Next-Generation Wearable/Implanted Sensors Based on Fiber Optic and Its Application: From in Vitro to in Vivo

Wearable sensors are significant for health status, diagnosing diseases, and adjusting postoperative interventions to monitor the physiological information on humans continuously. The first generation of wearable sensors has gained rapid growth in medical health for monitoring physical parameters. Recently, emerging fiber optics (FOs) with small diameters have been attached to desired locations of the human epidermis or fabrics for monitoring physiological change activity. Because of its strong soft tissue affinity and excellent biocompatibility, FO has been injected into human skin, blood vessels, and the brain for sensing of biological parameters. The detection of FO has been extended, ranging from physical parameters to chemical and biological parameters. Also, the application of FO has shifted from wearable sensors in vitro to implanted sensors in vivo. Thus, FO is expected to launch a milestone contribution to next-generation wearable/implanted sensors. Based on the success, this review focuses on wearable and implantable FO-based sensors. The three main design strategies of single point, distributed, and FO array were profiled. The significant application of the detection of the physical, chemical, and biological parameters was discussed. The opportunities and challenges of wearable/implantable FO-based sensors were highlighted to promote their development for commercial applications.