Biomedical Engineering Reference
In-Depth Information
electronics, medicine, environmental remediation, cosmetics, and solar
energy. Discovering distinctive properties that many materials display at
the extremely minuscule scale opens new opportunities for their conven-
tional use.
2
Of particular interest to most nanotechnology applications are
engineered nanoparticles (ENPs), which have much larger surface-to-mass
ratios. Nanosized ENPs have also been claimed to have a greater uptake,
absorption, and bioavailability in the body compared with their bulk equiva-
lents. This makes it possible to reduce the use of solvents in certain appli-
cations, such as certain cosmetics and personal care products, to allow the
dispersion of water-insoluble colors, flavors, and preservatives in low-fat
systems. Nanosized water-insoluble substances can enable their uniform
dispersion in aqueous formulations. This aspect alone has attracted a lot of
commercial interest in the use of nanosized ingredients.
3
Among other ENPs, interest in gold has not diminished; on the contrary, it
has increased enormously in recent years, particularly since the early 1980s,
when the mass production of nanoscaled chemical substances started, owing
to the invention of the scanning tunneling microscope and the atomic force
microscope. IBM scientists have enabled the manipulation of even individ-
ual atoms to design and synthesize materials for attaining desired features.
Later in the 2000s, IBM scientists, by precisely placing atom-by-atom 20,000
gold particles, each about 60 nm in diameter, reproduced an image of Robert
Fludd's seventeenth century drawing of the sun—alchemists' symbol for
gold. IBM scientists demonstrated a new nano “printing” bottom-up tech-
nique, which will lead to breakthroughs in ultratiny chips, lenses for optics,
and biosensors for health care.
As gold is the most studied chemical element, it is characterized as having
the most predictable behavior. However, gold nanoparticles may act abso-
lutely diversely. Bulk gold, which is usually characterized by its yellow color,
while being processed to a nano-dimensional scale, transforms its color to
orange, purple, red, or a greenish tinge owing to different particle sizes. The
most well-known cultural artifact in nanotechnology is housed in the British
Museum—the Lycurgus Cup (dated fourth century AD), which is a glass cup
of ruby red color due to its colloidal gold content and changes to a greenish
color upon light exposure. Nanogold was used in medieval times in stained
glass materials to attain almost all the colors of the rainbow. Today, nobody
will argue that nanosized gold particles do not act like bulk gold.
4
Traditionally, bulk gold was considered a chemically inert and biocompat-
ible material; owing to these features, it is utilized widely in medical appli-
cations, for example, in dental prosthesis and eyelid implants. Throughout
history, gold has been used to cure diseases. Finely ground gold particles in
the size range of 10-500 nm can be suspended in water. Such suspensions
were used for medical purposes in ancient Egypt over 5000 years ago. In
Alexandria, Egyptian alchemists used fine gold particles to produce a col-
loidal elixir known as “liquid gold,” which was intended to restore youth.
5
Dating back to the Roman Empire, colloidal gold was thought to have healing
