Phase Difference Optimization of Dual-Wavelength Excitation for the CW-Photoacoustic-Based Noninvasive and Selective Investigation of Aqueous Solutions of Glucose.

Serge Camou

doi:10.3390/s150716358

Abstract

Towards the noninvasive and continuous monitoring of blood glucose levels, we chose the continuous-wave photoacoustic (CW-PA) technique and developed the optical power balance shift (OPBS) method. However, operating with optical wavelengths in the near-infrared (NIR) region ensures deep penetration inside human soft-tissue, but also leads to two serious issues: strong background level noise from water molecules in this wavelength range and small differences between the absorbance spectra of diluted compounds. To resolve them, the OPBS method relies on simultaneous optical excitation at two wavelengths for differential measurements. However, the first validation in vitro with calibrated aqueous solutions of glucose and albumin revealed strong dependence on the phase difference between the two lights sources. In this paper, we report a systematic investigation of this parameter, from PA-based measurements over a wide range of phase differences and an extensive characterization in the frequency domain. The process of maintaining the phase quadrature of the two optical signals is demonstrated in real time through an analysis of the PA signal and therefore does not require any additional equipment. Finally, a comparison of aqueous glucose solution characterizations at high concentration levels with the two methods was performed and consistent results were obtained.

Highlights

Diabetes mellitus [1,2], often referred to as diabetes, comprises a group of common metabolic disorders that result in loose control of the blood glucose level (BGL) and can lead to hyperglycemia with multiple complications [3,4]
Despite significant efforts to minimize the volume of investigated blood samples and reduce the discomfort associated with finger-pricking, these sensors are still invasive by design and are not suitable for continuous monitoring, which is a major corner-stone for optimal BGL control [10,11]
The proposed optical power balance shift (OPBS) method was tested with aqueous solution of glucose at high concentration levels and optical wavelengths of 1382 and 1610 nm

Summary

Introduction

Diabetes mellitus [1,2], often referred to as diabetes, comprises a group of common metabolic disorders that result in loose control of the blood glucose level (BGL) and can lead to hyperglycemia (elevated blood sugar levels) with multiple complications [3,4]. Every time the BGL exceeds the normal limit [5,6], adequate actions, depending on the type of diabetes, should be taken to restore the level into the admissible range. Several commercially available sensors based on blood analysis have emerged. Due to their compact size, low cost, good accuracy, and fast response [7,8,9], these sensors have rapidly gained worldwide popularity, but have provided huge benefits to the diabetic population. Despite significant efforts to minimize the volume of investigated blood samples and reduce the discomfort associated with finger-pricking, these sensors are still invasive by design and are not suitable for continuous monitoring, which is a major corner-stone for optimal BGL control [10,11]

Methods

Results

Conclusion