A team of scientists at Princeton University, Princeton, NJ, report that they have developed a way to measure people's blood glucose using a portable laser that could one day allow diabetics to check their condition without pricking themselves to draw blood.

The new monitor uses a laser, instead of a blood sample, to read blood sugar levels. (Credit: Princeton University, Engineering School)

They explain that they measured blood sugar by directing a 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.

The key to the system is the infrared laser’s frequency. What we perceive as color is created by the number of light waves that pass a point within a certain time. Red has the lowest frequency of light that humans normally can see, infrared’s frequency is below that level, and current medical devices often use “near-infrared,” which is just beyond what the eye can see. This frequency can be used in the body, but it interacts with many acids and chemicals in the skin, making it impractical to use to detect blood sugar.

Mid-infrared light, they discovered, works well for detecting blood sugar, but is difficult to harness with standard lasers, and requires relatively high power and stability to penetrate the skin and scatter off bodily fluid.

The team’s breakthrough came from the use of a new type of device that is particularly adept at producing mid-infrared frequencies—a quantum cascade laser. In a quantum cascade laser, electrons pass through a “cascade” of semiconductor layers, so the beam can be set to one of a number of different frequencies. The ability to specify the frequency allowed the researchers to produce a laser in the mid-infrared region.

The researchers used the laser to measure the blood sugar of three healthy people before and after they each ate 20 jellybeans, which raise blood sugar levels. The researchers also checked the measurements with a finger-prick test. They conducted the measurements repeatedly over several weeks. Their results indicated that the laser measurements readings remained within the clinical requirement for accuracy.