July 26, 2021

I, Science

The science magazine of Imperial College


Spinning gold from straw is the stuff of fairytales, but Rumpelstiltskin might actually have been onto something.  It seems plants have the ability to suck up gold nanoparticles and incorporate the precious metal into their leaves.  This might sound like the next must-have bling homeware, but when the leaves get eaten, the gold gets transferred and accumulates as it travels up the food chain.  Experts are uncertain of the threat to humans, but a golden dose could make trees glow in the dark.

Nanotechnology is on the rise.   In the last five years the number of products employing materials of between 1 and 100 nanometres has risen from 54 to over one thousand.  Gold nanoparticles are particularly useful:  they’re the basis of groundbreaking cancer treatments, HIV drugs and catalysts in fuel cells.

As usage goes up, however, so does the amount of gold getting into waste water.  In Europe and America, 60% of the solid waste produced by sewage plants is used as fertiliser, and it’s in this sludge faction that the nanoparticles accumulate.

To study the implications, researchers at the University of Kentucky raised tobacco plants (Nicotiana tabacum L. cv Xanthi) – selected for their fast growth and similarity to tomato plants – on nutrient mixtures laced with variously-sized gold nanoparticles.  They then allowed tobacco hornworms (Manduca sexta) to munch on the plants for a week, before cutting both the worms and the plants into sections for study and using a variety of mass spectrometry techniques to measure the golden uptake.

Their results, published in the journal Environmental Science & Technology,  showed that gold particles were present throughout the tobacco’s leaf tissue – not just on the surface as had been observed in a previous study.  All nanoparticles were absorbed by the plants, irrespective of size.

In the hornworms, gold nanoparticles accumulated around the gut region and were found in concentrations up to ten times that of the plants – confirming the scientists’ suspicion that gold might accumulate up the food chain.

This is the first time nanoparticles have been observed passing from plants to grazers.  It’s too early to tell what a dose of gold might mean for higher animals and humans, but there may be a bizarre benefit…

Last year, scientists in Taiwan discovered that implanting gold nanoparticles into leaves made the foliage glow red.  Dr Yen-Hsun Su, leader of the research team, suggested that trees sporting ‘bio-LEDs’ could be used instead of streetlights in future.

So, is sewage about to light up our world?