Gold is an element used in jewelry, coins, dentistry, and electronic
devices. Gold is even used in some medicines. Bulk gold is considered an
inert material in that it doesn’t corrode or tarnish (which is why you
paid so much for that engagement ring). As with all metals, gold has
good electrical and thermal conductivity. Gold’s capability to resist
corrosion as well as its high electrical conductivity make it useful for
forming contacts in electronic devices.
Gold has been used in various medical treatments over the centuries
without harmful affects. It was therefore natural for researchers to
look to gold nanoparticles for medical applications rather than using
elements such as platinum, which can be toxic in certain circumstances.
Forming gold into nanoparticles allows researchers to use gold in areas
that are too small for bulk gold to reach and brings with it new
For targeted drug delivery uses (discussed later), it will be
interesting to see whether gold nanoparticles show any benefit versus
cheaper types of nanoparticles, such as iron nanoparticles. For other
uses, gold nanoparticles have some clear advantages.
When gold nanoparticles get really small, with a diameter of 5 nm or
less, they can be used as a catalyst to help reactions that, for
example, transform air pollutants into harmless molecules.
Using gold to clean up the air is somewhat surprising
given that bulk gold is considered to be an inert material in that it
doesn’t corrode or tarnish. Normally, gold would be a silly material to
use as a catalyst for chemical reactions because it doesn’t do much.
However, if you break down gold to nanosize (approximately 5
nanometers), it can act as a catalyst that can do things such as
oxidizing carbon monoxide.
Researchers attach molecules to gold nanoparticles that are attracted
to diseased regions of the body, such as cancer tumors, and other
molecules such as therapeutic drug molecules. This enables the
functionalized gold nanoparticles to be used to in targeted drug
Another property that gold nanoparticles have is the capability to
convert certain wavelengths of light into heat. As with all metals, gold
contains electrons that are not tied to a particular atom but free to
move throughout the metal. These electrons help to conduct a current
when a voltage is applied across the conductor. Depending on the size
and shape of the nanoparticles, these free electrons will absorb the
energy from a particular wavelength of light, at the right wavelength to
make the cloud of free electrons on the surface of the gold nanoparticle
resonate. It turns out that two types of gold nanoparticle shapes are
more efficient in converting light into heat:
- Gold nanorods: These solid cylinders of gold have a diameter as
small as 10 nm. By using nanorods with different combinations of
diameter and length, researchers can change the wavelength of light
that the nanorod absorbs.
- Nanospheres consist of a gold coating over a silica core: By
using nanospheres with variations in the thickness of the gold
coating and the diameter of the silica core, researchers can change
the wavelength of the light that the nanosphere absorbs.
Various researchers are using either nanorods or nanospheres to
develop methods for localized heat treatment of diseased regions of the
body. This method is called hyperthermia therapy.
Excerpted from Nanotechnology For Dummies (2nd
edition), from Wiley Publishing