Ion-Selective Micropipette Sensor for In Vivo Monitoring of Sodium Ion with Crown Ether-Encapsulated Metal–Organic Framework Subnanopores

In vivo sensing of the dynamics of ions with high selectivity is essential for gaining molecular insights into numerous physiological and pathological processes. In this work, we report an ion-selective micropipette sensor (ISMS) through the integration of functional crown ether-encapsulated metal–organic frameworks (MOFs) synthesized in situ within the micropipette tip. The ISMS features distinctive sodium ion (Na⁺) conduction and high selectivity toward Na⁺ sensing. The selectivity is attributed to the synergistic effects of subnanoconfined space and the specific coordination of 18-crown-6 toward potassium ions (K⁺), which largely increase the steric hindrance and transport resistance for K⁺ to pass through the ISMS. Furthermore, the ISMS exhibits high stability and sensitivity, facilitating real-time monitoring of Na⁺ dynamics in the living rat brain during spreading of the depression events process. In light of the diversity of crown ethers and MOFs, we believe this study paves the way for a nanofluidic platform for in vivo sensing and neuromorphic electrochemical sensing.