Laser device may end pin pricks, improve quality of life for diabetics

Princeton University researchers have developed a way to use a laser to measure people’s blood sugar, and, with more work to shrink the laser system to a portable size, the technique could allow diabetics to check their condition without pricking themselves to draw blood.

‘We are working hard to turn engineering solutions into useful tools for people to use in their daily lives,’ said Claire Gmachl, the Eugene Higgins Professor of Electrical Engineering and the project’s senior researcher. ‘With this work we hope to improve the lives of many diabetes sufferers who depend on frequent blood glucose monitoring.’

In an article, the researchers describe how they measured blood sugar by directing their specialized laser at a person’s palm. The laser passes through the skin cells, without causing damage, and is partially absorbed by the sugar molecules in the patient’s body. The researchers use the amount of absorption to measure the level of blood sugar.
Sabbir Liakat, the paper’s lead author, said the team was pleasantly surprised at the accuracy of the method. Glucose monitors are required to produce a blood-sugar reading within 20 percent of the patient’s actual level; even an early version of the system met that standard. The current version is 84 percent accurate, Liakat said.
‘It works now but we are still trying to improve it,’ said Liakat, a graduate student in electrical engineering.

When the team first started, the laser was an experimental setup that filled up a moderate-sized workbench. It also needed an elaborate cooling system to work. Gmachl said the researchers have solved the cooling problem, so the laser works at room temperature. The next step is to shrink it.
‘This summer, we are working to get the system on a mobile platform to take it places such as clinics to get more measurements,’ Liakat said. ‘We are looking for a larger dataset of measurements to work with.’

The key to the system is the infrared laser’s frequency. What our eyes perceive as colour is created by light’s frequency (the number of light waves that pass a point in a certain time). Red is the lowest frequency of light that humans normally can see, and infrared’s frequency is below that level. Current medical devices often use the ‘near-infrared,’ which is just beyond what the eye can see. This frequency is not blocked by water, so it can be used in the body, which is largely made up of water. But it does interact with many acids and chemicals in the skin, so it makes it impractical to use for detecting blood sugar.

Mid-infrared light, however, is not as much affected by these other chemicals, so it works well for blood sugar. But mid-infrared light is difficult to harness with standard lasers. It also requires relatively high power and stability to penetrate the skin and scatter off bodily fluid. (The target is not the blood but fluid called dermal interstitial fluid, which has a strong correlation with blood sugar.)
The breakthrough came from the use of a new type of device that is particularly adept at producing mid-infrared frequencies