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Sensors 2015, 15(7), 16358-16371; doi:10.3390/s150716358

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

NTT Device Technology Laboratories, NTT Corporation, Atsugi 243-0198, Japan
Academic Editors: Yoshiteru Ishida and Masahiro Tokumitsu
Received: 15 April 2015 / Revised: 18 June 2015 / Accepted: 30 June 2015 / Published: 7 July 2015
(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Japan 2015)
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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. View Full-Text
Keywords: CW-photoacoustic; noninvasive monitoring; glucose; differential measurement; dual wavelength excitation CW-photoacoustic; noninvasive monitoring; glucose; differential measurement; dual wavelength excitation
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Camou, S. Phase Difference Optimization of Dual-Wavelength Excitation for the CW-Photoacoustic-Based Noninvasive and Selective Investigation of Aqueous Solutions of Glucose. Sensors 2015, 15, 16358-16371.

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