Scientists Observe Radioactive Decay In Action For First Time
by Caroline Reid
Photo credit: Atoms of iodine-125 (purple) morph into tellurium-125 (green) on a gold surface (gold), courtesy of Sykes and Michaelides Labs
We use radiation to treat cancer, scan dinosaur bones, kill germs and produce electricity, to name just a few. But no one has ever actually seen an atom emitting this radiation. Until now, that is.
For the first time, scientists have observed atoms of one chemical element radioactively decay and morph into another element. Being able to study this process in more detail could help scientists understand how to safely treat cancer with radiation. In fact, the possibilities for new cancer therapies are quite startling.
Chemists saw the transformation whilst working with iodine-125, a radioactive isotope of iodine that is frequently used in cancer therapies. The team used a scanning tunneling microscope, which is so sensitive that it can create images of individual atoms. The team observed individual iodine-125 atoms releasing a proton and decaying into tellurium-125, a non-radioactive isotope.
This process isn’t as easy as pointing the microscope at a molecule and seeing a decay. Iodine-125 atoms can take up to 59 days to decay into tellurium-125, and there’s no knowing which atom will decay when. The entire process was mainly a waiting game, with the team spending up to 18 hours in the lab a day for several weeks to see the transformations.
It turns out that iodine-125 has quite a few diva-like demands. Before the experiment could begin, the iodine-125 had to be infused onto a bed of gold. To do this, the scientists mixed the iodine-125 with a single drop of water and then deposited this onto a thin layer of gold. When the water evaporated, the iodine-125 was comfortably bonded with the gold; this tiny sample was then scrutinized under the microscope.
The successful images, where iodine-125 had decayed into tellurium-125, showed little spots all over the surface of the gold. Angelos Michaelides, Ph.D., a professor at University College London (UCL), and Philipp Pedevilla, a doctoral candidate at UCL, identified these dots as tellurium-125 atoms.
So, is there a shimmering future for gold-plated iodine-125 therapy? The researchers have good reason to think there might be.
When recording the radiation coming from the gold-infused iodine sample, the team was particularly interested in low-energy electron emissions. These emissions have been very successful in radiation oncology because they travel a minuscule distance, and they break up the cancer cells’ DNA into pieces. This localized eradication means nearby organs and tissues are unaffected.
The team found that their gold-plated iodine-125 sample emitted six times more low-energy electrons than iodine-125 that was not gold-plated. The gold, says E. Charles H. Sykes, senior author of the paper, “was acting like a reflector and an amplifier. Every surface scientist knows that if you shine any kind of radiation on a metal, you get this big flux of low-energy electrons coming out.”
The prediction for the future of radiation oncology is very exciting. Cancer patients could take an injection containing tumor-targeting antibodies studded with gold nanoparticles that have iodine-125 atoms attached to the surface. Together, this gilded cancer-fighting ensemble would attach itself to a tumor, release low-energy electrons that destroy cancer DNA whilst leaving healthy tissue unscathed. The gold particles, with the iodine still attached, would then be flushed safely out of the patient’s system. Under normal circumstances, iodine-125 would accumulate in the thyroid gland and could potentially give rise to cancer. However, when accompanied by gold particles, which act as a safety net, it is escorted safely out of the body.
Via Nature Materials, Tufts University