Continuous-Wave Photoacoustic-Based Sensor for the Detection of Aqueous Glucose: Towards Non-invasive and Continuous Glycemia Sensing

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Abstract

Measurement of blood glucose levels (BGLs) is a basic procedure that diabetic patients need to perform several times a day. The conventional standard protocol for on-site measurement, despite several advantages such as portability, low cost, fast response time, and ease of operation, is based on the finger-prick technique to extract blood samples. This process is invasive and cannot provide continuous monitoring.

Towards the achievement of non-invasive and continuous BGL monitoring, we have developed two measurement methods based on the continuous-wave photoacoustic (CW-PA) protocol and we performed preliminary in vitro tests with aqueous solutions. The first method relies on the measurement of the frequency shift induced by the change in the composition of the propagation medium. This method is equivalent to an acoustic velocity measurement and provides high sensitivity but no selectivity to glucose compound. The second approach utilizes simultaneous optical excitation at two wavelengths for compound-selective measurements. After correcting the frequency shift mentioned previously, this protocol allows measurements equivalent to a differential absorption coefficient one at the two wavelengths used. It then combines the advantages of absorption spectroscopy without the limitation from scattering due to the use of acoustic detection. Furthermore, the combination of the two methods can be generalized to systems involving more than one changing parameter by using not only two optical wavelengths for the excitation sequence but also several pairs of wavelength sequentially.

These methods then represent an important step forward the non-invasive, selective, and continuous measurements of glucose compound concentrations from a complex mixture, typically blood.