Published: 27 Sep 2017

Small is wonderful – gold nanoparticles

When you think of nanometers, you have to think really, really, really small. A nanometer is a unit of length that is one billionth of a meter. Think of dividing a millimetre into a million pieces. At that level, the wonders of technology begin to look like magic. At that level, gold as a metal can work wonders.

Historically, gold has been used for different medical treatments – including dentistry, which is a story in itself – over the centuries, and remarkably, without harmful effects. Naturally, researchers experimented with gold nanoparticles for medical applications rather than using platinum (or silver), as these can be toxic in certain circumstances (silver is reactive).

Creating gold nanoparticles allows the use of gold in areas too small for larger gold particles to reach, bringing new capabilities into play. Scientists attached molecules to gold nanoparticles that are attracted to diseased regions of the body, such as cancerous tumours, to other molecules such as therapeutic drug molecules.

Scientists are researching other applications too. Even at that small size – millionths of a millimetre – the size of gold nanoparticles can make a difference. Depending on the application – for the drug delivery function, 5 nanometers (nm) is about standard. By tweaking the size, scientists can tweak the absorption spectrum; in other words, they absorb light and convert it to heat, that can be used to kill cancer cells.

Medical devices are another area of application, because of gold’s superb biocompatibility. Currently, there are a number of direct applications for the use of gold in medical devices. Wires for pacemakers, for instance, and gold-plated stents to inflate and support arteries in the treatment of heart disease. Gold is highly opaque to X-rays, and thus helps better positioning of the stent.

Gold is highly resistant to bacterial colonisation, and thus is the material of choice for implants that are at risk of infection, such as the inner ear (cochlear implants). For example, gold-plated myringotomy (surgical incisions that drain fluid or relieve pressure on the eardrum) tubes are used for implants, to drain and temporarily aerate the tympanic cavity.

In its medical applications, at least, the value from using gold is thousands of times the actual weight of the gold used. That makes it more than just precious.