The golden bullet

Futures analysts announced on 17 January that the price of gold may break the $2,000-per-ounce barrier by the end of the year. To a scientist, there is something vulgar about the rise of gold. Those betting on it are cynics who, as Oscar Wilde put it, know the price of everything and the value of nothing.

Gold is precious because it is rare - and it is rare because it is made in only one place in the universe: a supernova. As stars burn their fuel, the radiation produced creates a pressure that stops gravity from making the star collapse in on itself. When the fuel runs out, though, the collapse becomes inevitable. If the star is big enough - if it's of a type known as a red giant - the collapse creates pressures and temperatures that produce a cataclysmic explosion.

They also produce atoms of gold. The conditions created in the explosion are the only ones in the universe that can pull together 79 protons, 118 neutrons and 79 electrons to form a gold atom. In the aftermath of the explosion, those atoms are set adrift on the interstellar medium, the thin wisp of gas and dust that fills space.

About four and a half billion years ago, some of that gas, complete with gold atoms, got pulled into the gravitational field of the newly formed star that we know as the sun and gradually accumulated to become the planet that gave rise to human life. Eventually, those humans decided that lumps of gold atoms found in earth's crust could be useful.

Gold's draw comes from its chemical properties. Its atoms are largely unreactive; once they are forged in the supernova, they interact little with other types of atom. That's why gold doesn't oxidise, or tarnish, like many metals. That gold will stay shiny for centuries has made it the go-
to metal for jewellery and other objects of beauty.

But that chemical inactivity makes it useful in other ways, too. Gold is an excellent and corrosion-resistant electrical conductor, making it invaluable for many high-end electronics components. Because its electrons buzz around the nucleus at something like half the speed of light, the element has unique chemical properties; that's why gold is an essential catalyst in many chemical reactions - such as those that take place in a car's catalytic converter, helping reduce emissions. In medicine, its inert nature has been useful for implant technology - as a tooth-replacing material, for example. Yet it is deep within the body that we are beginning to see gold's true value.

The price is right

Create gold particles a few nanometres in diameter (imagine the diameter of a human hair split around 500 times) and the way the particles scatter radiation makes them the perfect diagnostic tool. The particles are engineered with a coating of antibody molecules that cause the gold
to bind to proteins found in unusually high concentrations on the outside of cancer cells.

Due to the physical size of the particles, they will scatter light that otherwise passes straight through tissue, making it easier to spot tumours. Fire in other wavelengths of radiation to engineered gold nanoparticles and they can convert the energy into heat, burning away diseased tissue; turn them into nano-sized cages and they can smuggle drug molecules past the immune system and into disease sites.

Gold teeth used to be one of the privileges of wealth and so there is a widespread misconception that treating cancer with gold would bankrupt the NHS. But the amounts of gold involved are so small that it's no more expensive than other medicines, such as insulin. Gold-based cancer treatments come in at around ten pence per dose. Now that's real value for money.

Michael Brooks's "Free Radicals: the Secret Anarchy of Science" is published by Profile Books (£12.99)

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