8.1 Glucose Sensing
Approximately 17 million people in the USA (6% of the population) and 140 million people worldwide (this number is expected to rise to almost 300 million by the year 2025) suffer from diabetes mellitus. The development of a noninvasive test method would considerably improve the quality of life for diabetic patients, facilitate their compliance for glucose monitoring, and reduce complications and mortality associated with this disease. Noninvasive and continuous monitoring of glucose concentration in blood and tissues is one of the most challenging and exciting applications of optics in medicine. The major difficulty preventing development and clinical application of a noninvasive blood glucose sensor is associated with the very low signal produced by glucose molecules. This results in low sensitivity and specificity of glucose monitoring.
8.1.2 Tissue and blood scattering spectroscopy
The concept of noninvasive blood glucose sensing using the scattering properties of blood as an alternative to spectral absorption and polarization methods for the monitoring of physiological glucose concentrations in blood of diabetic patients has been under intensive discussion for the last decade. Many of the considered early effects, such as RBC size, refractive index, packing, and aggregation changed under glucose variation are important for glucose monitoring in diabetic patients. Indeed, at physiological concentrations of glucose, ranging from 40 to 400 mgâdl, the role of some of the effects may be changed, and some other effects, such as glucose penetration inside the RBC and the following hemoglobin glycation may be important.
Noninvasive determination of glucose was attempted using light scattering of skin tissue components measured by a spatially resolved diffuse reflectance and NIR frequency-domain reflectance techniques. Both approaches are based on change in glucose concentration, which affects the refractive index mismatch between the interstitial fluid and tissue fibers, and hence Î¼sâ². A glucose clamp experiment (the concentrations of injected glucose and insulin are manipulated to result in a steady concentration of glucose ever a period of time) showed that Î´Î¼sâ² at 650 nm qualitatively tracked changes in blood glucose concentration for the volunteer with diabetes studied (Fig. 79).