The differential floating reference method for noninvasive blood glucose sensing by near-infrared spectroscopy

The near-infrared spectroscopy is considered as one of the most promising technologies for non-invasive blood glucose sensing due to its high penetrability to bio tissues. However, its accuracy is severely limited by the complicated and irregular background variations from the human body. So it’s quite important to eliminate the influence from background variations. When the glucose concentrations change, it will lead to the absorption effect and scattering effect. It’s possible that, the spectral variations induced by absorption effect and scattering effect are same in the intensity but opposite in the direction under some special source-detector distances, which is defined as the floating reference position. Obviously, the signal from the reference position is not dependent on the glucose concentrations change, but includes all the background variations during the measurement process, which can be used as the floating reference to fulfill the relative measurement. However, the reference position is wavelength dependent and it’s quite difficult to design the fiber probe if several wavelengths are applied. In this paper, a differential floating reference method is proposed, where the diffuse reflectance is collected at the inside and outside floating reference position respectively to calculate the difference. Firstly, the feasibility of this method to remove the influence of light source drift and temperature variation is analyzed theoretically and verified by the Monte Carlo simulations. Then, a measuring system based on annular fiber bundles with multi source-detector distance are developed, which is configured with six super luminescent diode (SLD, Inphenix, USA) with the wavelength of 1000-1600nm. And the phantom samples are prepared based on 3% intralipid with the glucose concentration ranged from 1000mg/dL to 6000mg/dL and the diffuse reflectance are collected under different light intensity by changing the power of SLD. Results show that, the differential signal is linear with the glucose concentration even disturbed by strong light source drift, which means the differential processing can effectively eliminate the influence of light source variations. Moreover, since the sensitivity of spectral signal to the glucose concentration at inside and outside reference position is opposite, the differential calculation can improve the signature signal of glucose. Therefore, the differential floating reference method is a possible way to reduce the influence of background variation thus improves the accuracy of glucose sensing by near-infrared spectroscopy.