Non-invasive hemoglobin concentration measurements with multi-wavelength reflectance mode PPG sensor and CNN data processing.

Possibility of non-invasive hemoglobin concentration measurements with wearable devices have been evaluated. The proposed solution is based on the assumption that PPG waveform shape measured at various wavelengths in the reflectance mode carries information about in-depth distribution of optical pathlength in the tissue. Decomposition of temporal and spectral features of PPG signal have been applied to correct estimation of hemoglobin concentration. The dataset including 840 PPG waveforms from 170 volunteers have been collected for the purpose of neural network training and validation. The achieved performance (MAE~13.6 g/l, R~0.62) is confirmed with the invasive blood test.Clinical Relevance - This paper establishes possibility of non-invasive real time hemoglobin concentration measurements by means of low-cost wearable sensor with accuracy comparable to non-invasive clinical instruments.

Microfluidic System for In-Flow Reversible Photoswitching of Near-Infrared Fluorescent Proteins.

We have developed a microfluidic flow cytometry system to screen reversibly photoswitchable fluorescent proteins for contrast and stability of reversible photoconversion between high- and low-fluorescent states. A two-color array of 20 excitation and deactivation beams generated with diffractive optics was combined with a serpentine microfluidic channel geometry designed to provide five cycles of photoswitching with real-time calculation of photoconversion fluorescence contrast. The characteristics of photoswitching in-flow as a function of excitation and deactivation beam fluence, flow speed, and protein concentration were studied with droplets of the bacterial phytochrome from Deinococcus radiodurans (DrBphP), which is weakly fluorescent in the near-infrared (NIR) spectral range. In agreement with measurements on stationary droplets and HeLa S3 mammalian cells expressing DrBphP, optimized operation of the flow system provided up to 50% photoconversion contrast in-flow at a droplet rate of few hertz and a coefficient of variation (CV) of up to 2% over 10 000 events. The methods for calibrating the brightness and photoswitching measurements in microfluidic flow established here provide a basis for screening of cell-based libraries of reversibly switchable NIR fluorescent proteins.