Precious Medicine: Gold in Tiny Amounts Can be a Cure-All
Precious metals like silver, gold, and platinum are all used in medicine to aid treatments as diverse as wound healing and cancer therapies.
Gold in particular is used for everything from imaging the human body to improving the immune system. Thankfully, its rarity is not a problem as tiny amounts make all the difference.
Gold nanoparticles, measured in billionths of a meter and thousands of times smaller than the width of a human hair, are invaluable for medical use because of the way they react to light. Nanoparticles suspended in liquids are widely used (known as colloidal gold) and their color, from deep red to pale blue, is a visual guide to their relative size.
Their light reflecting and absorbing qualities make them suitable for both electron microscopy, to examine the structure of microorganisms and cells, and photodynamic therapy, where the particles penetrate cancer cells and are then heated using light to destroy tumors.
Nanoparticles also fight infection. Specially engineered porous gold nanodisks made at the University of Houston can be heated using a laser to kill bacteria with a thermal shock. Medical instruments such as catheters could in future be coated with the particles and laser treatment administered at the patient’s bedside.
Of course, any tiny particle has the potential to cause harm to our vital organs or cells, especially once they are coated with chemical agents. Cell penetration is achieved using special polymer coatings, but to keep the cells healthy a team of researchers has identified several non-toxic compounds that work to allow entry and then seal the cell wall afterwards. Different coatings have been developed to target only specific types of cells to harmlessly deliver drugs, vaccines, or genes for treatment.
Illnesses associated with ageing are under the microscope too. Scientists are using gold nanoparticles to see the knot-like structures in the brain that cause Alzheimer's and other neurodegenerative diseases. By labelling these structures–called amyloid fibrils–with gold they can see the knots more clearly and identify their weak spots for treatment.
Another global health problem shows promise for gold use in medicine. Tropical disease malaria, transmitted by mosquitoes, infected 219 million people in 2017 and killed 435,000. Nanoparticles used in rapid diagnostic tests are cheap to use, can give results in 15 minutes, and help doctors target treatment for malaria where it is most needed.
Breakthroughs for Cancer Research
But some of the most exciting breakthroughs for gold nanoparticles are in cancer diagnosis and treatment. Cancer DNA has a special 3D structure that has an affinity for gold, according to one study, and nanoparticles change color when that DNA is present. Simple, fast tests could detect cancer in 10 minutes.
The University of Central Florida has created a one dollar test for prostate cancer that could be given in a doctor's surgery. Another group at the University of Maryland, Baltimore County is using chemicals to make tumors produce their own gold nanoparticles, which could then be used to image or destroy them.
Immunotherapists are also harnessing the special properties of spherical nanoparticles to deliver a boost to the body's immune system. Polymer-coated spheres of gold interact with B lymphocyte immune cells and can deliver drugs or vaccine to where it is most needed. In this way they hope to treat hard-to-reach brain tumors.
Going forward there is exciting potential for nanoparticles to help combat HIV and blood diseases. Medics use the gene editing tool CRISPR to deliver new genetic information to cells, but current methods can damage or even kill cells. Gold nanoparticles mounted with CRISPR can quickly cross the cell membrane into the nucleus to edit genes.