A Sensitive BLE-Enabled Wearable fNIRS Biosensor for Real-Time Monitoring and Mapping of Task-Evoked Oxygen Influxes...

To develop and validate a compact Bluetooth Low Energy (BLE)-enabled wearable functional near-infrared spectroscopy (fNIRS) device for real-time hemodynamic monitoring and proposes a task-evoked metric for identifying transient oxygenation events during cognitive engagement.

We designed a four-channel wearable fNIRS biosensor that integrates optical sensing, signal acquisition, and wireless transmission into a compact, cable-free platform using off-the-shelf electronic components. The device was characterized through optical power linearity, ADC voltage input, pulsed light acquisition, and signal-to-noise ratio analysis. Its performance was validated using forearm vascular occlusion and breath-hold experiments, followed by cortical recordings during breath-hold tasks, finger tapping, dynamic visual stimulation, and a screen-based spatial learning and memory task. We further formulated task-evoked instances of differential oxygen influx (tEIDO), computed from the instantaneous differential response between $\Delta$[HbO] and $\Delta$[Hb], as a hemodynamic index of task-locked neurovascular activity.

The device reliably detected expected oxy- and deoxy-hemoglobin changes during vascular and breath-hold validation experiments and captured task-evoked responses over motor, visual, and prefrontal cortices. The tEIDO metric identified transient differential oxygenation events during visual stimulation and revealed task-aligned oxygenation dynamics. During spatial navigation, differential oxygenation maps showed hemodynamic modulation around the target region only after memory acquisition.

The proposed BLE-enabled fNIRS platform, together with tEIDO, offers a compact and sensitive approach for untethered real-time cortical hemodynamic monitoring, with potential applications in mobile neuroimaging, neuroergonomics, cognitive-state monitoring, and brain-computer interface systems.