A graphite-PDMS composite-based solid-contact ion-selective electrode for continuous monitoring blood ionized calcium in vivo

Ionized Calcium (Ca 2+ ) is the physiologically active component involved in many physiological processes such as blood coagulation, muscle contraction, neurotransmitter release, and hormone secretion. It is known that derangement in Ca 2+ level is associated with adverse outcomes and increased mortality, therefore, the dynamic and continuous monitoring of blood Ca 2+ concentrations are essential for managing patients, which can avoid consequences of delayed treatment and overcorrection in critically ill and severely injured patients. This study presents a needle-shaped Ca 2+ solid-contact ion-selective electrode (SC-ISE) utilizing a graphite-polydimethylsiloxane (Gr-PDMS, GP) composite as the transduction layer. The composite integrates the excellent conductivity and low cost of Gr with enhanced double-layer capacitance, hydrophobicity, and adhesion, making it an ideal material for ISEs. The electrode demonstrates a near-Nernstian response (28.2 mV/decade) and exceptional long-term stability (potential drift: 25 μV/h). Its performance was validated through accurate Ca 2+ detections in serum and blood, with in vivo testing on New Zealand rabbits under dynamic conditions such as fluid administration and injection, highlighting its potential for real-time clinical applications.