MW-FlexNIRS: wearable, low-cost, LED-based, multi-wavelength NIRS oximeter for cytochrome c oxidase recovery in neonates

We present MW-FlexNIRS, a wearable, low-cost, LED-based, multi-wavelength near-infrared spectroscopy (NIRS) system designed for continuous monitoring of cerebral oxygenation and metabolic dynamics in neonates. The device extends the original FlexNIRS platform by integrating custom eight-wavelength LED sources, a new analog front-end, and Bluetooth low energy 5 communication onto a single flexible printed circuit board encapsulated in medical-grade silicone. To support quantitative analysis with broadband LED sources, we introduce a wavelength-weighted fitting (WWF) algorithm that explicitly accounts for LED emission spectra, photodiode responsivity, and tissue optical properties. System performance was characterized through spectral calibration, stability testing, and noise equivalent power measurements, yielding an average NEP of 123 ± 25 fW/√Hz. Validation experiments using solid silicone phantoms demonstrated accurate recovery of effective attenuation coefficients with a mean error of 2.1% using a calibrated multi-distance approach. Liquid phantom studies incorporating blood, Intralipid, and yeast were used to evaluate recovery of hemoglobin and to investigate cytochrome c oxidase (CCO) related spectral sensitivity, parameter coupling, and model limitations. Finally, a pilot measurement in a term infant with transient respiratory distress demonstrates the preliminary feasibility of stable, continuous cerebral oxygenation monitoring in the neonatal intensive care unit. Together, these results support MW-FlexNIRS as a promising platform for multi-wavelength wearable NIRS in neonates and highlight both the potential and current challenges of oxCCO quantification.