 700 to 800 nm. This enables these nanoparticles to eradicate targeted tumors. When light is applied to a tumor containing gold nanoparticles, the particles rapidly heat up, killing tumor cells in a treatment also known as hyperthermia therapy.
THERAPEUTIC AGENT DELIVERY
Therapeutic agents can also be coated onto the surface of gold nanoparticles. The large surface area-to-volume ratio of gold nanoparticles enables their surface to be coated with hundreds of molecules (including therapeutics, targeting agents, and anti-fouling polymers).
SENSORS
Gold nanoparticles are used in a variety of sensors. For example, a colorimetric sensor based on gold nanoparticles can identify if foods are suitable for consumption. Other methods, such as surface enhanced Raman spectroscopy, exploit gold nanoparticles as substrates to enable the measurement of vibrational energies of chemical bonds. This strategy could also be used for the detection of proteins, pollutants, and other molecules label-free.
DIAGNOSTICS
Gold nanoparticles are also used to detect biomarkers in the diagnosis of heart diseases, cancers, and infectious agents. They are also common in lateral flow immunoassays, a common household example being the home pregnancy test.
CATALYSIS
Gold nanoparticles are used as catalysts in a number of chemical reactions. The surface of a gold nanoparticle can be used for selective oxidation or in certain cases the surface can reduce a reaction (nitrogen oxides). Gold nanoparticles are being developed for fuel cell applications. These technologies would be useful in the automotive and display industry.
PROBES
Gold nanoparticles also scatter light and can produce an array of interesting colors under dark-field microscopy. The scattered colors of gold nanoparticles are currently used for biological imaging applications. Also, gold nanoparticles are relatively dense, making them useful as probes for transmission electron microscopy.
APPLICATIONS
The range of applications for gold nanoparticles of different sizes is growing rapidly and includes:
The ‘Phytocat’ project is led Andrew Hunt and Liz Rylott from the University of York in the UK. Their main mission is to research ‘phytomining’ of gold. This involves extracting gold from ‘mine waste’ or ‘tailings’ using specially selected ‘hyperaccumulating’ plants. Since the early part of the 20th century, there have been reports about the accumulation of gold by plants, particularly trees and, as a result, some mining companies use plant species as bioindicators of the presence of gold in soil (biogeochemical exploration).
