Ram Krishna of Toronto has had type 2 diabetes for almost 25 years, but he only started taking insulin a couple of years ago to help better control it. Since the insulin regimen began, he has had to test his blood glucose level more regularly — about three to five times a week.
To do so, he does what most of the two million to three million Canadians with diabetes do — he uses a blood glucose meter. Jabbing his finger with a spring-loaded lancet, he transfers a drop of blood to a very small test strip and inserts it into the meter, which delivers a glucose-level reading within seconds.
Although the testing isn’t difficult, it is inconvenient, particularly for people with diabetes who have to test often — some up to 10 times a day — and can be expensive, with each test strip costing about $1. “I don’t have private insurance, so I’m careful,” says Krishna, “and I compromise on how often I test.”
Test strips may eventually be a thing of the past, though, thanks to the work of chemical engineer Jin Zhang, a researcher at the University of Western Ontario. Zhang has developed a contact lens that monitors the wearer's blood glucose level by sampling tears instead of blood.
“There’s a relatively stable correlation between the level of glucose in blood and in tears that’s been studied for over 60 years,” says Zhang. “The challenge has been how to detect and measure it.”
Zhang overcame that challenge by creating a non-invasive sensor that is embedded in the lens. The sensor is made of a nanocomposite material — microscopic molecules that are engineered to react chemically with glucose. That reaction causes the material in the lens to turn various hues of red, depending on the concentration of glucose in the tear sample, which alerts the wearer of his or her glucose level without compromising vision.
Ian Blumer, chair of the Clinical Practice Guidelines Dissemination & Implementation Committee for the Canadian Diabetes Association and author of Diabetes for Canadians for Dummies, says the ability to more or less constantly monitor glucose levels would be a major step forward in helping people living with diabetes maintain good health.
“If you can keep blood sugar levels under control,” he says, “that will reduce the likelihood of damage to small blood vessels and, in turn, reduce the likelihood of blindness, kidney failure and amputations.”
There are many benefits to using nanocomposite material in the contact lenses, says Zhang. It increases oxygen permeability, making the lenses safer and more comfortable to wear. And because its scale is so small (10-9 metres), many sensors can be assembled in the lenses, creating a large surface-to-volume ratio, which aids in monitoring glucose levels accurately. “We cannot get a lot of the tear sample at once, compared with a blood sample, says Zhang. “By using nanomaterials, we can overcome this challenge.”
Collaborating with clinic doctors and other researchers, Zhang expects to begin a clinical trial within the next six months to get the product to market as quickly as possible. “I’ve received many emails from patients,” she says, “and I completely understand how eager they are to have such a device.”
For his part, Krishna says the technology sounds promising. “Any research like this is welcome,” he says. “I think the concept sounds good.”
Zhang says there are several possible applications for her contact lens. She currently has students using the lens sensor to detect and measure components such as calcium and potassium in tears. This may lead to advances for people with other chemical imbalances.