Multiplexed and implantable fiber sensor for real-time blood monitoring.

Accurate and real-time monitoring of blood electrolyte composition, particularly sodium (Na+) and potassium (K+), is crucial for guiding intraoperative and postoperative decisions, as these ions regulate critical bodily functions such as cardiac rhythm and fluid balance. Current blood analysis relies on ex vivo blood sampling, which introduces substantial time delays and can be susceptible to inaccuracies caused by temperature fluctuations. To address these challenges, we report here a multiplexed and implantable fiber sensor (MIFS) capable of monitoring Na+ and K+ ions in real time directly in the bloodstream. MIFS integrates three parallel liquid metal channels with a multilayer surface-electrode architecture, which synergistically enhances sensitivity, minimizes sensing drift, ensures mechanical flexibility, and offers outstanding biocompatibility for vascular implantation. In vivo testing in rabbit models and validation in human blood samples demonstrate MIFS's superior sensing accuracy, real-time, and stable sensing in agreement with conventional ex vivo measurements. This work paves the way for real-time blood monitoring in clinical practice.