Self-calibrated biosensor for measuring multiple physiological parameters

Nanophotonic techniques for diagnosis of a physiological tissue state are useful due to their noninvasive nature. Yet, light reflectance from a tissue is determined by the medium optical properties, absorption and scattering. Therefore, evaluating physiological parameters that correlate with absorption exclusively requires calibration of the scattering. While finding pulse rate is possible in a single wavelength, other parameters, such as oxygen saturation, require more than one light source and ratiometric measurements. As a result, the differences in the optical pathlength of the different wavelengths produce an inherent error. We have previously discovered the iso-path length (IPL) point, a specific position around a cylindrical media where the light intensity is not affected by the scattering. It was found by measuring the full scattering profile (FSP), meaning the angular distribution of light intensity of cylindrical tissues. Therefore, when measuring in this point, the absorption can be isolated from the scattering. This allows extracting physiological parameters such as oxygen saturation from a single wavelength measurement. In this research we designed an optic biosensor for measuring the reemitted light from the tissue, constructed with a single light source and several photodetectors, as one of them is in the IP point's location. We conducted several experiments for measuring the oxygen saturation, heart rate (HR) and respiratory rate (RR) in ordinary conditions. In addition, we conducted experiments in a hypoxic chamber for simulating extreme conditions of lack of oxygen. With our biosensor that utilizes the IPL point, we strive to continue experimenting and measuring other parameters as well.