Prior to them, non-invasive methods for monitoring glucose suggested the use of infrared light of small and medium intensity. Based on the property of glucose in the blood to “absorb” light of certain wavelengths and measuring the amount of absorbed light, it becomes possible to determine the level of glucose.
Analyzing this method, Japanese scientists came to the conclusion that it is very inaccurate, since in addition to glucose, water, protein and hemoglobin are involved in the absorption of light. To solve this problem, they decided to use more intense infrared light with a wavelength of 10 μm, which is better absorbed by glucose.
To realize their method, researchers used light hollow optical fibers with small prisms at the end as light sources. At the same time, scanning was performed not on the finger, where there is a rather thick layer of subcutaneous fat, but in the mouth cavity on the mucous membrane of the lips, which is much thinner.
As a result, measurements of glucose level had an error of no more than 20%, which is accurate enough for clinical use.