Gold has been a part of human history for a very, very long time – over 6000 years is our best guess. It has been cherished and coveted by kings and commoners alike. Even now, about half of the gold that is dug up every year is turned into jewellery. Most of the rest is invested, with just 10% being used in industry for electronic wiring, car parts, and satellites. Only the tiniest portion of that industrial use goes to gold nanoparticles; but that may soon change.
Gold nanoparticles have been used for years in stained glass – they can imbue liquidsw or glass with various colours, depending on how large the particles are. They are also useful for research, as they show up well under electron microscopes. Other recent uses for gold nanoparticles include detecting tumour cells, and printable electronics using a 3D printer and conducting ink. They can do all this because at the nanoparticle scale, they retain all the normal properties of gold, while also venturing into some new and weird territory.
So, why am I telling you stories about gold? Well, gold nanoparticles have a few new tricks up their metaphorical sleeve(s?), mostly in the realm of medical devices and diagnostics. Let’s dive right in.
Electronics that stretch
For me, the most exciting of these is the invention of stretchy electronics. The inventors, at the University of Michigan, embedded normal gold nanoparticles into polyurethane, a common compound that is used in everything from skateboard wheels to adhesives. The result looks like gold foil, but it can stretch like a rubber band while still being able to conduct electricity. This is fantastically useful – your average piece of electronics fails when an electrical contact is disrupted by rough handling. This technology can totally negate that problem, and will be especially useful for designing rugged electronics. But researchers have something a bit more outlandish in mind – your body. There is a growing need for a flexible electronic device that our bodies will accept, and gold has already proven to be useful for medical applications because it is not rejected as foreign.
Heart repair kit
This aspect of gold is being exploited by other researchers in the field of tissue engineering. A group at Tel Aviv University is making cardiac patches that incorporate gold nanofibres. Cardiac patches are small pieces of tissue grown from stem cells, which are intended to ‘patch up’ damage to the heart without replacing it entirely. The design has been around for some time, but has been limited because the cells aren’t able to transmit electrical signals – which defeats the purpose of a cardiac repair patch. To get around this, scientists grew the tissue on a scaffold with gold nanofibres intertwined. When the cells matured, they could use the gold fibers to transmit electrical signals. The cells functioned in unison, as they would in the heart.
One more exciting use for gold on the smallest scale, and something particularly relevant to my virology background, is as a vaccine. Researchers have used specially shaped gold particles, called nanorods, as a vaccine building block. Vaccines work by fooling your body into thinking it has a disease. This is more effective if the vaccine looks like the disease it’s protecting you against. So, scientists attached surface proteins of respiratory syncytial virus (RSV) to these nanorods, which are identical in shape and size to the virus, to fool the body into believing that it has been infected. When tested, cells responded as they would to a natural infection, and a really good immune response was triggered.
Amidst all this positive stuff, a word of caution: at least one study has shown that certain types of gold nanoparticle can cause health problems such as speeding up aging, and preventing wound repair. Other studies have revealed that nanoparticles in general can be toxic, but that toxicity varies due to shape, size and material.
The truth is, we just don’t know enough to make any solid assumptions about the health and safety of nanoparticles. But the possibilities that gold nanoparticles present for improving human health are certainly exciting.