Preliminary evaluation of optical glucose sensing in red cell concentrations using near-infrared diffuse-reflectance spectroscopy

Polarized light diffuse reflectance FT-NIR MEMS spectrometer enabling the detection of powder samples through a thin plastic layer

Polarized scattered light Fourier transform infrared (FTIR) spectroscopy is used for measuring the absorbance of highly scattering materials overcoming the multiple scattering effect. It has been reported for in vivo for biomedical applications and in-field for agricultural and for environmental monitoring. In this paper, we report a polarized light microelectromechanical system (MEMS)-based FTIR in the extended near infrared (NIR) that utilizes a bistate polarizer in a diffuse reflectance measurement setup. The spectrometer is capable of distinguishing between single backscattering from the uppermost layer and multiple scattering from the deep layers. The spectrometer has a spectral resolution of 64c m ^-1 (about 16 nm at a wavelength of 1550 nm) and operates in the spectral range of 4347c m ^-1 to 7692c m ^-1 (1300 nm to 2300 nm). The technique implies de-embedding of the MEMS spectrometer polarization response by normalizing its effect; this is applied on three different samples: milk powder, sugar, and flour in plastic bags. The technique is examined on different scattering size particles. The scattering particles diameter's range is expected to vary from 10 µm to 400 µm. The absorbance spectra of the samples are extracted and compared to the direct diffuse reflectance measurements of the samples, showing good agreement. By using the proposed technique, the calculated error for the flour was decreased from 43.2% to 2.9% at 1935 nm wavelength. The wavelength error dependence is also reduced.

In vivo glucose monitoring using dual-wavelength polarimetry to overcome corneal birefringence in the presence of motion

OBJECTIVE

Over the past 35 years considerable research has been performed toward the investigation of noninvasive and minimally invasive glucose monitoring techniques. Optical polarimetry is one noninvasive technique that has shown promise as a means to ascertain blood glucose levels through measuring the glucose concentrations in the anterior chamber of the eye. However, one of the key limitations to the use of optical polarimetry as a means to noninvasively measure glucose levels is the presence of sample noise caused by motion-induced time-varying corneal birefringence.

RESEARCH DESIGN AND METHODS

In this article our group presents, for the first time, results that show dual-wavelength polarimetry can be used to accurately detect glucose concentrations in the presence of motion-induced birefringence in vivo using New Zealand White rabbits.

RESULTS

In total, nine animal studies (three New Zealand White rabbits across three separate days) were conducted. Using the dual-wavelength optical polarimetric approach, in vivo, an overall mean average relative difference of 4.49% (11.66 mg/dL) was achieved with 100% Zone A+B hits on a Clarke error grid, including 100% falling in Zone A.

CONCLUSIONS

The results indicate that dual-wavelength polarimetry can effectively be used to significantly reduce the noise due to time-varying corneal birefringence in vivo, allowing the accurate measurement of glucose concentration in the aqueous humor of the eye and correlating that with blood glucose.