Using gold in medicine might sound like the ultimate in conspicuous overconsumption but proponents say it will revolutionise healthcare.
Gold offer a glitter of hope for medicine
Using gold in medicine might sound like the ultimate in conspicuous overconsumption, but proponents say it will revolutionise health care. John Henzell finds an Abu Dhabi researcher who's helping lead the way
It sounds like the ultimate in gratuitous bling: medicine delivered on gold.
But when the gold involved is only 1/10,000th the width of a human hair, the bling factor is unlikely to impress anyone - other than nanotechnologists, that is, such as the Khalifa University assistant professor Matt Martin, who says the dazzle factor comes from the potential that gold nanoparticles have to revolutionise medicine.
Martin has been working in the field of gold nanoparticles since 2006 and, since arriving at Khalifa University for a combined teaching and research position less than a year ago, his focus has been on attaching useful biomedical chemicals to the surface of nanoparticles, which hold the prospect of delivering exceptionally precise doses of medicine. And his work is helping make breakthroughs in the medical world.
"In nanomedicine, people haven't been controlling the nanoparticles precisely. I make some of the most precise nanoparticles, down below 10nm [nanometres]."
Previously, researchers have managed to create gold nanoparticles, but with significant variation in the sizes of the nanoparticles.
"The reason we can do it is because we're sticklers for reproducibility," says Martin.
The use of gold nanoparticles is still in the testing stages, but it's been found to increase effectiveness in cancer therapy drugs, where the drug is attached to the surface of a nanoparticle. A laser is then used on the drug and, when heated, kills whatever the drug is bound to.
Other potential uses include being able to target specific cancerous cells with extremely precise doses of anti-cancer drugs, in detecting cancers in the first place and in battling Alzheimer's disease.
For all its association with bling, nanotechnologists use gold for the same reason it has always been one of the world's most coveted metals: it naturally doesn't oxidise and only reacts with a few other materials.
"You won't ever get a rash from wearing a gold wedding band because gold is essentially inert," Martin explains.
"For human beings, it's harmless - you can go to Emirates Palace and eat gold filings on your ice cream and you'll be fine. It'll pass right through you.
"That's why we use it. Gold is called the most noble of the metals because it doesn't really oxidise or corrode but it does bond very strongly to some useful chemicals. It's a non-toxic and stable platform."
By comparison, other valuable and seemingly stable metals such as silver and titanium, oxidise, detracting from their suitability in nanomedicine.
Ironically, the new uses of gold in medicine takes the metal full circle. It was the key ingredient in what was called aurum potabile - Latin for "drinkable gold" - that the 16th-century European physician and alchemist Paracelsus favoured as an elixir of life and a cure-all.
Modern scientists would call aurum potabile a variation on the snake-oil cures of the less enlightened ages. Despite early promise as a rheumatism drug, the benefits were primarily of the placebo variety, but were associated with side effects of long-term use that include permanently turning the skin a mauve or purplish dark grey when exposed to sunlight and eventually causing renal failure and heart conditions.
Little wonder that most people decided that gold served a greater purpose as a medium to display wealth rather than to improve health.
But with improved technology, researchers found gold was beneficial on a nano-level, defined as molecular scale objects measuring between 1 and 100 nanometres. One nanometre is one billionth of a metre.
A recent example is photothermal therapy, where rod-shaped gold nanoparticles are absorbed into cancerous cells and then heated using near-infrared light, which can travel through skin and tissue. As the nanoparticles heat, it kills the cancerous cells around them but leaves healthy tissue mostly unaffected.
The gold nanorods used in the treatment are sized between 50nm and 100nm. But Martin has set his sights set much finer.
"These nanorods are 50 to 100 nanometre particles. To give you an idea, a human hair, which is about the smallest thing you can see, is between 50 to 100 micrometres, so what we're talking about is one thousandth the thickness of a hair.
"I create gold nanoparticles smaller than 10 nanometres. What I do is I control basic physical properties of nanoparticles, their size and charge and self assembly into larger structures.
"An example of something to do with nanotechnology is DNA. Each strand is about two nanometres thick and it features self assembly. Eventually you get humans.
"I'm interested in controlling the basic physical particles and tailoring them or engineering them so they self-assemble. The size is completely dependent on what you want to do."
Sulphur is one of the few materials that bonds strongly with gold, so the beneficial drug can be bonded to sulphur and in turn bonded to the gold nanoparticle for delivery. One such potential use for extremely small nanoparticles is to treat brain disorders such as Alzheimer's disease. The trouble was getting through the blood-brain barrier - a fine membrane that effectively isolates the brain.
"Most healthy people don't have bacteria or viruses in the brain and that's because bacteria and viruses have problems getting through a healthy and intact blood-brain barrier. Particles below 10nm can pass through," he said.
"If you want to attack something like Alzheimer's disease, which some people think is caused by plaque build-up in the brain, you need particles that can get through a healthy blood-brain barrier without damaging it. These are nanoparticles of 2 to 3nm coated in chemicals.
"It's not easy. It's challenging. Other people have been using outdated methods in synthesising particles. A lot of my work is on controlling the chemical parameters, like pH and salt concentration. Doing that controls the size and the charge.
"Our work is a continuous process. We can now obtain better than 1nm size tuning, which people didn't think was possible. It's essentially atomic-size tuning. I think they thought it was way too complicated but we proved it's not just possible but surprisingly easy."
Martin says doctors and researchers around the world are interested in the field of gold nanoparticles for medicine, but as yet, nobody has found another way to replicate the precision and tunablity that he has achieved during his time at Khalifa University, which makes all the difference when it comes to a medicine's effectiveness.
"There's a big difference between 2nm and 3nm. If you have some at 2nm and some at 3nm, they will act very differently in the blood-brain barrier than just particles of 2nm or just particles of 3nm.
"It's a big deal because if you're delivering particles which aren't the same size, they won't have the same surface area, so they won't have the same concentration of drugs on the surface.
"If you have a 2nm-diameter particle, the surface area is 12.5 square nanometres. That's related to the amount of drug dosage. A 4nm-diameter particle has twice the diameter but it's four times the surface area, so it's 50 square nanometres."
The exciting part of his work is that the scope of potential applications for the smallest nanoparticles is wide open. The nature of the field is that the full use of the technology will require multidisciplinary collaboration.
Other researchers have adopted Martin's precise gold nanoparticle formations to create a test for dengue fever, a mosquito-borne tropical virus, that produces accurate results within five minutes and at a reasonable cost. Previously, doctors usually reached the diagnoses by observing a grab bag of symptoms, which were often difficult to differentiate from other viral infections.
For Martin, it's just an example of the potential for this new field of science.
"It involves physics, biology, chemistry - it requires a lot of disparate knowledge. Things that haven't been connected before."
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