BME Seminar by Prof. Dror Fixler

Nanophotonic methods enable non‑invasive monitoring of physiological parameters, yet tissue reflectance depends on both absorption and scattering, making absorption‑based biomarker extraction challenging.

We employ the iso‑pathlength (IPL) point - a location around a cylindrical medium where detected light intensity is insensitive to scattering, identified via full scattering profile (FSP) measurements - to isolate absorption effects.

Using this principle, we developed a self‑calibrated optical biosensor with a single light source and multiple photodetectors, one positioned at the IPL point. While previous studies demonstrated extraction of HR, RR, and SpO₂, the present work focuses on blood pressure estimation. The sensor was placed on the upper arm of 20 subjects alongside a standard BP cuff. Optical signals were converted into PPG waveforms in absorption‑coefficient units, from which AC and DC components were derived.

The ratio between these components correlated with the systolic–diastolic pressure difference, yielding an 88%‑accurate linear fit. These findings support the feasibility of the method and its potential for further refinement through expanded experiments.