Blood component analysis using mid-infrared photoacoustic spectroscopy based on ultrasound detection: glucose analysis trial.

Significance: Noninvasive monitoring of blood components is important in daily health management. Conventional optical techniques such as attenuated total reflection (ATR) have limited penetration depth and sensitivity. Photoacoustic spectroscopy using a piezoelectric transducer (PZT-PAS) can detect components in the interstitial fluid beneath the stratum corneum with a relatively simple device.

Aim: We explored the feasibility of PZT-PAS for noninvasive analysis of blood components.

Approach: Biomimetic phantom experiments were conducted to evaluate depth sensitivity. A technique for enhancing signal strength by generating standing acoustic waves in tissue was validated by tuning the laser modulation frequency. Human trials were conducted to assess the capability of the method for predicting blood glucose levels.

Results: PZT-PAS successfully detected signals from depths beyond 10 to $20\mu m$ , outperforming ATR. Signal enhancement was achieved in a 2-mm-thick interdigital membrane using resonant acoustic conditions. In human trials, discriminant analysis to determine blood glucose levels relative to a threshold of 140 mg/dL showed an accuracy rate of 85.3%.

Conclusions: These results highlight the potential of PZT-PAS combined with signal processing for future wearable, noninvasive health care monitoring applications.