Blood Oxygen and Heart Rate Monitoring by a Flexible Hybrid Electronics Device Fabricated by Multilayer Screen-Printing

Finger-based pulse oximetry (SpO₂) and heart rate monitoring are widely used in medical settings and are penetrating the everyday life. However, SpO₂ response measured on the peripheral parts of the body (such as fingers and wrists) has a time lag and is less accurate compared to measuring on forehead. In addition, current devices are centimeter-thick, making seamless integration with the body difficult, hindering continuous monitoring and wide adoption. We designed, fabricated, and evaluated an SpO₂ and heart rate sensing device based on flexible hybrid electronics (FHE) technology. The marriage of flexible electronics with high performance commercially available IC chips makes it possible to have advanced sensing, data processing and wireless data transmission functionalities on a thin (1.5 mm) and flexible form that can be attached to various parts of the body. Differently from most devices using FHE technology, here we describe a cost-efficient and mass production compatible multilayer screen-printing process based on conducting Ag-based and non-conducting inks for making the flexible interconnection circuitry in detail, including advanced topographic analysis. By optimizing the printing steps, we could fabricate interconnecting lines vertically traversing up to five printed layers over several tens of micrometers, increasing the spatial density of functional units. By this, we widen the possibilities to utilize screen-printing for advanced wearable devices. Indeed, our FHE device reliably detects induced hypoxemia, and when applied on forehead, detects changes in SpO₂ more than 10 seconds earlier compared to a finger-based medical grade reference device.