Study On Reference Wavelength Method For Non-invasive Blood Glucose Sensing With Near Infrared Spectroscopy

Non-invasive sensing of human blood glucose concentration with near infrared spectroscopy is an international frontier topic which does not come into clinical realization yet. The reason lies in the fact that the human physiological change disturbs the spectrum seriously, and the measurement precision can not reach the clinical requirement. According to this problem, the variation regularities of absorption coefficient and scattering coefficient under different wavelength are studied based on the molecules displacement between glucose and water. The existence of reference wavelength, where the change of absorbance is independent of glucose concentration, is proved. And a method is proposed to use absorbance of reference wavelength to amend the sample's spectrum.Systemic investigation of reference wavelength's existence is carefully brought forward firstly in this paper. Base on the hydrogen bond recombinant principle, the molecules displacement between solute and water is studied. And the existence conditions of reference wavelength are derived in pure absorption media and turbid media. By using the glucose aqueous solution and 2% Intralipid solution as the two kinds of media, the experiments are designed to prove the existence of reference wavelength. The experiments show the same results as the theoretical results, which the reference wavelengths are 1525nm, 1832nm and 2062nm in glucose aqueous solution, and the reference wavelengths are 2090nm and 2180nm in 2% Intralipid solution. The change of sample's scattering state will affect the position of reference wavelength. The rule of its change is studied in this paper, which provides the principle to choose reference wavelength in non-invasive sensing of blood glucose concentration.A method is proposed to measure the temperature with high precision. The influences of temperature on the near infrared spectroscopy and measurement precision of glucose concentration are studied. Based on the principle that the absorbance is independent of glucose concentration on the reference wavelength, a temperature measurement method is suggested in this paper. The experiments are designed to prove the validity of the method in pure absorption media and turbid media. The experimental results show that the temperature measurement precision is 0.037℃and 0.1℃respectively in the two kinds of solutions, and the measurement precision is not affected by the change of solute concentration. As the method can measure the inner temperature of sample directly, it can be used potentially to measure the real spectrum temperature in human non-invasive sensing of blood glucose concentration. Furthermore, as the displacement effect is found commonly in various solutions, the principle of this method may be used to improve the accuracy of spectral analysis on many other solutions.The reference wavelength method is studied for spectrum correction. Firstly, the external interferences of spectrum in the process of non-invasive sensing of blood glucose concentration are discussed. And the normal data processing methods are introduced for spectrum correction. Then the theoretical expression of reference wavelength method is studied. The effects of the method for eliminating the influence of light intensity shift and temperature change are proved by experiments. The experimental results show that the measurement precisions of glucose concentration are improved by 21.7% and 11.7% in pure absorption media and turbid media respectively. The reference wavelength method uses the signal at the reference wavelength as an internal reference to correct the sample's spectrum, and it needs not referential object which optical characters change synchronously with the samples. The reference wavelength method can be a good choice for human non-invasive sensing of blood glucose concentration.