Non-invasive blood glucose measurement using infrared absorption spectroscopy with a CO_2 laser - design for miniaturization

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The non-invasive glucose measurement by analyzing Fourier transform infrared (FTIR) absorbance spectra through oral mucosa with an attenuated total reflection (ATR) prism was developed as an alternative way of long-term glycemic monitoring. In all experiments, the output from the ATR prism (zinc selenide) was detected by a MCT or TGS detector. The technique was based on the phenomena that the absorption intensity at a glucose-specific peak was directly related to the glucose concentration within a very thin layer of the sample adjacent to an ATR prism. In glucose aqueous solutions, glucose had a characteristic absorption at 1033 cm^<-1> and the absorption intensity was proportional to the glucose concentration. In serum and whole blood samples, however, red blood cell corpuscles and serum proteins interfered with the absorbance spectra of glucose and shifted the base line upward significantly. Therefore, to eliminate these interferences, the feasibility of the calibration curves obtain … More ed by using difference absorbance spectra with those of fasting samples was studied. As a result, highly significant correlation between the increases in the absorption intensities above those of fasting samples and the increases in glucose concentrations above those of fasting samples. From these experiments, it was concluded that by infrared spectroscopy glucose concentrations in serum and whole blood samples could be measured quantitatively and monitored. In absorbance spectra through oral mucosa, after correcting the spectral changes due to the prism attachment by using absorption peaks at 2920 cm^<-1>(CH_2 band) as reference peaks, high correlation between the second derivatives of absorbance spectra and blood glucose concentrations was observed by the use of a similar approach. In conclusion, it was demonstrated that Fourier transform infrared spectroscopy could be useful for non-invasive monitoring of blood glucose through oral mucosa. A carbon dioxide laser, furthermore, was introduced as a light source in Fourier transform infrared spectrometer for miniaturization and improvement of the sensitivity. Not only the achievement in stable output of laser but also the development of a protection system against laser beam and a laser beam divergence system enabled us to establish the non-invasive measurement of blood glucose concentrations based on spectral analysis. Less