Advances in fully integrated wearable near-infrared spectroscopy: hardware innovations and biomedical applications

The use of noninvasive near-infrared spectroscopy (NIRS) has grown significantly over the past few decades for use in the characterization of tissue optical properties and derived physiological parameters such as tissue oxygen saturation and hemoglobin composition to support human health and wellness. Wearable NIRS devices have been developed in recent years that enable real-time continuous monitoring. These devices have been enabled by advances in the dense integration of miniature integrated circuits, light sources and detectors, embedded processing, and wireless technologies. The most attractive aspect of wearable NIRS devices is that they enable real-time sensing both inside and outside of laboratory and clinical settings. This review paper focuses on recent hardware developments related to fully integrated wearable NIRS devices, including continuous wave, time domain, and frequency domain NIRS techniques, and their enabling technologies. We also review their application in biomedical fields such as neuroscience, musculoskeletal physiology, and others. We provide our perspective on the future technology research opportunities and direction of the field.