In Vivo Measurement of Calcium Ion with Solid-State Ion-Selective Electrode by Using Shelled Hollow Carbon Nanospheres as a Transducing Layer

In vivo monitoring of extracellular calcium ion (Ca2+) is of great importance due to its significant contributions in different (patho)physiological processes. In this study, we develop a potentiometric method with solid-state ion-selective electrodes (ISEs) for in vivo monitoring of the dynamics of the extracellular Ca2+ by using hollow carbon nanospheres (HCNs) as a transducing layer and solid contact to efficiently promote the ion-to-electron transduction between an ionophore-doped solvated polymeric membrane and a conducting substrate. We find that the use of HCNs essentially improves the stability of the signal response and minimizes the potential drift of the as-prepared ISEs. With three-shelled HCNs (3s-HCNs) as the transducing layer, we fabricate a solid-state Ca2+-selective microelectrode by forming a Ca2+-selective membrane with calcium ionophore II as the recognition unit, 2-nitrophenyl octyl ether as the plasticizer, sodium tetrakis[3,5-bis(trifluoromethyl)phenyl] borate as the ion exchanger, ...