Warren Chanof the University of Toronto poses with samples of quantum dots at a lab in Toronto. Chan custom designs tiny particles that glow red, blue or yellow and one day could be used instead of radioactive isotopes to help doctors determine if a patient's cancer has spread.Deborah Baic/The Globe and Mail
Warren Chan custom designs tiny particles that glow red, blue or yellow. One day, they could be used instead of radioactive isotopes to help doctors learn what is happening inside a patient's body.
It is a little like making Kool-Aid, says the researcher at the Institute of Biomaterials and Biomedical Engineering at the University of Toronto. You need $50,000 worth of lab equipment and a technician trained in synthetic chemistry. What you don't need is a nuclear reactor like the one recently shut down in Chalk River, Ont., leading to a shortage of isotopes used in heart, bone and cardiac scans.
Dr. Chan's work on particles known as quantum dots is at an early stage and many fundamental questions - including whether they are safe - still have to be answered. But like many in his field, Dr. Chan says that nanoscience - which involves building things atom by atom, molecule by molecule - could offer new approaches to medical imaging.
It isn't a short-term solution; the work won't be a quick fix for hospitals trying to round up enough isotopes for various procedures.
But the first magnetic nanoparticles are now being evaluated by the Food and Drug Administration for their use in contrast agents in medical imaging, he says. In the years to come, tiny custom-built probes and perhaps entirely new types of imagers could supplement, or perhaps even replace, current techniques that rely on isotopes, says Dr. Chan, who holds a Canada Research Chair in biotechnology.
Scientists can engineer particles under 100 nanometres that have optical, electrical and magnetic properties related to their size and shape. (A nanometre is a billionth of a metre, and is the unit scientists use to measure viruses.) Depending on their size, Dr. Chan's particles glow in different colours when they are excited by a laser. This is a useful property for diagnostic imaging, and could help doctors learn more about the causes of a disease at the molecular level.
They shimmer and blink under a microscope, and in theory can be designed to attach themselves to various molecules in the body - for example, a protein produced in unusually large quantities by cancerous cells at a late stage in the disease.
He now uses an optical imager designed for small animals to study the quantum dots in the bodies of laboratory animals. One day, there may be a similar scanner for patients, he says, or a multi-modal imager that would combine different technologies.
But there are challenges. His quantum dots are made of cadmium and selenium, and he is doing toxicity studies to assess if they pose a health risk. Other groups, however, are working on quantum dots made from other kinds of materials.
The other limitation is that this approach will only work for cancers that are in a part of the body where light can reach, like the skin, the breast or parts of the digestive tract.
That is not the case with the many radioactive isotopes now used by clinicians and researchers like François Bénard, senior scientist at the BC Cancer Research Centre in Vancouver.
He uses Positron Emission Tomography, or PET scans, to attach radioactive isotopes to various target molecules. PET scans rely on isotopes produced by particle accelerators known as cyclotrons, and are used in such small quantities they don't do any damage, he says.
They also allow doctors to see what is happening deep in the body, including in bones.
When cancer damages bone, the body tries to repair it. Isotopes attached to a chemical produced when this is happening allow doctors to tell if cancer in another part of the body has spread to the bones.
"It would be a mistake to completely turn away from isotopes," Dr. Bénard says.