Effect of Continuous NIR Exposure on the Absorbance Studies of Glucose Solutions at Physiological Levels

Non-invasive glucose monitoring is the need of the hour due to steep rise in diabetic patients worldwide. Monitoring of glucose level at regular interval is important for preventing the diabetes related complications. Several non-invasive methods Raman, MIR, NIR, photo acoustic, bio impedance and fluorescence spectroscopy, polarimetry, microwave assisted monitoring etc. have been explored for this purpose. However, none of the techniques have achieved accuracies that are suitable for clinical use. NIR spectroscopy is a popular technique which is being extensively employed for the development of a non-invasive glucose measurement device. However, the NIR spectra is prone to variations due to changes in temperature, machine drift, time drift, water content etc. and seem dominant because of extremely low level of absorption variation in glucose. In the present study, the variations in the glucose absorbance at 960 nm as a result of consecutive measurements are demonstrated. The study reveals that there is a decrease in the glucose absorbance because consecutive measurements cause long exposure of sample to NIR and hence the heating of the solutions which results in a rise in temperature. The absorbance at a wavelength of 960 nm is affected by temperature because it corresponds to OH stretching vibrations and the OH groups of sugars are sensitive to temperature. The results also reveal that even at 1 °C variation in the temperature of a 100 mg/dl glucose solution leads to a decrease in the glucose absorbance from 0.00301 to 0.00150 (δabs = 1.52 × 10–3). Even this small variation in the absorbance can cause large errors in the prediction of glucose concentrations. Therefore, for device fabrication using NIR spectroscopy temperature variations must be taken into consideration to improve the accuracy of glucose predictions.