A Sprinkling of Gold Dust: Fairytale or Modern Science? William Hotham discusses the many uses of gold, from drug delivery to renewable energy
"when we use very small quantities of gold such as nanoparticles, we discover new, magical properties that make it valuable"
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When we think of gold, many of us will see a gold ring, or perhaps an expensive item of jewellery. But what if we think about gold in a scientific way? A-Level chemistry tells us that gold has an atomic number of 79 and occurs naturally in a pure state. It is soft, malleable, and inert, which makes it resistant to corrosion. This is probably why we never used it in our chemistry experiments (nothing to do with budgeting!). However, when we use very small quantities of gold such as nanoparticles, we discover new, magical properties that make it valuable in applications from environmental science to medicine.
complementary charge interactions, and UV radiation is used to reverse the charge on the gold nanoparticle, releasing the DNA. This has been used for targeted gene delivery as once the DNA is removed, the gold nanoparticle will have no hazardous side effects within the body and is naturally excreted. These studies highlight the versatility of gold nanoparticles and how binding molecules to the surface can allow drug delivery via gold. If we go further, to nanoparticles as small as 30 nm, we can begin to manipulate the electron properties of gold.
Gold Catalytic Converters? | If we look at the structure of gold at the nanometer scale, the properties of gold can be manipulated. This was initially discovered by Dr Haruta of the Osaka Government Industrial Research Institute, who showed that smaller gold nanoparticles supported by metal oxides can exhibit a catalytic activity and facilitate the conversion of carbon monoxide to carbon dioxide. Before Dr Haruta, this catalytic activity had been reported but at low levels. By using smaller gold nanoparticles, Haruta displayed a greater efficiency of catalytic activity. This discovery revealed how nanoparticle size can affect the functional properties of gold.
Surface Plasmon Resonance — The Science | The use of gold nanoparticles relates to their basic photophysical responses that do not exist in nonmetallic particles. When gold is exposed to light (an oscillating electromagnetic field), the light induces a collective, coherent oscillation of electrons in the gold nanoparticle. This electron oscillation around the nanoparticle surface induces a charge separation across the nanoparticle. The amplitude of the oscillation reaches its maximum at a specific frequency, this is termed the surface plasmon resonance. Surface plasmon resonance induces a strong absorption of the light, which can be measured using a spectrometer.
A Golden Way of Delivering Drugs | Gold nanoparticles are now being used as drug delivery systems. Through controlled fabrication, gold nanoparticles sized 1-150 nm (1 nm is one billionth of a metre) can be bound directly to drugs. This binding can be applied to several different metals, however, the key benefit to using gold nanoparticles is that the gold ‘core’ is non-toxic, biocompatible, and inert thus will not promote an immune response in the body. Prodrugs are drugs that are inactive when administered and are then metabolised into pharmaceutically active drugs in the body. The conjugation of a prodrug to a gold nanoparticle enables the delivery of a drug to a cell and the drug can then be released to the cells via external stimuli such as ultraviolet (UV) radiation. This approach is now becoming applicable in genetic modification. DNA is bound to gold nanoparticles via
A Sprinkling of Gold Dust
The surface plasmon resonance is much stronger in gold than other metals due to its electron structure. The surface plasmon resonance intensity and wavelength depends on the factors affecting the electron charge density on the particle surface such as the metal type, particle size, shape, structure, and composition. Absorption or Scattering | Upon light striking a nanoparticle, there is energy loss. The two contributors of this loss are absorption and scattering. When light is absorbed, the energy is lost to the surroundings and converted to heat. On the other hand, scattering occurs when the energy causes electron fluctuations in the nanoparticle which in turn emits a form of scattered light. The absorption and scattering of light is largely dependent on the size of the nanoparticles. For the smaller gold nanoparticles, nearly all of the energy loss
Lent 2021
