Graphene-based flexible wearable sensors: mechanisms, challenges, and future directions

The increasing interest in wearable smart healthcare systems has sparked considerable attention toward flexible sensors owing to their high sensitivity and flexibility. However, these sensors still face challenges in terms of performance imbalances and instability. To address these issues, graphene-based conductive materials with exceptional mechanical and electrical properties have been incorporated into flexible sensors. Despite the potential of graphene, a comprehensive understanding of the sensing mechanisms and influence of fabrication methods on the performance of graphene-based flexible sensors is lacking. This article aims to bridge this gap by providing an overview of the latest research progress in flexible graphene sensors. We begin by analyzing the main properties of graphene materials, including tensile strength, specific surface area, thermal conductivity, and electrical conductivity. These properties highlight the superior characteristics of graphene for flexible sensor applications. The sensing mechanisms of strain/pressure, gas, and temperature flexible sensors are reviewed, with a focus on innovations in graphene composites, regular microstructures, and emerging preparation methods that enable an effective balance of the individual properties of a single flexible sensor. Furthermore, the article discusses graphene-based multifunctional flexible sensors that allow for the simultaneous monitoring of multiple stimuli, self-powered performance studies, and wireless communication performance studies. Performance analysis of these sensors in the context of flexible systems is provided. Finally, this article presents a comprehensive summary of flexible graphene sensors and offers an outlook for the future. We aim to provide theoretical guidance and technical support for the realization of individual whole-life physical sign detection using flexible graphene-based sensors.