Wearable and Biocompatible Blood Oxygen Sensor Based on Heterogeneously Integrated Lasers on a Laser-Induced Graphene Electrode

Wearable electronics or epidermal electronics have attracted growing interest for their expansion into markets as health monitors and for biological applications. However, a key obstacle lies in the light source and the optical path change caused by the deformation and displacement in the measurement. In this work, we demonstrated a wearable and biocompatible blood oxygen monitor by using heterogeneously integrated vertical cavity surface emitting lasers (VCSELs) and a Si photodetector (PD) on a Au-laser-induced-graphene hybrid electrode. The strategy for fabricating a flexible electrode provides advantages including large-scale fabrication, high cost performance, and simple operation. The full widths at half-maximum of the 680 and 808 nm VCSEL were 1.8 and 0.8 nm, respectively, which is useful to improve sensitivity. Then, the rigid optoelectronics including narrowband VCSELs and a thinned Si PD were heterogeneously integrated on the flexible electrodes. Owing to the great flexibility and excellent light source, the wearable device conformal to the skin’s surface can be utilized to extract blood oxygen (SpO2). It was successfully demonstrated that the flexible device can extract the photoplethysmography signals of various regions including the fingernail, the wrist, and the earlobe. This work proposes an alternative strategy to miniaturizing an integrated device for long-life and continuous medical monitoring.