Non-Consumptive Blood Potassium Detection Via Structurally Tunable Crown Ether Polymer Brush Interface on Quartz Crystal Microbalance

Maintaining serum potassium homeostasis is essential, as even small deviations can disrupt cardiac electrophysiology and lead to life-threatening complications. Here, we present a quartz crystal microbalance (QCM) sensing platform with potassium-selective poly(4-acryloylamidobenzo-15-crown-5) polymers brushes fabricated via surface-initiated Cu(0)-mediated controlled radical polymerization. This approach enables the in situ growth of ion-recognition polymer brushes and allows precise control of brush thickness through regulation of polymerization kinetics. The QCM chip with an optimized brush thickness of 20.2 nm exhibits well-defined K+-induced frequency shifts, establishing a clear correlation between K+ concentration and sensor response. The sensor achieves rapid (<60 s), selective, and quantitative detection over the 3–10 mM range, fully covering the physiological blood potassium range (3.5–5.5 mM), with a detection limit as low as 0.2 mM. The chips also demonstrate excellent reproducibility and stability, with a relative standard deviation of 7.8% across ten independently fabricated devices and 2.7% over ten consecutive measurement cycles using a single chip. Furthermore, reliable and reversible responses are confirmed in dynamic monitoring experiments and with simulated blood samples, without significant sample consumption. This work establishes a structurally tunable polymer–brush interface for selective ion recognition on QCM platforms and provides a robust analytical strategy for real-time electrolyte monitoring, offering strong potential for rapid and continuous clinical and point-of-care applications.